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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

Announcement

Lecture on Energy Plus

by Wesley Cole

Monday, December 1, 8 am

ECJ Computer lab


Lecture objectives
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
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


Whole building modeling
Whole building modeling

Load System Plant Model

Building

Heating/Cooling

System

Plant

QBuilding

QSystems


Example of system models schematic of simple air handling unit ahu
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]


Energy and mass balance equations for air handling unit model steady state case
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:


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


Chiller plant model cop f t oa q cooling chiller properties
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:


Detailed model
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


Empirical model
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


Source of inaccuracy when considering final results
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


How to evaluate the whole building simulation tools
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


Comparison with measured data
Comparison with measured data

Cranfield test rooms (from Lomas et al 1994a)


Bestest building energy simulation test
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



Reasons for energy simulations
Reasons for energy simulations

  • System development

  • Building design improvement

  • Economic benefits (pay back period)

  • Budget planning (fuel consumption)


System development
System development

  • Example: glass facade design tool

THERM: heat thermal bridge analysis


Building design improvement
Building design improvement

  • Your projects 1 and 2


Economic benefits life cycle cost analysis
Economic benefitsLife Cycle Cost Analysis

  • Engineering economics

Energy benefits


Parameters in life cycle cost analysis
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


Example
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


Reasons for energy simulations1
Reasons for energy simulations

  • System development

  • Building design improvement

  • Economic benefits (pay back period)

  • Budget planning (fuel consumption)

Least accurate


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