What Happens When an HVAC Blower Motor Fails

What Happens When an HVAC Blower Motor Fails

HVAC duct sealing

The importance of regular annual HVAC maintenance cannot be overstated, especially when considering the potential consequences of a failing blower motor. The HVAC system is an integral component of maintaining comfort within our homes and workplaces, ensuring that air circulates efficiently to provide both heating and cooling as required throughout the year. However, like all mechanical systems, it requires routine care to continue functioning optimally. Neglecting this essential maintenance can lead to several issues, including the failure of critical components such as the blower motor.


When an HVAC blower motor fails, it can have a significant impact on the overall performance of the system. The blower motor is responsible for moving heated or cooled air through your ductwork and into various rooms in your home or office. If it ceases to operate effectively or stops working altogether, you will likely experience reduced airflow, inconsistent temperatures across different areas, and increased energy bills due to the system overworking itself in an attempt to compensate for this inefficiency.


A sudden breakdown may mean you need HVAC repair services to prevent unexpected breakdowns during extreme weather..

Moreover, a failed blower motor can lead to more serious complications if not addressed promptly. For one, it may cause other parts of the HVAC system to strain and potentially fail as well; this could result in costly repairs or even necessitate a complete replacement of the unit. Additionally, inadequate airflow from a malfunctioning blower can compromise indoor air quality by allowing dust and allergens to accumulate rather than being filtered out properly.


Regular annual maintenance serves as a preventative measure against such setbacks. During these check-ups, technicians conduct thorough inspections and cleanings that help identify wear and tear before they escalate into major problems. This proactive approach ensures that all components-including the blower motor-are in good working order and any minor issues are resolved swiftly.


Furthermore, consistent maintenance extends the lifespan of your HVAC system by keeping it running smoothly and efficiently for longer periods. It reduces unexpected breakdowns that could otherwise disrupt your daily life or business operations while also providing peace of mind knowing that your indoor environment remains comfortable regardless of external weather conditions.


In conclusion, investing time in regular annual HVAC maintenance is crucial for preventing blower motor failures and ensuring optimal performance from your heating and cooling systems. By taking these preventive steps, homeowners and businesses alike can safeguard their investments while enjoying reliable indoor climate control year-round.

When it comes to the comfort of our homes, few components are as crucial as the HVAC system. Within this vital apparatus, the blower motor plays a central role by circulating air throughout the living space, ensuring consistent temperatures and a comfortable environment. However, like all mechanical devices, blower motors are not immune to wear and tear over time. Recognizing the common signs of a failing blower motor can help homeowners address issues promptly and avoid more significant problems down the road.


One of the primary indicators that a blower motor is on its last legs is unusual noise emanating from the HVAC unit. Normally, these systems operate quietly in the background, but when bearings or other internal parts begin to fail, they can produce grinding or squealing sounds. These noises are often early warning signs that should not be ignored, as they indicate that parts may be wearing out or becoming misaligned.


Another telltale sign of a failing blower motor is diminished airflow through vents. When operating correctly, an HVAC system should distribute air evenly throughout all rooms. If you notice certain areas feeling warmer or cooler than others or experience weak airflow from vents, it could mean that your blower motor is struggling to push air effectively due to damage or wear.


Frequent cycling of the HVAC system is also indicative of potential blower motor failure. If your system turns on and off more often than usual without reaching the set temperature on your thermostat, it could point to an inefficient blower motor unable to maintain consistent airflow and pressure within the ducts.


Additionally, increased energy bills without a corresponding increase in usage might signal an issue with your blower motor. As these motors age and lose efficiency, they must work harder-and thus consume more electricity-to achieve desired heating or cooling levels.


Sometimes homeowners may observe burning smells coming from their HVAC systems when running them for extended periods. This odor can result from overheating components within a struggling blower motor and serves as an immediate cue for investigation by professionals.


Finally, if your HVAC system fails to turn on altogether despite being connected to power and having no apparent thermostat issues, it's possible that your blower motor has reached complete failure.


In conclusion, understanding these common signs-unusual noises, reduced airflow, frequent cycling patterns, unexpected increases in energy consumption along with burning smells-can help you identify potential problems with your HVAC's blower motor before they escalate into costly repairs or total system breakdowns. Regular maintenance checks by qualified technicians can ensure any developing issues are caught early enough for effective intervention while prolonging both lifespan and performance efficiency of your home's climate control unit.

Citations and other links

Impact of a Blower Motor Failure on Overall HVAC Performance

When an HVAC blower motor fails, the impact on the overall performance of the heating, ventilation, and air conditioning (HVAC) system can be significant. The blower motor plays a critical role in ensuring that conditioned air is circulated throughout a building efficiently. Its failure can lead to a cascade of issues affecting comfort, energy efficiency, and even the longevity of the HVAC system itself.


The primary function of the blower motor is to push air through the ductwork after it has been heated or cooled by the furnace or air conditioner. When this component fails, airflow is severely restricted or completely halted. As a result, rooms may not receive adequate heating or cooling, leading to uneven temperatures throughout a space. This can cause discomfort for occupants as some areas become too warm while others remain too cold.


Moreover, without proper airflow from a functioning blower motor, other components within the HVAC system may also suffer. For instance, if hot air cannot be effectively distributed during winter months due to blower failure, heat exchangers may overheat and become damaged prematurely. Similarly, in summer months without effective cooling distribution, evaporator coils might freeze over because insufficient warm air passes over them to maintain appropriate temperatures.


Energy efficiency is another area that takes a hit with blower motor failure. An inefficient or non-operational motor forces other parts of the HVAC system to work harder than necessary in an attempt to compensate for lost airflow distribution. This increased strain leads to higher energy consumption and utility bills without delivering corresponding improvements in indoor climate control.


Furthermore, prolonged operation under these conditions can shorten the overall lifespan of an HVAC system. Components are forced into overdrive regularly when they must pick up slack from a non-functioning blower motor; thus wear and tear accelerate across various parts leading potentially expensive repairs sooner than expected.


Lastly yet importantly from an environmental standpoint: reduced efficiency means more resources consumed for less output - affecting both your wallet directly through bills but indirectly by increasing carbon footprint unnecessarily.


In conclusion: A failed HVAC blower motor negatively impacts comfort levels within buildings due largely due inadequate temperature regulation caused unequal distribution conditioned air throughout spaces being served . It also affects operational costs energy consumption ultimately reducing life expectancy entire unit making timely maintenance essential avoid these repercussions ensuring continued optimal performance your home business's climate control needs!

Impact of a Blower Motor Failure on Overall HVAC Performance
Steps to Take When a Blower Motor Fails During Routine Maintenance

Steps to Take When a Blower Motor Fails During Routine Maintenance

When an HVAC blower motor fails during routine maintenance, it can disrupt the comfort and efficiency of a home or business environment. The blower motor is integral to an HVAC system, as it circulates air throughout the ducts to maintain desired temperature levels. A failure can lead to inadequate heating or cooling, increased energy bills, or complete system shutdown. Understanding how to address this issue promptly is crucial for maintaining indoor comfort and preventing further damage.


The first step when a blower motor fails is to conduct a thorough inspection. This involves checking for any visible signs of damage or wear, such as burnt-out wires, loose connections, or physical blockages within the system. It's also important to listen for unusual noises that might indicate mechanical issues like grinding or squealing bearings. These initial observations can provide valuable clues about the cause of the failure.


Next, ensure that power is safely disconnected before proceeding with any repairs. Safety should always be a priority during maintenance tasks, and turning off power at the breaker box helps prevent electrical shocks or further damage to the system. Once safe to proceed, examine the electrical components using a multimeter to test for continuity and voltage levels; this will help determine if there are any issues with electrical supply or connectivity.


If no obvious electrical faults are found, consider testing the capacitor-a component responsible for providing initial energy boost needed by motors. Capacitors often fail due to age or heat exposure and can mimic symptoms of motor failure. Replacing a faulty capacitor is typically less expensive than replacing an entire motor.


In cases where inspection reveals significant wear and tear on the blower motor itself-such as damaged windings or seized bearings-it may be necessary to replace the motor entirely. Selecting a compatible replacement requires knowledge of specifications like horsepower rating and rotational direction; consulting manufacturer guidelines ensures proper fitment and performance.




What Happens When an HVAC Blower Motor Fails - air conditioning maintenance

  1. duct cleaning
  2. HVAC installation
  3. indoor air quality

After replacing any faulty components, reassemble the unit carefully and restore power cautiously while monitoring for proper operation. Listen for smooth running sounds without unusual vibrations or noise; check airflow from vents in multiple rooms ensuring even distribution throughout space serviced by HVAC unit.


Finally document all findings repairs made during maintenance session keeping detailed records aids future troubleshooting efforts contributes towards regular upkeep plan extending life expectancy overall efficiency your HVAC system remaining proactive rather than reactive reduces likelihood facing unexpected breakdowns potentially costly emergency repairs down line maintaining comfortable living working environment everyone benefits from well-functioning heating cooling systems especially those relying heavily seasonal climate variations daily routines dependability reliability utmost importance ensuring peace mind satisfaction occupants alike


In conclusion dealing effectively timely manner when confronted potential failures critical maintaining optimal performance functionality HVAC systems understanding root causes addressing them appropriately preventative measures helps mitigate risks associated unforeseen downtimes disruptions essential modern living working spaces making vital investment time effort resources worthwhile endeavors long term perspective

Preventive Measures to Avoid Blower Motor Failures

When it comes to maintaining a comfortable and efficient home environment, the HVAC system plays a pivotal role. At the heart of this system lies the blower motor, a crucial component responsible for circulating air throughout your home. However, like any mechanical part, blower motors are not immune to failure. Understanding preventive measures to avoid blower motor failures is essential for homeowners who wish to ensure their HVAC systems function smoothly and efficiently.


Regular maintenance is perhaps the most effective preventive measure one can undertake. Scheduling routine inspections with a qualified HVAC technician allows potential issues to be identified before they escalate into significant problems. During these inspections, technicians can check for signs of wear and tear on the motor, assess electrical connections, and ensure that all components are in optimal condition. Regular servicing not only prolongs the life of the blower motor but also enhances its performance.


Keeping air filters clean is another critical step in preventing blower motor failures.

