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Tropical Air
Conditioning

Mechanical Training
2 June 2016

Marco Hopman
What is tropical air conditioning??

2
What is tropical air conditioning??

Hot No Heating
Humid
Sunshine
Intense rain

HVAC designed to cool and

dehumidify 3
Definition of a tropical climate
In the Köppen climate classification it is a non-arid climate in which all twelve months have mean
temperatures of at least 18 °C.
Unlike the subtropics, where there are significant variations in day length and temperature to various
degrees, with season, tropical temperature remains relatively constant throughout the year and
seasonal variations are dominated by precipitation

4
Design Conditions

5
Design Conditions

6
Design Conditions

The Tropics

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Design Conditions
86
kJ/
kg

The Tropics

21 g/kg

48
k J/k
g

9 g/kg
24°C, 50% RH

24°C 33°C
Design Conditions
86
kJ/
kg

The Tropics

63 21 g/kg
kJ /
kg

48
k J/k
g

9 g/kg
24°C, 50% RH

24°C 33°C
Design Conditions
86
10L/s OA = kJ/
kg
480W
The Tropics

10L/s OA = 63 21 g/kg
kJ /
kg
180W

48
k J/k Vapour
g
pressure

9.3 g/kg
24°C, 50% RH

10

24°C 33°C
Typical Office Cooling Loads

11
Building Considerations

• Solar radiation • Infiltration of outside air

• Shading – Sun angles • Doors – Use self closing doors, or
• Prolonged elevated revolving doors
temperatures • Fenestration/Glazing – Double glazing has
• High Humidity reduced impact
• Intense rain periods • Insects and vermin including termites and
house mites
• Wind storm and storm surges
• Salt laden air
• Thermal insulation and vapour
barriers
• Impact noise from rain

12
Building Considerations – Sun Shading

Example of IES modelling to

optimise shading

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Building Considerations

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Building Consideration – The Mildew Square

Four necessary required form

mildew to grow

Remove any of the four to stop

mildew forming

In practice, mildew is controlled

by limiting the moisture in
materials by controlling the
indoor relative humidity

15
Building Considerations
– Vapour barrier to prevent condensation

Vapour barrier to be on the humid side of the wall 16

NOTE: It not practically possible to build an air tight and vapour proof building!
HVAC Design Considerations

Comfort Factors
• Air movement
• Temperature
• Radiant temperature
• Humidity
• Personal preference
• Clothing

What can the HVAC system

control?

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HVAC Design Considerations – Air Movement

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HVAC Design Considerations - Humidity

At full design load all seems OK!

- Psychometrics all good
- At design supply air temperature = 13.5°C
- Resultant space RH = 54%

At real world part loads it just does not work!!!

- HVAC system will operate at part load most of the time
- Part load SAT = 17°C, less dehumidification, resulting in higher RH
- Issues with DX plant cycling on/off
- VRF system do not have latent capacity

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HVAC Design Considerations – Humidity

• Need to carefully consider dehumidification control, particularly at part

load

• Simple Cool/Reheat operation is not energy efficient

• Decouple dehumidification and temperature control functions

• Many options, depends on what is most appropriate for project

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HVAC Design Considerations
– Dedicated Outside Air Unit

Cool outside air to same moisture levels as space design

24°C, 55% RH = 10.3 g/kg = 14.4°C dewpoint
Cool outside air to 14.4°C 21
HVAC Design Considerations
– Dedicated Outside Air Unit

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HVAC Design Considerations
– Dedicated Outside Air Unit

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HVAC Design Considerations
– Dedicated Outside Air Unit

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HVAC Design Considerations
– Dedicated Outside Air Unit

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HVAC Design Considerations
– Dedicated Outside Air Unit

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HVAC Design Considerations –
- Outside air coil inside AHU to decouple outside air cooling
from space cooling

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 HVAC Design Considerations
- DOAS with run-around coil Run-Around Heating Coil

HC: 149kW

DOAS can achieve up to 23.8°C SAT

SA
Designed for worst case scenario of 8000 L/s
25°C / 90% RH during rain event 18°C

6.7g/kg

OA 24°C
8°C

35°C 18.9 g/kg

6.7g/kg

18.9g/kg

Run-Around Cooling Coil Chilled Water Cooling Coil

TC: 149kW TC: 474kW 28

SC: 126kW SC: 199kW

HVAC Design Considerations
- DOAS with run-around coil

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 HVAC Design Consideration
- DOAS with twin wheels Chilled Water Cooling Coil

TC: 374kW

SC: 164kW

SA OA
8°C 24°C
8000 L/s 35°C
6.7g/kg 12.4g/kg
18°C 18.9g/kg

6.7g/kg

RA EA
14°C
25°C 25°C
10.1 g/kg
10.3g/kg 16.7g/kg

Sensible energy wheel Total energy wheel

TC: 142kW TC: 310 kW

SC: 130 kW SC: 138 kW 30

HVAC Design Considerations – VRF OA Units

Nominal design conditions for outside air

unit is based on 33°Cdb/28°Cwb in and
supply air of 18°C 31
HVAC Design Considerations
- AHU condensation

• Double skin panels

• Thermally broken frames

• Thermal bridging rating

TB1 or TB2 to EN1886

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HVAC Design Considerations
- Cooling Towers

Capacity / Efficiency of cooling

towers dependant of ambient
humidity

Cooling towers are less efficient

in humid tropical climates

Payback period for water cooled

chillers compared to air cooled
chillers will be lower than would
be realised for more temperate
climates

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HVAC Design Considerations
- Ductwork Condensation

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HVAC Design Consideration
– Ductwork Condensation

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HVAC Considerations
-Control valve condensation

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HVAC design for Tropical Air-conditioning - Summary

• Similar challenges as per normal HVAC

design but also:
• Humidity control is essential
• No heating
• Carefully consider part load operation

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The End

Thank You