Exploration of Summer Temperatures in New Zealand Houses and the Temperature Drivers L.J. French, M.T. Camilleri, N.P. Isaacs and A.R. Pollard BRANZ Ltd Private Bag 50 908 Porirua City New Zealand Contact author: LisaFrench@branz.co.nz Keywords: summer, temperature, residential, over-heating, New Zealand Abstract The Household Energy End-use Project (HEEP) has collected energy and temperature data on 397 randomly selected houses throughout New Zealand, providing a statistically representative national sample. This database has been used to explore the drivers of summer indoor temperatures. The general lack of air-conditioning means that summer temperatures are affected by passive influences (e.g. house design, construction) compared to winter temperatures where space heating is used. Summer temperatures are strongly influenced by the house age and the local climate – together these variables explain 69% of the variation in daytime (9 am to 5 pm) living room temperatures. Newer houses tend to have larger glazing areas, higher levels of thermal insulation and reduced eaves. Preliminary analysis suggests that as newer houses are warmer, climate change may be more important than in older houses. Human actions such as the opening of windows may have a large effect on the maximum temperature. Introduction The Household Energy End-use Project (HEEP) has collected temperatures from living rooms and bedrooms in 397 houses, a statistically representative sample of New Zealand. Annual reports have provided preliminary results through the project (e.g. Isaacs et al, 2005). 1 Both fuel usage and temperatures were monitored for a year in each house. Temperature data and survey data collected on the house and occupants have been used in this paper to explore the summer temperatures in New Zealand houses. HEEP monitoring of random houses began in 1999 and was completed early 2005 (see Figure 2 for locations). Limited funds restricted monitoring to fuels (electricity, LPG, natural gas, solid fuel, oil and solar hot water heaters) and temperatures. During installation information was collected on the house, appliances and the hot water system, as well as the occupants (Isaacs et al, 2002). Relative humidity, surface temperatures and occupant perception of comfort were not measured in HEEP. 1 For the latest report see www.branz.co.nz/main.php?page=HEEP 1