Glossary
1403
tightly controlled to limit contamination from airborne par-
ticles. (24)
cleaning solvent. A chemical compound used to remove oil,
grease, and sludge from a surface. (3)
cleaning tool. Any handheld tool that is used to clean sur-
faces in the ductwork of an HVAC system. These include
brushes, scrapers, and agitation and vacuum devices. (24)
clearance space. The volume of space between the top of
the piston head and the bottom of the valve plate when the
piston is at top-dead-center (TDC). (15)
client. The controllers and devices in a building control sys-
tem that uses BACnet. (40)
climate. In reference to outdoor conditions, the long-term
weather trends for a region. In reference to indoor environ-
ments, the conditions that are normally maintained in a con-
ditioned space. (21)
climate zone. An area of land that has a common tempera-
ture range and yearly precipitation level. (41)
closed circuit. An electrical circuit that is complete, provid-
ing a continuous path for electrons to follow. (9)
closed-loop control system. A type of control system in which
the system’s output modifies system input, which in turn helps
determine the next output. A sensor produces a signal based
on the conditions in the controlled area and transmits it to the
controller, which modifies the output accordingly. (13)
closed-loop cooling tower. A cooling tower arrangement in
which there are two isolated streams of water: one that flows
through the condenser and another that flows through the
cooling tower. The condenser water rejects its heat into the
cooling tower water through a shared heat exchanger. (45)
closed-loop heat pump system. A type of ground-source
heat pump system that continuously circulates the same
water or refrigerant. (34)
CO2
test. A test that measures the amount of carbon dioxide
in a furnace’s flue gas to determine if complete combustion
is taking place. (36)
coefficient of performance (COP). The ratio of energy out-
put to energy input. In HVACR, this represents efficiency
using a numerical value with no units. Refer to seasonal aver-
age COP. (41)
coefficient of performance (COP) (of refrigerants). The
ratio of refrigeration effect to heat of compression. Refrig-
erants with a high coefficient of performance produce their
refrigerating effect more efficiently. (6)
cogeneration. The use of energy byproducts from one pro-
cess as the primary energy source for another. (27)
cogeneration system. A system that produces both heat and
electricity. Also called a total energy system or a combined heat
and power (CHP) system. (41)
cold. The absence of heat, the result of the removal of heat. (1)
cold chisel. A metal tool with a beveled edge at one end
used for cutting through or carving into a solid material. (3)
cold thermal energy storage (CTES). An energy storage system
that cools the storage medium at night and uses the cooled
medium at peak electrical demand times of the day. (39)
combination (slip-joint) pliers. Pliers that have a pivot
point allowing the span of the jaws to be adjusted. (3)
combination gas valve. A single gas valve that contains
multiple components—such as a manual shutoff valve, mul-
tiple solenoid valves, and a pressure regulator—to control
gas pressure and gas supply to the burners of a gas-fired
heating system. (35)
combination thermostat. A thermostat that changes from
one mode of operation to another automatically. Also called
heating-cooling thermostat. (29)
combined heat and power (CHP) plant. A power plant that
produces electricity and useful steam. (27)
combined heat and power (CHP). A term used to describe
a system that produces both heat and electricity. This term
describes both total energy systems and cogeneration systems. (41)
combined-flow. An evaporative condenser design in which
there is a parallel flow of air and sprayed water over a con-
denser coil and a crossflow of air and water through the fill
surface. (45)
combustion. A chemical process of rapid oxidation in which
fuel and oxygen combine to produce heat and light. (35)
combustion blower. A motor-driven fan that brings fresh
air into a heating system’s combustion chamber and
expels combustion gases out through the heat exchanger
and flue. (32)
combustion head. A plate with slots and holes that is
designed to promote combustion in an oil-fired furnace by
directing airflow into the combustion chamber. It is located
at the end of the air tube. (36)
comfort cooling system. A system that reduces the tem-
perature and humidity in living and work spaces to a level
comfortable for the occupants. (25)
Comfort-Health Index. The sensation associated with each
temperature and the effects that each temperature have on
human physiology and health. (21)
common terminal. One of three motor terminals on a her-
metic compressor. The common terminal connects to a sin-
gle line that joins one end of the start winding to one end of
the run winding. (12)
common wire. A wire designation used in electrical dia-
grams for various systems. In domestic refrigeration appli-
ances, a wire with white insulation that runs directly to the
motor and carries the same amount of current as the hot
wire of the circuit. (19)
commutator. A slip ring that is split in half by an insulating
material with each end of the rotor attached to one half of
the ring. In a dc generator, a commutator forces the current
to flow in one direction, creating direct current. (9)
complete combustion. A form of combustion in which fuel
is burned in the presence of excess oxygen. (35)
complex circuit. An electrical circuit that includes a combi-
nation of series and parallel circuits. (9)
compound gauge. An instrument for measuring pressures
both above and below atmospheric pressure. Also called a
low-side gauge. (7)