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 ).
89-701: Marcy South is a 2 circuit high voltage power line in the U.S. State of New York . Each circuit is 345,000 volts, the one circuit runs from Fraser Substation in Delaware County to Marcy Substation in Oneida County and the other circuit runs from Coopers Corners Substation to the Marcy Substation. It was constructed amid heavy controversy in the late 1980s by the New York Power Authority . The Power Authority of
178-443: 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. 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. Natural ventilation
267-541: A 100-watt light bulb for approximately 2 months). However, an average bolt of positive lightning (from the top of a thunderstorm) may carry a current of 300 to 500 kiloamperes, transfer a charge of up to 300 coulombs, have a potential difference up to 1 gigavolt (a billion volts), and may dissipate 300 GJ of energy (72 tons TNT, or enough energy to light a 100-watt light bulb for up to 95 years). A negative lightning strike typically lasts for only tens of microseconds, but multiple strikes are common. A positive lightning stroke
356-497: A blast of high pressure air, a special dielectric gas (such as SF 6 under pressure), or immersion in mineral oil to quench the arc when the high voltage circuit is broken. Wiring in equipment such as X-ray machines and lasers requires care. The high voltage section is kept physically distant from the low voltage side to reduce the possibility of an arc forming between the two. To avoid coronal losses, conductors are kept as short as possible and free of sharp points. If insulated,
445-487: 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
534-736: A building that was not designed to receive it) because of the bulky air ducts required. (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
623-481: 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. 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
712-549: 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. Warm air systems distribute
801-413: A direct strike on persons or property. However, lightning can also create dangerous voltage gradients in the earth, as well as an electromagnetic pulse , and can charge extended metal objects such as telephone cables, fences, and pipelines to dangerous voltages that can be carried many miles from the site of the strike. Although many of these objects are not normally conductive, very high voltage can cause
890-527: A facility to be heated and cooled by a single piece of equipment by the same means, and with the same hardware. 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
979-417: A few small points of contact become the last to separate. The current becomes constricted to these small hot spots , causing them to become incandescent, so that they emit electrons (through thermionic emission ). Even a small 9 V battery can spark noticeably by this mechanism in a darkened room. The ionized air and metal vapour (from the contacts) form plasma , which temporarily bridges the widening gap. If
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#17327755521131068-518: A hazard is presented to maintenance and operating personnel due to the possibility of a high-intensity electric arc . Maximum temperature of an arc can exceed 10,000 kelvins , and the radiant heat, expanding hot air, and explosive vaporization of metal and insulation material can cause severe injury to unprotected workers. Such switchgear line-ups and high-energy arc sources are commonly present in electric power utility substations and generating stations, industrial plants and large commercial buildings. In
1157-410: 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
1246-416: 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
1335-421: A high-voltage transmission line or substation may result in high currents flowing along the surface of the earth, producing an earth potential rise that also presents a danger of electric shock. For high voltage and extra-high voltage transmission lines, specially trained personnel use " live line " techniques to allow hands-on contact with energized equipment. In this case the worker is electrically connected to
1424-459: A huge difference for the environment and help expand the knowledge of using different methods. 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. Multiple inventions within this time frame preceded the beginnings of
1513-406: A human body will be relatively constant as long as contact is maintained, unlike with electrostatic machines which generally take longer to build up charges, and the voltage will be much higher than the break-down voltage of human skin. As a consequence, the output of a Tesla coil can be dangerous or even fatal. Depending on the prospective short-circuit current available at a switchgear line-up,
1602-475: 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
1691-486: A leg. Electricity can flow between two conductors in high voltage equipment and the body can complete the circuit. To avoid that from happening, the worker should wear insulating clothing such as rubber gloves, use insulated tools, and avoid touching the equipment with more than one hand at a time. An electrical current can also flow between the equipment and the earth ground. To prevent that, the worker should stand on an insulated surface such as on rubber mats. Safety equipment
