The Benefits of Heat Pipes in Hot & Humid Climates

1. The Benefits of Heat Pipes in Hot & Humid Climates Allan Westbury Managing Director S & P Coils Ltd. Leicester, UK

2. Presentation Contents • Problems of Hot & Humid Climatic Conditions • What is a Heat Pipe? • Heat Pipes & how they can HELP • Conclusion

3. Problems of Hot & Humid Climates • Main influences on comfort: • Dry bulb temperature • Air speed • Air humidity • Radiation • Ideal Comfort Conditions: • RH 40 - 60 % • Temperature 20 - 23°C (68 - 75°F)

4. ASHRAE Recommended Safety margin Health Problems Mildew Growth Proper humidity levels 0 10 20 30 40 50 60 70 80 90 100 % Relative Humidity

5. 35°C @ 80% RH 45°C @ 30% RH 35°C @ 20% RH 20°C @ 90% RH 35°C @ 80% RH 45°C @ 30% RH 20°C @ 90% RH 35°C @ 20% RH Typical Ambient conditions 35°C @ 80% RH 45°C @ 30% RH 35°C @ 20% RH 20°C @ 90% RH

6. 35°C @ 80% RH 45°C @ 30% RH 20°C @ 90% RH 35°C @ 20% RH Comfort conditions Comfort condition, 20 to 24°C, 40 to 70% RH

7. Historical Air Conditioning Examples of wind towers on some older buildings.

8. Modern Air Conditioning

9. Dubai Convention Centre

10. Pyramid Centre

11. Mercato Mall

12. Doha – Sheraton Hotel

13. Decorative features

14. Saturated air, 18°C Warm humid air, 42°C Condensation Recent Practice • Air is cooled to supply conditions

15. Recent Practice Taking a point in this envelope, 42°C @ 35% RH, and then cooling to 18°C the air becomes saturated and unsuitable for supply.

16. Recent Practice • If this saturated air with a high moisture content is supplied into the space we will have two major problems:

17. HOTEL OFFICE Problem 1 The building occupants will feel very uncomfortable and health problems may arise. Dissatisfied, unhappy customers and even potential insurance claims. Reduction in employee efficiency and, at worst, lost working days due to sickness.

18. Problem 2 The building fabric and fittings will deteriorate due to the high moisture levels creating excessive maintenance costs. This can manifest itself in several ways • Discolouration of walls • Mould growth • Corrosion of metalworks • Detachment of tiles etc. from walls/ceilings

19. Comfortable air, 18- 22°C Warm humid air, 42°C Condensation Dehumidifying with coils • Generally the air is overcooled Reheat Coil

20. Additional Cooling load Heating load Increase in running costs Overcooling the air and then re-heating gives rise to additional cooling & heating loads. A B C D

21. The downside of reheat • The cost of reheating the air is high. • It also means we have to include a whole package of extra equipment and controls.

22. The pay-off • Overcooling means an increased cooling load. = increased running costs. • This in turn means a larger chiller unit. = increased capital costs. • Re-heating will require energy. = increased running costs. • Re-heating also adds equipment and complexity.= increased capital costs.

23. The Economic Solution • So, while the theory is very attractive, the economics present a large deterrent. • Ideally we would like to cool the air to a comfortable temperature and remove moisture, but without the need for expensive reheat. • It sounds impossible, but by using heat pipes it can be achieved.

24. Heat Pipes • The principle of heat pipe operation • Heat Pipes and dehumidification • Heat Pipes and heat recovery

25. What is a Heat Pipe ? • A heat pipe is an extremely efficient conductor of heat. • By using the latent capacity of the fluid the heat pipe transfers heat at a very high rate.

26. Heat out Heat out Heat in Heat in Basic principle of operation A simple heat pipe comprises a hollow tube partly filled with a working fluid Using the latent capacity of the fluid, we can transfer large amounts of heat very rapidly from a hot point to a cold point on the tube wall.

