Heat Losses and Gains in Residential Housing in Southern New Zealand

Abstract

The majority (70%) of houses in New Zealand were originally built before energy efficiency regulation came into force. Since the first standard was introduced in 1977, methods for controlling heat loss in new builds have gradually improved; these requirements have focused on insulation and the control of air insulation. In recent years, many local programs have focused on “easy” upgrades to existing housing, which typically involve insulating the floor and ceiling. Recent studies have questioned the efficacy of floor and ceiling insulation, showing minimal increase in indoor ambient temperature along with minimal decrease in energy use for space heating. These findings are more pronounced in cooler parts of the country, such as in Dunedin.

This thesis investigates heat loss control retrofit options for New Zealand homes. The study examines two houses, which were retrofitted in stages, as a range of improvements were made to the building envelope. Heat loss was measured at each stage, and heat loss from infiltration was estimated by measuring the air ingress. The experimental technique used was a novel total house calorimetric method known as co-heating.

With the exception of ceiling insulation, the observed upgrade performance matched predictions calculated using lumped thermal resistances. After the addition of wall, floor, and ceiling insulation, overall construction (lumped) thermal resistance increased from 0.8 m2KW-1 to 1.6 m2KW-1. After the upgrades, costing from around $123/m2 the heat loss was reduced by 32% for the entire house retrofit and 54% in the case of the living area-only retrofit.

The study also found that the addition of insulation alone would not allow a house to achieve adequate indoor temperatures at a space heating cost (using electric resistive heating) that might be affordable. Choice of heating systems must also be considered when renovating houses.

In addition the aspect of consumer preferences for energy efficient housing was investigated using a survey of Dunedin house insulation levels and heating practices.