AG 31-011 • REFRIGERANT PIPING DESIGN 38 www.DaikinApplied.com
Hot Gas Reheat:
A method of reheating supply air after it
has been cooled by using a second coil down stream of the
evaporator and passing discharge gas from the compressor
through it.
Intercooler:
A component in a refrigeration system used to
desuperheat compressed refrigerant with cool liquid refrigerant.
Commonly used in two stage refrigeration cycles to cool
refrigeration from the booster compressor.
Isentropic Efficiency (ŋ
s
):
Measure of compressor efficiency
defined as
∆
h
isnetropic
/
∆
h
actual
Isentropic Process:
A process where the entropy remains
constant. Such a process is said to be reversible and cannot
be more efficient. An example is isentropic compression
(which cannot actually occur but is used as a benchmark
to measure actual compressor performance against – See
isentropic efficiency.)
Isobaric Process:
A process that occurs at constant pressure.
An example is evaporation in the evaporator.
Isolators:
Components used to stop vibration and noise
from passing beyond the source. There are isolators for
compressors and refrigerant piping. Compressor isolators are
rubber in shear (RIS) or spring. Refrigerant piping isolators are
usually rubber grommets used with a clamping system.
Isothermal Process:
A process that occurs at constant
temperature. An example is evaporation in the evaporator.
Liquid Floodback Head Pressure Control:
A method
of maintaining proper head pressure during low ambient
operation by flooding the condenser with liquid refrigerant and
reducing the effective heat transfer surface of the condenser.
Liquid Line:
A refrigerant line that moves liquid high pressure
refrigerant from the condenser to an expansion device.
Liquid Overfeed System:
An evaporator where the
refrigerant is mechanically pumped faster than it is boiled so
liquid refrigerant exits the evaporator. The mixture leaving the
evaporator enters a low pressure receiver where the vapor
is drawn off to the compressor and the liquid is returned to
the evaporator. This arrangement is common in industrial
applications.
Liquid Subcooling Reheat:
A method of reheating supply air
after it has been cooled by using a second coil down stream
of the evaporator and passing liquid refrigerant from the
condenser through it.
Low Ambient Control:
A control process that maintains
condenser pressure at an acceptable level during periods of
low ambient temperature and/or load. Examples include, fan
cycling, fan speed control, and liquid flood back control.
Mass (m):
The quantity of a substance present. It is measured
in pounds or lb
m
or kilograms ( kg).
Oil Separator:
A vessel in a refrigeration circuit used to
separate oil from refrigerant. They are usually in the discharge
line. The oil is returned to the compressor sump.
Pressure (p):
Force over unit area. Bursts pipes or expands
balloons. It is measured in pounds per square inch (PSI) or
Pascals (Pa).
Quality (X):
The ratio of vapor mass to liquid mass refrigerant
during evaporation and/or condensation.
Receiver:
A container used to store liquid refrigerant. Typically
used when the condenser cannot hold the refrigerant charge or
for liquid flood back low ambient control.
Reversing Valve:
A device in a refrigeration circuit used to
convert an air conditioner into a heat pump. When powered,
the reversing valve will switch the evaporator and condenser to
reverse the rejection of heat.
Riser:
A refrigerant pipe that runs vertically.
Rubatex
®
:
A brand name for a moisture proof expanded
rubber insulation commonly used on refrigerant piping for
thermal insulation.
Saturation Condition:
A state where liquid and vapor
refrigerant are in direct contact with each other and all
properties remain unchanged overtime. When a refrigerant is
in saturation condition there can be only one temperature for a
given pressure and visa versa.
Saturated Condensing Temperature:
The saturation
condition that exists in the condenser.
Saturated Suction Temperature:
The saturation condition
that exists in the evaporator.
Service Valve:
A refrigerant valve that can be manually closed
to isolate part of a refrigeration circuitfor servicing.
Sight Glass:
A refrigerant piping fitting that has a window to
allow viewing of the refrigerant. They are used in the liquid line
as close to the TX valve as possible to visualize vapor bubbles.
Some sight glasses include a moisture indicator used to mark
the presences of moisture in the refrigeration system.
Solenoid Valve:
A two position valve (open with power, closed
without power) commonly used in refrigerant piping systems
to isolate a section of the refrigerant circuit. Also used in pump
down and hot gas bypass arrangements.
Specific Heat (c
p
):
The energy needed to raise the
temperature of a unit of mass one degree of temperature.
Measured in Btu/lb
m
°F or (kJ/(kg°C))
Sub-cooled Liquid:
A liquid that has been cooled below
the saturation condition resulting in lower temperature and
enthalpy. This is used to offset pressure losses in liquid
lines that lead to flashing and to increase the capacity of the
refrigeration circuit.