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Advanced Control Techniques for HVAC Systems: Economizers and Heat Recovery

This instructional resource covers advanced HVAC control techniques focusing on economizers and heat recovery systems. Learn about psychrometrics and how to control fresh air volume flow, utilizing dampers and valves. Discover the importance of controlling dampers and cooling coils based on temperature set points and room conditions. Gain insights into the sequence of operations for optimizing both temperature and humidity control in HVAC designs. Case examples include systems using desiccant wheels, regenerative heat exchangers, and hybrid cooling technologies.

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Advanced Control Techniques for HVAC Systems: Economizers and Heat Recovery

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Presentation Transcript

  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 Desiccantwheels

  7. Sensible and Enthalpy Wheels

  8. Heat recovery system in NSM building at UT

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

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