Comfort conditions 30% RH 80% RH 90% RH 20% RH Comfort condition, 20 to 24°C, 40 to 70% RH
Historical Air Conditioning Examples of wind towers on some older buildings.
Modern Air Conditioning
Dubai Convention Centre
Doha – Sheraton Hotel
Air is cooled to supply conditions Warm humid air, 42°C Condensation Recent Practice Saturated air, 18°C
Recent Practice and then cooling to 18°C the air becomes saturated and unsuitable for supply. Taking a point in this envelope, 35% RH,
Recent Practice If this saturated air with a high moisture content is supplied into the space we will have two major problems:
Problem 1 The building occupants will feel very uncomfortable and health problems may arise. HOTEL OFFICE Dissatisfied, unhappy customers and even potential insurance claims. Reduction in employee efficiency and, at worst, lost working days due to sickness.
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
Generally the air is overcooled Warm humid air, 42°C Condensation Dehumidifying with coils Comfortable air, °C Reheat Coil
Increase in running costs Overcooling the air and then re-heating gives rise Additional Cooling load Heating load to additional cooling & heating loads. A B CD
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.
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.
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.
Heat Pipes The principle of heat pipe operation Heat Pipes and dehumidification Heat Pipes and heat recovery
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.
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. Heat in Heat in Basic principle of operation Heat out Heat out
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.
Heat Pipe applications 1.) Heat Pipes for enhanced dehumidification.
Adding a Heat Pipe The heat pipe improves the efficiency of the system. 42°C36°C 12°C 18°C
Heat Pipe in practice Plan view of cooling coil. Airflow 42/28.5°C Heat Pipe pre-cool 36/27.1°C Cooling Coil 12/11.8°C Heat Pipe re-heat 18/14.1°C Airflow
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.
2-Row ‘Combi Coil’.
Heat Pipe Effect 1-2 Heat Pipe pre-cool 2-3 Cooling coil 3-4 Heat Pipe re-heat Resultant energy saving of up to 30%.
If the heatpipe is designed for a maximum temperature. What would the off condition be at other conditions? In Practice Additional Heating load
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.
Bin Data By using Bin Data we can identify the commonest or average condition.
Worked Example Based on average ambient condition, 32 58% RH. Cooling load kW Heating load - 7.2kW Total load kW
Air volume : 4.0 m3/s Air on: 40/27.8°C, 40%RH Supply air to room: 20/14.8°C Worked Example Add in the Heat Pipe, Heat Pipe Pre-cool - 7.2kW Heat Pipe Re-heat - 7.2kW New Clg load kW New Htg load - 0kW Saving 14.4kW
Cooling load kW Heating load - 0kW Worked Example At alternative conditions: Heat Pipe pre-cool : 9.5 kW Heat Pipe re-heat : 9.5 kW Saving 19kW Additional Cooling unit If the final air condition is required at 18 °C, then a secondary cooling unit can trim the temperature.
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.
Heat Pipe applications 2.) Heat and “coolth” recovery.
Heat and “coolth” recovery There is a large difference between supply and exhaust temperatures. There are high air volumes involved. Used to transfer heat between supply and exhaust air streams where :- Efficiencies of up to 65% can be achieved giving significant energy savings.
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
Heat Pipe efficiency
Orientation Available in both vertical & horizontal arrangements. The warmer airstream must be at the bottom in the vertical mode. Exhaust Air Supply Air
Benefits Requires no energy to run. No maintenance. No cross contamination. Can be sized to suit the ductwork or AHU. Easy condensation removal.
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 %
Completed projects ContractorConsultantAHU SupplierQty. Type of ProjectProject Garmco BAH York Aluminium Store Al Hamad - Shj.ArtekClever8NewPyramid shopping center SAS Raddison - Muscat Saiver4RetrofitRaddison Thermo - DubaiMario & Ass.SKM2RetrofitCrown Plaza Al HamedGHQCarrier3RetrofitMW-1699 Nael Est. - Al AinSyna dev.Clever4NewHiltonia Beach Al Hamad - Shj. Clever2NewSamar Tower- Shj. Al Hamad - Shj. Clever2NewAl Ansari Bldg. Geco - SharjahSharjah MunicipalitySKM6NewSwimm. Pool Sensaire - DubaiDubai MunicipalityClever3NewChildren's City Majid Al Futtaim Saiver2RetrofitCity Center Verger DelportW.S. AtkinsYork145NewIndustrial city - ADH VikingRPWViking2NewAl Nahdha Shopping VikingRPWViking2NewSharjah Mega Mall Al FuttaimArab ConsultantsSKM1NewSharjah Cricket Stadium ETASpectrum - DelhiNovair5NewGrand Hayat - Mumbai Carrier 37RetrofitLe-Meridian - Dubai Gibca - Sharjah Petra1RetrofitCoral Beach Resort
Completed projects (Cont..) ContractorConsultantAHU SupplierQty. Type of ProjectProject TransgulfRPWYork8NewSpinneys - Jumeira ETARMJMClever33NewWorld Convention centre Geco - SharjahCab - SharjahSKM90NewIndoor Sports Hall B K GulfRMJMInterklima6NewWorld Convention centre Sensaire - DubaiArif & BintoukCarrier8NewNovotel & Ibis Hotel Gibca - Sharjah Clever4NewCoral Beach Resort TransgulfRPWYork24NewRoyal Mirage hotel RemcoShadid Engg.Euroclima6NewDubai Women's association MekarRMJMMekar30NewExhibition Hall 1 & 2 Al FuttaimDPAAftron1NewDPA club CarrierShadid Engg.Carrier1NewEmaar bank Gulf Star - ADHPvt. Deptt.SKM2Newpvt. Villa at Jebel Dana SKM - SharjahIan BanhemSKM8NewKharbash Bldg. Dhabi ContractingAl TurathClever14NewWedding hall McQuayMott / EMSMcQuay6NewWest Side Marina FNCArkiteknikDunham Bush41NewNeighborhood centre Bu-HaleebaGemacMekar2RetrofitRuler's villa JunkerArtekJunker8NewDawoodi Bohra center
Heat Recovery Selection
Any Questions ? For further information or to download latest copies of our selection software, visit our website:www.spcoils.co.uk
HEAT PIPES: The Benefits of Heat Pipes in Hot & Humid Climates Allan Westbury Managing Director S & P Coils Ltd. Leicester, UK
Problems of Hot & Humid Climatic Conditions Main influences on comfort: Dry bulb temperature Air speed Air humidity Radiation Ideal Comfort Conditions: RH % Temperature °C ( °F)