What Happens When an HVAC Blower Motor Fails - air conditioning maintenance

  1. HVAC duct sealing
  2. compressor troubleshooting
  3. air conditioning maintenance
Dirty or clogged filters restrict airflow, forcing the blower motor to work harder than necessary. This increased strain can lead to overheating and eventual failure of the motor. Homeowners should make it a habit to check their air filters monthly and replace them every three months or as needed. Doing so ensures that air flows freely through the system, reducing stress on the blower motor.


Balanced ductwork is also vital in maintaining blower motor health. Leaks or blockages within duct systems hinder airflow efficiency and compel the blower motor to operate under additional stress conditions. Sealing leaks and cleaning ducts periodically will help maintain balanced airflow throughout your home.


Furthermore, installing a surge protector for your HVAC system can shield your blower motor from electrical surges that may occur due to lightning strikes or power outages. These surges can cause significant damage to electrical components within your HVAC unit, including the blower motor.


Lastly, being vigilant about unusual sounds or odors emanating from your HVAC system can be instrumental in early detection of potential issues with the blower motor. Unusual noises might indicate loose parts or failing bearings, while strange odors could signal burnt wires or overheating components.


In conclusion, preventive measures such as regular maintenance checks by professionals, keeping air filters clean, ensuring balanced ductwork, using surge protectors, and staying alert to unusual system behavior are effective strategies in avoiding blower motor failures. By taking these proactive steps, homeowners can enjoy uninterrupted comfort while extending the lifespan of their HVAC systems' critical components.

The Cost Implications of Neglecting Blower Motor Issues

The Cost Implications of Neglecting Blower Motor Issues


When discussing the functionality and efficiency of HVAC systems, the blower motor often doesn't get the attention it deserves. Yet, its failure can have significant repercussions on both your comfort and your wallet. Understanding what happens when an HVAC blower motor fails is crucial to prevent a cascade of issues that can arise from neglect.


First and foremost, the blower motor plays a pivotal role in circulating air throughout your home. It's responsible for pushing heated or cooled air through ducts, ensuring that each room maintains a consistent temperature. When this component malfunctions, airflow is compromised. You might notice uneven temperatures across different areas, making some rooms uncomfortable while others remain unaffected.


From a cost perspective, neglecting blower motor issues can lead to increased energy bills. A struggling or failed motor often forces the system to work harder to circulate air, consuming more electricity in the process. This inefficiency not only impacts utility costs but also places undue stress on other parts of the HVAC system.


Moreover, ignoring early signs of blower motor problems can result in extensive damage over time.

What Happens When an HVAC Blower Motor Fails - compressor troubleshooting

  1. carbon monoxide testing
  2. geothermal heating and cooling
  3. refrigeration repair
What might start as a minor issue could escalate into a major repair job if left unattended. For instance, overheating due to poor airflow can lead to burnt-out electrical components or even damage other mechanical parts within the system.


The financial implications extend beyond repairs and energy consumption; there's also the potential decrease in property value to consider. Prospective buyers are keenly aware of maintenance issues and may be deterred by an HVAC system that's known to have unresolved problems. This could result in lower offers or extended time on the market when selling your home.


Preventative maintenance is key to avoiding these complications. Regular inspections by qualified technicians can identify early warning signs before they develop into costly failures. Simple tasks such as cleaning filters and ensuring unobstructed vents play a significant role in prolonging the life of your blower motor and maintaining efficient operation.


In conclusion, while it's easy to overlook smaller components like the blower motor amid larger HVAC concerns, doing so can lead to severe cost implications down the line. Addressing minor issues promptly not only ensures consistent comfort but also protects you from unnecessary expenses related to energy waste and system repairs. Prioritizing regular maintenance checks will ultimately safeguard both your investment and peace of mind.

Rooftop HVAC unit with view of fresh-air intake vent
Ventilation duct with outlet diffuser vent. These are installed throughout a building to move air in or out of rooms. In the middle is a damper to open and close the vent to allow more or less air to enter the space.
The control circuit in a household HVAC installation. The wires connecting to the blue terminal block on the upper-right of the board lead to the thermostat. The fan enclosure is directly behind the board, and the filters can be seen at the top. The safety interlock switch is at the bottom left. In the lower middle is the capacitor.

Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).

HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels, and senior living facilities; medium to large industrial and office buildings such as skyscrapers and hospitals; vehicles such as cars, trains, airplanes, ships and submarines; and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.

Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air. Methods for ventilating a building are divided into mechanical/forced and natural types.[1]

Overview

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The three major functions of heating, ventilation, and air conditioning are interrelated, especially with the need to provide thermal comfort and acceptable indoor air quality within reasonable installation, operation, and maintenance costs. HVAC systems can be used in both domestic and commercial environments. HVAC systems can provide ventilation, and maintain pressure relationships between spaces. The means of air delivery and removal from spaces is known as room air distribution.[2]

Individual systems

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In modern buildings, the design, installation, and control systems of these functions are integrated into one or more HVAC systems. For very small buildings, contractors normally estimate the capacity and type of system needed and then design the system, selecting the appropriate refrigerant and various components needed. For larger buildings, building service designers, mechanical engineers, or building services engineers analyze, design, and specify the HVAC systems. Specialty mechanical contractors and suppliers then fabricate, install and commission the systems. Building permits and code-compliance inspections of the installations are normally required for all sizes of buildings

District networks

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Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[3][4][5]

Basing HVAC on a larger network helps provide an economy of scale that is often not possible for individual buildings, for utilizing renewable energy sources such as solar heat,[6][7][8] winter's cold,[9][10] the cooling potential in some places of lakes or seawater for free cooling, and the enabling function of seasonal thermal energy storage. By utilizing natural sources that can be used for HVAC systems it can make a huge difference for the environment and help expand the knowledge of using different methods.

History

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HVAC is based on inventions and discoveries made by Nikolay Lvov, Michael Faraday, Rolla C. Carpenter, Willis Carrier, Edwin Ruud, Reuben Trane, James Joule, William Rankine, Sadi Carnot, Alice Parker and many others.[11]

Multiple inventions within this time frame preceded the beginnings of the first comfort air conditioning system, which was designed in 1902 by Alfred Wolff (Cooper, 2003) for the New York Stock Exchange, while Willis Carrier equipped the Sacketts-Wilhems Printing Company with the process AC unit the same year. Coyne College was the first school to offer HVAC training in 1899.[12] The first residential AC was installed by 1914, and by the 1950s there was "widespread adoption of residential AC".[13]

The invention of the components of HVAC systems went hand-in-hand with the Industrial Revolution, and new methods of modernization, higher efficiency, and system control are constantly being introduced by companies and inventors worldwide.

Heating

[edit]

Heaters are appliances whose purpose is to generate heat (i.e. warmth) for the building. This can be done via central heating. Such a system contains a boiler, furnace, or heat pump to heat water, steam, or air in a central location such as a furnace room in a home, or a mechanical room in a large building. The heat can be transferred by convection, conduction, or radiation. Space heaters are used to heat single rooms and only consist of a single unit.

Generation

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Central heating unit

Heaters exist for various types of fuel, including solid fuels, liquids, and gases. Another type of heat source is electricity, normally heating ribbons composed of high resistance wire (see Nichrome). This principle is also used for baseboard heaters and portable heaters. Electrical heaters are often used as backup or supplemental heat for heat pump systems.

The heat pump gained popularity in the 1950s in Japan and the United States.[14] Heat pumps can extract heat from various sources, such as environmental air, exhaust air from a building, or from the ground. Heat pumps transfer heat from outside the structure into the air inside. Initially, heat pump HVAC systems were only used in moderate climates, but with improvements in low temperature operation and reduced loads due to more efficient homes, they are increasing in popularity in cooler climates. They can also operate in reverse to cool an interior.

Distribution

[edit]

Water/steam

[edit]

In the case of heated water or steam, piping is used to transport the heat to the rooms. Most modern hot water boiler heating systems have a circulator, which is a pump, to move hot water through the distribution system (as opposed to older gravity-fed systems). The heat can be transferred to the surrounding air using radiators, hot water coils (hydro-air), or other heat exchangers. The radiators may be mounted on walls or installed within the floor to produce floor heat.

The use of water as the heat transfer medium is known as hydronics. The heated water can also supply an auxiliary heat exchanger to supply hot water for bathing and washing.

Air

[edit]

Warm air systems distribute the heated air through ductwork systems of supply and return air through metal or fiberglass ducts. Many systems use the same ducts to distribute air cooled by an evaporator coil for air conditioning. The air supply is normally filtered through air filters[dubiousdiscuss] to remove dust and pollen particles.[15]

Dangers

[edit]

The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and the emission of carbon monoxide, nitrogen oxides, formaldehyde, volatile organic compounds, and other combustion byproducts. Incomplete combustion occurs when there is insufficient oxygen; the inputs are fuels containing various contaminants and the outputs are harmful byproducts, most dangerously carbon monoxide, which is a tasteless and odorless gas with serious adverse health effects.[16]

Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[17]

Ventilation

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Ventilation is the process of changing or replacing air in any space to control the temperature or remove any combination of moisture, odors, smoke, heat, dust, airborne bacteria, or carbon dioxide, and to replenish oxygen. It plays a critical role in maintaining a healthy indoor environment by preventing the buildup of harmful pollutants and ensuring the circulation of fresh air. Different methods, such as natural ventilation through windows and mechanical ventilation systems, can be used depending on the building design and air quality needs. Ventilation often refers to the intentional delivery of the outside air to the building indoor space. It is one of the most important factors for maintaining acceptable indoor air quality in buildings.

Although ventilation is an integral component of maintaining good indoor air quality, it may not be satisfactory alone.[18] A clear understanding of both indoor and outdoor air quality parameters is needed to improve the performance of ventilation in terms of ...[19] In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary.[20]

Methods for ventilating a building may be divided into mechanical/forced and natural types.[21]

Mechanical or forced

[edit]
HVAC ventilation exhaust for a 12-story building
An axial belt-drive exhaust fan serving an underground car park. This exhaust fan's operation is interlocked with the concentration of contaminants emitted by internal combustion engines.

Mechanical, or forced, ventilation is provided by an air handler (AHU) and used to control indoor air quality. Excess humidity, odors, and contaminants can often be controlled via dilution or replacement with outside air. However, in humid climates more energy is required to remove excess moisture from ventilation air.

Kitchens and bathrooms typically have mechanical exhausts to control odors and sometimes humidity. Factors in the design of such systems include the flow rate (which is a function of the fan speed and exhaust vent size) and noise level. Direct drive fans are available for many applications and can reduce maintenance needs.

