Objectives. Learn about 1) Control for HVAC systems - Economizers (Psychrometrics) and control - Heat recovery systems (Psychrometrics) 2) Some advance HVAC systems desiccant, enthalpy, sensible wheel . Economizer. Economizer (fresh air volume flow rate control).
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1) Control for HVAC systems
- Economizers (Psychrometrics) and control
- Heat recovery systems (Psychrometrics)
2) Some advance HVAC systems
desiccant, enthalpy, sensible wheel
Economizer (fresh air volume flow rate control)
Controlled device is damper
- Damper for the air
- Valve for the CC
T & RH sensors
How to control the fresh air volume flow rate?
If TOA < Tset-point → Supply more fresh air than the minimum required
The question is how much?
Open the damper for the fresh air
and compare the Troom with the Tset-point .
Open till you get the Troom = Tset-point
If you have 100% fresh air and your
still need cooling use cooling coil.
What are the priorities:
- Control the dampers and then the cooling coils or
- Control the valves of cooling coil and then the dampers ?
Defend by SEQUENCE OF OERATION
the set of operation which HVAC designer provides to the automatic control engineer
% fresh air
Example of SEQUENCE OF OERATIONS:
If TOA < Tset-point open the fresh air damper the maximum position
Then, if Tindoor air < Tset-point start closing the cooling coil valve
If cooling coil valve is closed and T indoor air < Tset-point start closing the damper
till you get T indoor air = T set-point
Other variations are possible
Define the sequence of operation for:
WINTER operation and:
- case when humidity is not controlled
- case when humidity is precisely controlled