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Cº
T
DROP
–
D
T
=
ºF
ACTION
53º
19
–
15
=
4
INCREASE THE AIRFLOW
58º
14
–
15
=
-1
(3º RANGE) NO CHANGE
62º
10
–
15
=
-5
DECREASE THE AIRFLOW
D
T
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
DR
Y-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
).
D
T
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
D
T
(T
DROP
–
D
T)
IS 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
D
T
= 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
D
T ARE 3º.
Figure 64. Checking Indoor Airflow over Evaporator Coil Using Delta-T Chart
