Why are the temperatures in our houses increasing
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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

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
Overview

  • Objectives

  • Background

  • Influences on summer temperatures

  • Thermal modelling

  • Early results


Objectives
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


Household energy end use project heep

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


Summer mean temperatures
Summer Mean Temperatures

85% of Living rooms

20oC 25oC

December, January & February – 9am to 5pm


How warm does it get
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


Influences on temperatures
Influences on Temperatures

  • Influence

    • Climate

    • House age

  • No observed influence

    • Floor area

    • Solar glazing

    • R-value of the House

    • Airtightness (self reported)


Temperatures climate
Temperatures & Climate

December, January & February – 9am to 5pm


Temperature house age

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


What s changing
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


Glazing age
Glazing & Age

The amount of glazing is increasing in our newer houses


Solar glazing temperatures
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


Modelling
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


Modelling early results
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


Early results
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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