27. Summary of Characteristics • Heat is transferred by latent means giving a heat transfer rate of around 1000 times that of a solid copper rod • Vaporisation and condensation take place at the same temperature allowing high heat transfer at low temperature differences • Heat pipes without wicks (Thermosyphons) rely on gravity to return the condensed liquid.

28. Heat Pipe applications 1.) Heat Pipes for enhanced dehumidification.

29. 18°C 42°C 36°C Adding a Heat Pipe • The heat pipe improves the efficiency of the system. 12°C

30. Heat Pipe pre-cool Heat Pipe re-heat Cooling Airflow Airflow Coil 42/28.5°C 18/14.1°C 36/27.1°C 12/11.8°C Heat Pipe in practice • Plan view of cooling coil.

32. 2-Row ‘Horseshoe’. • ‘Horseshoe’ Heat Pipes are used either for original supply or for retrofit applications. • The unit will be installed around an existing cooling coil.

33. 2-Row ‘Combi Coil’.

34. Heat Pipe Effect 1-2 Heat Pipe pre-cool 2-3 Cooling coil 3-4 Heat Pipe re-heat 2 1 Resultant energy saving of up to 30%. 3 4

35. Additional Heating load In Practice If the heatpipe is designed for a maximum temperature. What would the off condition be at other conditions?

36. Economic Design • Base design on commonest conditions not maximum conditions. • This in turn means removing need for additional reheat. • For close control some additional cooling may be required.

37. Bin Data • By using Bin Data we can identify the commonest or average condition.

38. Worked Example Based on average ambient condition, 32 °C @ 58% RH. Cooling load - 51.3kW Heating load - 7.2kW Total load - 58.5kW

39. Worked Example Air volume : 4.0 m3/s Air on: 40/27.8°C, 40%RH Supply air to room: 20/14.8°C Add in the Heat Pipe, Heat Pipe Pre-cool - 7.2kW Heat Pipe Re-heat - 7.2kW New Clg load - 44.1kW New Htg load - 0kW Saving 14.4kW

40. AdditionalCooling unit Worked Example At alternative conditions: Heat Pipe pre-cool : 9.5 kW Heat Pipe re-heat : 9.5 kW If the final air condition is required at 18 °C, then a secondary cooling unit can trim the temperature. Cooling load - 54.3kW Heating load - 0kW Saving 19kW

42. Summary • Requires no energy to run, being “driven” by the cooling coil. • Nett energy savings of around 30% compared to standard cooling and reheat. • Lower cooling load = smaller chiller/ compressor. • Design for average conditions to eliminate reheat. • Easy installation. • Controlled by the cooling coil.

43. Heat Pipe applications 2.) Heat and “coolth” recovery.

44. Heat and “coolth” recovery Used to transfer heat between supply and exhaust air streams where :- • There is a large difference between supply and exhaust temperatures. • There are high air volumes involved. Efficiencies of up to 65% can be achieved giving significant energy savings.

45. Basic design features • The Heat Pipe unit straddles the supply and exhaust ducts • A centre tube plate prevents cross contamination between airflows • No pump requirement to transfer the heat as with a run around coil system • Airstreams must be in counterflow

46. Orientation • Available in both vertical & horizontal arrangements. • The warmer airstream must be at the bottom in the vertical mode. Exhaust Air Supply Air

47. Horizontal orientation

48. Benefits • Requires no energy to run. • No maintenance. • No cross contamination. • Can be sized to suit the ductwork or AHU. • Easy condensation removal.

49. Conclusion • Heat Pipes are extremely efficient heat transfer devices • By installing across supply and exhaust ducts we can recover waste energy. • Typical efficiencies – 50% to 60 % • By wrapping The Heat Pipe around a cooling coil we bypass a certain amount of heat, saving on the cooling load and giving free reheat. • Nett energy savings - around 30 %

50. Completed projects