In summer, ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature by increasing evaporation of perspiration on the skin of the occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor.

Passive

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Ventilation on the downdraught system, by impulsion, or the 'plenum' principle, applied to schoolrooms (1899)

Natural ventilation is the ventilation of a building with outside air without using fans or other mechanical systems. It can be via operable windows, louvers, or trickle vents when spaces are small and the architecture permits. ASHRAE defined Natural ventilation as the flow of air through open windows, doors, grilles, and other planned building envelope penetrations, and as being driven by natural and/or artificially produced pressure differentials.[1]

Natural ventilation strategies also include cross ventilation, which relies on wind pressure differences on opposite sides of a building. By strategically placing openings, such as windows or vents, on opposing walls, air is channeled through the space to enhance cooling and ventilation. Cross ventilation is most effective when there are clear, unobstructed paths for airflow within the building.

In more complex schemes, warm air is allowed to rise and flow out high building openings to the outside (stack effect), causing cool outside air to be drawn into low building openings. Natural ventilation schemes can use very little energy, but care must be taken to ensure comfort. In warm or humid climates, maintaining thermal comfort solely via natural ventilation might not be possible. Air conditioning systems are used, either as backups or supplements. Air-side economizers also use outside air to condition spaces, but do so using fans, ducts, dampers, and control systems to introduce and distribute cool outdoor air when appropriate.

An important component of natural ventilation is air change rate or air changes per hour: the hourly rate of ventilation divided by the volume of the space. For example, six air changes per hour means an amount of new air, equal to the volume of the space, is added every ten minutes. For human comfort, a minimum of four air changes per hour is typical, though warehouses might have only two. Too high of an air change rate may be uncomfortable, akin to a wind tunnel which has thousands of changes per hour. The highest air change rates are for crowded spaces, bars, night clubs, commercial kitchens at around 30 to 50 air changes per hour.[22]

Room pressure can be either positive or negative with respect to outside the room. Positive pressure occurs when there is more air being supplied than exhausted, and is common to reduce the infiltration of outside contaminants.[23]

Airborne diseases

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Natural ventilation [24] is a key factor in reducing the spread of airborne illnesses such as tuberculosis, the common cold, influenza, meningitis or COVID-19. Opening doors and windows are good ways to maximize natural ventilation, which would make the risk of airborne contagion much lower than with costly and maintenance-requiring mechanical systems. Old-fashioned clinical areas with high ceilings and large windows provide the greatest protection. Natural ventilation costs little and is maintenance free, and is particularly suited to limited-resource settings and tropical climates, where the burden of TB and institutional TB transmission is highest. In settings where respiratory isolation is difficult and climate permits, windows and doors should be opened to reduce the risk of airborne contagion. Natural ventilation requires little maintenance and is inexpensive.[25]

Natural ventilation is not practical in much of the infrastructure because of climate. This means that the facilities need to have effective mechanical ventilation systems and or use Ceiling Level UV or FAR UV ventilation systems.

Alpha Black Edition - Sirair Air conditioner with UVC (Ultraviolet Germicidal Irradiation)

Ventilation is measured in terms of Air Changes Per Hour (ACH). As of 2023, the CDC recommends that all spaces have a minimum of 5 ACH.[26] For hospital rooms with airborne contagions the CDC recommends a minimum of 12 ACH.[27] The challenges in facility ventilation are public unawareness,[28][29] ineffective government oversight, poor building codes that are based on comfort levels, poor system operations, poor maintenance, and lack of transparency.[30]

UVC or Ultraviolet Germicidal Irradiation is a function used in modern air conditioners which reduces airborne viruses, bacteria, and fungi, through the use of a built-in LED UV light that emits a gentle glow across the evaporator. As the cross-flow fan circulates the room air, any viruses are guided through the sterilization module’s irradiation range, rendering them instantly inactive.[31]

Air conditioning

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An air conditioning system, or a standalone air conditioner, provides cooling and/or humidity control for all or part of a building. Air conditioned buildings often have sealed windows, because open windows would work against the system intended to maintain constant indoor air conditions. Outside, fresh air is generally drawn into the system by a vent into a mix air chamber for mixing with the space return air. Then the mixture air enters an indoor or outdoor heat exchanger section where the air is to be cooled down, then be guided to the space creating positive air pressure. The percentage of return air made up of fresh air can usually be manipulated by adjusting the opening of this vent. Typical fresh air intake is about 10% of the total supply air.[citation needed]

Air conditioning and refrigeration are provided through the removal of heat. Heat can be removed through radiation, convection, or conduction. The heat transfer medium is a refrigeration system, such as water, air, ice, and chemicals are referred to as refrigerants. A refrigerant is employed either in a heat pump system in which a compressor is used to drive thermodynamic refrigeration cycle, or in a free cooling system that uses pumps to circulate a cool refrigerant (typically water or a glycol mix).

It is imperative that the air conditioning horsepower is sufficient for the area being cooled. Underpowered air conditioning systems will lead to power wastage and inefficient usage. Adequate horsepower is required for any air conditioner installed.

Refrigeration cycle

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A simple stylized diagram of the refrigeration cycle: 1) condensing coil, 2) expansion valve, 3) evaporating coil, 4) compressor

The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device, and evaporator.

  • At the inlet of a compressor, the refrigerant inside the system is in a low pressure, low temperature, gaseous state. The compressor pumps the refrigerant gas up to high pressure and temperature.
  • From there it enters a heat exchanger (sometimes called a condensing coil or condenser) where it loses heat to the outside, cools, and condenses into its liquid phase.
  • An expansion valve (also called metering device) regulates the refrigerant liquid to flow at the proper rate.
  • The liquid refrigerant is returned to another heat exchanger where it is allowed to evaporate, hence the heat exchanger is often called an evaporating coil or evaporator. As the liquid refrigerant evaporates it absorbs heat from the inside air, returns to the compressor, and repeats the cycle. In the process, heat is absorbed from indoors and transferred outdoors, resulting in cooling of the building.

In variable climates, the system may include a reversing valve that switches from heating in winter to cooling in summer. By reversing the flow of refrigerant, the heat pump refrigeration cycle is changed from cooling to heating or vice versa. This allows a facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware.

Free cooling

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Free cooling systems can have very high efficiencies, and are sometimes combined with seasonal thermal energy storage so that the cold of winter can be used for summer air conditioning. Common storage mediums are deep aquifers or a natural underground rock mass accessed via a cluster of small-diameter, heat-exchanger-equipped boreholes. Some systems with small storages are hybrids, using free cooling early in the cooling season, and later employing a heat pump to chill the circulation coming from the storage. The heat pump is added-in because the storage acts as a heat sink when the system is in cooling (as opposed to charging) mode, causing the temperature to gradually increase during the cooling season.

Some systems include an "economizer mode", which is sometimes called a "free-cooling mode". When economizing, the control system will open (fully or partially) the outside air damper and close (fully or partially) the return air damper. This will cause fresh, outside air to be supplied to the system. When the outside air is cooler than the demanded cool air, this will allow the demand to be met without using the mechanical supply of cooling (typically chilled water or a direct expansion "DX" unit), thus saving energy. The control system can compare the temperature of the outside air vs. return air, or it can compare the enthalpy of the air, as is frequently done in climates where humidity is more of an issue. In both cases, the outside air must be less energetic than the return air for the system to enter the economizer mode.

Packaged split system

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Central, "all-air" air-conditioning systems (or package systems) with a combined outdoor condenser/evaporator unit are often installed in North American residences, offices, and public buildings, but are difficult to retrofit (install in a building that was not designed to receive it) because of the bulky air ducts required.[32] (Minisplit ductless systems are used in these situations.) Outside of North America, packaged systems are only used in limited applications involving large indoor space such as stadiums, theatres or exhibition halls.

An alternative to packaged systems is the use of separate indoor and outdoor coils in split systems. Split systems are preferred and widely used worldwide except in North America. In North America, split systems are most often seen in residential applications, but they are gaining popularity in small commercial buildings. Split systems are used where ductwork is not feasible or where the space conditioning efficiency is of prime concern.[33] The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control, and quiet operation.[34] In space conditioning, the duct losses can account for 30% of energy consumption.[35] The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting.

With the split system, the evaporator coil is connected to a remote condenser unit using refrigerant piping between an indoor and outdoor unit instead of ducting air directly from the outdoor unit. Indoor units with directional vents mount onto walls, suspended from ceilings, or fit into the ceiling. Other indoor units mount inside the ceiling cavity so that short lengths of duct handle air from the indoor unit to vents or diffusers around the rooms.

Split systems are more efficient and the footprint is typically smaller than the package systems. On the other hand, package systems tend to have a slightly lower indoor noise level compared to split systems since the fan motor is located outside.

Dehumidification

[edit]

Dehumidification (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below the dew point, moisture in the air condenses on the evaporator coil tubes. This moisture is collected at the bottom of the evaporator in a pan and removed by piping to a central drain or onto the ground outside.

A dehumidifier is an air-conditioner-like device that controls the humidity of a room or building. It is often employed in basements that have a higher relative humidity because of their lower temperature (and propensity for damp floors and walls). In food retailing establishments, large open chiller cabinets are highly effective at dehumidifying the internal air. Conversely, a humidifier increases the humidity of a building.

The HVAC components that dehumidify the ventilation air deserve careful attention because outdoor air constitutes most of the annual humidity load for nearly all buildings.[36]

Humidification

[edit]

Maintenance

[edit]

All modern air conditioning systems, even small window package units, are equipped with internal air filters.[citation needed] These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example, a building in a high dust environment, or a home with furry pets, will need to have the filters changed more often than buildings without these dirt loads. Failure to replace these filters as needed will contribute to a lower heat exchange rate, resulting in wasted energy, shortened equipment life, and higher energy bills; low air flow can result in iced-over evaporator coils, which can completely stop airflow. Additionally, very dirty or plugged filters can cause overheating during a heating cycle, which can result in damage to the system or even fire.

Because an air conditioner moves heat between the indoor coil and the outdoor coil, both must be kept clean. This means that, in addition to replacing the air filter at the evaporator coil, it is also necessary to regularly clean the condenser coil. Failure to keep the condenser clean will eventually result in harm to the compressor because the condenser coil is responsible for discharging both the indoor heat (as picked up by the evaporator) and the heat generated by the electric motor driving the compressor.

