Energy

Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Cooling

Currently, energy use for cooling is low in New Zealand but this may change.

In New Zealand, sufficient cooling can usually be achieved with passive design options such as shading and allowing natural summer airflows and ventilation, given that indoor air temperature comfort levels range from about 18–24ΊC and our current outdoor air temperatures do not often exceed 25ΊC.

Some situations may still require active cooling, to provide back-up or boost a passive system when temperatures and/or humidity are well above average.

Active cooling is more likely to be required in rooms:

  • with high solar heat gain or poor natural ventilation
  • that are used by a lot of people, or used for long periods
  • where people are very active (such as a rumpus room)
  • with lots of electrical equipment (such as lights and computers in a study)
  • in locations where weather conditions do not allow passive design to work effectively, e.g. strong hot or dry winds, dust, pollen
  • in calm, hot and humid climates.

Mechanical cooling options are fans, heat pumps, evaporative coolers and air conditioners.

Fans

Fans move air and increase air velocity within a room. They don’t actually change the air temperature, but the increase in air movement makes people feel cooler. Fans can be fixed or portable. They are generally cheap to buy, relatively easy to install and comparatively cheap to run.

Ceiling-mounted fans are often effective at moving the air in a room to provide cooling. They can also be useful in winter as they can be used to move the warmer air at ceiling level back down into the occupied space where it is more useful.

Heat pumps

Until recently in New Zealand, reverse cycle heat pumps have tended to be installed primarily to provide heating. However, more people with heat pumps have begun to use them for summer cooling as well as winter heating, resulting in an increase in their use as well as increased electricity costs to households that have traditionally not used active cooling systems.

A heat pump is a very efficient method of cooling, typically providing 2.5–4.0 times the amount of cooling energy than the electricity it takes to run – this is the energy efficiency ratio (EER). The EER for a heat pump will be listed by the supplier along with its heating coefficient of performance (COP).

It is important to note (and to advise your clients) that heat pump energy efficiency decreases as the difference between the indoor and outdoor temperature increases – as it gets hotter outside, it takes more time and electricity to cool the air inside the home.

A heat pump – cooling operation 
A heat pump – cooling operation


Evaporative coolers

An evaporative cooler uses a fan to move hot, dry outside air into the house through a wet filter. It adds moisture to the air, and the air temperature drops as warmth is used to evaporate the moisture. Evaporative coolers are only efficient in air that is consistently dry. They are not commonly used in New Zealand and should not be used in rooms that already have moisture problems.

Evaporative coolers:

  • are comparatively cheap to run as the only energy used is to run the fan – approximately 80% less than a refrigerated cooling system
  • are simple and inexpensive to buy – installation costs are lower than refrigerated systems by about 50%
  • use a significant amount of cold water
  • do not use a refrigerant
  • require regular filter maintenance
  • may require windows or vents to be left open to allow airflow.

More information