Heat pump water heating

Q: What is a heat pump water heater?

A: Interest in heat pump water heaters (HPWH) is growing. Energy savings are similar to that of a good quality, well installed solar system and, depending on location, energy efficiency can exceed solar.

Heat pump water heating uses energy stored in ambient air as its main energy source, which means the unit does not have to be oriented to direct sunlight.

Air-sourced heat pumps are among the most energy-efficient methods of heating water. Not only do they cut your hot water heating bills, but they also reduce the impact on the environment.

The technology uses the same principles as a fridge or air-conditioner but in reverse. In a fridge, heat from the air and food inside the fridge is pumped to the outside. In an HPWH, heat is extracted from the outside air, concentrated, and then transferred into the stored water.

The HPWH requires some electricity to operate its key components, including a compressor and fan. However, for every 1kW of electricity used, about 3kW of energy is transferred into the water. This means that for every $1 of electricity, the HPWH generates $3 worth of hot water.

The technology of heat pumps as used for heating water has advanced considerably in the last five years. There are two main types of systems: integrated and split. Integrated systems have the heat pump module either bolted on or fully integrated with the storage cylinder. Split systems separate the heat pump module from the storage cylinder and pump water between the two.

Just like space heating heat pumps, the module containing the compressor produces cool air and so needs to be located indoors. It emits some noise when running, so should be positioned away from bedrooms. It is also wise to avoid locating the unit close to corners with two hard walls that could reflect and amplify the sound towards neighbours.

Find more information about heat pump water heaters at the NZ Hot Water Association's website.

For information about heat pump water heater grants, visit the Energywise website.