passive design strategies in composite & warm-humid climates.
The Benefits of Heat Pipes in Hot & Humid Climates
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Transcript of The Benefits of Heat Pipes in Hot & Humid Climates
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The Benefits of Heat Pipes in Hot & Humid Climates
Allan WestburyManaging DirectorS & P Coils Ltd. Leicester, UK
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Presentation Contents
Problems of Hot & Humid Climatic Conditions
What is a Heat Pipe? Heat Pipes & how they can HELP Conclusion
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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)
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Proper humidity levels
0 10 20 30 40 50 60 70 80 90 100
Health Problems Mildew Growth
Safety margin
ASHRAE Recommended
% Relative Humidity
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Typical Ambient conditions
35°C @ 80% RH45°C @ 30% RH35°C @ 20% RH20°C @ 90% RH
45°C @ 30% RH
35°C @ 80% RH
20°C @ 90% RH
35°C @ 20% RH
35°C @ 80% RH45°C @ 30% RH35°C @ 20% RH20°C @ 90% RH
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Comfort conditions
45°C @ 30% RH
35°C @ 80% RH
20°C @ 90% RH
35°C @ 20% RH
Comfort condition,20 to 24°C,
40 to 70% RH
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Historical Air Conditioning
Examples of wind towers on some older buildings.
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Modern Air Conditioning
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Dubai Convention Centre
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Pyramid Centre
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Mercato Mall
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Doha – Sheraton Hotel
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Decorative features
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Air is cooled to supply conditions
Warm humid air, 42°C
Condensation
Recent Practice
Saturated air, 18°C
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Recent Practice
and then cooling to 18°C the air becomes saturated and unsuitable for supply.
Taking a point in this envelope, 42°C @ 35% RH,
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Recent Practice
If this saturated air with a high moisture content is supplied into the space we will have two major problems:
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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.
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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
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Generally the air is overcooled
Warm humid air, 42°C
Condensation
Dehumidifying with coils
Comfortable air, 18- 22°C
Reheat Coil
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Increase in running costs
Overcooling the air and then re-heating gives rise
Add
ition
al
Cool
ing
load
Hea
ting
load
to additional cooling &heating loads.
A
B
C D
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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.
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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.
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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.
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Heat Pipes
The principle of heat pipe operation Heat Pipes and dehumidification Heat Pipes and heat recovery
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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.
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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
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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.
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Heat Pipe applications
1.) Heat Pipes for enhanced dehumidification.
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Adding a Heat Pipe
The heat pipe improves the efficiency of the system.
42°C 36°C 12°C
18°C
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Heat Pipe in practice
Plan view of cooling coil.
Airflow
42/28.5°C
Heat Pipe pre-cool
36/27.1°C
CoolingCoil
12/11.8°C
Heat Pipe re-heat
18/14.1°C
Airflow
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42 / 28.5oC36 / 27.1oC
12 / 11.8oC18 / 14.1oC
Airflow
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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.
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2-Row ‘Combi Coil’.
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Heat Pipe Effect
1-2 Heat Pipe pre-cool
2-3 Cooling coil
3-4 Heat Pipe re-heat12
43
Resultant energysaving of up to 30%.
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If the heatpipe is designedfor a maximum temperature.What would the off condition be at other conditions?
In PracticeA
dditi
onal
H
eatin
g lo
ad
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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.
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Bin Data
By using Bin Data we can identify the commonest or average condition.
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Worked Example
Based on average ambientcondition, 32 °C @ 58% RH.Cooling load - 51.3kWHeating load - 7.2kWTotal load - 58.5kW
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Air volume : 4.0 m3/sAir on: 40/27.8°C, 40%RHSupply air to room:20/14.8°C
Worked Example
Add in the Heat Pipe,Heat Pipe Pre-cool - 7.2kWHeat Pipe Re-heat - 7.2kWNew Clg load - 44.1kWNew Htg load - 0kWSaving 14.4kW
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Cooling load - 54.3kWHeating load - 0kW
Worked Example
At alternative conditions:Heat Pipe pre-cool : 9.5 kWHeat Pipe re-heat : 9.5 kW
Saving 19kW
Add
ition
alCo
olin
g un
itIf the final air condition isrequired at 18 °C, then a secondary cooling unitcan trim the temperature.