Energy efficiency

[edit]

HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy.[37] Since the 1980s, manufacturers of HVAC equipment have been making an effort to make the systems they manufacture more efficient. This was originally driven by rising energy costs, and has more recently been driven by increased awareness of environmental issues. Additionally, improvements to the HVAC system efficiency can also help increase occupant health and productivity.[38] In the US, the EPA has imposed tighter restrictions over the years. There are several methods for making HVAC systems more efficient.

Heating energy

[edit]

In the past, water heating was more efficient for heating buildings and was the standard in the United States. Today, forced air systems can double for air conditioning and are more popular.

Some benefits of forced air systems, which are now widely used in churches, schools, and high-end residences, are

  • Better air conditioning effects
  • Energy savings of up to 15–20%
  • Even conditioning[citation needed]

A drawback is the installation cost, which can be slightly higher than traditional HVAC systems.

Energy efficiency can be improved even more in central heating systems by introducing zoned heating. This allows a more granular application of heat, similar to non-central heating systems. Zones are controlled by multiple thermostats. In water heating systems the thermostats control zone valves, and in forced air systems they control zone dampers inside the vents which selectively block the flow of air. In this case, the control system is very critical to maintaining a proper temperature.

Forecasting is another method of controlling building heating by calculating the demand for heating energy that should be supplied to the building in each time unit.

Ground source heat pump

[edit]

Ground source, or geothermal, heat pumps are similar to ordinary heat pumps, but instead of transferring heat to or from outside air, they rely on the stable, even temperature of the earth to provide heating and air conditioning. Many regions experience seasonal temperature extremes, which would require large-capacity heating and cooling equipment to heat or cool buildings. For example, a conventional heat pump system used to heat a building in Montana's −57 °C (−70 °F) low temperature or cool a building in the highest temperature ever recorded in the US—57 °C (134 °F) in Death Valley, California, in 1913 would require a large amount of energy due to the extreme difference between inside and outside air temperatures. A metre below the earth's surface, however, the ground remains at a relatively constant temperature. Utilizing this large source of relatively moderate temperature earth, a heating or cooling system's capacity can often be significantly reduced. Although ground temperatures vary according to latitude, at 1.8 metres (6 ft) underground, temperatures generally only range from 7 to 24 °C (45 to 75 °F).

Solar air conditioning

[edit]

Photovoltaic solar panels offer a new way to potentially decrease the operating cost of air conditioning. Traditional air conditioners run using alternating current, and hence, any direct-current solar power needs to be inverted to be compatible with these units. New variable-speed DC-motor units allow solar power to more easily run them since this conversion is unnecessary, and since the motors are tolerant of voltage fluctuations associated with variance in supplied solar power (e.g., due to cloud cover).

Ventilation energy recovery

[edit]

Energy recovery systems sometimes utilize heat recovery ventilation or energy recovery ventilation systems that employ heat exchangers or enthalpy wheels to recover sensible or latent heat from exhausted air. This is done by transfer of energy from the stale air inside the home to the incoming fresh air from outside.

Air conditioning energy

[edit]

The performance of vapor compression refrigeration cycles is limited by thermodynamics.[39] These air conditioning and heat pump devices move heat rather than convert it from one form to another, so thermal efficiencies do not appropriately describe the performance of these devices. The Coefficient of performance (COP) measures performance, but this dimensionless measure has not been adopted. Instead, the Energy Efficiency Ratio (EER) has traditionally been used to characterize the performance of many HVAC systems. EER is the Energy Efficiency Ratio based on a 35 °C (95 °F) outdoor temperature. To more accurately describe the performance of air conditioning equipment over a typical cooling season a modified version of the EER, the Seasonal Energy Efficiency Ratio (SEER), or in Europe the ESEER, is used. SEER ratings are based on seasonal temperature averages instead of a constant 35 °C (95 °F) outdoor temperature. The current industry minimum SEER rating is 14 SEER. Engineers have pointed out some areas where efficiency of the existing hardware could be improved. For example, the fan blades used to move the air are usually stamped from sheet metal, an economical method of manufacture, but as a result they are not aerodynamically efficient. A well-designed blade could reduce the electrical power required to move the air by a third.[40]

Demand-controlled kitchen ventilation

[edit]

Demand-controlled kitchen ventilation (DCKV) is a building controls approach to controlling the volume of kitchen exhaust and supply air in response to the actual cooking loads in a commercial kitchen. Traditional commercial kitchen ventilation systems operate at 100% fan speed independent of the volume of cooking activity and DCKV technology changes that to provide significant fan energy and conditioned air savings. By deploying smart sensing technology, both the exhaust and supply fans can be controlled to capitalize on the affinity laws for motor energy savings, reduce makeup air heating and cooling energy, increasing safety, and reducing ambient kitchen noise levels.[41]

Air filtration and cleaning

[edit]
Air handling unit, used for heating, cooling, and filtering the air

Air cleaning and filtration removes particles, contaminants, vapors and gases from the air. The filtered and cleaned air then is used in heating, ventilation, and air conditioning. Air cleaning and filtration should be taken in account when protecting our building environments.[42] If present, contaminants can come out from the HVAC systems if not removed or filtered properly.

Clean air delivery rate (CADR) is the amount of clean air an air cleaner provides to a room or space. When determining CADR, the amount of airflow in a space is taken into account. For example, an air cleaner with a flow rate of 30 cubic metres (1,000 cu ft) per minute and an efficiency of 50% has a CADR of 15 cubic metres (500 cu ft) per minute. Along with CADR, filtration performance is very important when it comes to the air in our indoor environment. This depends on the size of the particle or fiber, the filter packing density and depth, and the airflow rate.[42]

Circulation of harmful substances

[edit]

Poorly maintained air conditioners/ventilation systems can harbor mold, bacteria, and other contaminants, which are then circulated throughout indoor spaces, contributing to ...[43]

Industry and standards

[edit]

The HVAC industry is a worldwide enterprise, with roles including operation and maintenance, system design and construction, equipment manufacturing and sales, and in education and research. The HVAC industry was historically regulated by the manufacturers of HVAC equipment, but regulating and standards organizations such as HARDI (Heating, Air-conditioning and Refrigeration Distributors International), ASHRAE, SMACNA, ACCA (Air Conditioning Contractors of America), Uniform Mechanical Code, International Mechanical Code, and AMCA have been established to support the industry and encourage high standards and achievement. (UL as an omnibus agency is not specific to the HVAC industry.)

The starting point in carrying out an estimate both for cooling and heating depends on the exterior climate and interior specified conditions. However, before taking up the heat load calculation, it is necessary to find fresh air requirements for each area in detail, as pressurization is an important consideration.

International

[edit]

ISO 16813:2006 is one of the ISO building environment standards.[44] It establishes the general principles of building environment design. It takes into account the need to provide a healthy indoor environment for the occupants as well as the need to protect the environment for future generations and promote collaboration among the various parties involved in building environmental design for sustainability. ISO16813 is applicable to new construction and the retrofit of existing buildings.[45]

The building environmental design standard aims to:[45]

  • provide the constraints concerning sustainability issues from the initial stage of the design process, with building and plant life cycle to be considered together with owning and operating costs from the beginning of the design process;
  • assess the proposed design with rational criteria for indoor air quality, thermal comfort, acoustical comfort, visual comfort, energy efficiency, and HVAC system controls at every stage of the design process;
  • iterate decisions and evaluations of the design throughout the design process.

United States

[edit]

Licensing

[edit]

In the United States, federal licensure is generally handled by EPA certified (for installation and service of HVAC devices).

Many U.S. states have licensing for boiler operation. Some of these are listed as follows:

Finally, some U.S. cities may have additional labor laws that apply to HVAC professionals.

Societies

[edit]

Many HVAC engineers are members of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE). ASHRAE regularly organizes two annual technical committees and publishes recognized standards for HVAC design, which are updated every four years.[56]

Another popular society is AHRI, which provides regular information on new refrigeration technology, and publishes relevant standards and codes.

Codes

[edit]

Codes such as the UMC and IMC do include much detail on installation requirements, however. Other useful reference materials include items from SMACNA, ACGIH, and technical trade journals.

American design standards are legislated in the Uniform Mechanical Code or International Mechanical Code. In certain states, counties, or cities, either of these codes may be adopted and amended via various legislative processes. These codes are updated and published by the International Association of Plumbing and Mechanical Officials (IAPMO) or the International Code Council (ICC) respectively, on a 3-year code development cycle. Typically, local building permit departments are charged with enforcement of these standards on private and certain public properties.

Technicians

[edit]
HVAC Technician
Occupation
Occupation type
Vocational
Activity sectors
Construction
Description
Education required
Apprenticeship
Related jobs
Carpenter, electrician, plumber, welder

An HVAC technician is a tradesman who specializes in heating, ventilation, air conditioning, and refrigeration. HVAC technicians in the US can receive training through formal training institutions, where most earn associate degrees. Training for HVAC technicians includes classroom lectures and hands-on tasks, and can be followed by an apprenticeship wherein the recent graduate works alongside a professional HVAC technician for a temporary period.[57] HVAC techs who have been trained can also be certified in areas such as air conditioning, heat pumps, gas heating, and commercial refrigeration.

United Kingdom

[edit]

The Chartered Institution of Building Services Engineers is a body that covers the essential Service (systems architecture) that allow buildings to operate. It includes the electrotechnical, heating, ventilating, air conditioning, refrigeration and plumbing industries. To train as a building services engineer, the academic requirements are GCSEs (A-C) / Standard Grades (1-3) in Maths and Science, which are important in measurements, planning and theory. Employers will often want a degree in a branch of engineering, such as building environment engineering, electrical engineering or mechanical engineering. To become a full member of CIBSE, and so also to be registered by the Engineering Council UK as a chartered engineer, engineers must also attain an Honours Degree and a master's degree in a relevant engineering subject.[citation needed] CIBSE publishes several guides to HVAC design relevant to the UK market, and also the Republic of Ireland, Australia, New Zealand and Hong Kong. These guides include various recommended design criteria and standards, some of which are cited within the UK building regulations, and therefore form a legislative requirement for major building services works. The main guides are:

  • Guide A: Environmental Design
  • Guide B: Heating, Ventilating, Air Conditioning and Refrigeration
  • Guide C: Reference Data
  • Guide D: Transportation systems in Buildings
  • Guide E: Fire Safety Engineering
  • Guide F: Energy Efficiency in Buildings
  • Guide G: Public Health Engineering
  • Guide H: Building Control Systems
  • Guide J: Weather, Solar and Illuminance Data
  • Guide K: Electricity in Buildings
  • Guide L: Sustainability
  • Guide M: Maintenance Engineering and Management

Within the construction sector, it is the job of the building services engineer to design and oversee the installation and maintenance of the essential services such as gas, electricity, water, heating and lighting, as well as many others. These all help to make buildings comfortable and healthy places to live and work in. Building Services is part of a sector that has over 51,000 businesses and employs represents 2–3% of the GDP.

