The Benefits of Heat Pipes in Hot & Humid Climates

Allan WestburyManaging DirectorS & P Coils Ltd. Leicester, UK

Presentation Contents

Problems of Hot & Humid Climatic Conditions

What is a Heat Pipe? Heat Pipes & how they can HELP Conclusion

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)

Proper humidity levels

0 10 20 30 40 50 60 70 80 90 100

Health Problems Mildew Growth

Safety margin

ASHRAE Recommended

% Relative Humidity

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

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

Historical Air Conditioning

Examples of wind towers on some older buildings.

Modern Air Conditioning

Dubai Convention Centre

Pyramid Centre

Mercato Mall

Doha – Sheraton Hotel

Decorative features

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, 42°C @ 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, 18- 22°C

Reheat Coil

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

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°C 36°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

CoolingCoil

12/11.8°C

Heat Pipe re-heat

18/14.1°C

Airflow

42 / 28.5oC36 / 27.1oC

12 / 11.8oC18 / 14.1oC

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-heat12

43

Resultant energysaving of up to 30%.

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

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 ambientcondition, 32 °C @ 58% RH.Cooling load - 51.3kWHeating load - 7.2kWTotal load - 58.5kW

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

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.

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

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

Orientation Available in both

vertical & horizontal arrangements.

The warmer airstream must be at the bottom in the vertical mode.

Exhaust Air

Supply Air

Horizontal orientation

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

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

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

Dehumidification selection

Heat Recovery Selection

Any Questions ?

For further information or to download latest copies of our selection software, visit our website:

www.spcoils.co.ukwww.spcoils.co.uk

HEAT PIPES:The Benefits of Heat Pipes in Hot & Humid Climates

Allan WestburyManaging DirectorS & 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 40 - 60 % Temperature 20 - 23°C (68 - 75°F)