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Fan Coil Unit
Air Handling Unit
Duct Mounted Coil
38 / 27.5oC(45% RH)
19.5 / 14.5oC(60%RH)
18 / 14oC(65% RH)
Primary Cooling Secondary CoolingSecondary Cooling Schematic
18 / 14oC(65% RH)
18 / 14oC(65% RH)
FAHU
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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.
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Heat Pipe applications
2.) Heat and “coolth” recovery.
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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.
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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
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Orientation Available in both
vertical & horizontal arrangements.
The warmer airstream must be at the bottom in the vertical mode.
Exhaust Air
Supply Air
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Horizontal orientation
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Benefits
Requires no energy to run. No maintenance. No cross contamination. Can be sized to suit the ductwork or AHU. Easy condensation removal.
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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 %
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Completed projects
Contractor Consultant AHU Supplier Qty.Type of
Project ProjectGarmco BAH York Aluminium Store
Al Hamad - Shj. Artek Clever 8 New Pyramid shopping center
SAS Raddison - Muscat Saiver 4 Retrofit Raddison
Thermo - Dubai Mario & Ass. SKM 2 Retrofit Crown Plaza
Al Hamed GHQ Carrier 3 Retrofit MW-1699
Nael Est. - Al Ain Syna dev. Clever 4 New Hiltonia Beach
Al Hamad - Shj. Clever 2 New Samar Tower- Shj.
Al Hamad - Shj. Clever 2 New Al Ansari Bldg.
Geco - Sharjah Sharjah Municipality SKM 6 New Swimm. Pool
Sensaire - Dubai Dubai Municipality Clever 3 New Children's City
Majid Al Futtaim Saiver 2 Retrofit City Center
Verger Delport W.S. Atkins York 145 New Industrial city - ADH
Viking RPW Viking 2 New Al Nahdha Shopping
Viking RPW Viking 2 New Sharjah Mega Mall
Al Futtaim Arab Consultants SKM 1 New Sharjah Cricket Stadium
ETA Spectrum - Delhi Novair 5 New Grand Hayat - Mumbai
Carrier Carrier 37 Retrofit Le-Meridian - Dubai
Gibca - Sharjah Petra 1 Retrofit Coral Beach Resort
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Completed projects (Cont..)
Contractor Consultant AHU Supplier Qty.Type of
Project ProjectTransgulf RPW York 8 New Spinneys - Jumeira
ETA RMJM Clever 33 New World Convention centre
Geco - Sharjah Cab - Sharjah SKM 90 New Indoor Sports Hall
B K Gulf RMJM Interklima 6 New World Convention centre
Sensaire - Dubai Arif & Bintouk Carrier 8 New Novotel & Ibis Hotel
Gibca - Sharjah Clever 4 New Coral Beach Resort
Transgulf RPW York 24 New Royal Mirage hotel
Remco Shadid Engg. Euroclima 6 New Dubai Women's association
Mekar RMJM Mekar 30 New Exhibition Hall 1 & 2
Al Futtaim DPA Aftron 1 New DPA club
Carrier Shadid Engg. Carrier 1 New Emaar bank
Gulf Star - ADH Pvt. Deptt. SKM 2 New pvt. Villa at Jebel Dana
SKM - Sharjah Ian Banhem SKM 8 New Kharbash Bldg.
Dhabi Contracting Al Turath Clever 14 New Wedding hall
McQuay Mott / EMS McQuay 6 New West Side Marina
FNC Arkiteknik Dunham Bush 41 New Neighborhood centre
Bu-Haleeba Gemac Mekar 2 Retrofit Ruler's villa
Junker Artek Junker 8 New Dawoodi Bohra center
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Dehumidification selection
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Heat Recovery Selection
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Any Questions ?
For further information or to download latest copies of our selection software, visit our website:
www.spcoils.co.ukwww.spcoils.co.uk
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HEAT PIPES:The Benefits of Heat Pipes in Hot & Humid Climates
Allan WestburyManaging DirectorS & P Coils Ltd. Leicester, UK
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Problems of Hot & Humid Climatic Conditions
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)