Residential -Traditionally 7 1/2 Tons of Air Conditioning
or less. Used in residential buildings.
Commercial -A system that is used in commercial
buildings.
Industrial -Large Refrigeration or Air Conditioning
systems used in industrial and manufacturing
buildings.
Heating
Since heat flows from a warm to a less-warm object, it is
understandable that heat generated in a confined space can be
transferred to a less-warm location. Many different methods can
be used to obtain the same effect. The use of sensible heat (heat
that can be detected by a thermometer) could refer to a forced air
gas furnace. However, the use of latent heat (sometimes called
hidden heat) would be compared to a heat pump. Latent heat is
absorbed or discarded to change the state of matter, as in water
to steam or water to ice.
Forced Air
A heating system in which a fan is used to force the flow of air
across a heat exchanger coil or heat element. This could be a fire
place insert with a fan or a residential furnace, electric or gas.
Electric
Resistive:
A system in which heat from electrical resistance units
(sometimes called elements) is used to heat a building.
This method of heating is growing in popularity. It is
sometimes referred to as direct heating, because heating
is accomplished by forcing air over a set of resistive
coils that produce heat as a result of resistance to
electrical current flowing through the coils.
Some advantages of electric heat are:
- Low initial equipment cost.
- No oxygen supply is needed.
- No flue exhaust is needed.
- The system is considered to be safer.
- Equipment usually requires less space.
- Very clean operation.
- No heat lost through flue exhaust (therefore
considered 100% efficient).
Some disadvantages to electric heat are:
- The cost per unit of heat is higher than for some
fuels.
- Humidity control problems may occur.
- Added electrical circuits are required.
- Increased electrical capacity may be required.
Heat Pump:
A compression cycle system (sometimes referred to as
a reverse cycle air conditioner) used to absorb heat
(from a remote location, usually outside) and
transfer that heat to a temperature-controlled space.
The same system (in a reversed cycle mode) can remove
undesired heat (inside) to a more desirable location
(outside). A reversing valve (sometimes called a
4-way valve) is used to change the direction of the
flow of refrigerant through the coil: however, the
flow of the refrigerant through the compressor always
remains the same. This system typically contains
electric resistive heat elements and controls to
provide additional heat to the conditioned space
when needed.
Gas
Forced Air:
A gas furnace that has a combustion chamber, heat
exchanger, and flue exhaust. A thermostat in the
conditioned space calls for heat and energizes a
circuit-board that sends 24 volts to a spark ignition
module (or glow plug), then the gas valve and
establishes a flame in the heat exchanger. Air from
the conditioned space is then forced across the
heat-exchanger and heat is transferred to desired
location.
Radiant:
A heating system which uses warm or hot surfaces to
radiate heat into a space much the same as a
'wood-burning stove' does. A fire is established in
the 'stove' to heat the outer shell of the stove at
which point heat is radiated into the room from the
metal shell of the stove. Another type of radiant
heat would be an open flame or fire-place.
Boilers
A container or tank used to heat and supply liquid or
vapor to a circulation pump for transfer to a remote
location for heating purposes. This tank is heated
by a gas burner much the same as a water heater does
in residential applications.
Hydronic
A system that uses a thermostatically
controlled circulation pump to circulate
heated water (or other liquid) through a
coil or radiator. This coil may be located
inside an 'air handler' and air forced across
the coil thus removing heat from the coil to
the desired space.
Steam
A system in which steam is generated in a
boiler and piped to a coil or radiator.
Traditionally the heat is radiated rather
than forced air.
Air Conditioning
Air conditioning is the process of controlling the temperature,
humidity, and cleanliness of the air in a confined space.
Direct Exchange cooling is indicative of using no other medium than
forced air. The air is forced across the coils of a condensing unit
and condenses the vaporized refrigerant (freon) to a liquid.
Chilled Water systems use water that is cooled in a chiller barrel
(as it is circulated through the piping system) by pumping liquid
refrigerant through tubes that penetrate the wall of the chiller
barrel and absorb heat (vaporizing the refrigerant) from the water.
The water is then pumped through a coil as a blower system forces
air across the coil and heat from the air transfers to the water.
Absorption systems utilize a brine (water saturated with salt)
solution mixed with ammonia and a heat generator that causes the
ammonia to separate from the water. As the ammonia cools, it
absorbs heat from the surrounding area and produces a refrigeration
effect.
Refrigeration
Medium Temperature refrigeration may be used in residential
applications such as a refrigerator. Commercial application
would include restaurants, floral shops, and grocery stores.
Low Temperature applications may include commercial freezers
found in food storage plants or walk-in freezers at the
supermarket.
Cryogenic is the use of temperatures from 116 degrees Kelvin
(-251F) to 0 degrees Kelvin (-460F).
address is:
Bruce D. Oliver is a graduate of the College of Education and the
Graduate School at
Auburn
University.