2
Air Handlers—Supply Air Temperature Control with Modulated Dampers and Modulated Cooling
The following compounds also provide temperature control through
modulated dampers, heating devices, or cooling devices.
•
CLM compound
—modulated cooling control
•
DM compound
—modulated damper control
•
HTM compound
—modulated heating control
•
HTMCLM compound
—sequential control of modulated heating and
modulated cooling control
•
HTMDM compound
—sequential control of modulated heating and
modulated damper control
•
HTMDMCLM compound
—sequential control of modulated
heating, dampers, and cooling control
The PID algorithm, embedded in the DC-TRL (PIDL object) in the Digital
Control Module (DCM), provides the necessary control.
As the feedback temperature increases above the setpoint, the dampers are
modulated to their maximum position, based on the difference between the
setpoint and the feedback temperature.
As the feedback temperature increases further, the cooling device is
modulated to full cooling, and the dampers are held at their maximum
position.
For simplicity, the above statements reflect the PID algorithm’s
proportional response to a change in feedback. To understand the
algorithm’s actual control, you must incorporate the effect of the
proportional, integral, and derivative responses.
Modulation occurs in the following manner:
Table 1: Modulation
Device
Command From DC-CTRL
Result
Cooling
200.0
Full cooling
100.0
No cooling
Dampers
100.0
Maximum position
0.0
Minimum position
The CLG-PTP (PIDL object) has been added to allow the addition of the
independent lockout of cooling control and dehumidification features. The
PID algorithm of the CLG-PTP (PIDL object) is disabled. With this
algorithm disabled, the command from the DC-CTRL (PIDL object) is
routed to the other switches and selectors in the CLG-PTP (PIDL object).
Alternate Schemes
How It Works