Lecture Objectives: -Define the midterm project -Lean about eQUEST -Review exam problems

Midterm Project Objective: - Learn to use eQUEST - Learn to conduct parametric analyses for design optimization

Midterm Project Use eQUEST to model 2 buildings: Residential house –Duplex – 2 floors single zone per floor –Focus on envelope, zoning, and internal loads Commercial Building –ECJ building 18’ 60’ 40’

Midterm Project Major Output: Energy consumption for both buildings –Electricity and –Gas Part 1: Parametric analysis for residential building –Windows (glazing and shading) –Wall insulation –Wall surface properties –Shading Part 2: Complex geometry, internal loads, and detailed mode

eQUEST Example of –Defining envelope and internal loads –Selecting HVAC system –Presenting results –Finding design cooling and heating loads – Extracting simulation detail

Review Heat transfer Thermal analysis of building elements External and internal boundary conditions Weather data for boundary conditions Modeling procedures –Numerical methods for solving equations

Review of heat transfer How to model: –Convection at surfaces –Radiation between surfaces –Conduction through building elements Steady state or unsteady state

Building elements

Weather data (TMY2 database) Use them for External boundary conditions Convection Long-wave Radiation Solar radiation Direct Diffuse Reflected (diffuse)

Discretization

Discretization for conduction Section considered in the following discussion Discretization in space Discretization in time T – temperature [C] ρ – density [kg/m 3 ] c p – specific capacity [J/kgK] k- conductivity [W/mK]  time [sec] x distance [m]

Finite volume (difference) method Boundaries of control volume Fir each node conservation of energy: implicit explicit

Implicit methods - example  =0 To Tw Ti  =36 system of equation Tw Ti  =72 system of equation Tw Ti After rearranging: 2 Equations with 2 unknowns!

Unsteady-state conduction Implicit method with linearization Matrix equation M × T = F for each time step Air b 1 T 1  +  +c 1 T 2  +  =f(T air,T 1 ,T 2  ) a 2 T 1  +  b 2 T 2  +  +c 2 T 3  +  =f(T 1 ,T 2 , T 3  ) a 3 T 2  +  b 3 T 3  +  +c 3 T 4  +  =f(T 2 ,T 3 , T 4  ) a 6 T 5  +  b 6 T 6  +  =f(T 5 ,T 6 , T air ) ……………………………….. M × T = F

Numerical methods System of equations for unsteady state process (nonlinear) Explicit Implicit Linearization (Matrix solver) Nonlinear (Newton-Raphson method) For each time step PROBLEM Steady-state Unsteady-state System of equations for steady state process (nonlinear) Implicit

Integration of HVAC and building physics models Building Heating/Cooling System Plant Building Heating/Cooling System Plant Load System Plant model Integrated models Q buiolding Q including Ventilation and Dehumidification

Modeling steps Define the domain Analyze the most important phenomena and define the most important elements Discretize the elements and define the connection Write the energy and mass balance equations Solve the equations (use numeric methods or solver) Present the result

Practice for the Exam Example #1 Walmart store (L>>H, D>>H) H-5m L=200 m D=100m door Plenum (air) Room (air) Floor concrete Q HVAC insulation acoustic tile TRTR TFTF L concrete L insulation L plenum L tile m S,T S

Practice for the Exam Example #2 You are considering using the ventilated windows for ventilation of your new building and a sales person claims that it will reduce your annual energy bill by 10%. To check this claims you decided to model the performance of this window for your climate condition. Air cavity open to outdoor air at the top, and to indoor air at the bottom Building fan creates under pressure in the room T RA Q HVAC T RA Q HVAC Building fan creates pressure in the room