Australia

[edit]

The Air Conditioning and Mechanical Contractors Association of Australia (AMCA), Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH), Australian Refrigeration Mechanical Association and CIBSE are responsible.

Asia

[edit]

Asian architectural temperature-control have different priorities than European methods. For example, Asian heating traditionally focuses on maintaining temperatures of objects such as the floor or furnishings such as Kotatsu tables and directly warming people, as opposed to the Western focus, in modern periods, on designing air systems.

Philippines

[edit]

The Philippine Society of Ventilating, Air Conditioning and Refrigerating Engineers (PSVARE) along with Philippine Society of Mechanical Engineers (PSME) govern on the codes and standards for HVAC / MVAC (MVAC means "mechanical ventilation and air conditioning") in the Philippines.

India

[edit]

The Indian Society of Heating, Refrigerating and Air Conditioning Engineers (ISHRAE) was established to promote the HVAC industry in India. ISHRAE is an associate of ASHRAE. ISHRAE was founded at New Delhi[58] in 1981 and a chapter was started in Bangalore in 1989. Between 1989 & 1993, ISHRAE chapters were formed in all major cities in India.[citation needed]

See also

[edit]

References

[edit]
  1. ^ a b Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, GA, 2005
  2. ^ Designer's Guide to Ceiling-Based Air Diffusion, Rock and Zhu, ASHRAE, Inc., New York, 2002
  3. ^ Rezaie, Behnaz; Rosen, Marc A. (2012). "District heating and cooling: Review of technology and potential enhancements". Applied Energy. 93: 2–10. Bibcode:2012ApEn...93....2R. doi:10.1016/j.apenergy.2011.04.020.
  4. ^ Werner S. (2006). ECOHEATCOOL (WP4) Possibilities with more district heating in Europe. Euroheat & Power, Brussels. Archived 2015-09-24 at the Wayback Machine
  5. ^ Dalin P., Rubenhag A. (2006). ECOHEATCOOL (WP5) Possibilities with more district cooling in Europe, final report from the project. Final Rep. Brussels: Euroheat & Power. Archived 2012-10-15 at the Wayback Machine
  6. ^ Nielsen, Jan Erik (2014). Solar District Heating Experiences from Denmark. Energy Systems in the Alps - storage and distribution … Energy Platform Workshop 3, Zurich - 13/2 2014
  7. ^ Wong B., Thornton J. (2013). Integrating Solar & Heat Pumps. Renewable Heat Workshop.
  8. ^ Pauschinger T. (2012). Solar District Heating with Seasonal Thermal Energy Storage in Germany Archived 2016-10-18 at the Wayback Machine. European Sustainable Energy Week, Brussels. 18–22 June 2012.
  9. ^ "How Renewable Energy Is Redefining HVAC | AltEnergyMag". www.altenergymag.com. Retrieved 2020-09-29.
  10. ^ ""Lake Source" Heat Pump System". HVAC-Talk: Heating, Air & Refrigeration Discussion. Retrieved 2020-09-29.
  11. ^ Swenson, S. Don (1995). HVAC: heating, ventilating, and air conditioning. Homewood, Illinois: American Technical Publishers. ISBN 978-0-8269-0675-5.
  12. ^ "History of Heating, Air Conditioning & Refrigeration". Coyne College. Archived from the original on August 28, 2016.
  13. ^ "What is HVAC? A Comprehensive Guide".
  14. ^ Staffell, Iain; Brett, Dan; Brandon, Nigel; Hawkes, Adam (30 May 2014). "A review of domestic heat pumps".
  15. ^ (Alta.), Edmonton. Edmonton's green home guide : you're gonna love green. OCLC 884861834.
  16. ^ Bearg, David W. (1993). Indoor Air Quality and HVAC Systems. New York: Lewis Publishers. pp. 107–112.
  17. ^ Dianat, I.; Nazari, I. "Characteristic of unintentional carbon monoxide poisoning in Northwest Iran-Tabriz". International Journal of Injury Control and Promotion. Retrieved 2011-11-15.
  18. ^ ANSI/ASHRAE Standard 62.1, Ventilation for Acceptable Indoor Air Quality, ASHRAE, Inc., Atlanta, GA, US
  19. ^ Belias, Evangelos; Licina, Dusan (2024). "European residential ventilation: Investigating the impact on health and energy demand". Energy and Buildings. 304. Bibcode:2024EneBu.30413839B. doi:10.1016/j.enbuild.2023.113839.
  20. ^ Belias, Evangelos; Licina, Dusan (2022). "Outdoor PM2. 5 air filtration: optimising indoor air quality and energy". Building & Cities. 3 (1): 186–203. doi:10.5334/bc.153.
  21. ^ Ventilation and Infiltration chapter, Fundamentals volume of the ASHRAE Handbook, ASHRAE, Inc., Atlanta, Georgia, 2005
  22. ^ "Air Change Rates for typical Rooms and Buildings". The Engineering ToolBox. Retrieved 2012-12-12.
  23. ^ Bell, Geoffrey. "Room Air Change Rate". A Design Guide for Energy-Efficient Research Laboratories. Archived from the original on 2011-11-17. Retrieved 2011-11-15.
  24. ^ "Natural Ventilation for Infection Control in Health-Care Settings" (PDF). World Health Organization (WHO), 2009. Retrieved 2021-07-05.
  25. ^ Escombe, A. R.; Oeser, C. C.; Gilman, R. H.; et al. (2007). "Natural ventilation for the prevention of airborne contagion". PLOS Med. 4 (68): e68. doi:10.1371/journal.pmed.0040068. PMC 1808096. PMID 17326709.
  26. ^ Centers For Disease Control and Prevention (CDC) "Improving Ventilation In Buildings". 11 February 2020.
  27. ^ Centers For Disease Control and Prevention (CDC) "Guidelines for Environmental Infection Control in Health-Care Facilities". 22 July 2019.
  28. ^ Dr. Edward A. Nardell Professor of Global Health and Social Medicine, Harvard Medical School "If We're Going to Live With COVID-19, It's Time to Clean Our Indoor Air Properly". Time. February 2022.
  29. ^ "A Paradigm Shift to Combat Indoor Respiratory Infection - 21st century" (PDF). University of Leeds., Morawska, L, Allen, J, Bahnfleth, W et al. (36 more authors) (2021) A paradigm shift to combat indoor respiratory infection. Science, 372 (6543). pp. 689-691. ISSN 0036-8075
  30. ^ Video "Building Ventilation What Everyone Should Know". YouTube. 17 June 2022.
  31. ^ CDC (June 1, 2020). "Center for Disease Control and Prevention, Decontamination and Reuse of Filtering Facepiece Respirators". cdc.gov. Retrieved September 13, 2024.
  32. ^ "What are Air Ducts? The Homeowner's Guide to HVAC Ductwork". Super Tech. Retrieved 2018-05-14.
  33. ^ "Ductless Mini-Split Heat Pumps". U.S. Department of Energy.
  34. ^ "The Pros and Cons of Ductless Mini Split Air Conditioners". Home Reference. 28 July 2018. Retrieved 9 September 2020.
  35. ^ "Ductless Mini-Split Air Conditioners". ENERGY SAVER. Retrieved 29 November 2019.
  36. ^ Moisture Control Guidance for Building Design, Construction and Maintenance. December 2013.
  37. ^ Chenari, B., Dias Carrilho, J. and Gameiro da Silva, M., 2016. Towards sustainable, energy-efficient and healthy ventilation strategies in buildings: A review. Renewable and Sustainable Energy Reviews, 59, pp.1426-1447.
  38. ^ "Sustainable Facilities Tool: HVAC System Overview". sftool.gov. Retrieved 2 July 2014.
  39. ^ "Heating and Air Conditioning". www.nuclear-power.net. Retrieved 2018-02-10.
  40. ^ Keeping cool and green, The Economist 17 July 2010, p. 83
  41. ^ "Technology Profile: Demand Control Kitchen Ventilation (DCKV)" (PDF). Retrieved 2018-12-04.
  42. ^ a b Howard, J (2003), Guidance for Filtration and Air-Cleaning Systems to Protect Building Environments from Airborne Chemical, Biological, or Radiological Attacks, National Institute for Occupational Safety and Health, doi:10.26616/NIOSHPUB2003136, 2003-136
  43. ^ "The Inside Story: A Guide to Indoor Air Quality". 28 August 2014.
  44. ^ ISO. "Building environment standards". www.iso.org. Retrieved 2011-05-14.
  45. ^ a b ISO. "Building environment design—Indoor environment—General principles". Retrieved 14 May 2011.
  46. ^ "010.01.02 Ark. Code R. § 002 - Chapter 13 - Restricted Lifetime License".
  47. ^ "Boiler Professionals Training and Licensing".
  48. ^ "Michigan Boiler Rules".
  49. ^ "Minn. R. 5225.0550 - EXPERIENCE REQUIREMENTS AND DOCUMENTATION FOR LICENSURE AS AN OPERATING ENGINEER".
  50. ^ "Subchapter 24.122.5 - Licensing".
  51. ^ "Chapter 90 - BOILERS, PRESSURE VESSELS, AND REFRIGERATION".
  52. ^ "Article 33.1-14 - North Dakota Boiler Rules".
  53. ^ "Ohio Admin. Code 1301:3-5-10 - Boiler operator and steam engineer experience requirements".
  54. ^ "Subchapter 13 - Licensing of Boiler and Pressure Vessel Service, Repair and/or Installers".
  55. ^ "Or. Admin. R. 918-225-0691 - Boiler, Pressure Vessel and Pressure Piping Installation, Alteration or Repair Licensing Requirements".
  56. ^ "ASHRAE Handbook Online". www.ashrae.org. Retrieved 2020-06-17.
  57. ^ "Heating, Air Conditioning, and Refrigeration Mechanics and Installers : Occupational Outlook Handbook: : U.S. Bureau of Labor Statistics". www.bls.gov. Retrieved 2023-06-22.
  58. ^ "About ISHRAE". ISHRAE. Retrieved 2021-10-11.

