Energy clawback

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Increasing the energy efficiency of hot water and space heating in New Zealand homes should reduce energy use and power bills.  However, the phenomenon of ‘clawback’ - where occupants use the improved heating system to increase comfort, can alter the effect of energy efficiency upgrades.

Data from the Papakowhai Renovation project and the Waitakere NOW Home® was used to assess the clawback from water heating and space heating upgrades in ten New Zealand homes.

 

Water and space heating interventions

Improvements to the Papakowhai Renovation homes included:

  • the replacement of three storage electric hot water systems with solar hot water systems
  • the replacement of three aging woodburners with a pellet burner, a new woodburner and a heat pump, and a wetback woodburner.
  • the installation and modification of heat transfer systems
  • insulation of walls, floors, windows and ceilings through a variety of means
  • the installation of hot water cylinder insulation wraps
  • the installation of two gas-fired instant hot water systems

The Waitakere NOW Home® was designed with high levels of insulation, double glazing and good solar design.  The solar hot water system was supplemented with water efficient taps and shower heads.

 

Results

In the nine Papakowhai homes:

  • Demand for space heating in the winter period is strongly influenced by household composition.
  • Occupants of homes which are heated in winter to lower temperature levels are more likely to clawback increased service levels as comfort.
  • Extensive upgrades to the thermal envelope are more likely to result in large improvements in indoor temperatures and reductions in space heating energy use, irrespective of whether clawback occurs.
  • Annual variations in hot water use overwhelm the anticipated energy efficiency improvements rendered by the installation of hot water cylinder wraps.
  • Solar hot water systems had similar or reduced water heating demand after their installation, and could therefore be considered as effective energy efficiency intervention with little or no clawback.

Clawback of solar water heating service in the Waitakere NOW Home was very obvious with a 25% increase in demand.

The conclusions show that the full value of potential reductions in space and water heating energy use due to improved energy efficiency were not delivered from the homes assessed due to householders clawing back savings as improved comfort and levels of service. 

It is important to consider the role of clawback in large scale energy savings programmes and whether these programmes will deliver the savings expected.   It is possible that it will only be once the New Zealand housing stock has been improved to provide high levels of comfort and service, that energy efficiency upgrade programmes deliver the reduced demand that they promise.


  • 28-Feb-2010 (Report HR2420/12)

    Clawback of heating services in Beacon research homes (PDF 523KB)

    Andrew Pollard, Nikki Buckett

    Increased energy efficiency of hot water and space heating should reduce the cost of providing these services. However, the phenomenon of 'clawback' - where occupants use the improved heating system to increase comfort, can alter the effect of energy efficiency upgrades. In this work, the data from the Papakowhai Renovation Project, and the Waitakere NOW Home® are used to assess the clawback from the water heating and space heating services in ten New Zealand homes.