Click on the alphabet links below to search specific term and definitions
A B C D E F G I J K L M N P Q R S T U V W X Y Z
Absorption Chiller
-- A chiller which creates a cooling effect using a chemical reaction instead
of mechanical compression of refrigerant. Common Absorption chillers use a Lithium-Bromide
Solution as the "refrigerant" and a source of heat to power the chiller.
The heat source can be
waste heat in the form of steam or hot water or the chiller can be direct fired.
Typical absorption
chillers are Water Cooled Chillers, requiring a cooling tower for the condenser.
Air Conditioner -- Device used to control
temperature, humidity, cleanliness and movement of
air in a confined space.
Air Conditioning -- Control of the temperature,
humidity, air movement and cleaning of air in a
confined space.
Air Cooled Chiller -- A chiller that utilizes
an Air Cooled Condenser for rejection of heat; Air
Cooled Chillers are typically designed for outdoor use, but smaller units may
be used indoors in
manufacturing facilities and shops.
Air Cooled Condenser -- A condenser that
rejects heat to the surrounding environment by
moving air across a coil to condense the refrigerant moving through the coil
as part of the
mechanical refrigeration cycle.
Ambient -- The surrounding atmosphere; encompassing
on all sides; the environment surrounding
a body but undisturbed or unaffected by it.
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Boiler -- A device for generating steam
for power, processing, or heating purposes or for producing
hot water for heating purposes or hot water supply. Heat from an external combustion
source is
transmitted to a fluid contained within the tubes in a boiler shell, a closed
vessel in which water is
converted to pressurized steam. This fluid is delivered to an end-use at a desired
pressure,
temperature, and quality.
BTU -- a unit of heat equal to the amount
of heat required to raise one pound of water one degree
Fahrenheit at one atmosphere pressure
BTUH (British Thermal Unit Per Hour) --
Establishes a time reference to btu input or output rates.
A BTUH is how many BTUs are used per hour.
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Celsius -- A temperature scale based on
the freezing (0 degrees) and boiling (100 degrees) points
of water. Abbreviated as C in second and subsequent references in text. Formerly
known as Centigrade.
To convert Celsius to Fahrenheit, multiply the number by 9, divide by 5, and
add 32. For example: 10
degrees Celsius x 9 = 90; 90 / 5 = 12; 18 32 = 50 degrees Fahrenheit.
CFM (Cubic Feet per Minute) -- A standard
measurement of airflow that indicates how many cubic
feet of air pass by a stationary point in one minute. The higher the number,
the more air is being forced
through the system. A typical system produces 400 CFM per ton of air conditioning.
A measure of
air-flow. Volume X Air Changes per hour / 60 minutes.
Chiller -- A device that produces chilled
water to provide air conditioning for large buildings or cooling
for process applications. A chiller is a mechanical refrigeration device like
an air conditioner except that
it cools a fluid (usually water) instead of cooling air. When a large air conditioner
is required it is sometimes
more feasible to use one large chiller instead of many small air conditioners.
Chillers are also used
wherever there is a need for cooling a fluid such as a chemical process or for
plastics molding. To simplify
the concept of a chiller you should compare it to a drinking fountain where
you get cold "chilled" water.
Chillers are primarily used in applications requiring LWT, (Leaving Water Temperature),
of 65 F and lower.
Chiller Ton -- One Chiller Ton = 12,000
BTU's. A quick rule of thumb is: GPM's multiplied by /\T (Delta T)
divided by 24. This will calculate the actual heat removal in Tons. Chillers
are usually nominally rated with
LWT (Leaving Water Temperature) of about 45F.
Compressor -- The heart of an air conditioning
or heat pump system., as well as an integral component
of a chiller. The large part in the condenser (outdoor unit) that pumps refrigerant.
The pump of a refrigerating
mechanism which draws a low pressure on cooling side of refrigerant cycle and
squeezes or compresses
the gas into the high pressure or condensing side of the cycle. The compressor
maintains adequate
pressure to cause refrigerant to flow in sufficient quantities to meet the cooling
requirements of the system.
Condenser -- This is the unit that will
sit outside and is part of a split system, it contains the compressor
which is the heart of your air conditioner or Heat Pump, it pumps the refrigerant
through your system.
Some people call the condenser the compressor, but the compressor is a component
of the condenser along
with the fan motor and condenser coil. Coil or outdoor coil dissipates heat
from the refrigerant, changing the
refrigerant from vapor to liquid.
Cooling tower -- A heat transfer device,
which cools warm water using outside air. Cooling towers are
used in conjunction with Water Cooled Chiller, but have many stand-alone uses
as well. Cooling generally
are used when LWT (Leaving Water Temperature) requirements are 75F or higher.
The term cooling tower
may be used to describe both open and closed circuit cooling towers, (see Evaporative
Condenser). An
example of an open system is a cooling tower condenser loop to a water cooled
chiller. The circuit is open
on the cooling tower end in that water enters the cooling tower at for example
95?F, is cooled to 85?F by
falling through the fill with air circulating through it, and is returned to
the chiller condenser to be heated to
95?F and begin the cycle again. An example of a closed circuit system is an
evaporative condenser used
in conjunction with a particular process cooling a chemical or fluid other than
water. The liquid would pass
through a series tubes within the structure of tower. The tower would still
utilize water recirculated within
the tower to reject the heat, only the liquid is within the tubes, closed to
the environment. Make-up water is
required for both applications, since evaporation will take place in either
case.
Cooling Tower Ton -- One Cooling Tower Ton
= 12,000 Btu's. A quick rule of thumb is: GPM's multiplied
by /\T (Delta T) divided by 30. This will calculate the actual heat removal
in Tons. Cooling Towers are usually
nominally rated with LWT (Leaving Water Temperature) of about 85?F.
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Delta T - /\T -- A difference in temperature.
In Chiller applications, the ?T is used for the difference in
temperature between the EWT, (Entering Water Temperature), and the LWT, (Leaving
Water Temperature)
of the chilled water, either through the chiller or through the process.
Dewpoint -- Is the temperature at which
air becomes saturated with water and begins to condense
- forming a dew. Therefore at 100 % RH the ambient or process temperature equals
the dewpoint
temperature. The more negative the dewpoint temperature is from the ambient
temperature the less the
risk of condensation and the drier the gas or air stream.
Direct Expansion (Refrigeration) -- Any
system that, in operation between an environment where heat
is absorbed (heat source), and an environment into which unwanted heat is directed
(heat sink) at two
different temperatures, is able to absorb heat from the heat source at the lower
temperature and reject
heat to the heat sink at the higher temperature. The cooling effect is obtained
directly from a fluid called
a refrigerant that absorbs heat at a low temperature and pressure, and transfers
heat at a higher
temperature and higher pressure.
Dry Bulb Temperature (DB) -- The temperature
measured by a standard thermometer. A measure of the
sensible temperature of air.
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Entering Water Temperature -- The temperature
of the water or fluid when entering chiller, cooling tower,
or other similar refrigeration device. Used with LWT, (Leaving Water Temperature),
and flow rate in
calculating /\T (Delta T) for a refrigeration device. May also be used in reverse
with LWT and flow rate to
calculate for a process or piece of equipment's rise in /\T.
Enthalpy -- Enthalpy is a measurement of
energy of air. It consists of both sensible (temperature) and
latent (moisture content) heat of air. The amount of Enthalpy of a given condition
can be found on the
Psychometric Chart. The quantity of heat necessary to raise the temperature
of a substance from one
point to a higher temperature. The quantity of heat includes both latent and
sensible.
Evaporative Cooler -- A type of cooling
equipment that turns air into moist, cool air by saturating the air
with water vapor. It does not cool air by use of a refrigeration unit. This
type of equipment is commonly
used in warm, dry climates.
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Fahrenheit (F) -- A temperature scale in
which the boiling point of water is 212 degrees and its freezing
point is 32 degrees. To convert Fahrenheit to Celsius, subtract 32, multiply
by 5, and divide the product by
9. For example: 100 degrees Fahrenheit - 32 = 68; 68 x 5 = 340; 340 / 9 = 37.77
degrees Celsius.
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Gallons Per Minute -- Flow rate used in
refrigeration formulas. Gallons per hour divided by sixty.
GPM -- see Gallons per Minute
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Heat Transfer --
Flow of heat energy induced by a temperature difference. Heat flow through a
building
envelope typically flows from a heated, or hot area to a cooled, or cold area.
Horsepower (HP) -- A unit for measuring
the rate of doing work. One horsepower equals about
three-fourths of a kilowatt (745.7 watts).
Humidifier -- A device that adds moisture
to warm air being circulated or directed into a space. This
adds necessary moisture to protect your furnishings and reduce static electricity
Humidity -- The amount of moisture in the
air. Air conditioners remove moisture for added comfort.
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IWC (Inches of water column) -- IWC (Inches
of water column) Commonly used in the USA
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Joule -- A unit of work or energy. It takes
~ 1,000 joules to equal a British thermal unit. It typically
takes ~ 1 million joules to make a pot of coffee.
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kW (kilowatt or kW) -- A kilowatt equals
one thousand (1,000) watts. A unit of measure of the
amount of electric power production needed to operate given equipment. On a
hot summer afternoon
a typical home, with central air conditioning and other equipment in use, might
have a demand of four
kW. An electric power capacity of one kW is sufficient to power ten 100-watt
light bulbs.