Further reading

[edit]
[edit]

Media related to Climate control at Wikimedia Commons

Related media at Wikimedia Commons:

 

 

A digital thermostat
Honeywell's "The Round" model T87 thermostat, one of which is in the collection of the Smithsonian.
A touch screen thermostat
An electronic thermostat in a retail store

A thermostat is a regulating device component which senses the temperature of a physical system and performs actions so that the system's temperature is maintained near a desired setpoint.

Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating, central heating, air conditioners, HVAC systems, water heaters, as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators. In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Thermostatically controlled loads comprise roughly 50% of the overall electricity demand in the United States.[1]

A thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures. Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat. The word thermostat is derived from the Greek words θερμός thermos, "hot" and στατός statos, "standing, stationary".

Overview

[edit]

A thermostat exerts control by switching heating or cooling devices on or off, or by regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature. A thermostat can often be the main control unit for a heating or cooling system, in applications ranging from ambient air control to automotive coolant control. Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating, central heating, and air conditioners, kitchen equipment such as ovens and refrigerators, and medical and scientific incubators.

Construction and control

[edit]

Thermostats use different types of sensors to measure temperatures and actuate control operations. Mechanical thermostats commonly use bimetallic strips, converting a temperature change into mechanical displacement, to actuate control of the heating or cooling sources. Electronic thermostats, instead, use a thermistor or other semiconductor sensor, processing temperature change as electronic signals, to control the heating or cooling equipment.

Conventional thermostats are example of "bang-bang controllers" as the controlled system either operates at full capacity once the setpoint is reached, or keeps completely off. Although it is the simplest program to implement, such control method requires to include some hysteresis in order to prevent excessively rapid cycling of the equipment around the setpoint. As a consequence, conventional thermostats cannot control temperatures very precisely. Instead, there are oscillations of a certain magnitude, usually 1-2 °C.[2] Such control is in general inaccurate, inefficient and may induce more mechanical wear; it however, allows for more cost-effective compressors compared to ones with continuously variable capacity.[3][clarification needed]

Another consideration is the time delay of the controlled system. To improve the control performance of the system, thermostats can include an "anticipator", which stops heating/cooling slightly earlier than reaching the setpoint, as the system will continue to produce heat for a short while.[4] Turning off exactly at the setpoint will cause actual temperature to exceed the desired range, known as "overshoot". Bimetallic sensors can include a physical "anticipator", which has a thin wire touched on the thermostat. When current passes the wire, a small amount of heat is generated and transferred to the bimetallic coil. Electronic thermostats have an electronic equivalent.[5]

When higher control precision is required, a PID or MPC controller is preferred. However, they are nowadays mainly adopted for industrial purposes, for example, for semiconductor manufacturing factories or museums.

Sensor types

[edit]

Early technologies included mercury thermometers with electrodes inserted directly through the glass, so that when a certain (fixed) temperature was reached the contacts would be closed by the mercury. These were accurate to within a degree of temperature.

Common sensor technologies in use today include:

These may then control the heating or cooling apparatus using:

  • Direct mechanical control
  • Electrical signals
  • Pneumatic signals

History

[edit]

Possibly the earliest recorded examples of thermostatic control were built by a Dutch innovator, Cornelis Drebbel (1572–1633), about 1620 in England. He invented a mercury thermostat to regulate the temperature of a chicken incubator.[6] This is one of the first recorded feedback-controlled devices.

Modern thermostatic control was developed in the 1830s by Andrew Ure (1778–1857), a Scottish chemist. The textile mills of the time needed a constant and steady temperature to operate optimally, so Ure designed the bimetallic thermostat, which would bend as one of the metals expanded in response to the increased temperature and cut off the energy supply.[7]

Warren S. Johnson (1847–1911), of Wisconsin, patented a bi-metal room thermostat in 1883, and two years later sought a patent for the first multi-zone thermostatic control system.[8][9] Albert Butz (1849–1905) invented the electric thermostat and patented it in 1886.

One of the first industrial uses of the thermostat was in the regulation of the temperature in poultry incubators. Charles Hearson, a British engineer, designed the first modern incubator for eggs, which was taken up for use on poultry farms in 1879.[10]

Mechanical thermostats

[edit]

This covers only devices which both sense and control using purely mechanical means.

Bimetal

[edit]

Domestic water and steam based central heating systems have traditionally been controlled by bi-metallic strip thermostats, and this is dealt with later in this article. Purely mechanical control has been localised steam or hot-water radiator bi-metallic thermostats which regulated the individual flow. However, thermostatic radiator valves (TRV) are now being widely used.

Purely mechanical thermostats are used to regulate dampers in some rooftop turbine vents, reducing building heat loss in cool or cold periods.

Some automobile passenger heating systems have a thermostatically controlled valve to regulate the water flow and temperature to an adjustable level. In older vehicles the thermostat controls the application of engine vacuum to actuators that control water valves and flappers to direct the flow of air. In modern vehicles, the vacuum actuators may be operated by small solenoids under the control of a central computer.

Wax pellet

[edit]

Automotive

[edit]
Car engine thermostat

Perhaps the most common example of purely mechanical thermostat technology in use today is the internal combustion engine cooling system thermostat, used to maintain the engine near its optimum operating temperature by regulating the flow of coolant to an air-cooled radiator. This type of thermostat operates using a sealed chamber containing a wax pellet that melts and expands at a set temperature. The expansion of the chamber operates a rod which opens a valve when the operating temperature is exceeded. The operating temperature is determined by the composition of the wax. Once the operating temperature is reached, the thermostat progressively increases or decreases its opening in response to temperature changes, dynamically balancing the coolant recirculation flow and coolant flow to the radiator to maintain the engine temperature in the optimum range.

On many automobile engines, including all Chrysler Group and General Motors products, the thermostat does not restrict flow to the heater core. The passenger side tank of the radiator is used as a bypass to the thermostat, flowing through the heater core. This prevents formation of steam pockets before the thermostat opens, and allows the heater to function before the thermostat opens. Another benefit is that there is still some flow through the radiator if the thermostat fails.

Shower and other hot water controls

[edit]

A thermostatic mixing valve uses a wax pellet to control the mixing of hot and cold water. A common application is to permit operation of an electric water heater at a temperature hot enough to kill Legionella bacteria (above 60 °C, 140 °F), while the output of the valve produces water that is cool enough to not immediately scald (49 °C, 120 °F).

Analysis

[edit]

A wax pellet driven valve can be analyzed through graphing the wax pellet's hysteresis which consists of two thermal expansion curves; extension (motion) vs. temperature increase, and contraction (motion) vs. temperature decrease. The spread between the up and down curves visually illustrate the valve's hysteresis; there is always hysteresis within wax driven valves due to the phase transition or phase change between solids and liquids. Hysteresis can be controlled with specialized blended mixes of hydrocarbons; tight hysteresis is what most desire, however some applications require broader ranges. Wax pellet driven valves are used in anti scald, freeze protection, over-temp purge, solar thermal energy or solar thermal, automotive, and aerospace applications among many others.

Gas expansion

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Thermostats are sometimes used to regulate gas ovens. It consists of a gas-filled bulb connected to the control unit by a slender copper tube. The bulb is normally located at the top of the oven. The tube ends in a chamber sealed by a diaphragm. As the thermostat heats up, the gas expands applying pressure to the diaphragm which reduces the flow of gas to the burner.

Pneumatic thermostats

[edit]

A pneumatic thermostat is a thermostat that controls a heating or cooling system via a series of air-filled control tubes. This "control air" system responds to the pressure changes (due to temperature) in the control tube to activate heating or cooling when required. The control air typically is maintained on "mains" at 15-18 psi (although usually operable up to 20 psi). Pneumatic thermostats typically provide output/ branch/ post-restrictor (for single-pipe operation) pressures of 3-15 psi which is piped to the end device (valve/ damper actuator/ pneumatic-electric switch, etc.).[11]

The pneumatic thermostat was invented by Warren Johnson in 1895[12] soon after he invented the electric thermostat. In 2009, Harry Sim was awarded a patent for a pneumatic-to-digital interface[13] that allows pneumatically controlled buildings to be integrated with building automation systems to provide similar benefits as direct digital control (DDC).

Electrical and analog electronic thermostats

[edit]

Bimetallic switching thermostats

[edit]
Bimetallic thermostat for buildings.

Water and steam based central heating systems have traditionally had overall control by wall-mounted bi-metallic strip thermostats. These sense the air temperature using the differential expansion of two metals to actuate an on/off switch.[14] Typically the central system would be switched on when the temperature drops below the setpoint on the thermostat, and switched off when it rises above, with a few degrees of hysteresis to prevent excessive switching. Bi-metallic sensing is now being superseded by electronic sensors. A principal use of the bi-metallic thermostat today is in individual electric convection heaters, where control is on/off, based on the local air temperature and the setpoint desired by the user. These are also used on air-conditioners, where local control is required.

Contact configuration nomenclature

[edit]

This follows the same nomenclature as described in Relay § Terminology and Switch § Contact terminology. A thermostat is considered to be activated by thermal energy, thus “normal” refers to the state in which temperature is below the setpoint.

  • "NO" stands for "normally open". This is the same as "COR" ("close on rise"). May be used to start a fan when it is becoming hot, and to stop the fan when it has become cold enough.
  • "NC" stands for "normally closed". This is the same as "OOR" ("open on rise"). May be used to start a heater when it is becoming cold, and to stop the heater when it has become warm enough.
  • "CO" stands for "change over". This serves both as "NO" and "NC". May be used to start a fan when it is becoming hot, but also (on the opposite terminal), to start a heater when it is becoming cold.

Any leading number stands for number of contact sets, like "1NO", "1NC" for one contact set with two terminals. "1CO" will also have one contact set, even if it is a switch-over with three terminals.

