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see Zones 2 and 3.

BREAK THE MOULD, OR LET IT BREAK YOU!

DA20

HUMID TROPICAL AIR CONDITIONING

THE AUSTRALIAN INSTITUTE OF REFRIGERATION, AIR CONDITIONING AND HEATING

AIR CONDITIONING, COOLING AND COMFORT IN HOT HUMID TROPICAL CLIMATES DA20

DA20 AIR CONDITIONING, COOLING AND COMFORT IN HOT HUMID TROPICAL CLIMATES

3

Building design and system selection

Climate zones based on temperature and humidity

■ Hot humid summer ■ Hot dry summer, mid winter

■ Warm summer, cold winter ■ Warm humid summer

■ Hot dry summer, cold winter ■ Mild / warm summer, cold winter

Figure 2.2: Six Australian Climate Zones.

Northern Territory and Western Australia. Zones which have been excluded are known as desert, grassland and temperate zones( see Figure 2.1) which include the whole of New South Wales, South Australia, Victoria, ACT and Tasmania and large parts of Western Australia. The tropical regions of Australia which include hot humid zones and warm humid zones add up to a significant portion of the total area of the continent.

A climate analysis and zone mapping for air conditioners and heat pump devices carried out for the Australian and New Zealand governments proposed a three zone map for air conditioning; Hot-humid( predominantly cooling) Mixed( Cooling and heating) and Cold( predominantly heating) refer to Figure 2.3.

Australia and New Zealand cold and hot-humid regions with mixed demand between consideration when designing comfort systems for hot humid tropical climates. The use of suitable maps showing summer dew-point contours are useful when assessing the likeliness of condensation and air moisture content.

Figure 2.4 shows the average 3pm January vapour pressure which relates directly to dew-point temperature using the table. These maps reflect the information in the BoM climate zone and climate classification figures above but quantifies the moisture content in the air and also shows the drop in moisture content moving inland from the northern coastline and down the west and east coasts of Australia.

Note: The data contours are not as high as summer design conditions, being only average 3pm data for a particular month and year. Figures showing other months and time periods are available from the BoM.

Vapour

Pressure, 22 24 26 28 30 32 34 36 hPa

Dew- Point 19.0 20.4 21.7 23.0 24.1 25.2 26.2 27.2

Temp, ° C

3pm Vapour pressure( hPa) January 2013

36 hPa 34 hPa 32 hPa 30 hPa 28 hPa 26 hPa 24 hPa 22 hPa 20 hPa 18 hPa 16 hPa 14 hPa 12 hPa 10 hPa 8 hPa 6 hPa 4 hPa 2 hPa

DA20

HUMID TROPICAL AIR CONDITIONING

3.1 Section introduction

This section discusses the considerations that building and HVAC & R designers must give to designing building and systems for application in tropical climates. Information and advice is provided on

• Passive design strategies;

• Low energy design strategies;

• Effects and design implications of tropical climate characteristics;

• Building moisture migration design strategies;

• Design strategies for minimising and controlling the infiltration of outdoor air.

This section also provides guidance on appropriate comfort system selection including; Ventilative cooling, evaporative air cooling, refrigerative air conditioning, spot cooling and hybrid applications.

3.2 Passive design strategies

Passive design can improve the internal conditions of buildings that are not air conditioned and can significantly reduce the cooling loads of buildings that are to be air conditioned.

Well insulated roofs, optimal solar orientation, overhanging eaves both north and south, external window shades on both east and west, shade trees, and for naturally ventilated spaces large openable windows with louvres allowing free air movement and cross-ventilation are desirable. Light weight construction reduces thermal capacity and therefore cools quickly after sunset.

The following are all important passive building design strategies for buildings in tropical climates. The application of these strategies reduces cooling loads and improves comfort in the building:

• Solar orientation with long axis aligned east / west( i. e. the longer walls should be oriented to the north and south) reduces the thermal load on external walls and windows. This also provides optimal photovoltaic and solar hot water orientations.

• Ceiling fans are a low cost, low energy cooling option and should be considered where possible. They can be highly effective during the drier months.

• Quality ceiling insulation reduces downward heat flows.

• Low-e glazing reduces internal radiant heat. Tropical locations can experience high diffuse radiation.

• All external and internal solar exposed surfaces should be lightly coloured.

• Eaves on the northern and southern walls reduce wall and window heat gains.

• Externally shaded windows on the east and west oriented walls reduce heat load.

• Shade trees to the east and west reduce heat load.

• Low mass construction will cool quicker at night time but may heat quicker during the day. Thermal bridging should be eliminated. If high thermal mass is used then internal insulation may be considered, particularly if the building is to be air conditioned. Solar exposed high thermal masses should be provided with summer shading.

• Cooling breezes can be encouraged by design elements such as wing walls. Avoid orienting buildings to face breezes.

• Reflective insulation should be used with other insulation materials to decrease the absorption of heat.

• Sealing the building to ensure a continuous vapour barrier encompasses the building, especially if the building is to be air conditioned.

If the building is to be air conditioned it should be well sealed and insulated and provided with well positioned high performance glazing. Outdoor air ventilation systems incorporating heat recovery should be provided in high occupancy spaces.

Infiltration can be hard to minimise in building types such as shopping centres, shops, restaurants, hotels( particularly foyers) and the like, with frequent opening of doors. Positive pressurisation is essential and air locks( see 3.5.4) or air curtains( see 3.5.5) can be utilised.

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Residential HVAC system zones

■ Hot-humid( air conditioning) ■ Mixed( heating and cooling)

■ Cold( heating required)

Figure 2.3: Three zone heating / cooling regions map.

2.2.3 Dew-point temperatures in tropical regions

One definition for the“ Hot Humid Tropics” could be;“ areas where the summer outdoor design dew-point temperature exceeds the indoor design dry-bulb temperature”. Dew-point temperatures are a critical

Figure 2.4: Average 3pm January vapour pressures.

2.2.4 Evaporative cooling in tropical regions

Evaporative air coolers are not suitable for comfort cooling in hot humid tropical climates, see Figure 2.5 Zone 1. Evaporative air coolers are suitable in the southern coastal area and most of the inland areas of Australia,

APPLICATION MANUAL

••• 33

AIRAH’ s bestselling technical application manual, DA20, is available as a hard copy. n Simple user-friendly format

n Covers the application, selection, design installation, commissioning, operation, and maintenance of AC and other comfort systems in hot humid tropical climates n Standardises and promotes best-practice design, installation, and management n Outlines principles and processes applicable to any building type or size in hot humid conditions. n A must-have design resource.

Order you copy online at www. airah. org. au / DAmanuals

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