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Why are the temperatures in our houses increasing?

Why are the temperatures in our houses increasing?. Lisa French Victoria University of Wellington (MBSc) and BRANZ Supervisors: Michael Donn, VUW & Nigel Isaacs, BRANZ. Overview. Objectives Background Influences on summer temperatures Thermal modelling Early results. Objectives.

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Why are the temperatures in our houses increasing?

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

  2. Overview • Objectives • Background • Influences on summer temperatures • Thermal modelling • Early results

  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

  4. MonitoredLocations 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

  5. Summer Mean Temperatures 85% of Living rooms 20oC 25oC December, January & February – 9am to 5pm

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

  7. Influences on Temperatures • Influence • Climate • House age • No observed influence • Floor area • Solar glazing • R-value of the House • Airtightness (self reported)

  8. Temperatures & Climate December, January & February – 9am to 5pm

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

  10. What’s 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

  11. Glazing & Age The amount of glazing is increasing in our newer houses

  12. Solar Glazing & Temperatures 40 35 Low Mass (theoretical) Low Mass (theoretical) 30 Mean temperature between 2.30 and 3.30pm (oC) 25 20 High Mass (theoretical) High Mass (theoretical) 15 0.05 0.10 0.15 0.20 0.25 0.30 Solar Glazing Area/Floor Area

  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

  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

  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 0.25oC 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

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