Exam is on November 7, 2013 in class exam

1. Exam is on November 7, 2013 in class exam Example exams are posted on the course website

2. Lecture Objectives: • Introduce HW3 • Solar systems design • Finish building physics equation solvers • Introduce HVAC Systems • modeling of HVAC Systems

3. HW3 - Net zero energy house Model of the house Solar collectors PV system

4. Energy consumptionNew single family 2262 sf, 2-story home in Austin (AE data)

5. Energy consumption: kWh/year Units are in kW/h per year

6. Building physics equation solvers QHVAC

7. Example Tair is unknown and it is solved by system of equation :

8. Discretization of a non-homogeneous wall structure Section considered in the following discussion

9. System of equations (matrix) for single zone (room) 8 elements Three diagonal matrix for each element x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Air equation x

10. System of equations for a building Matrix for the whole building 4 rooms Rom matrixes Connected by common wall elements and airflow in-between room – Airflow simulation program (for example CONTAM) Energy Simulation program “meet” Airflow simulation program

11. Preprocessor Solver Postprocessor ES program Modeling steps • Define the domain • Analyze the most important phenomena and define the most important elements • Discretize the elements and define the connection • Write energy and mass balance equations • Solve the equations • Present the result

12. Modeling

13. Modeling

14. Modeling

15. Modeling 1) External wall (north) node Qsolar+C1·A(Tsky4 - Tnorth_o4)+ C2·A(Tground4 - Tnorth_o4)+hextA(Tair_out-Tnorth_o)=Ak/(Tnorth_o-Tnorth_in) A- wall area [m2] • - wall thickness [m] k – conductivity [W/mK]  - emissivity [0-1] • - absorbance [0-1] • =  - for radiative-gray surface, esky=1, eground=0.95 Fij –view (shape) factor [0-1] h – external convection [W/m2K] s – Stefan-Boltzmann constant [5.67 10-8 W/m2K4] Qsolar=asolar·(Idif+IDIR)A C1=esky·esurface_long_wave·s·Fsurf_sky C2=eground·esurface_long_wave·s·Fsurf_ground 2) Internal wall (north) node C3A(Tnorth_in4- Tinternal_surf4)+C4A(Tnorth_in4- Twest_in4)+hintA(Tnorth_in-Tair_in)= =kA(Tnorth_out--Tnorth_in)+Qsolar_to_int_ considered _surf Qsolar_to int surf =portion of transmitted solar radiation that is absorbed by internal surface C3=eniort_in·s·ynorth_in_to_ internal surface for homeworkassume yij = Fijei

16. Modeling b1T1 + +c1T2+=f(Tair,T1,T2) a2T1+b2T2 + +c2T3+=f(T1 ,T2, T3) a3T2+b3T3+ +c3T4+=f(T2 ,T3 , T4) ……………………………….. a6T5+b6T6+ =f(T5 ,T6 , Tair) Matrix equation M × t = f for each time step M × t = f

17. Modeling

18. HVAC systems in eQUEST

19. eQUEST HVAC Models • Predefined configuration (no change) • Divided according to the cooling and heating sources • Details in e quest help file: For example: DX CoilsNo Heating • Packaged Single Zone DX (no heating) • Packaged single zone air conditioner with no heating capacity, typically with ductwork. • Split System Single Zone DX (no heating) • Central single zone air conditioner with no heating, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. • Packaged Terminal AC (no heating) • Packaged terminal air conditioning unit with no heating and no ductwork. Unit may be window or through-wall mounted. • Packaged VAV (no heating) DX CoilsFurnace • Packaged direct expansion cooling system with no heating capacity. System includes a variable volume, single duct fan/distribution system serving multiple zones each with it's own thermostatic control. • Packaged Single Zone DX with Furnace • Central packaged single zone air conditioner with combustion furnace, typically with ductwork. • Split System Single Zone DX with Furnace • Central single zone air conditioner with combustion furnace, typically with ductwork. System has indoor fan and cooling coil and remote compressor/condensing unit. • Packaged Multizone with Furnace • Packaged direct expansion cooling system with combustion furnace. System includes a constant volume fan/distribution system serving multiple zones, each with its own thermostat. Warm and cold air are mixed for each zone to meet thermostat control requirements.

20. Building HVAC Systems (Primary and Secondary Building Systems) AHU – Air Handling Unit Distribution systems Fresh air For ventilation AHU Primary systems Air transport Electricity Secondary systems Cooling (chiller) Heating (boilers) Building envelope HVAC systems affect the energy efficiency of the building as much as the building envelope Gas (or Gas)

21. 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

22. 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]

23. 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: