29
Typically the maximum ventilation rate will be about 5 to
10% more than the typical cfm required per person, using
normal outside air design criteria.
A proportional anticipatory strategy should be taken with
the following conditions: a zone with a large area, varied occu-
pancy, and equipment that cannot exceed the required ventila-
tion rate at design conditions. Exceeding the required ventila-
tion rate means the equipment can condition air at a maximum
ventilation rate that is greater than the required ventilation rate
for maximum occupancy. A proportional-anticipatory strategy
will cause the fresh air supplied to increase as the room CO2
level increases even though the CO2set point has not been
reached. By the time the CO2level reaches the set point, the
damper will be at maximum ventilation and should maintain
the set point.
CONTROL
CURVE
A
B
C
D
CONTROL POINT
APPROX. °F (°C)
AT 50% RH
73 (23)
70 (21)
67 (19)
63 (17)
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46
90
100
80
70
60
50
40
30
20
10
ENTHALPY—BTU PER POUND DRY AIR
85
(29)
90
(32)
95
(35)
100
(38)
105
(41)
110
(43)
35
(2)
35
(2)
40
(4)
40
(4)
105
(41)
110
(43)
45
(7)
45
(7)
50
(10)
50
(10)
55
(13)
55
(13)
60
(16)
60
(16)
65
(18)
65
(18)
70
(21)
70
(21)
75
(24)
75
(24)
80
(27)
80
(27)
85
(29)
90
(32)
95
(35)
100
(38)
APPROXIMATE DRY BULB TEMPERATURE— °F (°C)
A
A
B
B
C
C
D
D
RELATIVE HUMIDITY (%)
HIGH LIMIT
CURVE
Fig. 41 — Enthalpy Changeover Set Points
TR1
24 Vac
COM
TR
24
Vac
HOT
12
34
5
EF EF1
+_
P1
T1
P
T
N
EXH
2V 10V
EXH
Set
Set
2V 10V
2V 10V
DCV
DCV
Free
Cool
BC
AD
SO+
SR+
SR
SO
AQ1
AQ
DCV
Min
Pos
Open
Max
N1