Discharge Termperature Setpoint - Carrier 35E Installation And Start-Up Instructions Manual

DISCHARGE TEMPERATURE SETPOINT —
tional SSR Heat comes with a discharge temperature setpoint
(DTS) option. This option allows a maximum temperature to
be set at the board to prevent overheating of discharge air.
When the unit receives a signal to start heating, the board will
take an initial temperature reading and modulate heat from that
point to the maximum temperature. For example, if a thermo-
stat requires only a 10% heating output of air that was initially
60°F and has a maximum temperature setting of 90°F, the
EHM will modulate the heater's output temperature to 63°F
(the additional 3 degrees calculated from (90 – 60) x 10%).
This allows heaters to be sized for morning warm-up in the
winter and still comfortably operate on those days when the in-
let temperatures are slightly warmer.
The discharge temperature sensor comes with a 9 ft cable
for mounting in the downstream ductwork. The sensor should
be mounted a minimum of 3 in. from the discharge of the unit
and centered in the side of the ductwork. Avoid installing the
sensor near an elbow, take off, or transition. The sensor can be
mounted by drilling a 1 / -in. hole into the ductwork, inserting
2
the sensor, and securing it with 2 sheet metal screws. The sen-
sor is 6 in. long, and the tip should not touch any part of the
ductwork.
Neither the jumper settings nor the controls wiring needs to
be changed when this option is installed. The EHM control
board will detect if a sensor has been connected, and it will ad-
just the control function accordingly. The sensor wires are con-
nected to the screw terminals at the Sensor (Fig. 14, item 6) lo-
cation on the EHM. The connection at this termination is not
polar sensitive and the two wires may be switched with no ef-
fect.
TEMP
dc VOLT
(°F)
68 0.00
69 0.05
70 0.10
71 0.15
72 0.20
73 0.26
74 0.30
75 0.35
76 0.40
77 0.44
78 0.49
79 0.53
Propor-
Table 10 — DTS Voltage per Temperature
TEMP TEMP
dc VOLT
(°F) (°F)
80 0.58 90
81 0.62 91
82 0.66 92
83 0.70 93
84 0.74 94
85 0.77 95
86 0.81 96
87 0.85 97
88 0.88 98
89 0.91 99
The desired discharge temperature is set by rotating the dis-
charge temperature set point dial arrow to the maximum outlet
temperature desired. To fine tune the discharge temperature set
point, connect the positive and negative leads of a multimeter
to Tcal and Com (Fig. 14, item 7), respectively, on the EHM.
Then place a jumper between the two screw heads on the sen-
sor termination. Rotate the discharge temperature set point dial
until the desired voltage per temperature is obtained. See Table
10. After the voltage is obtained, the EHM board must be reset.
To reset the board, remove the jumpers and then place back in
correct position.
It should be noted that the ASHRAE Fundamentals Hand-
book (Chapter 31) states that discharging air at a temperature
more than 15°F above the room (90°F in a 75°F room) will
likely result in significant unwanted air temperature stratifica-
tion.
It is recommended that heater output be ramped or staged
when switching from cooling to heating modes. On initial call
for maximum or near maximum heat, from cooling mode, the
heater may overshoot the desired temperature by up to 20°F for
10 to 20 seconds (on oversized heaters). As the EHM begins
modulating heater output, the discharge temperature will
quickly drop to the desired set point.
±2°F of the desired setpoint are reached within 90 seconds with
oversized heaters.
TEMP
dc VOLT
(°F)
0.95 100
0.98 101
1.01 102
1.04 103
1.07 104
1.10 105
1.12 106
1.15 107
1.18 108
1.20 109
23
Temperatures within
TEMP
dc VOLT dc VOLT
(°F)
1.23 110
1.25 111
1.27 112
1.30 113
1.32 114
1.34 115
1.36 116
1.38 117
1.40 118
1.42 119
120
1.44
1.46
1.48
1.50
1.51
1.53
1.55
1.56
1.58
1.60
1.61