Heating Mode; Refrigerant Lines; Linear Vs Equivalent Line Length; Connecting Refrigerant Lines - Bosch SM024 Installation, Operation And Maintenance Manual

12 | Refrigerant Lines

Once the thermostat is satisfied, the compressor
shuts down accordingly and the fan ramps down to
either fan only mode or off over a span of 30 seconds
(ECM Motors).
Note that a fault condition initiating a lockout will
de-energize the compressor.

Heating Mode

Heating operates in the same manner as cooling,
but with the reversing valve de-energized. The
compressor will run until the desired setpoint
temperature on the thermostat is achieved.
Once the thermostat is satisfied, the compressor
shuts down and the fan ramps down in either fan
only mode or turns off over a span of 30 seconds.
Auxiliary electric heating coils are not available on
the EP product line.
REFRIGERANT LINES
The installation of the copper refrigerant tubing
must be done with care to obtain reliable, trouble-
free operation. This installation should only be
performed by qualified refrigeration service and
installation personnel.
Refrigerant lines generally can and should be
routed and supported so as to prevent the
transmission of vibrations into the building
structure. Experience and good design practice
dictate 75 feet as the maximum practical length for
interconnecting refrigerant lines in split system
heat pumps without special considerations.
Beyond 75 feet, system losses become substantial
and the total refrigerant charge required can
compromise the reliability and design life of the
equipment.
Refrigerant lines should be sized in accordance
with Figure #13 in the following instructions.
Copper tubing should be clean and free of
moisture and dirt or debris. The suction and liquid
lines MUST be insulated with at least 3/8" wall,
closed-cell foam rubber insulation or the
equivalent.
Some points to consider are:
8733920846 (2015/01)
• Pressure drop (friction losses) in refrigerant
suction lines reduces system capacity and
increases power consumption by as much as
2% or more, depending on the line length,
number of bends, etc. Pressure drop in liquid
lines affects system performance to a lesser
degree, provided that a solid column of liquid
(no flash gas) is being delivered to the
refrigerant metering device, and that the liquid
pressure at the refrigerant metering device is
sufficient to produce the required refrigerant
flow.
• Oil is continually being circulated with the
refrigerant so, oil return to the compressor is
always a consideration in line sizing. Suction
lines on split system heat pumps are also hot
gas lines in the heating mode, but are treated
as suction lines for sizing purposes. If the
recommended suction lines sizes are used,
there should be no problem with oil return.
• Vertical lines should be kept to a minimum.
Vertical liquid lines will have a vertical liquid lift
in either heating or cooling, and the weight of
the liquid head is added to the friction loss to
arrive at the total line pressure drop.
• Wherever possible, the air handler should be
installed at a higher elevation than the
condensing section to aid with oil return to the
compressor.

Linear vs Equivalent Line Length

Linear Line Length - is the actual measured length
of the line including bends. This is used to
calculate the additional refrigerant charge that
must be added to the system. (See Figure #14 and
examples)
Equivalent Line Length - is the combination of the
actual length of all the straight runs and the
equivalent length of all bends valves and fittings in
a particular line. The equivalent length of a bend,
valve or fitting is equal to the length of a straight
tube of the same diameter having the same
pressure drop as the particular valve or fitting. The
ASHRAE Fundamentals Handbook provides tables
for determining the equivalent length of various
bends, valves and fittings.

Connecting Refrigerant Lines

• Use only ACR grade copper tubing and keep
ends sealed until joints are made.
• For best performance, select routing of
refrigerant lines for minimum distance and
fewest number of bends.
• Size lines in accordance with Figure #14.
Subject to change without prior notice
SM AH Series Heat Pump
SM AH Series Heat Pump