Beacon

Overall energy savings

The Rotorua NOW Home® tenants used 6800 kWh per year, comparing well to the 7400 kWh used in the first year in the Waitakere NOW Home®.   As Housing New Zealand tenants, the household was in a low income bracket and had to provide their own whiteware. 

While they had fewer appliances and electronic equipment than the Waitakere NOW Home® tenants, the appliances tended to be older and less efficient.  The house was using less energy despite this.

Keeping the house warm

In the family living areas the Rotorua NOW Home® has had acceptable temperatures in daytimes and evenings, but sometimes dropped below the 16ºC recommended by the World Health Organisation for good health overnight.  Of concern though is that the comfort range of between 20ºC and 25ºC was only achieved for a small proportion of the time.

Our analysis suggests this is less a design problem and more a need for occupants to understand how the ‘new’ features of their home work. 

• For a concrete floor to absorb the most possible sun, it must be left exposed.  Unfortunately there were quality issues with the coating applied to the concrete floor and the tenants covered much of the floor with rugs and mats.  The floor absorbed less heat and consequently, not only reflected less heat at night, but also took longer to dry out.  A concrete floor can take up to a year to dry out fully and work at optimal levels.
• Pellet burners put out a convective heat (they blow the heat out) rather than the radiant heat of a wood burner (which will feel hot if you sit by it).   However as heat rises, they heat from the top down and it may take some time for the heat to reach occupant level.  Also the fans can increase the rate of air movement which means that occupants only gradually feel warmer.  Using the timer and thermostat allows you to maintain a base temperature through the day and overnight.  The profile of use of the pellet burner indicated it was not being used optimally to effectively heat the house. Our conclusion: training in operation of pellet burners effectively is needed. 

The bedrooms however have been below healthy temperatures over half the time, and have been particularly cold during winter nights.  A heat transfer system, recommended on the plans, was not installed during construction, and the pellet burner was moved from an optimal position to a suboptimal one to meet concerns about health and safety. 

Heat transfer systems can effectively heat all the bedrooms where they are separated from living areas.

Free energy

The solar water heater chosen for the Rotorua NOW Home® has not performed to expectations.  It has needed much more electrical boosting than is the unit installed in the Waitakere NOW Home®, using 41% of the total electricity use.
A contributing factor to the solar panel’s poor performance is that, despite advice from BRANZ building scientists, the system was not installed to make the most of winter sun.   BRANZ  Ltd advice is that solar panels should be inclined at an angle at least equal to the latitude of the site, rather than matching the angle of the roof.  

Since the expansion of EECA’s subsidy scheme for solar hot water installations there has been a greater emphasis on correct installation and performance.  Both products and their installers now need to comply with a range of eligibility requirements, including providing some performance data, in order to be eligible for a subsidy.  This will help with guidance in choosing a system and installer that perform well.

Energy surprises

Twelve percent of energy use in the Rotorua NOW Home® went toward lighting, considerably more than the 6% used in the Waitakere NOW Home®.  This is thought to be due to a combination of factors:

• the much larger number of light fittings
• the use of halogen lights in some fittings
• an insufficient number of switching circuits – meaning that one switch turned on lights in several locations, leading to overlighting of the home.

Running the pellet burner over winter time was also a surprising energy user. Testing has shown that the pellet burner requires a minimum of 250W – to power the control panel, the fan and the auger. In addition, approximately twice this amount of power is required for ignition.