1780-467: A person's body provides a path for current flow, causing tissue damage and heart failure. Other injuries can include burns from the arc generated by the accidental contact. These burns can be especially dangerous if the victim's airway is affected. Injuries may also be suffered as a result of the physical forces experienced by people who fall from a great height or are thrown a considerable distance. Low-energy exposure to high voltage may be harmless, such as
1869-465: A relatively few electrons move. These devices have a limited amount of stored energy, so the average current produced is low and usually for a short time, with impulses peaking in the 1 A range for a nanosecond. The discharge may involve extremely high voltage over very short periods, but to produce heart fibrillation, an electric power supply must produce a significant current in the heart muscle continuing for many milliseconds , and must deposit
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#17327755521131958-494: 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. 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
2047-617: A total energy in the range of at least millijoules or higher. Relatively high current at anything more than about fifty volts can therefore be medically significant and potentially fatal. During the discharge, these machines apply high voltage to the body for only a millionth of a second or less. So a low current is applied for a very short time, and the number of electrons involved is very small. Despite Tesla coils superficially appearing similar to Van de Graaff generators, they are not electrostatic machines and can produce significant radio frequency currents continuously. The current supplied to
2136-485: A transmitting antenna is dangerous for this reason, and a high-frequency Tesla coil can sustain a spark with only one endpoint. Protective equipment on high-voltage transmission lines normally prevents formation of an unwanted arc, or ensures that it is quenched within tens of milliseconds. Electrical apparatus that interrupts high-voltage circuits is designed to safely direct the resulting arc so that it dissipates without damage. High voltage circuit breakers often use
2225-934: A voltage as high voltage are the possibility of causing a spark in air, and the danger of electric shock by contact or proximity. The International Electrotechnical Commission and its national counterparts ( IET , IEEE , VDE , etc.) define high voltage as above 1000 V for alternating current , and at least 1500 V for direct current . In the United States, the American National Standards Institute (ANSI) establishes nominal voltage ratings for 60 Hz electric power systems over 100 V. Specifically, ANSI C84.1-2020 defines high voltage as 115 kV to 230 kV, extra-high voltage as 345 kV to 765 kV, and ultra-high voltage as 1,100 kV. British Standard BS 7671 :2008 defines high voltage as any voltage difference between conductors that
2314-481: Is U+26A1, the symbol "⚡︎" . The common static electric sparks seen under low-humidity conditions always involve voltage well above 700 V. For example, sparks to car doors in winter can involve voltages as high as 20,000 V. Electrostatic generators such as Van de Graaff generators and Wimshurst machines can produce voltages approaching one million volts at several amps, but typically don't last long enough to cause damage. Induction coils operate on
2403-787: Is a stub . You can help Misplaced Pages by expanding it . High voltage High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, high voltage refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant special safety requirements and procedures . High voltage is used in electrical power distribution , in cathode-ray tubes , to generate X-rays and particle beams , to produce electrical arcs , for ignition, in photomultiplier tubes , and in high-power amplifier vacuum tubes , as well as other industrial, military and scientific applications. The numerical definition of high voltage depends on context. Two factors considered in classifying
2492-403: 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
2581-410: 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
2670-463: 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. 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
2759-877: 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
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2848-530: Is classified as voltages in the range of 345,000– 765,000 V. In electronics systems, a power supply that provides greater than 275,000 volts is called an EHV Power Supply , and is often used in experiments in physics. The accelerating voltage for a television cathode ray tube may be described as extra-high voltage or extra-high tension (EHT), compared to other voltage supplies within the equipment. This type of supply ranges from 5 kV to about 30 kV. The Unicode text character representing "high voltage"
2937-503: Is extinguished every time the current goes through a zero crossing , and must reignite during the next half-cycle to maintain the arc. Unlike an ohmic conductor, the resistance of an arc decreases as the current increases. This makes unintentional arcs in an electrical apparatus dangerous since even a small arc can grow large enough to damage equipment and start fires if sufficient current is available. Intentionally produced arcs, such as used in lighting or welding , require some element in
3026-675: Is higher than 1000 VAC or 1500 V ripple-free DC, or any voltage difference between a conductor and Earth that is higher than 600 VAC or 900 V ripple-free DC. Electricians may only be licensed for particular voltage classes in some jurisdictions. For example, an electrical license for a specialized sub-trade such as installation of HVAC systems, fire alarm systems, closed-circuit-television systems may be authorized to install systems energized up to only 30 volts between conductors, and may not be permitted to work on mains-voltage circuits. The general public may consider household mains circuits (100 to 250 VAC), which carry
