Why are the temperatures in our houses increasing? Lisa French Victoria University of Wellington...

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


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

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


5

Summer Mean Temperatures

December, January & February – 9am to 5pm

85% of Living rooms 20oC 25oC


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


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


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



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

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


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

)


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

Why are the temperatures in our houses increasing? Lisa French Victoria University of Wellington...

Documents

Transcript of Why are the temperatures in our houses increasing? Lisa French Victoria University of Wellington...