Energy efficiency in the Rotorua NOW Home®
Keeping the heat in
Passive solar heating
Making the most of the sun’s warmth, and retaining the heat is important in the colder climate of Rotorua. The Rotorua NOW Home® is oriented north, with both living areas, the dining area and one bedroom on the northern face of the house. Large windows and doors on the northern side admit the maximum amount of sunlight during winter while 900mm overhanging eaves provide summer shade.
The Rotorua NOW Home® sits on a 100mm thick concrete slab and footings. This acts as a heat store, absorbing warmth from the sun and releasing it gradually overnight. It is insulated with expanded polystyrene insulation panels both underneath and around the edges to prevent heat loss into the ground.
The concrete floor, coloured with black oxide and sealed with water-based polyurethane, is exposed through the house, except in the bedrooms which are carpeted for greater comfort.
The Rotorua NOW Home® is in a cooler Climate Zone and BRANZ Ltd scientists calculate that it would take four times as much energy to heat the Rotorua house as the Waitakere house.
The Rotorua NOW Home® has higher levels of insulation than recommended in the New Zealand Building Code. The ceiling insulation has an R value (a measure of its effectiveness) of R 3.6, considerably more than the Code minimum in 2006 of R1.9. The wall insulation has an R value of R2.6, more than the Code minimum in 2006, R1.5. These insulation values are also higher than the new minimum standards introduced in 2008.
Preventing heat loss through windows
Thermal modelling by BRANZ Ltd scientists showed that double glazing was critical, and that as much heat could be retained by installing double glazing as by adding insulation to walls, floor and ceiling.
The choice for the Rotorua NOW Home® windows and ranch sliders was sealed unit, clear double glazing in aluminium frames. The double glazing has an R value of 0.26, which saves 35% of energy compared to the then Building Code minimums. Recent changes to the Building Code mean that this standard is now required in Rotorua and other cooler parts of the country.
At night, heat loss through windows is prevented by using curtains with thermal linings. The curtain rail is mounted close to the wall to minimise heat loss.
Using free energy
A solar water heating system was used in the Rotorua NOW Home® to use the free energy from the sun and significantly reduce energy costs.
The solar water heater has a single piece solar collector panel and storage tank on the roof. An electric booster unit provides supplementary heat to the water held in the storage tank when there is not enough sun and/or heavy hot water demand.
Using less energy
Although still designed to maximise and retain solar warmth, the Rotorua NOW Home® is situated in a cooler climate zone, and supplementary space heating was needed.
A pellet fire was installed in the living area. Burning pellets made from wood waste, pellet fires are very efficient and have very little emissions. They produce a very clean burning fire, with no dust or debris to irritate asthma or allergy sufferers.
A planned heat transfer system was missed during construction and, consequently, bedroom temperatures have been lower than expected. A heat transfer system with appropriate size ducting and fan is a good way to spread heat from a central heat source to outlying bedrooms.
Housing New Zealand does not provide a fridge, washing machine or dryer for tenants. A revolving clothes line has been installed at the rear of the house. Drying clothes outside saves power and is a healthy option as bacteria are killed by UV light. On wet days laundry can be dried on a rack directly in the garage.
With extensive windows and sliding doors to trap sun, the Rotorua house has plenty of natural light, especially on its north face.
Halogen lights have been used for task lighting in the kitchen and bathrooms of the Rotorua NOW Home®. Although not energy efficient, they are not likely to be on as long as general room lighting.
Instead of recessed downlights which create gaps in the ceiling insulation in a home, batten light fittings compatible with energy efficient bulbs were used.
Home Energy Rating
The Rotorua NOW Home® was rated under the Home Energy Rating Scheme and received:
• 5.5 stars for the energy efficiency rating of the building
01-Jul-2013 (Publication Case study/12)
Covers energy efficient lighting design in two demonstration homes.
01-Jul-2013 (Publication Case study/11)
Thermal Mass in the Rotorua NOW Home (PDF 46KB)
Covers the use of thermal mass in the Rotorua NOW Home and why it proved less successful.
- The layout and design of the Rotorua NOW Home®
- Energy efficiency in the Rotorua NOW Home®
- Healthy living indoors in the Rotorua NOW Home®
- Water conservation in the Rotorua NOW Home®
- Waste management in the Rotorua NOW Home®
- The Rotorua neighbourhood