3115-481: Is inexpensive. 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. 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. For hospital rooms with airborne contagions
3204-480: Is invisible but has a sweet odor. It oxidizes to nitrogen dioxide within a few minutes, which has a yellow or reddish-brown color depending on concentration and smells of chlorine gas like a swimming pool. Ozone is invisible but has a pungent smell like that of the air after a lightning storm. It is a short-lived species and half of it breaks down into O 2 within a day at normal temperatures and atmospheric pressure. Hazards due to lightning obviously include
3293-499: Is known as room air distribution . 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
3382-581: Is needed to improve the performance of ventilation in terms of ... In scenarios where outdoor pollution would deteriorate indoor air quality, other treatment devices such as filtration may also be necessary. Methods for ventilating a building may be divided into mechanical/forced and natural types. 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
3471-407: Is not a fixed minimum for producing spark breakdown, but it is a rule-of-thumb. For air at STP, the minimum sparkover voltage is around 327 volts, as noted by Friedrich Paschen . While lower voltages do not, in general, jump a gap that is present before the voltage is applied, interrupting an existing current flow with a gap often produces a low-voltage spark or arc . As the contacts are separated,
3560-450: Is not feasible or where the space conditioning efficiency is of prime concern. The benefits of ductless air conditioning systems include easy installation, no ductwork, greater zonal control, flexibility of control, and quiet operation. In space conditioning, the duct losses can account for 30% of energy consumption. The use of minisplits can result in energy savings in space conditioning as there are no losses associated with ducting. With
3649-691: Is now used in modified form in U.S. National Electrical Code and in the Canadian Electrical Code . Intrinsic safety apparatus is now approved for use in North American applications. Electrical discharges, including partial discharge and corona , can produce small quantities of toxic gases, which in a confined space can be a health hazard. These gases include oxidizers such as ozone and various oxides of nitrogen . They are readily identified by their characteristic odor or color, and thus contact time can be minimized. Nitric oxide
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3738-436: Is required for any air conditioner installed. The refrigeration cycle uses four essential elements to cool, which are compressor, condenser, metering device, and evaporator. 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
3827-458: 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
3916-649: Is tested regularly to ensure it is still protecting the user. Test regulations vary according to country. Testing companies can test at up 300,000 volts and offer services from glove testing to Elevated Working Platform (or EWP) testing. Contact with or close approach to line conductors presents a danger of electrocution . Contact with overhead wires can result in injury or death. Metal ladders, farm equipment, boat masts, construction machinery, aerial antennas , and similar objects are frequently involved in fatal contact with overhead wires. Unauthorized persons climbing on power pylons or electrical apparatus are also frequently
4005-497: 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
4094-408: 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
4183-404: Is typically a single event, but the larger peak current may flow for hundreds of milliseconds, making it considerably more energetic than negative lightning. The dielectric breakdown strength of dry air, at Standard Temperature and Pressure (STP), between spherical electrodes is approximately 33 kV/cm. This is only a rough guide, since the actual breakdown voltage is highly dependent upon
4272-560: The chest area. The voltage at which there is the danger of electrocution depends on the electrical conductivity of dry human skin. Living human tissue can be protected from damage by the insulating characteristics of dry skin up to around 50 volts. If the same skin becomes wet, if there are wounds, or if the voltage is applied to electrodes that penetrate the skin, then even voltage sources below 40 V can be lethal. Accidental contact with any high voltage supplying sufficient energy may result in severe injury or death. This can occur as
4361-568: 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
4450-430: The electrical breakdown of such insulators, causing them to act as conductors. These transferred potentials are dangerous to people, livestock, and electronic apparatus. Lightning strikes also start fires and explosions, which result in fatalities, injuries, and property damage. For example, each year in North America, thousands of forest fires are started by lightning strikes. Measures to control lightning can mitigate
4539-553: The high-voltage line but thoroughly insulated from the earth so that he is at the same electrical potential as that of the line. Since training for such operations is lengthy, and still presents a danger to personnel, only very important transmission lines are subject to maintenance while live. Outside these properly engineered situations, insulation from earth does not guarantee that no current flows to earth—as grounding or arcing to ground can occur in unexpected ways, and high-frequency currents can burn even an ungrounded person. Touching
