Energy

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

Space Heating: Key Principles

Space heating accounts for approximately 34% of energy use in an average New Zealand house. Therefore, improving the energy efficiency of space heating has the potential to provide significant economic and environmental benefits. Currently, energy use for cooling is low but this may change.

Energy consumption for heating and cooling can be reduced in most homes by using passive design features such as correct orientation, thermal insulation and thermal mass, as well as incorporating effective passive ventilation to maintain indoor air quality. However, even with good passive design, many New Zealand homes will need some form of active heating for at least part of the year.

Key active heating design decisions will cover:

  • the amount of heating required
  • the heater capacity and efficiency
  • how heat is generated
  • how the heat is distributed through the home.

Heating options must also address safety and comfort issues such as fire risk, noise and impact on air quality.

As a rough guide, older non-insulated houses will require approximately 150 W/m2 of energy for heating and well-insulated houses around 120 W/m2.

How much heating is required?

For health and comfort, inside temperatures should be between 18ºC and 24ºC. The World Health Organisation recommends that all living and sleeping areas be maintained at a temperature of at least 16ºC (and preferably 18 ºC).
Factors that influence indoor air temperature (and occupants’ perceived air temperature) include:

  • outside air temperature range
  • relative humidity (both outside and inside)
  • exposure to direct sunlight (which is warming)
  • ventilation air flow (which is cooling)
  • stratification (i.e. warm air rising within a space)
  • occupants’ activities and ages
  • occupants’ personal preferences
  • draughts and air leakage in older, less airtight homes that allow heated air to escape and cold air in
  • the efficiency of the heating provided  – the effectiveness or efficiency of conversion of energy inputs to heat varies with the type of the heat source specified and the energy used.

Active ventilation can sometimes help to reduce the amount of air that needs to be heated (by bringing in warm air from other rooms, and/or by creating positive pressure which prevents cool air from getting into the heated space).

Distribution of heat

Distributing heat – i.e. getting heat efficiently to where it’s needed – involves decisions about:

  • the location, number and size of the heating units in the building
  • whether to use convection or radiant heaters
  • the control systems (i.e. thermostats for individual rooms or a single control thermostat for the house)
  • how heat is moved around the building – natural convection or an active system (fans within the heater, ducted, or ceiling fans)
  • the response time of the heating system to allow it to deal with rapid temperature changes – options are a thermal storage slow-release heaters or rapid output heaters
  • a centralised ducted system or individual within room units.

For your clients

To help your clients make decisions about space heating options, refer them to www.smarterhomes.org.nz/energy/heating.