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Lecture Objectives:

Lecture Objectives:. Model HVAC Systems HW3 Asignemnet Learn about eQUEST software How to conduct parametric analysis of building envelope. Refrigeration Cycle. Released energy (condenser). T outdoor air. T cooled water. - What is COP? - How the outdoor air temperature

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Lecture Objectives:

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Presentation Transcript

  1. Lecture Objectives: • Model HVAC Systems • HW3 Asignemnet • Learn about eQUEST software • How to conduct parametric analysis of building envelope

  2. Refrigeration Cycle Released energy (condenser) T outdoor air T cooled water - What is COP? - How the outdoor air temperature affects chiller performance? Cooling energy (evaporator)

  3. HW3System simulation Simplified model (use in your HW3): • Use the results from HW2 and calculate the sensible cooling requirement for 24 hours for ten identical rooms like the one from HW2. • If infiltration/ventilation provides 1 ACH calculate the latent load from infiltration 24 hours for ten identical rooms like the one from HW2. • Calculate the total cooling load for 24 hours for ten identical rooms like the one from HW2. • Use this as Q cooling () for HW3 Note: This method: - assumes perfect process in AHU to control RH sometimes we need to heat and cool at the same time - neglects fan power - dos not consider system properties and control Variable Air Volume or Constant Air Volume

  4. Plant Models:Chiller P electric () = COP () x Q cooling coil () TOA What is COP for this air cooled chiller ? T Condensation = TOA+ ΔT Evaporation at 1oC TCWS=5oC TCWR=11oC water Building users (cooling coil in AHU) COP is changing with the change of TOA

  5. Modeling of Chiller The consumed electric power [KW] under any condition of load Chiller model acronyms: Available capacity as function of evaporator and condenser temperature CAPacity as Function of Temperature Full load efficiency as function of condenser and evaporator temperature Energy Input Ratio as Function of Temperature Efficiency as function of percentage of load Energy Input Ratio as Function of Part Load Ratio Part load: Part Load Ratio

  6. HW3Chiller model: COP= f(TOA , Qcooling , chiller properties) Chiller data: QNOMINAL nominal cooling power, PNOMINAL electric consumption forQNOMINAL The consumed electric power [KW] under any condition Available capacity as function of evaporator and condenser temperature Cooling water supply Outdoor air Full load efficiency as function of condenser and evaporator temperature Efficiency as function of percentage of load Percentage of load: The coefficient of performance under any condition:

  7. Roof top AHU fresh air filter mixing Fan air from building to building Evaporator Gas/Electric Heater Air-conditioning in Air Handling Unit (AHU) AHU AHU schematic Exhaust From room Return fan flow control dampers Supply fan Compressorand Condenser Fresh air To room Outdoor air hotwater coolwater

  8. Processes in AHU presented in Psychrometric in psychrometric Case for Summer in Austin OA MA IA SA

  9. Building-System-Plant HVAC System (AHU and distribution systems) Plant (boiler and/or Chiller) Building

  10. Building Heating/Cooling System Plant Integration of HVAC and building physics models Load System Plant model Building Qbuiolding Heating/Cooling System Q including Ventilation and Dehumidification Plant Integrated models

  11. System Models:Schematic of simple air handling unit (AHU) Mixing box m - mass flow rate [kg/s], T – temperature [C], w [kgmoist/kgdry air], r - recirculation rate [-], Q energy/time [W]

  12. Energy and mass balance equations for Air handling unit model – steady state case The energy balance for the room is given as: mS is the supply air mass flow rate cp- specific capacity for air, TRis the room temperature, TS is the supply air temperature. The air-humidity balance for room is given as: wRand wS are room and supply humidity ratio - energy for phase change of water into vapor The energy balance for the mixing box is: ‘r’ is the re-circulated air portion, TO is the outdoor air temperature, TM is the temperature of the air after the mixing box. The air-humidity balance for the mixing box is: wOis the outdoor air humidity ratio and wM is the humidity ratio after the mixing box The energy balance for the heating coil is given as: The energy balance for the cooling coil is given as:

  13. eQUEST software

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