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| Absolute humidity |
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Amount of moisture in the air, indicated in grains per cubic foot. |
| Absolute temperature - temperature measured from absolute zero. |
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| Absolute ventilation efficiency |
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A quantity which expresses the ability of a ventilation system to reduce a pollution concentration relative to the feasible theoretical maximum performance. |
| Absorption chiller |
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A chiller, that uses a brine solution and water to provide refrigeration without the aid of a compressor. |
| Absorption refrigerator |
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A refrigerator, which creates low temperatures by using the cooling effect formed when a refrigerant is absorbed by a chemical substance. |
| Acceptable air quality |
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Air in which there are no known contaminants at harmful concentrations as determined by specialist authorities and with which a substantial majority (80 % or more) of the people exposed do not express dissatisfaction. (ASHRAE 62-1989). |
| Acid condition in system |
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Condition in which refrigerant or oil in system is mixed with fluids which are acid in nature. |
| Air Conditioner |
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Is good for you.. |
| Air Filter |
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Cleans the air coming into your system. |
| Air Handling Unit |
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If your system has an air conditioner, this unit can be a gas furnace or an oil furnace. |
| Attic Fan |
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Heat should naturally rise out of the home. However, when it becomes trapped the home demands additional cooling from the comfort system. An attic fan will remove this trapped heat. This reduces the home’s demand for cooling and can reduce utility costs (for cooling) by up to 15-20%. |
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| Balance Point |
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An outdoor temperature - usually between 30°F to 45°F - at which a heat pump's output exactly equals the heating needs of the house. Below the balance point supplementary electric resistance heat is needed to maintain indoor comfort. |
| British Thermal Unit (BTU) |
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Stands for British Thermal Units. This number indicates the amount of heat it takes to raise one pound of water one degree Fahrenheit. The higher the BTU rating, the larger the heating capacity of the furnace or air conditioner. Homes are measured to determine the number of BTUs required from a heating or cooling system. |
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| Carbon Monoxide |
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A colorless, odorless, highly poisonous gas produced when carbon burns without sufficient air nearby. |
| Central Duct System |
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Distributes air throughout the home. This is achieved by using many different "take offs," which connect to the supply air registers. There is also a larger (in most cases) grill for the "return" air delivery, which is directed back to the air-handling unit. The duct system, when installed correctly, balances the temperature throughout the home, providing comfort for your family. |
| Coefficient of air change performance |
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This is the ratio between the nominal time constant and the room mean age. The coefficient of air change performance equals twice the air change efficiency. This term is equivalent to the ventilation effectiveness definition of ASHRAE standard 62-1989, ""Ventilation for Acceptable Indoor Air Quality"". |
| Compressor Pumps |
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Similarly to the human heart by pumping and creating a scenario very similar to your own blood pressure. There is a high side and a low side and the chemical reaction created by the produced pressure actually forces the refrigerant to cool the home. |
| Condensation |
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The precipitation of liquid from its vapor phase resulting from the lowering of temperature at constant pressure: especially the deposition of water from moist, warm air onto a relatively cold surface or between two surfaces such as within a cavity wall. |
| Condenser coil |
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The outdoor portion of a heating or cooling system that either releases or collects heat from the outside air, depending on the time of year. The Condenser Coil is connected directly to the home's Air Handler and is also known as the Outdoor Coil. |
| Condensing unit |
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As heat pump except cools only and does not therefore incorporate a reversing valve. |
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| Deaeration |
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The act of separating air from a substance. |
| Deck |
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In HVAC terminology, the air discharge of the hot or cold coil in a duct serving a conditioned space. |
| Deck (Coil Deck) |
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The insulated horizontal partition between refrigerated space and evaporator space. |
| Dehumidification |
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The process of reducing the moisture content of the air; serves to increase the cooling power of the air and can contribute to occupant comfort. |
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| Ebulator |
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A pointed or sharp edged solid substance inserted in flooded type evaporators to improve evaporation (boiling) of refrigerant in coil. |
| Economizer control |
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An energy management function, which aims to minimize energy consumption by the use of 'free-cooling'. Internal heat generation in a building may require the HVAC to provide cooling, even though the air temperatures are lower than the thermostat set point. Under this condition, it is possible to introduce outdoor air into the building to provide all or part of the cooling normally accomplished by refrigeration equipment. To use this 'free-cooling', the economizer measures the dry-bulb temperature of the return air and the outdoor air, and selects an appropriate amount of the cooler air for the building conditioning by adjusting outdoors, return, and exhaust dampers. |
| Electric / Gas |
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An electric (heat pump) is not as warm as gas. A combination of gas and an electric heat pump is best. |
| Energy Efficiency Ratio (EER) |
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A ratio calculated by dividing the cooling capacity in Btu's per hour (Btuh) by the power input in watts at a given set of rating conditions, expressed in Btuh per watt (Btuh/watt). |
| Evaporator coil |
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This is where refrigerant evaporates as it removes heat from the air that is passed over it. The Evaporator Coil is located in the indoor unit and is also referred to as the Indoor Coil. |
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| Fuse |
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A metal strip in an electrical circuit that melts and breaks the circuit when excessive current flows through it. The fuse is designed to break in order to save more expensive electrical components. |
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| Gauge Manifold |
