Multiple Coil Control From Outdoor And Supply Air - Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual

2
MA
1
OA 1.5 C DB, -1.5 C WB

MULTIPLE COIL CONTROL FROM OUTDOOR AND SUPPLY AIR

Functional Description
OA
TEMPERATURE
9 4
1.5
3
7
-12
OPEN
OA
VALVE 2
PERCENT
OPEN TEMPERATURE
0
12
100
1.5
Item
No. Function
1,2 Control system energizes when fan is turned on
(See FAN SYSTEM START-STOP CONTROL).
3 OA damper opens when fan runs.
4-6 Supply air PID control loop modulates the coil #3
valve to maintain constant supply temperature.
7-9 Coil #1 is under open loop control by OA
temperature.
10-12 Coil #2 is under open loop control by coil #1
leaving air temperature.
13 Control program coordinates temperature,
ventilation, and fan interlock control.
14 Coil #2 leaving air temperature is for operator
information (unless alarm monitoring is desired).
ENGINEERING MANUAL OF AUTOMATIC CONTROL
RA 24 C DB, 17 C WB
MA
PREHEAT AIR
21 C DB
C3243
VALVE 1
PERCENT
OPEN
0
CONTROL
PROGRAM
100
100
8
V1
N.O.
COIL
N.C.
NO. 1
COIL 1
4
AIR HANDLING SYSTEM CONTROL APPLICATIONS
The following results are obtained:
Item
No. Explanation
1 Heating of OA occurs along a line of constant
moisture content from 1.5 C to 21 CF.
2 This condition represents the mixing of
preheated air and RA supplied to the system.
13
60 11
11
4
V2
N.O.
N.O.
COIL
NO. 2
10
14
3
FEATURES
1. The multiple inline coil system heats below-freezing air
with little danger of freezing the coils or overheating
the space.
2. The supply temperature is constant (or may be dictated
by other HVAC controls).
3. In this sequence, individual Coil 1 and 2 Valves are opened
fully just before freezing air enters to prevent freezing.
4. The low temperature control (Item 2) is intended to
protect the coils from freezing due to the loss of heat.
Low temperature controls cannot be installed in the
leaving air of Coils 1 and 2 because leaving air
temperatures below freezing may be normal. If water flow
is lost through Coils 1 or 2, they could freeze without
detection by the low temperature control (Item 2).
Differential temperature (software) monitor points across
231
18
SA
6
18
5
2
V3
NORMAL
1
COIL
ON
NO. 3
14
M15166