Why are the temperatures in our houses increasing?
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Transcript of Why are the temperatures in our houses increasing?
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
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Overview
• Objectives
• Background
• Influences on summer temperatures
• Thermal modelling
• Early results
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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
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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
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Summer Mean Temperatures
December, January & February – 9am to 5pm
85% of Living rooms 20oC 25oC
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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
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Influences on Temperatures
• Influence– Climate– House age
• No observed influence– Floor area– Solar glazing– R-value of the House
– Airtightness (self reported)
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Temperatures & Climate
December, January & February – 9am to 5pm
NorthlandAuckland
BOP
WaikatoGisborne/Hawkes Bay
Taranaki/Manawatu-Wanganui
WellingtonTasman/Nelson/Marlborough
Canterbury
Otago/Southland
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Me
an
Liv
ing
Ro
om
Te
mp
era
ture
- d
ayt
ime
(oC
)Mean External daytime temperature
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Temperature & House Age
before 19101910-1919
1920-19291930-1939
1940-19491950-1959
1960-19691970-1979
1980-19891990-1999
2000-2010
Decade house built
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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
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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
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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
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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
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20
25
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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
)
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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
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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
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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?
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