Integrated Ventilation and Heating System for Low Energy Buildings

1. Integrated Ventilation and Heating System for Low Energy Buildings Anne Iversen, s001280 Dorthe Kragsig Mortensen, s02172 June 25th 2007, BYG●DTU Supervisors: Svend Svendsen, Jianhua Fan, Peter Weitzmann & Toke R. Nielsen

2. Agenda • Product Development • Weather Data • Solar Wall • Heat Exchanger • Concrete floor • Comparison • Conclusion

3. PRODUCT DEVELOPMENT

4. Product Development Step 1: Clarifying objectives Step 2: Establishing functions Step 3: Setting requirements Step 4: Determining characteristics Step 5: Generating alternatives Step 6: Evaluating alternatives Step 7: Improving details

5. Step 1: Clarifying objectives The purpose is to clarify design objectives based on the client's needs

6. Step 2: Establishing functions The purpose is to analyze the functions within the product

7. Step 3: Setting requirements The purpose is to make an accurate specification of the performance required for a design solution.

8. Step 4: Determining characteristics The purpose is to set the targets to be achieved for the engineering characteristics of the product, such that they satisfy the client's needs

9. Step 5: Generating alternatives The purpose is to generate possible solutions of the product

10. Sequence of the Solar Wall and Heat Exchanger

11. Operational Situations • Defrosting: The solar wall is placed before the heat exchanger and defrosting is possible. • Optimized energy output: The heat exchanger is placed before the solar wall and high temperatures can be achieved. • Heat exchange only: Only the heat exchanger is active to preheat the ventilation air. • Bypass of all elements: The heat exchanger, solar wall and the storage is not used as there is no heating demand.

12. WEATHER DATA

13. Investigation of Weather Data with Respect to Cold Periods

14. Ice days in the DRY file and in the period of 15 years from 1975-1990 6 consecutive ice days in the DRY file 17 consecutive ice days in a period of 15 years

15. SOLAR WALL

16. Preheating of Air with Solar Energy • CFD simulations were used to investigate the flow pattern within a solar wall and the output temperature of the solar wall • The investigation was based on a solar wall of 4 m2 where the absorber had a porosity of 1%

17. Flow Pattern within and Output Temperature from the Solar Wall

18. CFD Simulations Pressure [Pa] Vectors by velocity [m/s] Temp [C] Vectors by temperature [C]

19. Evaluation of Solar Wall • Convection occurred at the top of the solar wall • Output temperature: • Improvements: • Geometry of the absorber • Pressure loss

20. HEAT EXCHANGER

21. Air Heat Exchanger with a Solar Wall as Defrosting Strategy • A model of a counterflow heat exchanger was used to simulate frost formation • The simulation was based on the weather data from the periods with 6 and 17 consecutive ice days

22. Formation of Frost in a Heat Exchanger Moisture content indoor: • Outdoor moisture content • Moisture production in the building • Ventilation rate Defrosting strategies: • Two section heat exchanger • Large air flow passages • Reverse flow • Preheating of air

23. Simulink Model of a Counterflow Heat Exchanger

24. Output Temperature from the Solar Wall

25. Ice Formation in the Heat Exchanger

26. Evaluation of the Solar Wall as a Defrosting Strategy • Solar wall was able to defrost the heat exchanger during daytime • Maximum accumulated ice was 4 kg, this can be used as guideline for future design of heat exchangers

27. CONCRETE FLOOR

28. Supply and Storage of Heat in a Concrete Floor by Use of Ventilation air • Estimations of heat transfer and pressure loss in the system • Detailed investigation of energy consumption and indoor climate in the airborne floor heating system

29. Estimation of Heat Transfer and Pressure Loss in the System • Turbulent flow: • High heat transfer coefficient • High pressure loss • Laminar flow: • Lower heat transfer coefficient • Lower pressure loss 2 or 3 ducts pr. meter Diameter of 20, 30 or 40mm

30. Detailed Investigation with FHSim • Properties of the medium were changed • Internal resistance of the duct • Series-connected to parallel-connected • Return air enters the room instead of being recirculated in the ducts • Internal surface resistances changed to values from DS418 • Extended with modules of the heat exchanger and the solar wall and control of these

31. Laminar vs. Turbulent Flow Return air temperature Floor surface temperature

32. The Systems Performance with Different Designs Duct layout of two 30mm ducts pr. meter

33. Evaluation of the Airborne Floor Heating System • The ventilation air should always be sent through the floor • It should be possible to switch the sequence of the solar wall and the heat exchanger

34. COMPARISON

35. Comparison of an Integrated and Separate Ventilation and Heating System Based on a House of 112 m2 • Initial cost and operational cost of the integrated system was less expensive than the separate system. • Defrosting is possible in the integrated system. • No leakage concern in integrated system. • Exchange of heat to DHW in the integrated system.

36. CONCLUSION

37. Conclusion of the Integrated Ventilation and Heating System • A solar wall can be used to defrost a counterflow heat exchanger during daytime. • The solar wall contributes to heating of domestic water and room heating. • The ventilation air should always be sent through the embedded ducts. • The sequence of the solar wall and heat exchanger should be able to be switched. • The integrated system is a potential low cost alternative to a separate ventilation and heating system.