Lecture Objectives: Differences in Conduction Calculation in Various Energy Simulation Programs Modeling of HVAC Systems

Methods for conduction calculation Finite difference or finite volume method Weighting factor method Response factor method or Response function method

Methods for conduction calculation Finite difference or finite volume methods Used in your HW assignments Energy simulation program ESPr Some models in TRANSYS Some models in EnergyPlus

Conduction with finite difference (volume) method Example room

System with the finite difference (volume) method for conduction calculation

Weighting factor methods The simplest method T external air T internal air Q solar Orientation and Wall (or element) structure Heat flux on internal surface database q Q HVAC q Building

System when we know the fluxes thought building walls We need to find other way to calculate fluxes

Response function methods Used in eQUEST program

Response function methods NOTATION: θ(x,t)=T(x,)

Laplace transformation Laplace transform is given by Where p is a complex number whose real part is positive and large enough to cause the integral to converge.

Laplace transformation table

Principles of Response function methods The basic strategy is to predetermine the response of a system to some unit excitation relating to the boundary conditions anticipated in reality. Reference: JA Clarke Book form the Reference List

Modeling of HVAC systems Review Psychrometrics Air-conditioning in Air Handling Units (AHU) Refrigeration cycles Building-System-Plant connection

Psychrometrics – review

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

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

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

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

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

HW3 System simulation Simplified model (use ii in your HW3a): Use the results from HW2 and calculate the sensible cooling requirement for 24 hours for ten identical rooms like the one from HW2b. If infiltration/ventilation provides 1 ACH calculate the latent load from infiltration 24 hours for ten identical rooms like the one from HW2b. Calculate the total cooling load for 24 hours for ten identical rooms like the one from HW2b. Use this as Q cooling () for HW3b 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

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

HW3 Chiller model: COP= f(TOA , Qcooling , chiller properties) Chiller data: QNOMINAL nominal cooling power, PNOMINAL electric consumption for QNOMINAL 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: