Checking Indoor Airflow Over Evaporator Coil Using Delta-T Chart - Lennox XP25-024-230-01 Installation And Service Procedure

AIRFLOW
DRY
BULB
C
T
DROP
53º
19º
AIR
FLOW
ALL TEMPERATURES ARE
EXPRESSED IN ºF
ASSUME DT = 15 AND A TEMP. = 72º, BELOW C TEMPERATURES REQUIRE ACTION:
DT =
Cº
T –
DROP
=
53º
19 – 15
=
58º
14 – 15
=
62º
10 – 15
Figure 64. Checking Indoor Airflow over Evaporator Coil Using Delta-T Chart
INDOOR COIL
TEMPERATURE OF AIR
ENTERING INDOOR COIL ºF
A
AIR
FLOW
INDOOR
COIL
ºF ACTION
4 INCREASE THE AIRFLOW
-1 (WITHIN +3º RANGE) NO CHANGE
-5 DECREASE THE AIRFLOW
80 24 24 24 23 23 22 22 22 20 19 18 17 16 15
78 23 23 23 22 22 21 21 20 19 18 17 16 15 14
76 22 22 22 21 21 20 19 19 18 17 16 15 14 13
74 21 21 21 20 19 19 18 17 16 16 15 14 13 12
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
A
USE THE FOLLOWING PROCEDURE TO ADJUST FOR OPTIMAL
72º
AIR FLOW ACROSS THE INDOOR COIL:
1. DETERMINE THE DESIRED DT — MEASURE ENTERING AIR
TEMPERATURE USING DRY BULB (A) AND WET BULB (B).
B
DT IS THE INTERSECTING VALUE OF A AND B IN THE
64º
TABLE (SEE TRIANGLE).
DRY BULB
2. FIND TEMPERATURE DROP ACROSS COIL — MEASURE
THE DRY BULB AIR TEMPERATURE ENTERING AND LEAV­
ING THE COIL (A AND C). TEMPERATURE DROP FORMULA:
(T
DROP
WET
BULB
3. DETERMINE IF FAN NEEDS ADJUSTMENT — IF THE DIF­
FERENCE BETWEEN THE MEASURED T
SIRED DT (T
NEEDED. SEE EXAMPLE AT LEFT:
NOTE - CHANGING AIR FLOW AFFECTS ALL TEMPERA­
TURES; RECHECK TEMPERATURES TO CONFIRM THAT THE
TEMPERATURE DROP AND DT ARE WITHIN +3º.
4.
ADJUST THE FAN SPEED
STRUCTIONS TO INCREASE/DECREASE FAN SPEED.
Page 86
DT
57 58 59 60 61 62 63 64 65 66 67 68 69 70
B
) = A MINUS C.
–DT) IS WITHIN +3º, NO ADJUSTMENT IS
DROP
—
SEE INDOOR UNIT IN­
AND THE DE­
DROP
XP25