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#17327755521134628-421: The CDC recommends a minimum of 12 ACH. The challenges in facility ventilation are public unawareness, ineffective government oversight, poor building codes that are based on comfort levels, poor system operations, poor maintenance, and lack of transparency. UVC or Ultraviolet Germicidal Irradiation is a function used in modern air conditioners which reduces airborne viruses , bacteria , and fungi , through
4717-462: 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 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
4806-552: The State of New York announced plans to deliver hydroelectric power from Canada to the New York City region in 1982. It became fully operational on June 1, 1988. The power line met with vigorous and sometimes highly contentious and violent opposition from local property owners from its proposition to its planning and surveying, and even its construction. The Marcy South Series Compensation Project began in 2016 and involved
4895-1039: The United States, the National Fire Protection Association has published a guideline standard NFPA 70E for evaluating and calculating arc flash hazard , and provides standards for the protective clothing required for electrical workers exposed to such hazards in the workplace. Even voltages insufficient to break down air can supply enough energy to ignite atmospheres containing flammable gases or vapours, or suspended dust. For example, hydrogen gas, natural gas , or petrol/ gasoline vapor mixed with air can be ignited by sparks produced by electrical apparatus. Examples of industrial facilities with hazardous areas are petrochemical refineries, chemical plants , grain elevators , and coal mines . Measures taken to prevent such explosions include: In recent years, standards for explosion hazard protection have become more uniform between European and North American practice. The "zone" system of classification
4984-433: 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. 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
5073-484: 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. 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
5162-483: 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. Ventilation
5251-440: 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. A clear understanding of both indoor and outdoor air quality parameters
5340-445: The circuit to stabilize the arc's current/voltage characteristics. Electrical transmission and distribution lines for electric power typically use voltages between tens and hundreds of kilovolts. The lines may be overhead or underground. High voltage is used in power distribution to reduce ohmic losses when transporting electricity long distance. It is used in the production of semiconductors to sputter thin layers of metal films on
5429-520: 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. 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
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#17327755521135518-413: 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. HVAC is significantly responsible for promoting energy efficiency of buildings as the building sector consumes the largest percentage of global energy. Since the 1980s, manufacturers of HVAC equipment have been making an effort to make
5607-446: 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
5696-415: 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,
5785-567: The electrode shape and size. Strong electric fields (from high voltages applied to small or pointed conductors) often produce violet-colored corona discharges in air, as well as visible sparks. Voltages below about 500–700 volts cannot produce easily visible sparks or glows in air at atmospheric pressure, so by this rule these voltages are "low". However, under conditions of low atmospheric pressure (such as in high-altitude aircraft ), or in an environment of noble gas such as argon or neon , sparks appear at much lower voltages. 500 to 700 volts
5874-646: 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. 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
5963-610: 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. The first residential AC was installed by 1914, and by the 1950s there was "widespread adoption of residential AC". The invention of
6052-453: The flyback effect resulting in voltages greater than the turns ratio multiplied by the input voltage. They typically produce higher currents than electrostatic machines, but each doubling of desired output voltage roughly doubles the weight due to the amount of wire required in the secondary winding. Thus scaling them to higher voltages by adding more turns of wire can become impractical. The Cockcroft-Walton multiplier can be used to multiply
6141-433: 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
6230-717: The hazard; these include lightning rods , shielding wires, and bonding of electrical and structural parts of buildings to form a continuous enclosure. HVAC 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)
6319-417: 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 to remove dust and pollen particles. The use of furnaces, space heaters, and boilers as a method of indoor heating could result in incomplete combustion and