Simple two wire thermostats

[edit]
Millivolt thermostat mechanism

The illustration is the interior of a common two wire heat-only household thermostat, used to regulate a gas-fired heater via an electric gas valve. Similar mechanisms may also be used to control oil furnaces, boilers, boiler zone valves, electric attic fans, electric furnaces, electric baseboard heaters, and household appliances such as refrigerators, coffee pots and hair dryers. The power through the thermostat is provided by the heating device and may range from millivolts to 240 volts in common North American construction, and is used to control the heating system either directly (electric baseboard heaters and some electric furnaces) or indirectly (all gas, oil and forced hot water systems). Due to the variety of possible voltages and currents available at the thermostat, caution must be taken when selecting a replacement device.

  1. Setpoint control lever. This is moved to the right for a higher temperature. The round indicator pin in the center of the second slot shows through a numbered slot in the outer case.
  2. Bimetallic strip wound into a coil. The center of the coil is attached to a rotating post attached to lever (1). As the coil gets colder the moving end — carrying (4) — moves clockwise.
  3. Flexible wire. The left side is connected via one wire of a pair to the heater control valve.
  4. Moving contact attached to the bimetal coil. Thence, to the heater's controller.
  5. Fixed contact screw. This is adjusted by the manufacturer. It is connected electrically by a second wire of the pair to the thermocouple and the heater's electrically operated gas valve.
  6. Magnet. This ensures a good contact when the contact closes. It also provides hysteresis to prevent short heating cycles, as the temperature must be raised several degrees before the contacts will open. As an alternative, some thermostats instead use a mercury switch on the end of the bimetal coil. The weight of the mercury on the end of the coil tends to keep it there, also preventing short heating cycles. However, this type of thermostat is banned in many countries due to its highly and permanently toxic nature if broken. When replacing these thermostats they must be regarded as chemical waste.

Not shown in the illustration is a separate bimetal thermometer on the outer case to show the actual temperature at the thermostat.

Millivolt thermostats

[edit]

As illustrated in the use of the thermostat above, all of the power for the control system is provided by a thermopile which is a combination of many stacked thermocouples, heated by the pilot light. The thermopile produces sufficient electrical power to drive a low-power gas valve, which under control of one or more thermostat switches, in turn controls the input of fuel to the burner.

This type of device is generally considered obsolete as pilot lights can waste a surprising amount of gas (in the same way a dripping faucet can waste a large amount of water over an extended period), and are also no longer used on stoves, but are still to be found in many gas water heaters and gas fireplaces. Their poor efficiency is acceptable in water heaters, since most of the energy "wasted" on the pilot still represents a direct heat gain for the water tank. The Millivolt system also makes it unnecessary for a special electrical circuit to be run to the water heater or furnace; these systems are often completely self-sufficient and can run without any external electrical power supply. For tankless "on demand" water heaters, pilot ignition is preferable because it is faster than hot-surface ignition and more reliable than spark ignition.

Some programmable thermostats - those that offer simple "millivolt" or "two-wire" modes - will control these systems.

24-volt thermostats

[edit]

The majority of modern heating/cooling/heat pump thermostats operate on low voltage (typically 24 volts AC) control circuits. The source of the 24 volt AC power is a control transformer installed as part of the heating/cooling equipment. The advantage of the low voltage control system is the ability to operate multiple electromechanical switching devices such as relays, contactors, and sequencers using inherently safe voltage and current levels.[15] Built into the thermostat is a provision for enhanced temperature control using anticipation.

A heat anticipator generates a small amount of additional heat to the sensing element while the heating appliance is operating. This opens the heating contacts slightly early to prevent the space temperature from greatly overshooting the thermostat setting. A mechanical heat anticipator is generally adjustable and should be set to the current flowing in the heating control circuit when the system is operating.

A cooling anticipator generates a small amount of additional heat to the sensing element while the cooling appliance is not operating. This causes the contacts to energize the cooling equipment slightly early, preventing the space temperature from climbing excessively. Cooling anticipators are generally non-adjustable.

Electromechanical thermostats use resistance elements as anticipators. Most electronic thermostats use either thermistor devices or integrated logic elements for the anticipation function. In some electronic thermostats, the thermistor anticipator may be located outdoors, providing a variable anticipation depending on the outdoor temperature.

Thermostat enhancements include outdoor temperature display, programmability, and system fault indication. While such 24 volt thermostats are incapable of operating a furnace when the mains power fails, most such furnaces require mains power for heated air fans (and often also hot-surface or electronic spark ignition) rendering moot the functionality of the thermostat. In other circumstances such as piloted wall and "gravity" (fanless) floor and central heaters the low voltage system described previously may be capable of remaining functional when electrical power is unavailable.

There are no standards for wiring color codes, but convention has settled on the following terminal codes and colors.[16][17] In all cases, the manufacturer's instructions should be considered definitive.

Terminal code Color Description
R Red 24 volt (Return line to appliance; often strapped to Rh and Rc)
Rh Red 24 volt HEAT load (Return line Heat)
Rc Red 24 volt COOL load (Return line Cool)
C Black/Blue/Brown/Cyan 24 volt Common connection to relays
W / W1 White Heat
W2 Varies/White/Black 2nd Stage / Backup Heat
Y / Y1 Yellow Cool
Y2 Blue/Orange/Purple/Yellow/White 2nd Stage Cool
G Green Fan
O Varies/Orange/Black Reversing valve Energize to Cool (Heat Pump)
B Varies/Blue/Black/Brown/Orange Reversing valve Energize to Heat (Heat Pump) or Common
E Varies/Blue/Pink/Gray/Tan Emergency Heat (Heat Pump)
S1/S2 Brown/Black/Blue Temperature Sensor (Usually outdoors on a Heat Pump System)
T Varies/Tan/Gray Outdoor Anticipator Reset, Thermistor
X Varies/Black Emergency Heat (Heat Pump) or Common
X2 Varies 2nd stage/emergency heating or indicator lights
L Varies Service Light
U Varies User programmable (usually for humidifier)
K Yellow/Green Combined Y and G
PS Varies Pipe Sensor for two pipe heat/cool systems
V Varies Variable speed (many can function as W2)

Older, mostly deprecated designations:

Terminal code Description
5 / V 24 volt ac supply
4 / M 24 volt HEAT load
6 / blank Not heat to close valve
F Cool fan relay or Fault light
G Heat fan relay
H Heat valve
M Heat Pump compressor
P Heat Pump defrost
R Heat pump reversing valve
VR 24 volt auxiliary heat
Y Auxiliary heat
C Clock power (usually two terminals) or Cool relay
T Transformer common
Z Fan power source for "Auto" connection

Line-voltage thermostats

[edit]

Line voltage thermostats are most commonly used for electric space heaters such as a baseboard heater or a direct-wired electric furnace. If a line voltage thermostat is used, system power (in the United States, 120 or 240 volts) is directly switched by the thermostat. With switching current often exceeding 40 amperes, using a low voltage thermostat on a line voltage circuit will result at least in the failure of the thermostat and possibly a fire. Line voltage thermostats are sometimes used in other applications, such as the control of fan-coil (fan powered from line voltage blowing through a coil of tubing which is either heated or cooled by a larger system) units in large systems using centralized boilers and chillers, or to control circulation pumps in hydronic heating applications.

Some programmable thermostats are available to control line-voltage systems. Baseboard heaters will especially benefit from a programmable thermostat which is capable of continuous control (as are at least some Honeywell models), effectively controlling the heater like a lamp dimmer, and gradually increasing and decreasing heating to ensure an extremely constant room temperature (continuous control rather than relying on the averaging effects of hysteresis). Systems which include a fan (electric furnaces, wall heaters, etc.) must typically use simple on/off controls.

Digital electronic thermostats

[edit]
Residential digital thermostat
Lux Products' Model TX9000TS Touch Screen Thermostat.
Lux Products WIN100 Heating & Cooling Programmable Outlet Thermostat shown with control door closed and open.

Newer digital thermostats have no moving parts to measure temperature and instead rely on thermistors or other semiconductor devices such as a resistance thermometer (resistance temperature detector). Typically one or more regular batteries must be installed to operate it, although some so-called "power stealing" digital thermostats (operated for energy harvesting) use the common 24-volt AC circuits as a power source, but will not operate on thermopile powered "millivolt" circuits used in some furnaces. Each has an LCD screen showing the current temperature, and the current setting. Most also have a clock, and time-of-day and even day-of-week settings for the temperature, used for comfort and energy conservation. Some advanced models have touch screens, or the ability to work with home automation or building automation systems.

Digital thermostats use either a relay or a semiconductor device such as triac to act as a switch to control the HVAC unit. Units with relays will operate millivolt systems, but often make an audible "click" noise when switching on or off.

HVAC systems with the ability to modulate their output can be combined with thermostats that have a built-in PID controller to achieve smoother operation. There are also modern thermostats featuring adaptive algorithms to further improve the inertia prone system behaviour. For instance, setting those up so that the temperature in the morning at 7 a.m. should be 21 °C (69.8 °F), makes sure that at that time the temperature will be 21 °C (69.8 °F), where a conventional thermostat would just start working at that time. The algorithms decide at what time the system should be activated in order to reach the desired temperature at the desired time.[18] Other thermostat used for process/industrial control where on/off control is not suitable the PID control can also makes sure that the temperature is very stable (for instance, by reducing overshoots by fine tuning PID constants for set value (SV)[19] or maintaining temperature in a band by deploying hysteresis control.[20])

Most digital thermostats in common residential use in North America and Europe are programmable thermostats, which will typically provide a 30% energy savings if left with their default programs; adjustments to these defaults may increase or reduce energy savings.[21] The programmable thermostat article provides basic information on the operation, selection and installation of such a thermostat.

Thermostats and HVAC operation

[edit]

Ignition sequences in modern conventional systems

[edit]
Gas
  1. Start draft inducer fan/blower (if the furnace is relatively recent) to create a column of air flowing up the chimney
  2. Heat ignitor or start spark-ignition system
  3. Open gas valve to ignite main burners
  4. Wait (if furnace is relatively recent) until the heat exchanger is at proper operating temperature before starting main blower fan or circulator pump
Oil
Similar to gas, except rather than opening a valve, the furnace will start an oil pump to inject oil into the burner
Electric
The blower fan or circulator pump will be started, and a large electromechanical relay or TRIAC will turn on the heating elements
Coal, grain or pellet
Generally rare today (though grains such as corn, wheat, and barley, or pellets made of wood, bark, or cardboard are increasing in popularity); similar to gas, except rather than opening a valve, the furnace will start a screw to drive coal/grain/pellets into the firebox

With non-zoned (typical residential, one thermostat for the whole house) systems, when the thermostat's R (or Rh) and W terminals are connected, the furnace will go through its start-up procedure and produce heat.

