Lecture Objectives:

1. Lecture Objectives: • Discuss HW3 parts d) & e) • Learn about HVAC systems • Role of HVAC system in the energy performance • Differences between typical systems (examples) • Modeling

2. Example of Energy Consumption in an Office Building (Austin; 20,000 sf) Questions: 1) How to put gas and electric consumptions on the same graph 2) Which part of the building is the most responsible for the energy performance

3. Gas and Electric Consumptions a) Use pricing b) Convert gas to electricity 70 x106 Btu (76 x106 kJ or 21,000 kWh) 185,000 kWh Gas is ~ 4.5% of an energy bill 11.5% When we convert gas to electricity: ~3.8 %

4. Energy Principles:Site Energy vs. Primary Energy Primary Energy Site (End-use)energy is the energy directly consumed by end users Primary energy is site energy plus the energy consumed in the production and delivery of energy products Light Thermal Fresh air HVAC System Site energy (End use) HVAC – Heating, Ventilation and Air-Conditioning Site Energy Primary Energy Distribution Storage Generation

5. Gas (Thermal) Energy vs. Electric Energy Two approaches for comparison: • Convert everything to electric energy • Convert everything to primary energy General conversion factor 1kWh thermal energy ~ 1/3 kWh electric energy

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

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

8. 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! Gas (or Gas)

9. 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.

10. 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)

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

12. 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)

13. Building Heating/Cooling System Plant 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

14. Example of a HVAC ModelSchematic 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]

15. 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

16. 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)

17. Chiller 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: