An Overview on Heat Pump Water Heaters

An Overview on Heat Pump Water Heaters
September 20, 2012 Lorelie

A water heating system is often a necessity in homes, particularly if the home is located in a cold region.  There many types of water heating systems and each system may use a different energy source for heating.  Among the many types of water heating system is the heat pump.  A heat pump generally uses electricity in moving heat from one place to another as opposed to generating heat directly.  This means they can be several times more energy efficient than standard electric water heaters.

A lot of homeowners use heat pumps to both heat and cool their homes.  The truth is a heat pump can also be used in heating water.  This can be either as stand-alone water heating or as combination space conditioning and water heating.

A heat pump works similarly to how refrigeration works, only that the process is reversed.  A refrigerator cools by taking heat away inside the unit and dumping it outside.  A heat pump water heating system on the other hand takes the heat being dumped by space conditioning and places it into a tank to heat water.  Heat pump water heaters can be purchased as stand-alone units or as an integrated unit with a built-in storage tank.  They can also be modified to work along with existing standard tank water heater.

If you want to have a heat pump installed for your home, you need to be located in an area that has 5 to 32 degrees Celsius all year round and have at least 28 cubic meters of air space around to work on.  They need to be installed in areas that create excess heat as it will not work efficiently on a cool environment.  The cool air it then generates can be ducted towards rooms or the outdoors.  Combination systems are able to provide heating, cooling, and water heating.  They pull out the heat indoors during summer and expel it outdoors, and pull out heat outdoors during the cold seasons and duct it indoors.  Since heat pumps remove heat from the air, heat pump systems, particularly air-source types, works best in warmer climates.

Homeowners mainly use geothermal heat pumps.  These heat pumps draw heat from the indoors during summer and expel the heat outside to cool the indoors, and drawing heat from the ground during winter to heat the indoors.  This serves as the cooling and heating of the home.  To add water heating into the geothermal heat pump system, you need to add a desuperator.  A desuperator is a heat exchanger which uses superheated gas coming from the heat pump’s compressor so as to heat water.  The heated water will then circulate via a pipe towards the storage tank.

You will also find desuperators for tankless water heaters.  During the warmer seasons, the desuperator uses the excess heat that will likely just be expelled outdoors.  This means that when a geothermal pump is running during summer, it can heat all the water in your tank.  However, during the winter, the desuperator will not be able to generate much heat.  This means you need to rely more on your storage or tankless water heating unit.  There are some manufacturers though that have triple function geothermal heat pump systems and are able to provide households heating, cooling, and hot water.  They make this possible by using a separate heat exchanger in order to provide the hot water needs of the household.

Choosing a Heat Pump Water Heater

The initial cost of the heat pump unit and its installation is usually what deters others from using it.  Although the unit and installation has a high initial price, this can be offset with a significantly low operating cost.  When purchasing a heat pump for your water heating, it is important that you consider the following:

Energy Efficiency – using the energy factor (EF) helps to determine the overall energy efficiency of a heat pump water heater.  The computation is based on the amount of hot water produced per unit of fuel used.  This will include:

  • Recovery Efficiency – this is how efficient the heat coming from the energy source is transferred towards the water being heated.
  • Standby Losses – this would be the percentage on how much heat is lost in a given hour of the stored water towards the heat content of the water.
  • Cycling Losses – this would be the amount of heat lost as water circulates through the storage tank, and inlet and outlet pipes.

A water heater is more efficient the higher the energy factor it has.  The only thing is high energy factor values do not always signify lower operating cost, particularly if you were to compare different energy sources.

If you are interested in seeing the energy factor of a water heater unit, consult the user’s manual as this will usually be printed inside on the product information page.

Sizing – to get the right water heater size for your home, this will include the heat pump and storage tank, you need to use the unit’s first hour rating.  The first hour rating is the volume of water the water heater can supply on a given hour, starting with a tank full of hot water.  First hour rating is dependent on the capacity of the tank, the energy source, and size of the heating element.

Installation and Maintenance – the proper installation and maintenance of your water heater unit helps to optimize its energy efficiency.  The proper installation of your heat pump water heater involves many factors.  This will include fuel type, climate, safety issues, and local building code requirements.  This means a contractor should be both a qualified plumber and a heating contractor/designer before they are allowed to install a heat pump.

When hiring a qualified professional installer, make sure to ask or do the following:

  1. Cost estimates in writing.
  2. References.
  3. Whether the company can get a permit and understands local building codes.
  4. Check their company with the local Better Business Bureau.

Always remember that regular maintenance of your heat pump water heating system will help to extend its life as well as minimize its loss of efficiency.  For more particular maintenance recommendations, read the owner’s manual.

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