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Energy Efficient Buildings Design Calculation Worksheet

A. Heat Loss

Parameters

1. Assume an approximate R value for the building: ______________K/W

2. Assume an approximate T for December: ______________K

3. For how long a period should the building stay warm after sunset? ______________seconds

Calculations4. What is the rate heat loss from your building? ______________W

5. How much energy will the building need to keep it warm for the period after sunset? ______________J

B. Heat Storage

Parameters

6. The approximate dimensions of the model building are: _____ m wide by _____ m deep by _____ m tall

7. What is a reasonable percentage of the building's interior that can be used for the thermal mass? ______________%

Calculations

8. What is the approximate volume of your building from step 6? ______________m3

9. What is the volume of your thermal mass from steps 7-8? ______________m3

10. If the entire volume of the thermal mass was water (w=1000 kg/m3), what would its mass be? ______________kg

11. What is the total heat capacity of the water (Cw=4200 J/kgK) in step 10? ______________J/K

12. By how much would the water need to cool to release the energy required in step 5? ______________K

13. Assuming the thermal mass cools to 293 K, at what "hot" temperature does it need to start at sunset? ______________K

C. Solar Gain

Parameters

14. Assume a reasonable solar flux in the afternoon: ______________W/m 2

15. During the day, how quickly should the thermal mass heat from 293 K to its hot temperature in step 13? ______________seconds

16. What is the estimated absorption coefficient of your windows or solar collector? ______________

17. What is the approximate angle ( ) between your window direction and the sun's rays in the afternoon? ______________degrees

18. What is the approximate maximum area available for windows (width x height in step 6)? ______________m2

Calculations

19. How much energy is required to heat the thermal mass in step 11? ______________ J

20. How much power is required to achieve the heating rate in step 15? ______________ W

21. How much power is needed to counter the heat loss in step 4? ______________ W

22. What is the total solar power needed to heat the thermal mass and keep the building warm? ______________ W

23. What is the window area required to capture the needed power in step 22? ______________ m 2

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C. Ventilation

Parameters

24. What is the mass-flow rate of the forced ventilation (0.00022 m3/sec per fan)? ______________kg/sec (with air 1.2kg/m3)

25. Are there any other means of ventilation that will help lowerT during warm weather? ______________

Calculations

26. What is the expected steady-state T for your building when the fan is on (see slides from Nov 8)? ______________K

27. Based on experiments and/or intuition, estimate the reduction in T due to any additional ventilation? ______________K

D. Electrical System Budget

Parameters

28. Complete the table below to estimate the electrical power budget.

Component Load Current Time On Number Used Average Load Current

Microcontroller 7 mA 100% 1 7 mA

Fan 120 mA _______% _______ _______ mA

LED 4-10 mA _______% _______ _______ mA

Servo (no load) 10 mA 100% _______ _______ mA

29. What is the total current and voltage produced by your photovoltaic solar cell array (50 mA, 3V each)? _________ mA ________ V

30. What is battery voltage and capacity? _________ V ________ mAhours

Calculations

31. What is the load during the night (sum from the table in step 28 above)? ______________ mA

32. How long will the battery run your house at night? ______________ hours

33. What is the net current use during the day (may be negative, indicating battery will charge)? ______________ mA

34. At night (with no solar energy input), how long will a fully-charged 200 mAhr battery run your system? ______________ hours

E. Check the Design

Does your building's thermal mass heat up reasonably fast in the sun (in less than 1-2 hours)? __________

Is the steady-stateT > 20 K with the ventilation turned off? __________Is the steady-stateT< 10 K with the ventilation on? __________

Is the required window area less than the maximum available area in step 18? __________

F. Review by AllTeam Members

I have reviewed the calculations in this document and herby testify to their accuracy.

Signature ____________________________________________________ Date: _________________________

Signature ____________________________________________________ Date: _________________________

Signature ____________________________________________________ Date: _________________________Signature ____________________________________________________ Date: _________________________