Table of Contents
Advertisement
PSYCHROMETRIC ASPECTS
In the following chart it is assumed that:
1. The manual positioning setpoint value provides 25
percent minimum OA.
2. The MA controller is set at 13 C.
3. The OA controller closes the OA damper to the minimum
position when OA temperature is 27 C.
4. RA condition is 24 C DB and 15 C WB for winter; 27 C
DB and 18 C WB for summer.
5. OA condition is 1.5 C DB and –1.5 C WB for winter;
38 C DB and 23.5 C WB for summer.
6. Other components exist in the complete system which
hold the RA at the desired condition.
13 C DB MA
CONTROLLER
SETPOINT
3
RA WINTER
1
24 C DB, 15 C WB
MA WINTER
2
OA WINTER
1.5 C DB, -1.5 C WB
ECONOMIZER CYCLE CONTROL OF SPACE TEMPERATURE WITH SUPPLY AIR
TEMPERATURE SETPOINT RESET
Functional Description
EA
83
6
OA
83
5
12
ECONOMIZER DECISION.
REFER TO PREVIOUS
ECONOMIZER OPTIONS
ENGINEERING MANUAL OF AUTOMATIC CONTROL
27 C DB OA
CONTROLLER
OA SUMMER
SETPOINT
38 C DB, 23.5 C WB
4
MA SUMMER
RA SUMMER
27 C DB, 18 C WB
C3237
3
ON
MA
ON
1
14
CONTROL
PROGRAM
11
22
OA MINIMUM SETPOINT
(NOTE: THE TEST AND BALANCE INITIAL VALUE
AIR HANDLING SYSTEM CONTROL APPLICATIONS
7. The desired MA temperature can be maintained during
economizer periods until the OA temperature falls below
the temperature at which only minimum OA is admitted
if the OA is less than 13 C.
The following results are obtained:
Item
No.
Explanation
1
At OA temperatures below -26 C DB (25
percent OA set by manual positioning setpoint
value), the MA condition lies to the left of the
13 C DB line.
2
As the OA temperature varies between –26 C
and 13 C, MA conditions lie on the 13 C
DB line.
3
As the OA temperature varies between 13 C
and 24 C, 100 percent OA is admitted and
the MA lies in the area between 13 C and
24 C DB.
4
As the OA temperature rises above 27 C DB,
the system operates on 25 percent OA and
the MA temperature varies from 35 C to
29.5 C DB.
RA
2
NORMAL
SA
15
4
7
10
15
9
FOR PROPER VENTILATION IS 22)
221
23.5
13
8
23.5
SPACE
TEMPERATURE
MIXED AIR
TEMPERATURE
RESET SCHEDULE
SUPPLY AIR
SPACE
TEMPERATURE
COOLING
SETPOINT
DEMAND
0
24
100
13
M15158
Advertisement
Chapters
Table of Contents
