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.
A heat pump is a device that consumes work to transfer heat from a cold heat sink to a hot heat sink. Specifically, the heat pump transfers thermal energy using a refrigeration cycle, cooling the cool space and warming the warm space. In cold weather, a heat pump can move heat from the cool outdoors to warm a house ; the pump may also be designed to move heat from the house to the warmer outdoors in warm weather. As they transfer heat rather than generating heat, they are more energy-efficient than other ways of heating or cooling a home.
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.
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications.
Cogeneration or combined heat and power (CHP) is the use of a heat engine or power station to generate electricity and useful heat at the same time.
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning systems, which can both cool and warm interior spaces.
A storage heater or heat bank (Australia) is an electrical heater which stores thermal energy during the evening, or at night when electricity is available at lower cost, and releases the heat during the day as required. Alternatively, solar storage heaters are designed to store solar energy as heat, to be released during the night or other periods where it is required, often making it more cost effective than selling surplus electricity to the grid and buying it back at night.
In the United States, the efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute, a trade association, in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment. A similar standard is the European seasonal energy efficiency ratio (ESEER).
A thermal power station is a type of power station in which the heat energy generated from various fuel sources is converted to electrical energy. The combustion or nuclear reaction of the fuel source in a boiler or reactor generates heat, which is converted into mechanical energy using a thermodynamic power cycle, where a working fluid is heated and boiled under immense pressure in a large pressure vessel to produce high-pressure steam. This high pressure-steam is then directed to a turbine through a series of pipes, where the force of the steam rotates the turbine's blades. The rotating turbine, which is mechanically connected to an electric generator, turns the generator's rotor with conductive coils. A stationary magnetic field interacts with rotating coils to produce electricity in them via electromagnetic induction. Fuels such as natural gas or oil can also be burnt directly in gas turbines. These plants can be of the open cycle or the more efficient combined cycle type.
A fan heater, also called a blow heater, is a heater that works by using a fan to pass air over a heat source. This heats up the air, which then leaves the heater, warming up the surrounding room. They can heat an enclosed space such as a room faster than a heater without a fan, but like any fan, create a degree of noise.
Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technologies include renewable biofuels, solar heating, geothermal heating, heat pumps and heat exchangers. Insulation is almost always an important factor in how renewable heating is implemented.
Underfloor heating and cooling is a form of central heating and cooling that achieves indoor climate control for thermal comfort using hydronic or electrical heating elements embedded in a floor. Heating is achieved by conduction, radiation and convection. Use of underfloor heating dates back to the Neoglacial and Neolithic periods.
A space heater is a device used to heat a single, small- to medium-sized area. This type of heater can be contrasted with central heating, which distributes heat to multiple areas.
A convection heater, also known as a convector heater, is a type of heater that utilizes convection currents to heat and circulate air. These currents move through the appliance and across its heating element, using thermal conduction to warm the air and decrease its density relative to colder air, causing it to rise.
An oil heater, also known as an oil-filled heater, oil-filled radiator, or column heater, is a common form of convection heater used in domestic heating. Although filled with oil, it is electrically heated and does not involve burning any oil fuel; the oil is used as a heat reservoir (buffer).
Radiators and convectors are heat exchangers designed to transfer thermal energy from one medium to another for the purpose of space heating.
Tankless water heaters — also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters — are water heaters that instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil unless the unit is equipped with an internal buffer tank. Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication. However, copper heat exchangers are more susceptible to scale buildup than stainless steel heat exchangers.
A storage water heater, or a hot water system (HWS), is a domestic water heating appliance that uses a hot water storage tank to maximize water heating capacity and provide instantaneous delivery of hot water. Conventional storage water heaters use a variety of fuels, including natural gas, propane, fuel oil, and electricity. Less conventional water heating technologies, such as heat pump water heaters and solar water heaters, can also be categorized as storage water heaters.
The Glossary of Geothermal Heating and Cooling provides definitions of many terms used within the Geothermal heat pump industry. The terms in this glossary may be used by industry professionals, for education materials, and by the general public.
