What is a Heat Pump Hot Water Cylinder?

A heat pump hot water cylinder is a hot water cylinder that instead uses heat pump technology instead of drawing direct power to heat the water inside the cylinder like standard rudimentary Mains pressure or Low pressure Hot water cylinders.

The importance of These Hot Water Systems

Heat pump water heater is gaining popularity in New Zealand as they provide alternative means to heat your water. Popular systems at the moment include gas and electric hot water cylinders and gas continuous flow systems.

Heat pump water heaters work very similar to a heat pump heating your home, where they extract heat from the outside air to heat your water. There are two types of systems, one where the heat pump is part of the hot water cylinder and one where the system is split. The heat pump unit is located outside and the hot water cylinder is located inside your home. 

Research has shown that a properly specified and installed heat pump water heating unit could reduce you hot water bill by two thirds when compared to standard electric water heating units.

Heat pump hot water heaters are long term investments, as they can cost upwards of $5,000 to install (not including the cylinder if the system is split) but the efficient operating costs will save you money on term. 

Heat Pump Water Cylinder Components

If the system has a heat pump module fitted on top of the storage tank, it will have the following components:

  • Air inlet and outlet louvre on the heat pump module
  • A heat pump monitor LED with a status display on the heat pump module
  • Condensate Drain on the heat pump module
  • Cold water inlet at the bottom of the storage tank
  • Hot water outlet at the top of the storage tank
  • Temperature pressure relief valve and drain line 
  • A thermostat is fitted to the storage tank to control the temperature

If the system is split, the compressor unit is installed separate to the storage tank, which can be installed inside or outside. This system has the following components:

  • Ambient air inlet at the back of the compressor unit
  • Air outlet at the front of the unit
  • A temperature sensor lead from the storage tank to the compressor unit
  • An outlet pipe for hot water to the storage tank
  • An inlet pipe for water from the storage tank

Heat Pump Water Cylinder Operation

Heat pump water heaters use heat transfer to heat up the water. Outdoor air passes over an evaporator (or heat exchanger), transferring heat to a liquid refrigerant, vaporising the refrigerant, which then enters the compressor.

The compressor uses electrical energy to increase the refrigerant pressure and temperature, circulating it around the condenser or heat exchanger. Here the refrigerant cools as it heats up the water.

The condensed liquid refrigerant then passes through an expansion valve and the cycle continues. 

Advantages and disadvantages

There are many advantages to using a heat pump water heater. These include:

  • It efficiently converts energy to heat
  • The energy source is always available
  • It can efficiently provide large amounts of hot water for space heating (underfloor), hot tubs or spa pools and swimming pools
  • This system can supplement other hot water systems to boost available hot water

There are also some disadvantages to this system, these include:

  • If the temperature decreases below 6-7 degrees, there may be a loss of efficiency. However, some systems may continue heating water in temperatures down to -10 to -15 degrees
  • The cost of purchasing the units and installation are much higher than other readily available systems
  • The exterior unit and water cylinder will require space to be installed
  • Outdoor units can be very noisy
  • These units become less efficient with lower water use (smaller households)
  • The performance of individual units varies greatly between manufacturers, so seeking advice from independent agencies is recommended

Are these system energy efficient?

Heat pump water heaters are the most energy efficient electric-based water heaters, mosly because electricity is used to transfer heat from the outside air to the water, instead of creating it.

The coefficient of performance (COP) lies between two and three, which means the system creates two to three times the energy to heat water than the energy it uses in electricity to run the heat pump and fan.

The heat pump efficiency, particularly in air-to-water models, is reduced by colder outdoor temperatures. There are ways to improve the efficiency, the heat pump unit could be operated when the outdoor temperatures are warmer (for example, during the afternoon), which improves the performance of the system.

You can also run the heat pump water heater when the electricity prices are at their lowest. The energy efficiency of air-to-water heat pumps is comparable to solar energy when considered throughout the year, therefore, heat pump heating is particularly suited to locations with poor solar gains. 

Heat Pump Water Cylinder Installation

Building consent is required when changing to a heat pump water heater, or when adding a split heat pump water heater to an existing hot water cylinder.

Building consent will not be required when a registered plumber replaces an existing water storage heater with a heat pump storage water heater; replaces and reposition an existing internal water storage heater with an external heat pump water heater; or replaces an existing external water storage heater with an external heat pump water storage heater. 

The outdoor components must be positioned to allow unimpeded air flow through the entire system and ideally the location is warm. The outdoor components can turn on at irregular times; to avoid the heat pump hot water unit becoming a nuisance it should be placed far away from bedrooms.

An isolation switch should be placed on the exterior wall of the house, if the cable breaks away, the electricity supply to the cable can be shut off from the isolation switch. All hard wiring should be carried out by a registered electrician and have an electrical certificate of compliance.

There are several manufacturers that make a number of models suitable for domestic and commercial use. These manufacturers include Rheem, Rinnai and Bosch. Contact us today to discuss a hot water solution for your needs.