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Device constructed to hold compound and high pressure gauges and valved to control flow of fluids through it. |
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| Heat exchangers |
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This term refers to the components in a gas furnace in which the actual combustion takes place. Typically the manufacturers place a 20 year limited warranty on the heat exchangers. On the highest efficiency furnaces the heat exchangers are warranted for as long as you own your home. |
| Heat Pump |
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Unit outside very similar to an air conditioning unit except it is designed to produce heat during cold weather. If you have a gas or oil furnace as an air delivery system inside your home then you have an air conditioner outside that only runs during the warmer months for cooling. |
| HVAC |
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Acronym for Heating, Ventilating, and Air-Conditioning. |
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| Indoor coil |
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The portion of a heat pump or central air conditioning system that is located in the house and functions as the heat transfer point for warming or cooling indoor air. |
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| Junction box |
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A group of electrical terminals housed in protective box or container. |
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| Kata Thermometer (K) |
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A large bulb alcohol thermometer used to measure air velocities or atmospheric conditions by means of cooling effect. |
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| Latent heat transfer |
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Heat added or removed during a change of state of a substance i.e. solid, to a liquid to a gas or vice versa, the temperature remaining constant. |
| Low ambient controllers / head pressure controllers |
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When equipment is required to provide cooling in cold weather the external unit will over condense i.e. will reject too much heat. To overcome this problem it is necessary to fit a low ambient controller also known as a head pressure controller. This device slows down the condenser fan or uses other methods to prevent over condensing. Some equipment has this fitted as standard others do not. |
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| Mean active repair time (MART) |
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This applies to repairable items, and means the average time an item may be expected to be out of service for maintenance and repair, given that the require tools/parts are to hand. |
| Multizone |
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A building or part of a building that comprises a number of zones or cells. |
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| Night setback control |
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An energy management function which acts to reduce the occupancy temperature by a few degrees, with the heating ticking over to maintain it. It is not usually as effective compared to the modern practice of intermittent heating, where the system is switched off overnight. |
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| Off cycle |
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That part of a refrigeration cycle when the system is not operating. |
| Optimum start/stop controller |
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Alters the time that the HVAC equipment starts/stops depending on the weather conditions. It works by using an external sensor and, occasionally, an internal sensor, to bring in the heating/cooling plant at the latest possible time to get the building/zone(s) to the required temperature by the start of occupancy. |
| Outdoor coil/Condensing unit |
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The portion of a heat pump or central air conditioning system that is located outside the home and functions as a heat transfer point for collecting heat from or dispelling heat to the outside air. |
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| Plenum |
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Air compartment connected to a duct or ducts. |
| Plenum chamber |
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A chamber, at higher/lower pressure than surrounding air, which receives air before/after delivery to a conditioned space or combustion system. |
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| Quenching |
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Submerging hot solid object in cooling fluid. |
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| Radiation |
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A transmission of heat, through space, by the propagation of infrared energy. The passage of heat from one object to another without necessarily warming the space between. Radiation does not need a transport medium and so it can take place in vacuum (or in space; i.e. solar radiation). Heat and light are forms of electromagnetic radiation; other forms are microwaves, X-rays, radio broadcast waves. The different forms of electromagnetic radiation differ in wavelength and frequency. |
| Recirculated air |
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Extracted air, which is re-supplied to a space. Recirculated air is normally blended with outside air and is reconditioned. It can then be used for ventilation, heating, cooling, humidification, or dehumidification. |
| Refrigerant |
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In most cases R-22, interacts chemically inside the entire system. |
| Refrigerant Lines |
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The copper tubing lines that connect the indoor and outdoor sections. These pipes allow the refrigerant to flow from indoor to outdoor. |
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| SEER |
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Seasonal Energy Efficiency Rating – It is the most commonly used term to measure the efficiency, or miles per gallon, of a consumer central air-conditioning system. |
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| Thermostat |
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Control device that regulates what cycle you are in; heat or cool. It also regulates the indoor temperature. There are many different models, including standard mercury type, digital, and digital programmable. |
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| Ultraviolet |
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Iinvisible radiation waves with frequencies shorter than wave lengths of visible light and longer than X-Ray. |
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| Variable air volume system |
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The air handling system that conditions the air to a constant temperature and varies the outside airflow to ensure thermal comfort. Ventilation Air-Defined as the total air, which is a combination of the air brought into the system from the outdoors and the air that is being recirculated within the building. Sometimes, however, used in reference only to the air brought into the system from the outdoors. |
| VAV |
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An acronym for a Variable Air Volume system. |
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| Zones |
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The number of zones depend on the square footage of the space. It is always best and more comfortable to divide different floor levels into separate zones. |
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