Honeywell AUTOMATIC CONTROL SI Edition Engineering Manual page 257

FEATURES
1. The outdoor air quantity is modulated from a minimum
to take advantage of free cooling based on space
temperature demand.
2. The SA temperature will not fall below a set minimum.
3. Air is supplied at the temperature necessary to make up
the sensible heat loss of the space.
4. Space relative humidity is maintained at a minimum value
by a space humidity controller controlling the humidifier.
5. Separate setpoints for heating and cooling.
CONDITIONS FOR SUCCESSFUL OPERATION
See FAN SYSTEM START-STOP CONTROL.
1. An appropriate schedule of settings.
2. The low temperature limit controller located to respond
to the lowest temperature in the duct.
LIMITATIONS
This application used in applications that do not require
mechanical cooling.
SPECIFICATIONS
Anytime the supply fan runs, control system shall be enabled.
Anytime the space relative humidity drops below the setpoint,
the space humidity PI loop shall modulate the humidifier,
subject to an SA humidity high limit override set at 88%.
As the space heating load varies from 0 to 100%, the SA
heating PID loop setpoint shall be reset from 13 C to 41 C.
The hot water valve shall be modulated as required to maintain
the SA temperature setpoint.
Anytime the fan runs, the mixing dampers shall position to a
minimum ventilation setting.
As the space cooling load varies from 0 to 100%, the SA cooling
PI loop setpoint shall be reset from 27 C to 13 C. The outdoor
and return (and relief if applicable) air dampers shall be modulated
as required to maintain the SA temperature setpoint.
Cooling damper control shall be returned to minimum
position anytime the economizer mode is disabled.
Separate space heating and cooling setpoints shall be provided.
PSYCHROMETRIC ASPECTS
In the following charts it is assumed that:
1. Design outdoor air condition is –18 C DB and 50 percent
relative humidity.
ENGINEERING MANUAL OF AUTOMATIC CONTROL
AIR HANDLING SYSTEM CONTROL APPLICATIONS
2. SA condition at design load is 32 C DB and 7.0 grams
of moisture per kilogram of dry air.
3. Light load outdoor air condition is 13 C DB and 11.5 C
WB.
4. SA condition at light load is 24 C DB and 7.0 grams of
moisture per kilogram of dry air.
5. Minimum outdoor air is 25 percent.
6. RA condition is 23.5 C DB and 35% RH.
Design Load
RA 23.5 C DB,
35% RH
OA
MA 13 C DB,
-18 C DB,
7.5 C WB
50% RH
1
HEAT
2
The following results are obtained:
Item
No. Explanation
1 Design outdoor air condition is –18 C DB and
50 percent relative humidity.
2 Mixed air condition is 12.5 C DB and
7.5 C WB.
3 Heated air condition is 32 C DB and 16 C WB.
4 SA condition is 32 C DB and 7.0 grams of
moisture per kilogram of dry air.
Light Sensible Load
5
OA
13 C DB,
11.5 C WB
The following results are obtained:
Item
No. Explanation
5 Mixed air condition is 15 C DB and 11.5 C WB.
6 SA condition is 24 C DB, and 7.5 grams of
moisture per kilogram of dry air.
247
HUMIDIFY
4
MIX
SA 32 C DB,
7.0g H O/kg DRY AIR
2
3
32 C DB,
16 C WB
DESIGN LOAD
MA 15 C DB, 11.5 C WB
SA 24 C DB, 15.5 C WB
7.5g H O/kg DRY AIR
6
2
RA 22 C DB, 13 C WB
LIGHT SENSIBLE LOAD
C3256
C3257