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Published byDamon Lang Modified over 9 years ago

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

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

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HW3 System 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

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T OA water Building users (cooling coil in AHU) T CWR = 11 o C T CWS =5 o C Evaporation at 1 o C T Condensation = T OA + ΔT What is COP for this air cooled chiller ? COP is changing with the change of T OA Plant Models: Chiller P electric ( ) = COP ( ) x Q cooling coil ( )

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

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HW3 Chiller model: COP= f(T OA, Q cooling, chiller properties) Chiller data: Q NOMINAL nominal cooling power, P NOMINAL electric consumption for Q NOMINAL Cooling water supplyOutdoor 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: The consumed electric power [KW] under any condition Available capacity as function of evaporator and condenser temperature

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Air-conditioning in Air Handling Unit (AHU) Compressor and Condenser Roof top AHU Gas/Electric Heater to building Fan air from building fresh air Evaporator filter mixing hot water cool water Return fan Supply fan flow control dampers AHU Fresh air AHU schematic Outdoor air To room ExhaustFrom room

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

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

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

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

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Energy and mass balance equations for Air handling unit model – steady state case m S is the supply air mass flow rate c p - specific capacity for air, T R is the room temperature, T S is the supply air temperature. w R and w S are room and supply humidity ratio - energy for phase change of water into vapor The energy balance for the room is given as: The air-humidity balance for room is given as: The energy balance for the mixing box is: ‘r’ is the re-circulated air portion, T O is the outdoor air temperature, T M is the temperature of the air after the mixing box. The air-humidity balance for the mixing box is: w O is the outdoor air humidity ratio and w M 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:

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eQUEST software

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