1. 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

2. Economizer Economizer (fresh air volume flow rate control)
Controlled device is damper
- Damper for the air
- Valve for the CC
fresh
air
damper
mixing
recirc.
air
T & RH sensors

3. Economizer – cooling regime
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
100%
Minimum for
ventilation

4. Economizer – cooling regime
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

5. Sequence of operation for the humidity control system design
Adiabatic
humidifier CC HC SA OA
mixing RA
Define the sequence of operation for:
WINTER operation and:
- case when humidity is not controlled
- case when humidity is precisely controlled

6. Sensible and Enthalpy and Desiccant wheels

7. Sensible and Enthalpy Wheels

8. Heat recovery system in NSM building at UT

9. Desiccant wheel
Figure 3 – A desiccant-based cooling system combined with regenerative heat exchanger, vapor compression cooling, and evaporative humidifier (hybrid system).