Designing Comfortable Homes - Part 1

If you're thinking about building a new home, there are some important design elements to consider that are key to making it comfortable and energy efficient. Homes can be naturally warm in winter and cool in summer if they are built with the appropriate combinations of glass, thermal mass and insulation.

The Cement & Concrete Association of New Zealand (CCANZ), with support from the Energy Efficiency and Conservation Authority (EECA), has recently published a guide on the use of glass, mass and insulation for energy efficiency called Designing Comfortable Homes (second edition). This book describes the ways that New Zealand homeowners can incorporate passive solar principles into the design of new homes.

This edition of How To features the first of a series of excerpts from Designing Comfortable Homes that will run in 5 editions. The series will cover the three principles of passive solar design that follow the path of solar heat gain through the house. It starts with heat collection that allows the sun's heat to enter the house, moves onto heat storage to keep this heat and concludes with heat containment, which traps heat in the house.

The publication in full is available for free download from www.ccanz.org.nz

Heat collection

Good passive solar design simply makes effective use of the sun (and, to a lesser extent, other natural resources such as wind and landscape) to ensure comfortable and energy efficient houses. All houses make use of passive solar design to some extent, but many don't make very good use of the sun. By providing detailed information on passive solar principles and the impact of design decisions, this book should help you to get the most from your house design.


Glass

Windows provide the simplest way for heat from the sun to be collected - they are also the most poorly insulated part of the building and therefore allow large heat losses. To maximise solar collection benefits and minimise energy losses, window size, type and orientation need to be carefully planned.

Significant energy and comfort benefits can be achieved by using more energy efficient windows, like double-glazing, which is now widely used throughout New Zealand.
In addition to improved energy performance, double-glazing also minimises window condensation and reduces noise transmission. The higher the performance specification of double glazing, the higher the inside surface temperature of a double glazed window, and therefore the warmer people will feel when close to this glass.

Orientation

Unobstructed north-facing glazing is best as it captures solar energy in winter (when the sun is low in the sky) and it is easiest to shade from direct sun during summer by providing north facing eaves.

North facing glass provides the best access to solar gain and it is therefore preferable to orientate your house with the long axis in the east-west direction. This orientation to north can be plus or minus 20 degrees without having a major impact on solar gain.

Living areas should be located on the north face to maximise solar gain in these rooms. Living areas should be protected from the cold south face by placing the garage and service rooms to act as a buffer on this face.

Where practical, the longer axis of a house should be orientated east to west to optimise the north-facing exposure. Rooms may also be stacked or staggered to achieve a greater north-facing aspect. North-facing clerestory windows and skylights can be used to get direct sun into deep plan shapes. Particular care should be taken over the positioning of skylights as they are typically placed in a sloping roof so they tend to collect heat more in summer than in winter and they can be difficult to shade.

Heat loss through a skylight, particularly on cold nights, is also much greater than through a window of the same size. East- and west-facing windows allow penetration of morning and evening sun, which can cause problems with glare (morning or evening) and overheating (more often in the evening). These factors should be considered when positioning east and west glazing.


South-facing glazing receives very little direct sun and therefore allows heat loss without any significant compensating solar gain. South-facing windows are generally required for light and air but don't necessarily need to be large to achieve this. If you want to be able to enjoy a view to the south one effective option is to use smaller windows that frame or shape the view rather than large picture windows.


Site selection

Site selection is critical to house performance, as a site that receives limited sun during the winter will obviously get very little heating benefit from the sun when it is needed most.

Next issue: Heat Storage – thermal mass