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Objectives

Objectives. Discuss Project Topics Learn to design VAV and DOAS System. 3D model – Biomedical Engineering (BME) Building. 3D model – Biomedical Engineering (BME) Building. 3D model – Biomedical Engineering (BME) Building. 3D model – Biomedical Engineering (BME) Building. VAV Example .

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Objectives

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  1. Objectives • Discuss Project Topics • Learn to design VAV and DOAS System

  2. 3D model – Biomedical Engineering (BME) Building

  3. 3D model – Biomedical Engineering (BME) Building

  4. 3D model – Biomedical Engineering (BME) Building

  5. 3D model – Biomedical Engineering (BME) Building

  6. VAV Example • One system • Multiple Spaces/Zones • - VAV box for each space/zone http://www.trane.com/commercial/library/vol242/v24b6.asp

  7. VAV System Terms & Equations(you can find them in ASHRAE Standard 62) • Fraction of minimum outdoor air in space/zone supply air Xi = VOAi / VSAi • Critical space Space with maximumXi , Z=max(Xi) • Fraction of outdoor air in system supply air X = sum(VOA ) / sum(VSA) • Required Fraction of outdoor air: Y=X/(1+X-Z)

  8. Example Solution

  9. Other Issues Related to VAV • Fan control • Minimum supply air • Occupancy sensors

  10. DOAS System • http://doas.psu.edu/

  11. Enthalpy wheel

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

  13. HVAC Control Example 1: Economizer (fresh air volume flow rate control) Controlled device is damper - Damper for the air - Valve for the liquids fresh air damper mixing recirc. air T & RH sensors

  14. Economizer Fresh air volume flow rate control % fresh air 100% enthalpy Fresh (outdoor) air TOA (hOA) Minimum for ventilation damper mixing Recirc. air T & RH sensors

  15. 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

  16. 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

  17. HVAC Control Example 2: Dew point control (Relative Humidity control) fresh air damper filter cooling coil heating coil filter fan mixing T & RH sensors Heat gains Humidity generation We should supply air with lower humidity ratio (w) and lower temperature We either measure Dew Point directly or T & RH sensors substitute dew point sensor

  18. Relative humidity control by cooling coil Cooling Coil Mixture Room Supply TDP Heating coil

  19. Relative humidity control by cooling coil (CC) • Cooling coil is controlled by TDP set-point if TDP measured > TDP set-point → send the signal to open more the CC valve if TDP measured < TDP set-point → send the signal to close more the CC valve • Heating coil is controlled by Tair set-point • if Tair < Tair set-point → send the signal to open more the heating coil valve • if Tair > Tair set-point → send the signal to close more the heating coil valve Control valves Fresh air mixing cooling coil heating coil Tair & TDP sensors

  20. Mixture 3 DPTSP Set Point (SP) Mixture 2 Mixture 1 DBTSP Sequence of operation(ECJ research facility) Control logic: Mixture in zone 1: IF (( TM<TSP) & (DPTM<DPTSP) ) heating and humidifying Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease humid. Mixture in zone 2: IF ((TM>TSP) & (DPTM<DPTSP) ) cooling and humidifying Cool. coil cont.: IF (TSP<TSA) increase cooling or IF (TSP>TSA) decrease cooling Humidifier: IF (DPTSP>DPTSA) increase humidifying or IF (DPTSP<DPTSA) decrease hum. Mixture in zone 3: IF ((DPTM>DPTSP) ) cooling/dehumidifying and reheatin Cool. coil cont.: IF (DPTSP>DPTSA) increase cooling or IF (DPTSP<DPTSA) decrease cooling Heater control: IF (TSP>TSA) increase heating or IF (TSP<TSA) decrease heating

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