Why are the temperatures in our houses increasing?

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
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
Temperature House Age
20oC to 25oC

• 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

December, January February 9am to 5pm
10
Whats 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