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Refrigerated air-conditioners

 

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With the highest purchase and running costs, refrigerated air-conditioners are best suited to very hot climates where comfort can't be provided by other cooling options.

Refrigerated air-conditioners work by removing hot air from inside the home and transferring it outside, cooling, dehumidifying and recirculating room air as a closed system (windows and doors must be shut).

Types include portable units, suitable for small rooms up to 20m2; window/wall units, for a single room up to 50m2; split system units, for rooms up to 60m2; and ducted split systems, for whole home cooling. Reverse-cycle models also provide heating.

What size should I buy?

Getting the size right is important. An oversized air-conditioner will result in over cooling, and frequent turning on and off to compensate will wear it out; an under-sized system won't cool the area adequately.

The capacity of an air-conditioner to heat or cool a room is measured in kilowatts (kW). As a guide to the size you may need:

  • A home with no insulation requires approximately 140 w/m2 (0.140 kW/m2).
  • A home with ceiling insulation requires 100 w/m2 (0.100 kW/m2).
  • A fully insulated house requires 70-80 w/m2 (0.07-0.08 kW/m2).

Some suppliers express output in an older measurement, British Thermal Units (BTU). One kilowatt is equal to 3412.14BTU. The following table is a guide to required cooling outputs for rooms of various sizes:

Running costs

Room size

Suitable cooler type

Energy star rating

Annual cost ~

Small room
(10 m2)

Electric split system air-conditioner 3 kW output

4

$75

$65

Portable or ceiling fan

N/A

$12

Medium room
(35 m2)

Electric split system air-conditioner 5.5 kW output

2

$165

3

$149

Portable or ceiling fan

N/A

$12

Large area
(60 m2)

Electric split system air-conditioner 8 kW output

$216

4

$194

2 x portable or ceiling fans

N/A

$24

Whole house
(166 m2)

Ducted air-conditioning 20 kW (not zoned)

$674

2

$633

Evaporative cooling 16 kW

N/A

$240

4 x portable or ceiling fans

N/A

$48

~ Approximate annual running costs, based on 500 hours usage per year (over a 10-year period) at 65 per cent capacity, with NSW household electricity prices at July 2013, and on a comparison of one and 3.5 star rated air-conditioners with a power output of approximately 5  kW.

 

Insulated homes require lower heating/cooling outputs because the treated air is trapped inside. In summer, an insulated home will not get as hot as an uninsulated one.

Ceiling height is not as important as insulation, so the figures in the table are based on heat flow rates through walls, ceilings, roofs and floors. However, ceiling sweep fans will help move warm/cool air back down to floor level in rooms with very high ceilings (e.g. cathedral ceilings).

What else do I need to know?

  • Always look for Energy Rating Labels on single-phase domestic air-conditioners. An energy-efficient model will be cheaper to run. Compare the star ratings: The more stars you see, the less money you’ll waste on power bills. Every extra star on the Energy Rating Lfabel can save around 10 per cent on the running costs of an air-conditioner.
  •  Use the Energy Rating Calculator to compare the running costs of electrical appliances before you decide whether to buy.
  • Set thermostats between 23°C and 26°C for summer cooling. Every time you lower the thermostat by one degree you are looking at a potential 10 per cent increase in running costs.
  • Consider purchasing a system with inverter technology; this can significantly improve the air-conditioner's efficiency.
  • Doors and windows in rooms where air-conditioning is being used should be closed, so the cool air is recirculated.
  • Whole-house systems should be zoned to cool living and sleeping areas at appropriate times.
  • Ductwork should be well insulated and sealed to prevent condensation.
  • If possible, locate window and wall units on the south side of the house. Shade the unit if it is exposed to full sun during the day, but don't restrict air flow over it.

 

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Page last updated: 10 December 2015