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Lecture Objectives:

Lecture Objectives:. Solution of Exam Problems HVAC Systems Life Cycle Cost Analysis. Building-System-Plant. HVAC System (AHU and distribution systems). Plant (boiler and/or Chiller). Building. Building. Heating/Cooling System. Plant.

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Lecture Objectives:

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  1. Lecture Objectives: • Solution of Exam Problems • HVAC Systems • Life Cycle Cost Analysis

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

  3. 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

  4. 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)

  5. Example of 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]

  6. 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:

  7. Non-air system Radiant panel heat transfer model

  8. Non-air system Radiant panel heat transfer model The total cooling/heating load in the room The energy extracted/added by air system The energy extracted/added by the radiant panel: The energy extracted/added by the radiant panel is the sum of the radiative and convective parts: The radiant panel energy is:

  9. Example of 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

  10. 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:

  11. Example of HVAC system in eQUEST

  12. Life Cycle Cost Analysis • Engineering economics

  13. Life Cycle Cost Analysis • Engineering economics • Compound-amount factor (f/p) • Present worth factor value (p/f) • Future worth of a uniform series of amount (f/a) • Present worth of a uniform series of amount (p/a) • Gradient present worth factor (GPWF)

  14. Parameters in life cycle cost analysis Beside energy benefits expressed in $, you should consider: • First cost • Maintenance • Operation life • Change of the energy cost • Interest (inflation) • Taxes, Discounts, Rebates, other Government measures

  15. Example • Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - variable frequency drive

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