A+ 2025/2026
Dry bulb temperature - the temperature of the air water mixture as measured with a
standard dry bulb thermometer
Enthalpy - the total heat in a substance, including latent heat and sensible heat
Latent heat - heat that causes a change of state of a substance, such as the heat
required to change water into steam
Resistance - the number of hours needed for 1 Btu to pass through 1 ft² of material or
assembly of a given thickness when the temperature differential is 1 °F. It is the
reciprocal of conductance
Sensible heat - heat that causes a change in temperature of a substance but not a
change of state
Specific heat - the number of Btus (joules) required to raise the temperature of a
specific material by 1 °F (1K)
Wet bulb temperature - the temperature of the air as measured with a sling
psychrometer
Radiation - the transfer of heat energy through electromagnetic waves from one surface
to a cooler surface
Conduction - the transfer of heat through direct contact between two objects of different
temperatures
Viewed angle - the solid angle formed between the measuring position and the outer
edges of the object
Emissivity - the measure of an objects ability to absorb and then radiate heat
Mean radiant temperature (MRT) - the weighted average of the various surface
temperatures in a room and the angle of exposure of the occupant to these surfaces as
well as of any sunlight present
Operative temperature - an average of the air temperature of a space and the mean
radiant temperature (MRT) of the space, measured with a globe thermometer
clo - unit for measuring human comfort of clothing, equal to an American man's
business suit or 0.15 clo/lbm
psychrometry - the study of the content of air
,enthalpy - the total amount of both sensible and latent heat in the air moisture mixture
conduction - the transfer of heat through direct contact between molecules
convection - the transfer of heat through the movement of air
radiation - the transfer of heat energy through electromagnetic waves from one surface
to a colder surface
building envelope - consists of the walls, roof, doors, windows, and foundation
conductivity (k) - the amount of heat lost through 1ft² of a 1 in thickness other than 1 in
resistance (R) - the number of hours needed for 1 Btu to pass through a material of a
given thickness when the temperature differential is 1K
design equivalent temperature difference (DETD) - value calculated as part of heat gain,
takes into account the air temperature differences, effects of the sun, thermal mass,
storage effects of materials, colors of finishes exposed to the sun, and the daily
temperature range
sol air temperature - an outdoor temperature that combines the effects of temperature
difference with solar radiation
design cooling load factor (DCLF) - takes into account several variables that affect how
solar heat gain occurs including the type of glazing, the type of interior shading, and the
outdoor design temperature
heat pump - device that can either heat in the winter or cool in the summer
degree days - a measure of the approximate average yearly temperature difference
between the outside and the inside in a particular location
furnace - burn either gas or oil to heat air, then distribute throughout the building
boiler - use fuel to heat water, and steam or hot water is used to distribute heat
upflow furnace - return air is supplied at the bottom of the unit and the heated air is
delivered to the bonnet above the furnace where it's distributed through ductwork
downflow furnace - used in cases where the duct work is in a basement or crawl space
and the furnace is locate on the first floor
horizontal furnace - used where headroom is limited, such as in crawl spaces
,compressive refrigeration - based on the transfer of heat during the liquification and
evaporation of a refrigerant
compressor - takes the refrigerant in a gaseous form and compresses it to a liquid
a ton of refrigeration - unit used to describe the capacity of a refrigeration system
direct expansion - also called DX system or incremental unit, self contained unit that
passes nonducted air, which is to be cooled over the evaporator and back into the room
(placed in an exterior wall)
all air system - cool or heat spaces by conditioned air alone, heat is transported with
supply & return air ducts
single duct system - used in residential and small commercial applications, air is heated
and cooled in a central furnace or air conditioner and is distributed throughout the
building in duct work at a constant volume w/one central thermostat to control the
furnace
variable air volume system - VAV, air is heated or cooled as required in a central plant
and distributed to the building at a constant temperature through a single duct, a
thermostat in each zone controls a damper that varies the volume of conditioned air
entering the space to respond to the users needs
dual duct system - high velocity system, provides two parallel ducts, one with hot air and
one with cool air, streams of air are joined in a mixing box in proportions to suit the
temperature requirements of the conditioned space
reheat constant volume system - constant volume system, takes return air and fresh
outdoor air and cools and dehumidifies the mixture which is distributed in a constant
volume at low temperature throughout the building
absorption cooling - produces chilled water and is accomplished by the loss of heat
when water evaporates
economizer cycle - allows outdoor air to be used for cooling when temperatures are low
enough (adjusts with dampers)
multizone system - supplies air into a central mixing unit where separate heating and
cooling coils produce hot and cold air streams, then mixed with dampers controlled by
zone thermostats and resulting tempered air is delivered to zones
all water systems - uses a fan coil unit in each conditioned space, fan coils are
connected to one or two water circuits
, air water induction systems - rely on central air to provide humidity control and
ventilation air to conditioned spaces, used where return air cannot be recirculated
(hospitals & laboratories), outside air is supplied and return air is exhausted to the
exterior
nuisance - legal term meaning that which is dangerous to human life or detrimental to
health
desiccant - a material either liquid or solid that absorbs water
direct contact water heater - heats water by passing hot gasses directly through water
recuperative gas boiler - recovers the sensible and latent heat from the high heat of
exhaust flue gases that would normally be discharged to the atmosphere
displacement ventilation - an air distribution system in which supply air originates at
floor level and rises to return air grilles in the ceiling
water loop heat pump - compose a heating and cooling system that uses a series of
heat pumps for different zones of a building which are all connected to the same piping
system of circulating water
thermal energy storage - uses water, ice, or rock beds to store excess heat or coolness
for use at a later time
energy recovery ventillators - air to air heat exchangers, reclaim waste energy from the
exhaust air stream and use it to condition the incoming fresh air
energy transfer wheels - enthalpy heat exchangers, transfer heat between two air
streams through the use of a heat exchanger wheel consisting of small openings
through which air passes
heat pipe - self contained device that transfers sensible heat energy from the hot
exhaust air to cool outdoor air
extract air windows - uses a double paned insulated glass unit which other pane of
glass is placed on the inside of the building
ground coupled heat exchangers - heat of cool outside air by circulating it through pipes
buried in the ground
chilled beams - ceiling mounted unit that uses water to provide cooling and heating
(passive, and active)
building automation system - computer based integrated system used to monitor and
control building systems