6408-525: The highest voltages they normally encounter, to be high voltage . Voltages over approximately 50 volts can usually cause dangerous amounts of current to flow through a human being who touches two points of a circuit, so safety standards are more restrictive around such circuits. In automotive engineering , high voltage is defined as voltage in range 30 to 1000 VAC or 60 to 1500 VDC. The definition of extra-high voltage (EHV) again depends on context. In electric power transmission engineering, EHV
6497-531: The installation of three series capacitor banks. The capacitor banks were installed to raise the voltage and keep it constant, which enhances transmission efficiency. Two capacitor banks were installed by New York Power Authority , the other installed by NYSEG at the Fraser Substation. Since its construction, other projects including a high-voltage DC line have been proposed for the same route. This article about electric power transmission
6586-568: The interior air. Methods for ventilating a building are divided into mechanical/forced and natural types. 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
6675-494: 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. All modern air conditioning systems, even small window package units, are equipped with internal air filters. These are generally of a lightweight gauze-like material, and must be replaced or washed as conditions warrant. For example,
6764-658: The isolation and discovery of the element argon from atmospheric air. Induction coils powered early X-ray tubes. Moseley used an X-ray tube to determine the atomic number of a selection of metallic elements by the spectrum emitted when used as anodes. High voltage is used for generating electron beams for microscopy . Cockcroft and Walton invented the voltage multiplier to transmutate lithium atoms in lithium oxide into helium by accelerating hydrogen atoms. Voltages greater than 50 V applied across dry unbroken human skin can cause heart fibrillation if they produce electric currents in body tissues that happen to pass through
6853-400: The opening of this vent. Typical fresh air intake is about 10% of the total supply air. 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
6942-572: The overall heating-portion of the DHC network (likely with energy added to boost the temperature). 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, winter's cold, 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
7031-405: The plastic coating should be free of air bubbles which result in coronal discharges within the bubbles. A high voltage is not necessarily dangerous if it cannot deliver substantial current . Despite electrostatic machines such as Van de Graaff generators and Wimshurst machines producing voltages approaching one million volts, they deliver a brief sting. That is because the current is low, i.e. only
7120-448: The power supply and load allow sufficient current to flow, a self-sustaining arc may form. Once formed, an arc may be extended to a significant length before breaking the circuit. Attempting to open an inductive circuit often forms an arc, since the inductance provides a high-voltage pulse whenever the current is interrupted. AC systems make sustained arcing somewhat less likely, since the current returns to zero twice per cycle. The arc
7209-406: 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 (air drying) in an air conditioning system is provided by the evaporator. Since the evaporator operates at a temperature below
7298-410: The spark produced in a dry climate when touching a doorknob after walking across a carpeted floor. The voltage can be in the thousand-volt range, but the average current is low. The standard precautions to avoid injury include working under conditions that would avoid having electrical energy flow through the body, particularly through the heart region, such as between the arms, or between an arm and
7387-438: 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
7476-477: The surface of the wafer . It is also used for electrostatic flocking to coat objects with small fibers that stand on edge. Spark gaps were used historically as an early form of radio transmission. Similarly, lightning discharges in the atmosphere of Jupiter are thought to be the source of the planet's powerful radio frequency emissions. High voltages have been used in landmark chemistry and particle physics experiments and discoveries. Electric arcs were used in
7565-447: 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
7654-524: 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. 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
7743-525: 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. 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
7832-443: The victims of electrocution. At very high transmission voltages even a close approach can be hazardous, since the high voltage may arc across a significant air gap. Digging into a buried cable can also be dangerous to workers at an excavation site. Digging equipment (either hand tools or machine driven) that contacts a buried cable may energize piping or the ground in the area, resulting in electrocution of nearby workers. A fault in
7921-482: The voltage produced by an induction coil. It generates DC using diode switches to charge a ladder of capacitors. Tesla coils utilize resonance, are lightweight, and do not require semiconductors. The largest scale sparks are those produced naturally by lightning . An average bolt of negative lightning carries a current of 30 to 50 kiloamperes, transfers a charge of 5 coulombs , and dissipates 500 megajoules of energy (120 kg TNT equivalent , or enough to light
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