Lennox XP25-036-230-01 - Checking Indoor Airflow over Evaporator Coil Using Delta-T Chart

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