Carrier WEATHERMASTER 50HJQ004-016 Product Data page 170

Application data (cont)
→
Compressor staging — The EconoMi$er IV is an inte-
grated economizer and has the ability to utilize simulta-
neous outdoor air and compressors. The EconoMi$er IV
can be configured to support economizer and compressor
operation for up to 4 compressors. Only one or two com-
pressor operation is available with 3 to 12
Changeover strategies — The EconoMi$er IV control-
ler can be configured to accommodate all available econo-
mizer control strategies that place the rooftop unit in
economizer mode including:
Switch — Used when a remote signal from an energy man-
agement system will enable and disable the EconoMi$er IV
(remote enable control).
Outdoor dry bulb — EconoMi$er IV will be enabled based
on the outside air temperature. This is provided standard
with the EconoMi$er IV.
CONTROL
CURVE
A
B
C
D
170
1 / ton units.
2
→ ECONOMIZER CHANGEOVER CURVES
CONTROL POINT
APPROX. °F (°C)
AT 50% RH
73 (23)
70 (21)
67 (19)
63 (17)
60
(16)
A
55
(13)
B
50
C
(10)
D
45
(7)
40
(4)
35
(2)
35 40 45 50 55 60
(2) (4) (7) (10) (13) (16)
APPROXIMATE DRY BULB TEMPERATURE— °F (°C)
Differential dry bulb — EconoMi$er IV will be enabled
whenever the outside air temperature is lower than the
return-air temperature.
Outside air enthalpy — EconoMi$er IV will be enabled
based on the outside air enthalpy curves as shown in the
EconoMi$er IV Changeover diagram below. The A, B, C,
and D curves shown have been in use for many years and
have been included as part of the latest ASHRAE 90.1
energy efficiency code. The curves are designed to take
into consideration both outdoor temperature and humidity.
These curves are used to set up the EconoMi$er IV con-
troller to use the EconoMi$er IV for free cooling when the
conditions to the left of the curve exist. When the condi-
tions are to the right of the curve, then outdoor air cooling
will not be used and the outdoor air damper position will be
set at the minimum position.
85 90 95
(29) (32) (35)
80
(27)
75
(24)
70
(21)
→
65
(18)
A
B
C
D
65 70 75 80 85 90 95
(18) (21) (24) (27) (29) (32) (35)
905
100 105 110
(38) (41) (43)
HIGH LIMIT
CURVE
100 105 110
(38) (41) (43)