Design your home for the Sun

Our healthiest energy source is free

NZ may face energy crises

We have heard lately that future power crises are likely on the basis of an assumed doubling in electricity demand over the next 20 years. Given the environmental costs of damming rivers, the difficulty in finding new gas fields, and the fact that oil prices are expected to increase dramatically, some in the energy field are starting a new discussion questioning the wisdom of New Zealand’s nuclear free stance. They suggest nuclear power as an environmentally friendly power source that does not contribute to global warming, particularly when compared to the abundantly available coal resource.

After recent power crises, we are now facing the prospect of steep increases in power prices. The Consumers’ Institute has warned that these may double over the next four to five years. It seems that we, the consumers, are the victims in this game and, as one reader put it in his letter to the NZ Herald, “we either pay up or go without – it’s as simple as that”. Or is it?

'...we, as consumers, can act to get out of the victim’s trap and at the same time contribute to our own and the planet’s health.'

There is no need for us, as individuals, to accept the role of victim. In all of the discussions there is a conspicuous lack of alternatives presented. The possibilities of saving power through efficiency measures are barely considered, while wind and solar power generation often only get a token and dismissive mention as minor energy contributors. However, these areas are precisely where we, as consumers, can act to get out of the victim’s trap and at the same time contribute to our own and the planet’s health.
Being energy-wise by reducing the wasteful use of energy is one possibility. In addition, anybody who builds a new house or embarks on renovating an existing one has the unique opportunity to reduce their energy needs by making better use of the sun's energy without any additional cost. The technique is called Passive Solar Design.

What is Passive Solar Design?

In a nutshell, this design approach provides for a maximum of the low winter sun to enter the house (through large northerly windows), for it to warm thermal mass (like concrete, bricks, earth or tiles) which will store the sun’s heat, releasing it after the sun has set. This way the thermal mass acts as a radiator providing heat and contributing to a dry, comfortable and healthy indoor climate. The best part is that it is free while simultaneously reducing our energy needs.

Housing in New Zealand

Looking at New Zealand as a whole there is enormous scope for energy saving using this method. A closer look at the existing housing stock from a perspective of passive use of solar energy gives a clear indication.

Floor layouts were almost identical and the master bedroom and parlour were at the front and the kitchen and bathroom at the rear, regardless of sun orientation.

In the suburbs and towns of New Zealand during the first half of the last century, when bay villas and bungalows were being built en masse, very little consideration, if any, was given to the orientation of houses in order to make the most of the varying seasonal angles of the sun. Floor layouts were almost identical and the master bedroom and parlour were at the front and the kitchen and bathroom at the rear, regardless of sun orientation. Street appeal was everything and only in the country were houses placed on more practical orientations. Surprisingly, many homes today are still designed and built with a similar lack of consideration.

How does Passive Solar Design work?

Passive solar design is not just about letting the sun in during winter, but also about keeping it out during summer. It utilises the varying positions of the sun at different times of the day and year to control indoor temperature, thus reducing or even eliminating the need for additional heating or cooling. An advantage of New Zealand’s climate is the relatively high number of winter sunshine hours, throughout the country. One of the most efficient forms of thermal mass is a concrete floor slab, providing it is not covered with low-density coverings such as carpet or wood in the area where the sun will strike it. Tiles or slate are ideal floor coverings.

An advantage of New Zealand’s climate is the relatively high number of winter sunshine hours, throughout the country.

A thermal mass wall can also be used and variations range from direct gain, as described above, to isolated gain, where the storage is completely out of the occupied space such as in a conservatory.

Efficient thermal insulation, more than is required by the building code, is an integral part of maximising solar design benefits, as is the correct ratio of glass area to thermal mass. Too much, or wrongly placed mass will also be detrimental.

It is recommended that the house be placed on an east-west axis with most of the windows facing north. During the summer sunrise and sunset, deciduous trees can to some degree control the excess sun on east and west facing windows. In order to get sunlight into rooms on the southern side of the house, clerestory windows can be used. Ideally there would be a thermal mass wall for the sun to strike opposite the window, this being the southern external wall. Although clerestory windows provide good ventilation potential, they are prone to excessive heat loss and should be double-glazed for greater efficiency. For a similar reason roof glazing in general should be avoided as heat rises and glass is a very poor insulator.

It is recommended that the glassed area be kept to a minimum necessary on south and west walls, south in particular to prevent heat loss during winter and west to avoid over-heating during summer afternoons.

Deciding on glass area along the northern side of the house becomes a balancing act between letting in as much natural light as possible and maintaining temperature control. For this reason there should be no obstruction to light directly outside the window, and in general tinting should be avoided - also because it disrupts the natural light spectrum. It is recommended that the glassed area be kept to a minimum necessary on south and west walls, south in particular to prevent heat loss during winter and west to avoid over-heating during summer afternoons.

The flow created by heat rising can be used to advantage during summer as a means of drawing in cool air from the south side of the house. Windows can be designed and placed in ways to optimise cross-flow ventilation, taking predominant summer breezes into account.

Fortunately street appeal is no longer the only consideration for people building or renovating a house. Northerly aspect, making the most of sunny private spaces and a good indoor–outdoor flow are now of primary concern to most of us. This is the perfect precondition for incorporating passive solar design, at no extra cost but resulting in a considerable drop in the individual heating bill. And the accumulated nationwide reduction of greenhouse gases, and the end to any suggestion of the need for nuclear power, come as a spin off – just to make us feel even better.