Why are the temperatures in our houses increasing? Lisa French Victoria University of Wellington (MBSc) and BRANZ Supervisors: Michael Donn, VUW & Nigel Isaacs, BRANZ

July 2007 Energy Postgraduate Conference 2 Overview Objectives Background Influences on summer temperatures Thermal modelling Early results

July 2007 Energy Postgraduate Conference 3 Objectives Using HEEP data determine drivers of summer temperatures Establish which elements of design and construction contribute to high temperatures –Use thermal modelling to explore design features –Rate design features in terms of significance for affecting temperatures

July 2007 Energy Postgraduate Conference 4 Household Energy End-use Project (HEEP) Nationwide, multi-year, multi- discipline Nationally representative Monitoring completed 2005 Measures all energy usage and interior temperatures for 12 months –2 temperatures in living room –1 temperature in bedroom –Monitored at 10 minutes Monitored Locations

July 2007 Energy Postgraduate Conference 5 Summer Mean Temperatures December, January & February – 9am to 5pm 85% of Living rooms 20 o C 25 o C

July 2007 Energy Postgraduate Conference 6 How warm does it get? Nearly 80% of houses spend more than ½ of the daytime between 20 o C and 25 o C 20% spend more than 2 hours above 25 o C 1% spend over ½ of the day (4 hrs) above 25 o C 4% of the houses in HEEP have air conditioners 3% of the houses in HEEP heat for 12 months VUW 06

July 2007 Energy Postgraduate Conference 7 Influences on Temperatures Influence –Climate –House age No observed influence –Floor area –Solar glazing –R-value of the House –Airtightness (self reported)

July 2007 Energy Postgraduate Conference 8 Temperatures & Climate December, January & February – 9am to 5pm

July 2007 Energy Postgraduate Conference 9 Temperature & House Age Newer houses are warmer in summer 0.25 o C increase per decade of construction (Linear models) Climate and age explain 69% of the variance in temperature 20 o C to 25 o C December, January & February – 9am to 5pm

July 2007 Energy Postgraduate Conference 10 Whats changing? Newer houses have: –Increased amount of glazing –Air tightness –Higher R-values for insulation –Larger floor area –Lower ceiling levels –Reduced eaves –Sheet construction

July 2007 Energy Postgraduate Conference 11 Glazing & Age The amount of glazing is increasing in our newer houses

July 2007 Energy Postgraduate Conference 12 Solar Glazing & Temperatures Low Mass (theoretical) High Mass (theoretical) Solar Glazing Area/Floor Area High Mass (theoretical) Low Mass (theoretical) Mean temperature between 2.30 and 3.30pm ( o C)

July 2007 Energy Postgraduate Conference 13 Modelling 5 HEEP houses in SUNREL Calibrate to reality Ability to alter one feature at a time –Ventilation –Insulation –Glazing type and amount –Shading –Orientation –Mass levels

July 2007 Energy Postgraduate Conference 14 Modelling – early results Most significant difference to increasing the living room summer peak temperatures: –Increasing window size –Increasing insulation –Orientating the living room towards north –Increasing internal gains Most significant decrease in reducing the summer peaks: –Increasing usable mass –Decreasing window size –Increasing ventilation

July 2007 Energy Postgraduate Conference 15 Early Results The age of the house and the ambient temperature explain 69% of the variation in summer living room daytime temperatures Summer living room daytime temperatures are increasing by 0.25 o C per decade of construction NZ Houses can be considered comfortable in summer based on international comfort temperatures Our new houses are warmer – a concern with climate change, increased cooling –We do not know what elements of construction and design are causing our houses to be warmer? VUW 06