Optimizing System Refrigerant Charge - Lennox Elite XP16−024−230 Installation Instructions Manual

Optimizing System Refrigerant Charge

This section provides instructions on optimizing the
system charge. This section includes:
S
Optimizing procedure
S
Adjusting indoor airflow
S
Using subcooling method
S
Approved matched components, targeted subcooling
(SC) values and add charge values
S
Normal operating pressures
S
Temperature pressures
OPTIMIZING PROCEDURE
1. Move the low−side manifold gauge hose from the
vapor line service valve to the true suction port (see
figure 21).
2. Set the thermostat for either cooling or heating
demand. Turn on power to the indoor unit and close
the outdoor unit disconnect switch to start the unit.
3. Allow unit to run for five minutes to allow pressures to
stabilize.
4. Check the airflow as instructed under Adjusting Indoor
Airflow to verify or adjust indoor airflow for maximum
Temp.
80 24 24 24 23 23 22 22 22 20 19 18 17 16 15
of air
entering
78 23 23 23 22 22 21 21 20 19 18 17 16 15 14
indoor
76 22 22 22 21 21 20 19 19 18 17 16 15 14 13
coil ºF
74 21 21 21 20 19 19 18 17 16 16 15 14 13 12
A 72 20 20 19 18 17 17 16 15 15 14 13 12 11 10
70 19 19 18 18 17 17 16 15 15 14 13 12 11 10
Wet−bulb ºF
57 58 59 60 61 62 63 64 65 66 67 68 69 70
T
Drop
C
19º
53º
air flow
DRY
BULB
All temperatures are
expressed in ºF
Figure 23. Checking Airflow over Indoor Coil Using Delta−T Formula
ADJUSTING INDOOR AIRFLOW
DT
B
B
air flow
64º
INDOOR WET
BULB
COIL
efficiency. Make any air flow adjustments before
continuing with the optimizing procedure.
5. Use subcooling method to optimize the system
charge (see figure 24). Adjust charge as necessary.
ADJUSTING INDOOR AIRFLOW
Heating Mode Indoor Airflow Check
(Only use when indoor unit has electric heat)
Indoor blower airflow (CFM) may be calculated by
energizing electric heat and measuring:
S
Temperature rise between the return air and supply air
temperatures at the indoor coil blower unit,
S
Measuring voltage supplied to the unit,
S
Measuring amperage being drawn by the heat unit(s).
Then, apply the measurements taken in the following
formula to determine CFM:
CFM =
Cooling Mode Indoor Airflow Check
Check airflow using the Delta−T (
23.
1. Determine the desired DT Measure entering air temper-
ature using dry bulb (A) and wet bulb (B). DT is the intersect-
ing value of A and B in the table (see triangle).
2. Find temperature drop across coil
bulb entering and leaving air temperatures (A and C). Tem-
perature Drop Formula: (T
3. Determine if fan needs adjustment
the measured T
+3º, no adjustment is needed. See examples: Assume DT =
A
15 and A temp. = 72º, these C temperatures would necessi-
72º
tate stated actions:
T –
Cº
Drop
19 –
53º
DRY
14 –
58º
BULB
10 –
62º
4. Adjust the fan speed
crease/decrease fan speed.
Changing air flow affects all temperatures; recheck tempera-
tures to confirm that the temperature drop and DT are within
+3º.
Page 26
Amps x Volts x 3.41
1.08 x Temperature rise (F)
DT)
Measure the coil's dry
) = A minus C.
Drop
If the difference between
and the desired DT (T
Drop
DT =
ºF ACTION
=
15 4 Increase the airflow
=
15 −1 (within +3º range) no change
=
15 −5 Decrease the airflow
See indoor unit instructions to in-
process using figure
–DT) is within
Drop