Long Lineset Instructions
Page 34
Glossary of Terms
accumulator A tank located in the suction line just ahead of
the compressor. The purpose of the accumulator is to
prevent liquid from entering the compressor.
ambient The temperature of the air surrounding an object.
For a liquid line passing through an attic, the ambient can
approach 180F. OEM cooling and heat pump equipment is
designed to provide adequate cooling when the outdoor
ambient is 115F.
bypass See Hot Gas Bypass.
bypass valve A valve used in hot gas bypass systems. The
valve is plumbed so that when the unit is operating at
reduced capacity, liquid refrigerant and hot gas are
metered into the suction line. See also Hot Gas Bypass.
capillary tube (cap tube) Refrigerant metering device
consisting of one or more small diameter tubes feeding
liquid refrigerant into the evaporator. Cap tubes must never
be used in long refrigerant line applications as they provide
fair to poor refrigerant control in extreme conditions.
capacity (capacity loss) A measure of the quantity of
refrigeration available, measured in Btu per hour or watts.
capacity reduction Air conditioning and heat pump
systems designed to operate at reduced capacity. OEM
two stage equipment is designed to operate at 60% of full
capacity during low stage operation. Some commercial
systems use hot gas bypass as a form of capacity
reduction. A form of capacity reduction is used in almost all
zoning systems.
column of liquid A length of liquid refrigeration line
completely filled with 100% liquid (no bubbles).
condenser A heat transfer device which removes heat
from refrigerant gas, reduces its temperature, removes
latent heat from the refrigerant converting the gas into
liquid, then subcools the liquid.
condensing temperature The temperature in the
condenser coil below which latent heat is removed and gas
is converted into liquid.
distributor A manifold or multi-port fitting located at the
outlet of an expansion valve designed to feed multiple
circuits through the evaporator.
double suction riser A type of suction riser used in
capacity reduction systems to improve oil entrainment
during reduced capacity operation. A double suction riser
consists of a small riser sized for the capacity of the system
when operating at reduced capacity. A second larger riser
is plumbed in parallel with the small riser to handle the
increased flow when the system is operating at full
capacity.
drier See Filter Drier.
drop 1) A measure of the downward vertical distance
(measured in feet) liquid refrigerant must travel in order to
reach the coil. The weight of the liquid refrigerant increases
the liquid line pressure 1/2 pound per foot. 2) See pressure
drop.
elbow Wrought copper 90 or 45 elbows. Only long radius
elbows should be used as fittings in long refrigerant lines
used with OEM equipment.
entrainment The process of moving oil along the inside
surface of a refrigerant vapor line. Oil droplets/film attach to
the inner surface of the pipe. The refrigerant velocity must
be sufficient to sweep the oil along (entrain the oil) so it may
be returned to the compressor.
expansion valve See Thermostatic Expansion Valve.
equivalent length (total equivalent length) Wrought
copper fittings, filter driers and other devices placed in the
refrigerant line add restriction to the line. The restriction
added to the line is expressed in terms of equivalent feat.
The total equivalent length of a ling is equal to the length of
the pipe plus the equivalent length of all the fittings, filter
driers, etc. placed in the line.
evaporator A heat transfer device (coil) which adds heat to
liquid refrigerant, increases its temperature, adds latent
heat to the refrigerant converting the liquid into gas, then
superheats the gas.
filter drier A device placed in the liquid or suction
refrigerant lines to filter contaminants from the system and
protect the expansion valve and compressor from potential
damage.
flash gas in a liquid refrigerant line, liquid which has lost
temperature and pressure to the point that gas bubbles
begin to form significantly reducing the efficiency of the
system. Flash gas can form as a result of friction losses or
running the liquid line through areas with extremely high
ambients or both.
friction loss
See Pressure Drop.
hammer See Liquid Hammer.
hot gas bypass A form of capacity reduction. The system
diverts hot discharge gas and liquid into the suction line
bypassing the evaporator coil. The most desirable form of
hot gas bypass is the type which feeds hot gas into a side
tap on the distributor on the evaporator coil.
indoor coil The name given to the coil in the indoor unit in
heat pump systems.
lift A measure of the upward vertical distance liquid
refrigerant must travel in order to reach the coil measured in
feet. The weight of the liquid refrigerant reduces the liquid
line pressure 1/2 psi per foot. In air conditioning systems, lift
is a factor only if the evaporator is located above the
condenser. In heat pump systems, lift is always a factor due
to the system's ability to reverse refrigerant flow.
line size The outside diameter (O.D.) of copper pipe used
in refrigeration.
liquid hammer An audible sound heard in liquid refrigerant
lines when solenoid valves close. The noise is a result of
liquid refrigerant traveling at high velocity then stopping
abruptly when the valve closes.
low ambient (temperature) The use of the compressor for
cooling when outdoor temperature is below 50F. Field
installed kits are required to protect the compressor and
ensure proper operation in the event low ambient cooling
below 50 F is required.
main In systems with multiple refrigerant lines, the name
given to the line which feeds or collects refrigerant from
multiple smaller refrigerant lines.