Why are the temperatures in our houses increasing?

Lisa FrenchVictoria University of Wellington (MBSc) and BRANZ

Supervisors: Michael Donn, VUW& Nigel Isaacs, BRANZ

July 2007Energy Postgraduate Conference

2

Overview

• Objectives

• Background

• Influences on summer temperatures

• Thermal modelling

• Early results

July 2007Energy 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 2007Energy 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

MonitoredLocations

July 2007Energy Postgraduate Conference

5

Summer Mean Temperatures

December, January & February – 9am to 5pm

85% of Living rooms 20oC 25oC

July 2007Energy Postgraduate Conference

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

July 2007Energy 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 2007Energy Postgraduate Conference

8

Temperatures & Climate

December, January & February – 9am to 5pm

NorthlandAuckland

BOP

WaikatoGisborne/Hawkes Bay

Taranaki/Manawatu-Wanganui

WellingtonTasman/Nelson/Marlborough

Canterbury

Otago/Southland

15

17

19

21

23

25

Me

an

Liv

ing

Ro

om

Te

mp

era

ture

- d

ayt

ime

(oC

)Mean External daytime temperature

July 2007Energy Postgraduate Conference

9

Temperature & House Age

before 19101910-1919

1920-19291930-1939

1940-19491950-1959

1960-19691970-1979

1980-19891990-1999

2000-2010

Decade house built

15

17

19

21

23

25

Mea

n te

mpe

ratu

re d

urin

g th

e da

y D

ec-F

eb (

oC

)

Mean temperatures by 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

20oC to 25oC

December, January & February – 9am to 5pm

July 2007Energy Postgraduate Conference

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

July 2007Energy Postgraduate Conference

11

Glazing & Age

before 19101910-1919

1920-19291930-1939

1940-19491950-1959

1960-19691970-1979

1980-19891990-1999

2000-2010

Decade House built

0.0

0.1

0.2

0.3

0.4P

ropo

rtio

n o

f gl

azin

g to

wa

ll ar

ea

Window area proportion of wall area

The amount of glazing is increasing in our newer houses

July 2007Energy Postgraduate Conference

12

Solar Glazing & Temperatures

Low Mass (theoretical)

High Mass (theoretical)

0.05 0.10 0.15 0.20 0.25 0.30

Solar Glazing Area/Floor Area

15

20

25

30

35

40

High Mass (theoretical)

Low Mass (theoretical)

Me

an

te

mp

era

ture

be

twe

en

2.3

0 a

nd

3.3

0p

m (

oC

)

July 2007Energy 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 2007Energy 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 2007Energy 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 0.25oC 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