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SYSTEM DESCRIPTION
The EMWT-HACW heat pump is a stand alone reversing
system which contains both a hot and cold buffer tank. The unit
will maintain each of the tanks at the desired setpoint by auto-
matically switching modes between heating and cooling.
COMPRESSOR OPERATION
The compressor operates based on the combination of the
calls for heating and cooling loads. The operation is as shown
in
TABLE 5
for when the unit is set to heating priority and
BLE 6
for when the unit is set for cooling priority. Impossible
combinations have been removed from the table for simplicity.
There are three different operating scenarios for this unit:
heating load only, cooling load only, and simultaneous heating
and cooling loads. Each of these scenarios is explained in the
following sections.
HEATING LOAD ONLY OPERATION
As described previously, this unit has three heating stages:
Stage 1 = Stage 1 compressor (part load), Stage 2 = Stage 2
compressor (full load), and Stage 3 = heating tank electric ele-
ments.
In the heating load only scenario the Hot Tank will see a
temperature drop due to the heating load. When the Hot Tank
reaches the heating Stage 1 activation temperature, the com-
pressor will start (part load mode) and the Hot Indoor circulator
will be turned on to circulate fluid between the heat exchanger
and the tank.
If the heating load is large enough, the Hot Tank will con-
tinue to drop in temperature. When the heating Stage 2 activa-
tion temperature is reached, the compressor solenoid will be
energized to operate the compressor in full load mode.
If the heating load is still too large, the Hot Tank will once
again continue to drop in temperature. When the heating Stage
3 activation temperature is reached, the electric elements will be
brought on.
As the heating load becomes satisfied, the Hot Tank will
begin to rise in temperature. Each heating stage will shut off at
its setpoint value and the Hot Tank will be satisfied.
COOLING LOAD ONLY OPERATION
As described previously, this unit has two cooling stages:
Stage 1 = Stage 1 compressor (part load), and Stage 2 = Stage
2 compressor (full load).
In the cooling load only scenario, the Cold Tank will see a
temperature rise the due to the cooling load. When the Cold
Tank reaches the Stage 1activation temperature the compres-
sor will start (part load mode), the Hot Indoor and Cold Indoor
circulators will be turned on to circulate fluid between the heat
exchangers.
If the cooling load is still too large, the Cold Tank will once
again continue to rise in temperature. When the cooling Stage 2
activation temperature is reached, the compressor solenoid will
be energized to operate the compressor in full load mode.
01 MAR 2012
Theory of Operation
TA-
Page 11
TABLE 5 - Compressor Truth Table
(Heating Priority)
Heating
Cooling
Stage 1 Stage 2 Stage 1 Stage 2 Stage 1 Stage 2
0
0
0
0
0
1
0
0
1
1
0
0
1
0
1
1
0
1
1
1
0
1
1
1
1
1
1
TABLE 6 - Compressor Truth Table
(Cooling Priority)
Heating
Cooling
Stage 1 Stage 2 Stage 1 Stage 2 Stage 1 Stage 2
0
0
0
0
0
1
0
0
1
1
0
0
1
0
1
1
0
1
1
1
0
1
1
1
1
1
1
SIMULTANEOUS HEATING AND
COOLING LOAD OPERATION
When there are both heating and cooling loads pre-
sent, the heat pump will operate in the mode that has been set
as prioriy until the priority tank has been satisfied. It will then
switch to the default mode in order to satisfy the default tank.
In addition, if there is a Stage 1 call on one mode and a Stage 2
call of the other mode occurs, the compressor will automatically
be set to Stage 2 to complete the cycle as fast as possible in
order to switch to the other mode and satisfy the demand.
PRIORITY SELECTION
To set the cooling mode as priority, connect a jumper wire be-
tween the two PR terminals in the electrical box (refer to the
SCH and ELB diagrams).
To set the heating mode as priority, disconnect the jumper be-
tween the two PR terminals in the electrical box.
Units are shipped with a jumper wire between the PR terminals.
Compressor
Mode
0
0
0
0
1
0
1
1
1
0
1
0
0
1
0
1
1
1
0
1
1
0
1
1
1
1
1
Compressor
Mode
0
0
0
0
1
0
1
1
1
0
1
0
0
1
0
1
1
1
0
1
1
0
1
1
1
1
1
000662MAN-03
0
C
C
H
H
H
H
H
H
0
C
C
H
C
C
H
C
C
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