Lecture Objectives: Learn about detailed vs. empirical modeling Discuss accuracy of energy modeling Introduce life-cycle cost analysis –integrated in eQUEST

What are the reasons for energy simulations? System Development Building design improvement Economic benefits Budget planning

Building design improvement Your projects 1 and 2

Whole building modeling Building Heating/Cooling System Plant Load System Plant Model Q Building Q Systems

Example of System Models: Schematic of simple air handling unit (AHU) m - mass flow rate [kg/s], T – temperature [C], w [kg moist /kg dry air ], r - recirculation rate [-], Q energy/time [W] Mixing box

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, T O is the outdoor air temperature, T M is the temperature of the air after the mixing box. The air-humidity balance for the mixing box is: w O is the outdoor air humidity ratio and w M is the humidity ratio after the mixing box 2) The energy balance for the heating coil is given as: The energy balance for the cooling coil is given as:

Detailed model Building Heating/Cooling System Plant Load System Plant Model Q Building Q Systems Building Heating/Cooling System Plant Integrated Model Q Building Q Systems Feedback eQUEST EnergyPlus

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

Therm

How to evaluate the whole building simulation tools Two options: 1)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

Source of inaccuracy when 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 Two options: 1)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 Cranfield test rooms (from Lomas et al 1994a)

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

Example of best test comparison

Economic benefits Life Cycle Cost Analysis Engineering economics Energy benefits

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 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 simulations System development Building design improvement Economic benefits (pay back period) Budget planning (fuel consumption) Least accurate

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

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

Example of best test comparison

What are the reasons for energy simulations? System Development Building design improvement Economic benefits Budget planning

Life Cycle Cost Analysis Engineering economics

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)

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 Using eQUEST analyze the benefits (energy saving and pay back period) of installing - low-e double glazed window - variable frequency drive in the school building in NYC

What are the reasons for energy simulations? System Development Building design improvement Economic benefits Budget planning

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

Moisture transport (WUFI)

Moisture transport - fundamentals However, you should be very carful how you use vapor barrier ! Theory & application (on the whiteboard)