1.
Space-cooling in the Tropics
Notes by Terry Thomas, Warwick University
Notes for Smart Villages/LCEDN Webinar
“The big chill: Off-grid cooling”
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2.
Space-cooling in the Tropics
Space cooling is mostly about lowering air temperature
but also includes dehumidification. ‘Work’ and ‘heat’ are
physically different forms of energy: ‘cold’ is an
intermediate form in terms of both difficulty and cost.
What is deemed a ‘comfortable’ or ‘tolerable’
temperature in a room is strongly influenced by the past
experience of its occupants and by their clothing, but the
AC industry has adopted largely N American comfort
limits expressed as a zone on a ‘psychrometric chart’. For
example where temp is between 22C & 28C and relative
humidity between 20% & 80%.
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3.
Space-cooling in the Tropics
Temperate-to-tropical technology transfer
Improving the energy efficiency of space heating
has been a major process in temperate countries
since 1970: reducing heat losses, increasing boiler
efficiencies, upgrading standards, regulations and
labelling, & generally progressing from ‘low energy
house’ to ‘passivhaus’ to ‘power-exporting house’.
Is there any corresponding process to be expected
for space cooling in the tropics? Will ‘air-
conditioning’ soon become as normal in the tropics
as winter heating is in temperate zones?
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4.
Space-cooling in the Tropics
Space-cooling strategies:
1. Employ architecture, modern or vernacular, that
reduces solar gain, especially through roofs and
through glass
2. In very dry climates use evaporative cooling
3. In climates with big day-night temperature
differences, export indoor heat by night & seal
the building by day: maximise thermal mass,
raise ceilings
4. Increase the indoor airspeed locally above 0.2
m/s via fans or lavish ventilation
5. Use ‘heat pumping’ only as a last resort
6. ‘Import’ cold from lakes and seas.
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5.
Space-cooling in the Tropics
Cooling is mainly an urban problem because
• Urban areas are hotter (‘Urban heat island’
effect) by several degrees & rising dangerously
• Urban life is dominantly ‘indoors’
• Urban areas are richer, have better electrical
supply, have copied ‘international’ glass & steel
architecture
• Wind speeds are lower, space for ‘blue-green’
land-use is less
• Air conditioning within close-packed city
buildings raises the outdoor air temperature
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6.
Space-cooling in the Tropics
Is space-cooling relevant to tropical villages?
• Urban AC is overloading electrical networks
and thereby depriving rural areas of power
• Neither heat-driven nor diesel-powered space
cooling are affordable in villages: daytime-only
PV-powered AC is just a possibility. Biomass-
powered cooling may become cheaper.
• Vernacular architecture, and use of outdoor
space, can minimise need for space-cooling
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7.
Space-cooling in the Tropics
Low-cost cooling
Limit cooling to 1 room and restricted hours
Don’t design for the ‘hottest day ever’ but just
for common hot day conditions – this may save
½ the capital cost and ¼ of the running cost
Maximise shading (trees, 60 cm roof overhang,
east/west-end vegetation, verandahs)
Install ceilings and roof-space ventilation
Have big but closeable windows/shutters
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