27 September 2005
All new housing should be warmer, but some is not.
Owners denied thermal performance by shortcuts
It's a well known fact that New Zealand's older houses are almost impossible to keep warm enough to maintain good health, unless they ve had a major retrofit with new heating systems and improved thermal insulation. Without this kind of upgrade, these houses offer little more protection from the cold than a tent.
The thermal performance of new housing is expected to be adequate, and is a great improvement on the original timber-frame bungalows of old. But if we examine the running costs of some of these newer houses we find their performance has not improved as much as it should, given the advances in technologies and building systems.
Here is an example: An elderly woman living in a near new 2-bedroom unit at a residential village has been paying more than $7 per day for electricity, almost all of it for heating, during the winter months. With the latest price increase this month, this could rise to $8 per day, or around $240 a month for just one person.
Why is it that a near-new retirement unit, which is very well sited for the sun, can perform so badly? The answer lies in the way owners, designers, builders and developers are using constructions designed to meet the code and no more. It is still possible, and entirely legal, to build a new home or residential unit without thermal insulation under the concrete floor slab and with recessed down-lights that allow warm air to be ducted into the ceiling cavity. Double glazing too is still an optional extra, even though we know it is a key to achieving recommended healthy home temperatures of 20 degrees C during the day and 16 degrees C at night.
And while the rules on double glazing are set to change (it will soon become the norm in the South Island) there are still a number of thermal inefficiencies that have been allowed to go on for too long.
In my view any concrete floor slab for housing built on land that was once part of a swamp or with a high water table (which is most of Christchurch) should have thermal insulation under that slab. Without this simple, low cost improvement, there is a significant continuous heat flow between the concrete and damp ground below.
Recessed down-light fittings that are vented into the ceiling space, with no insulation over them or around them, are little more than small chimneys for the warm air below. They are cheap and they deny people the benefit of the heat they have paid for. Better fittings are available now to improve both thermal performance and reduce on going lighting costs, through the use of compact fluorescent globes. These units use 85% less energy than a halogen down-light and its high-energy transformer.
In our example of a near-new retirement unit we also find that the fibreglass insulation above the ceiling (and adjacent to the recessed down-lights) is so poorly installed that its effectiveness is greatly reduced.
After just a few years, it has become clear that the overall performance of the retirement unit is so poor that the owner has no choice but to install a heat pump. Based on a heating efficiency of around 300 per cent the heat pump is likely to reduce the unit s heating costs by between $500 and $800 in the next 12 months. Total consumption will fall to below 8000 kW hours per year, which means further savings can be achieved by moving to a Low User Christchurch Residential rate (through the main retailer in Christchurch, Meridian Energy). But here we run into another hitch. The retirement unit has a Day/Night meter installed, even though there is very little opportunity for the occupant to shift demand from the day to the night.
After tracking the retirement unit's performance for more than a year it is clear there are major inefficiencies in our building systems. When we know that the end user is elderly and likely to be at home for long periods during the winter, how is it possible to build a retirement unit that is so thermally inefficient? Some architects and designers are embracing the principles of passive solar energy, but clearly some housing is falling well below its potential.
We might also question why it should be necessary to retrofit with a heat pump in such a new building. Owners and occupiers of modern homes and units should be able to buy or invest with the confidence that their property will have a thermal performance much higher, not just a little higher, than the draughty wooden tents build through much of last century.
Finally, we need to question why retail electricity prices are so high. It is interesting to note that Meridian's website calculator only goes to 20c/kWh, indicating that the current daytime unit pricing was something they never anticipated. We need to ask ourselves if 23c/kWh for day heating is really acceptable for people on modest incomes when the standard of housing is so variable and much is below international performance standards.
The problem seems to be with the decisions made when new housing is planned. Typically the available budget is used to build the maximum floor area, with the minimum thermal performance permitted. Few home owners appear to be concerned with the life cycle costing of what they plan to live in. A useful first step would be to consider a trade-off between some of the total built area and the building system to be used, to ensure that the end product not only looks good but provides the necessary comfort for healthy living with a modest amount of purchased energy.
Footnote: Research at Lincoln University from studying side-by-side buildings has shown the benefits of thermal comfort and reduction in energy from the effective use of thermal mass (externally insulated concrete walls). BRANZ Study Report No 116 (2003) Energy Efficiency of Buildings with Heavy Walls is available at: www.branz.co.nz
Don Mackenzie is Senior Lecturer in Natural Resources Engineering at Lincoln University.