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Announcement

Announcement. Lecture on Energy Plus by Wesley Cole Monday, December 1, 8 am ECJ Computer lab. Lecture Objectives:. Finish with TMY weather data Compare detailed and empirical modeling discus accuracy Show how to use life-cycle cost analysis integrated in eQUEST. TMY weather data.

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Announcement

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  1. Announcement Lecture on Energy Plus by Wesley Cole Monday, December 1, 8 am ECJ Computer lab

  2. Lecture Objectives: • Finish with TMY weather data • Compare detailed and empirical modeling • discus accuracy • Show how to use life-cycle cost analysis • integrated in eQUEST

  3. TMY weather data • TMY, TMY2, TMY3 • http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/ 1991, 1992, ……………...1994, 1995 TMY3: January , February , March, ….December Each location - different set

  4. Whole building modeling Load System Plant Model Building Heating/Cooling System Plant QBuilding QSystems

  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 1) 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 2) The energy balance for the cooling coil is given as:

  7. 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

  8. Chiller (plant) 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:

  9. Detailed model Load System Plant Model Building Heating/Cooling System Plant QBuilding QSystems eQUEST Integrated Model Building Heating/Cooling System Plant QBuilding QSystems EnergyPlus Feedback

  10. Empirical model Load vs. dry bulb temperature Measured for a building in Syracuse, NY Model For an average year use TMY2 =835890ton hour = 10.031 106 Btu

  11. Source of inaccuracywhen considering final results • Assumptions related to the model • Lack of precise input data • Modeling software (tool) limitations • Limitation related to available computational resources • Result interpretations

  12. How to evaluate the whole building simulation tools Two options: • Comparison with the experimental data - monitoring - very expensive - feasible only for smaller buildings 2) Comparison with other energy simulation programs - for the same input data - system of numerical experiments - BESTEST

  13. Comparison with measured data Cranfield test rooms (from Lomas et al 1994a)

  14. BESTEST Building Energy Simulation TEST • System of tests (~ 40 cases) - Each test emphasizes certain phenomena like external (internal) convection, radiation, ground contact • Simple geometry • Mountain climate COMPARE THE RESULTS

  15. Example of best test comparison

  16. Reasons for energy simulations • System development • Building design improvement • Economic benefits (pay back period) • Budget planning (fuel consumption)

  17. System development • Example: glass facade design tool THERM: heat thermal bridge analysis

  18. Building design improvement • Your projects 1 and 2

  19. Economic benefitsLife Cycle Cost Analysis • Engineering economics Energy benefits

  20. 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

  21. Example • Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - economizer in the school building in NYC

  22. Reasons for energy simulations • System development • Building design improvement • Economic benefits (pay back period) • Budget planning (fuel consumption) Least accurate

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