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Latent Heat -- Heat, that when added or
removed, causes a change in state - but no change in
temperature. A change in the heat content that occurs without a corresponding
change in temperature,
usually accompanied by a change of state (as from liquid to vapor during evaporation)
Leaving Water Temperature - LWT -- The temperature
of the water or fluid when leaving chiller,
cooling tower, or other similar refrigeration device. Used with EWT, (Entering
Water Temperature),
and flow rate in calculating /\T (Delta T) for a refrigeration device. May also
be used in reverse with
EWT and flow rate to calculate for a process or piece of equipment's rise in
/\T.
Lithium-Bromide --
A chemical solution commonly used in absorption refrigeration systems
LWT - Leaving Water Temperature -- See Leaving
Water Temperature
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Megawatt (MW) -- One thousand kilowatts
(1,000 kW) or one million (1,000,000) watts. One megawatt
is enough energy to power 1,000 average California homes.
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Natural Ventilation -- The supply of outdoor
air through passive flow from windows, chimneys, doors,
and other infiltration.
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Ohm -- A unit of measure of electrical resistance. One volt can produce
a current of one ampere through
a resistance of one ohm.
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Package Unit or Package System -- A self-contained
unit or system that has the Air Handler
Psychometric Chart -- A chart that was developed
to graphically display the properties of various mixtures
of air and water vapor. It graphically plots the following: Dry Bulb Temperatures,
Wet Bulb Temperatures,
Enthalpy, Relative Humidity, Specific Humidity, Dew Point and Vapor Pressure.
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Q -- Q
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Refrigerant -- Substance used in refrigerating
mechanism. A substance that produces a refrigerating
effect while expanding or vaporizing. Air conditioning systems use Refrigerant
in the Evaporator Coil to
cool air as it passes by. Refrigerants absorb heat in evaporator by change of
state from a liquid to a gas,
and releases its heat in a condenser as the substance returns from the gaseous
state back to a liquid state.
Relative Humidity (RH) -- Relative humidity
is defined as the ratio of the water vapor pressure to the
saturation vapor pressure (over water) at the temperature of the gas. RH = Pw/Pws
* 100
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Sensible Heat -- Heat, that when added or
removed, causes a change in temperature but not in state.
Heat that results in a temperature change.
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Temperature -- Degree of hotness or coldness
measured on one of several arbitrary scales based on
some observable phenomenon (such as the expansion).
Temperature Differential -- The difference
between the entering and leaving temperature for a given
fluid. For example, a 10-degree evaporator temperature differential for a chiller
would describe an operating
condition where the entering water temperature is 54 degrees and the leaving
is 44 degrees.
Ton or "Ton of Cooling"
-- A cooling unit of measure. Each ton equals the cooling effect of 12,000 Btuh.
Heat pumps and air conditioners are generally sized in tons. Typical sizes for
single family residences are
between two and five tons. It is important to note that actual capacity is not
constant and will change based
on outdoor or indoor temperatures. The published capacity rating of air conditioners
and heat pumps is based
on performance at the ARI standard temperature levels of 95 F outside, 80 F
inside, and 50% relative humidity.
The number of tons a system has is the total BTU capacity of the system. The
size of the area to be cooled will
determine the correct size of the system in tons. While an air conditioner may
be called a three ton unit, it may
not produce 36,000 Btu/h in cooling. There is a wide variety of actual capacities
that are called "three tons."
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Unconditioned Space -- A space that is neither
directly nor indirectly conditioned space, which can be isolated
from conditioned space by partitions and/or closeable doors.
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VFD (Variable Frequency Drive) -- Electronic
speed control for motors.
volt -- equivalent to the potential difference across a resistance of
1 ohm when 1 ampere of current flows through it
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W (Watt) --
A watt is a unit of electricity. A unit of measure of electric power at a point
in time, as capacity or
demand. It is the rate of energy transfer equivalent to 1 ampere flowing under
a pressure of 1 volt at unity power
factor. One watt of power maintained over time is equal to one joule per second.
Some Christmas tree lights use
one watt. The watt is named after Scottish inventor James Watt and is capitalized
when shortened to w and
used with other abbreviations, as in kWh.
Water Cooled Chiller
-- A chiller that utilizes a Water Cooled Condenser for rejection of heat; Water
Cooled
Chillers are typically designed for indoor use, with the condenser piped to
a cooling tower or other source of
cooling water. The heat is ultimately rejected to the environment through the
cooling tower or discharge water.
Wet Bulb Temperature -- The temperature
at which water, by evaporating into air, can bring the air to
saturation at the same temperature. Wet-bulb temperature is measured by a wet-bulb
psychrometer. Traditionally
this was the temperature indicated by a thermometer whose bulb is wrapped in
a wet sheath. The wet bulb
temperature and the dry bulb temperature (i.e air temperature) would then be
used to calculate relative humidity
or dewpoint. Alternatively charts or tables can be used.
Wet-bulb Temperature -- When a wet wick
is placed over a standard thermometer and air is blown across
the surface, the water evaporates and cools the thermometer below the dry-bulb
temperature. This cooler
temperature (called the wet-bulb temperature) depends on how much moisture is
in the air.
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