With zoned systems (some residential, many commercial systems — several thermostats controlling different "zones" in the building), the thermostat will cause small electric motors to open valves or dampers and start the furnace or boiler if it is not already running.

Most programmable thermostats will control these systems.

Combination heating/cooling regulation

[edit]

Depending on what is being controlled, a forced-air air conditioning thermostat generally has an external switch for heat/off/cool, and another on/auto to turn the blower fan on constantly or only when heating and cooling are running. Four wires come to the centrally-located thermostat from the main heating/cooling unit (usually located in a closet, basement, or occasionally in the attic): One wire, usually red, supplies 24 volts AC power to the thermostat, while the other three supply control signals from the thermostat, usually white for heat, yellow for cooling, and green to turn on the blower fan. The power is supplied by a transformer, and when the thermostat makes contact between the 24 volt power and one or two of the other wires, a relay back at the heating/cooling unit activates the corresponding heat/fan/cool function of the unit(s).

A thermostat, when set to "cool", will only turn on when the ambient temperature of the surrounding room is above the set temperature. Thus, if the controlled space has a temperature normally above the desired setting when the heating/cooling system is off, it would be wise to keep the thermostat set to "cool", despite what the temperature is outside. On the other hand, if the temperature of the controlled area falls below the desired degree, then it is advisable to turn the thermostat to "heat".

Heat pump regulation

[edit]
Thermostat design

The heat pump is a refrigeration based appliance which reverses refrigerant flow between the indoor and outdoor coils. This is done by energizing a reversing valve (also known as a "4-way" or "change-over" valve). During cooling, the indoor coil is an evaporator removing heat from the indoor air and transferring it to the outdoor coil where it is rejected to the outdoor air. During heating, the outdoor coil becomes the evaporator and heat is removed from the outdoor air and transferred to the indoor air through the indoor coil. The reversing valve, controlled by the thermostat, causes the change-over from heat to cool. Residential heat pump thermostats generally have an "O" terminal to energize the reversing valve in cooling. Some residential and many commercial heat pump thermostats use a "B" terminal to energize the reversing valve in heating. The heating capacity of a heat pump decreases as outdoor temperatures fall. At some outdoor temperature (called the balance point) the ability of the refrigeration system to transfer heat into the building falls below the heating needs of the building. A typical heat pump is fitted with electric heating elements to supplement the refrigeration heat when the outdoor temperature is below this balance point. Operation of the supplemental heat is controlled by a second stage heating contact in the heat pump thermostat. During heating, the outdoor coil is operating at a temperature below the outdoor temperature and condensation on the coil may take place. This condensation may then freeze onto the coil, reducing its heat transfer capacity. Heat pumps therefore have a provision for occasional defrost of the outdoor coil. This is done by reversing the cycle to the cooling mode, shutting off the outdoor fan, and energizing the electric heating elements. The electric heat in defrost mode is needed to keep the system from blowing cold air inside the building. The elements are then used in the "reheat" function. Although the thermostat may indicate the system is in defrost and electric heat is activated, the defrost function is not controlled by the thermostat. Since the heat pump has electric heat elements for supplemental and reheats, the heat pump thermostat provides for use of the electric heat elements should the refrigeration system fail. This function is normally activated by an "E" terminal on the thermostat. When in emergency heat, the thermostat makes no attempt to operate the compressor or outdoor fan.

Thermostat location

[edit]

The thermostat should not be located on an outside wall or where it could be exposed to direct sunlight at any time during the day. It should be located away from the room's cooling or heating vents or device, yet exposed to general airflow from the room(s) to be regulated.[22] An open hallway may be most appropriate for a single zone system, where living rooms and bedrooms are operated as a single zone. If the hallway may be closed by doors from the regulated spaces then these should be left open when the system is in use. If the thermostat is too close to the source controlled then the system will tend to "short a cycle", and numerous starts and stops can be annoying and in some cases shorten equipment life. A multiple zoned system can save considerable energy by regulating individual spaces, allowing unused rooms to vary in temperature by turning off the heating and cooling.

Setback temperature

[edit]

HVAC systems take a long time, usually one to several hours, to cool down or warm up the space from near outdoor conditions in summer or winter. Thus, it is a common practice to set setback temperatures when the space is not occupied (night and/or holidays). On the one hand, compared with maintaining at the original setpoint, substantial energy consumption can be saved.[23] On the other hand, compared with turning off the system completely, it avoids room temperature drifting too much from the comfort zone, thus reducing the time of possible discomfort when the space is again occupied. New thermostats are mostly programmable and include an internal clock that allows this setback feature to be easily incorporated.

Dummy thermostats

[edit]

It has been reported that many thermostats in office buildings are non-functional dummy devices, installed to give tenants' employees an illusion of control.[24][25] These dummy thermostats are in effect a type of placebo button. However, these thermostats are often used to detect the temperature in the zone, even though their controls are disabled. This function is often referred to as "lockout".[26]

See also

[edit]

Notes and references

[edit]
  1. ^ Energy Information Administration, Residential energy consumption survey, U.S. Dept. Energy, Washington, DC, Tech. Rep., 2001.
  2. ^ thermostathub (June 26, 2023). "Easy Home Heating: Get Started with the Danfoss Wireless Thermostat". Thermostat Hub. Retrieved October 23, 2023.
  3. ^ Homod, Raad Z.; Gaeid, Khalaf S.; Dawood, Suroor M.; Hatami, Alireza; Sahari, Khairul S. (August 2020). "Evaluation of energy-saving potential for optimal time response of HVAC control system in smart buildings". Applied Energy. 271: 115255. Bibcode:2020ApEn..27115255H. doi:10.1016/j.apenergy.2020.115255. S2CID 219769422.
  4. ^ Roots, W. K. (1962). "An introduction to the assessment of line-voltage thermostat performance for electric heating applications". Transactions of the American Institute of Electrical Engineers, Part II: Applications and Industry. 81 (3): 176–183. doi:10.1109/TAI.1962.6371813. ISSN 0097-2185. S2CID 51647958.
  5. ^ James E. Brumbaugh, AudelHVAC Fundamentals: Volume 2: Heating System Components, Gas and Oil Burners, and Automatic Controls, John Wiley & Sons, 2004 ISBN 0764542079 pp. 109-119
  6. ^ "Tierie, Gerrit. Cornelis Drebbel. Amsterdam: HJ Paris, 1932" (PDF). Retrieved May 3, 2013.
  7. ^ "An Early History Of Comfort Heating". The NEWS Magazine. Troy, Michigan: BNP Media. November 6, 2001. Retrieved November 2, 2014.
  8. ^ "Thermostat Maker Deploys Climate Control Against Climate Change". America.gov. Archived from the original on April 18, 2009. Retrieved October 3, 2009.
  9. ^ "Johnson Controls Inc. | History". Johnsoncontrols.com. November 7, 2007. Retrieved October 3, 2009.
  10. ^ Falk, Cynthia G. (2012). Barns of New York: Rural Architecture of the Empire State (paperback) (First ed.). Ithaca, New York: Cornell University Press (published May 1, 2012). ISBN 978-0-8014-7780-5. Retrieved November 2, 2014.
  11. ^ "Dr-Fix-It Explains a Common Pneumatic Comfort Control Circuit". dr-fix-it.com. RTWEB. 2005. Archived from the original on December 6, 2017. Retrieved November 2, 2014.
  12. ^ Fehring, T.H., ed., Mechanical Engineering: A Century of Progress, NorCENergy Consultants, LLC, October 10, 1980 - Technology & Engineering, p. 22
  13. ^ "Pneumatic-to-digital devices, systems and methods" (PDF).
  14. ^ Salazar, Diet (October 21, 2019). "Thermostats: Everything You Need to Know". Engineer Warehouse. Retrieved March 12, 2021.
  15. ^ Electrical potentials at and below 24 volts are classed as "Safety Extra-Low Voltage" under most electrical codes when supplied through an isolation transformer.
  16. ^ Sawyer, Doc. "Thermostat Wire Color Codes". dr-fix-it.com. Archived from the original on September 23, 2015. Retrieved March 7, 2015.[1]
  17. ^ Transtronics, Inc. "Thermostat signals and wiring". wiki.xtronics.com. Retrieved March 7, 2015.
  18. ^ Honeywell smart response technology
  19. ^ "Smart PID temperature control". smartpid.com. September 19, 2016. Retrieved October 10, 2018.
  20. ^ "Temperature Controllers Using Hysteresis". panasonic.com. October 18, 2011. Retrieved October 10, 2018.
  21. ^ "Summary of Research Findings From the Programmable Thermostat Market" (PDF). Energy Star. Retrieved March 12, 2021.
  22. ^ KMC Controls. "Room Sensor and Thermostat: Mounting and Maintenance Application Guide" (PDF). Retrieved April 12, 2021.
  23. ^ Moon, Jin Woo; Han, Seung-Hoon (February 1, 2011). "Thermostat strategies impact on energy consumption in residential buildings". Energy and Buildings. 43 (2): 338–346. Bibcode:2011EneBu..43..338M. doi:10.1016/j.enbuild.2010.09.024. ISSN 0378-7788.
  24. ^ Sandberg, Jared (January 15, 2003). "Employees Only Think They Control Thermostat". The Wall Street Journal. Retrieved September 2, 2009.
  25. ^ Katrina C. Arabe (April 11, 2003). ""Dummy" Thermostats Cool Down Tempers, Not Temperatures". Retrieved February 13, 2010.
  26. ^ Example datasheet of current art thermostat, exhibiting lockout functionality : http://cgproducts.johnsoncontrols.com/MET_PDF/12011079.pdf
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Frequently Asked Questions

During your annual HVAC maintenance, signs that your blower motor may be failing include unusual noises like squealing or grinding, weak or no airflow from vents, and overheating issues. Additionally, a technician may notice burnt smells or find that the systems circuit breaker frequently trips.
A failed blower motor significantly impacts your HVAC system’s ability to circulate air throughout your home. This results in uneven heating or cooling, increased energy bills due to inefficient operation, and potential strain on other components of the system.
Yes, regular annual maintenance can help prevent a blower motor failure. During these checks, technicians clean and lubricate parts, identify early signs of wear and tear, replace filters regularly, and ensure all components are functioning properly to extend the life of the blower motor.