Lecture Objectives: Discuss HW4 parts Learn about modeling of HVAC systems

Which part of the building is the most responsible Which part of the building is the most responsible? Building Envelope vs. HVAC System (AHU and distribution systems) Plant (boiler and/or Chiller) Building

Building Envelope vs. HVAC System Load - System - Plant Model Building Qbuiolding Heating/Cooling System Q including Ventilation and Dehumidification Plant Electric Energy Gas

Building HVAC Systems (Primary and Secondary Building HVAC Systems) AHU – Air Handling Unit Distribution systems Fresh air for ventilation AHU Primary systems Air transport Electricity Secondary systems Cooling (chiller) Heating (boilers) Building envelope HVAC systems affect the energy efficiency of the building as much as the building envelope. In many situation even more! (or Gas) Gas

eQUEST HVAC Models Predefined configuration for typical systems (no change) Divided according to the cooling and heating sources Details in eQUEST help file: For example: DX Coils No Heating Packaged Single Zone DX (no heating) Packaged single zone air conditioner with no heating capacity, typically with ductwork. Split System Single Zone DX (no heating) Central single zone air conditioner with no heating, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. Packaged Terminal AC (no heating) Packaged terminal air conditioning unit with no heating and no ductwork. Unit may be window or through-wall mounted. Packaged VAV (no heating) DX Coils Furnace Packaged direct expansion cooling system with no heating capacity. System includes a variable volume, single duct fan/distribution system serving multiple zones each with it's own thermostatic control. Packaged Single Zone DX with Furnace Central packaged single zone air conditioner with combustion furnace, typically with ductwork. Split System Single Zone DX with Furnace Central single zone air conditioner with combustion furnace, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. Packaged Multizone with Furnace Packaged direct expansion cooling system with combustion furnace. System includes a constant volume fan/distribution system serving multiple zones, each with its own thermostat. Warm and cold air are mixed for each zone to meet thermostat control requirements.

Examples of HVAC System Multizone Dual Duct System Multi zone VAV with Re-heaters 55°F 90°F 55°F P C P C Perimeter (P) Core (C)

Dual Duct vs. VAV with Re-heaters for Different Weather Conditions What happens if outdoor air is A, B, C A B C

Example of a Plant System (Chilled Water System) Air cooled chiller Chiller with a cooling tower COP ~ 3 COP ~ 5 COP = Cooling Energy / Electric Energy ( same units)

Two Basic Approaches for Modeling of HVAC and Building Envelope Load System Plant model Building Qbuiolding Heating/Cooling System Q including Ventilation and Dehumidification Plant Integrated models Building Heating/Cooling System Plant

Example of a HVAC Model 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]

Example of a 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

Plant model 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)

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: