Solar Thermal Collectors Connected to Heat Pumps

There can be some advantages gained by connecting Solar Thermal Collectors to Heat Pump water heaters, but there are some important points to assess before this combination can be recommended.  The first point to consider is the economics of the project.   In other words will the addition of Solar Thermal Panels provide sufficient reduction in traditional energy use, which can then be calculated as a cost reduction when compared to the actual initial cost of supplying and fitting the Solar Thermal Collector Panels?

                                                              Schematic Image Only

There is an unwritten expectation for energy efficient products such as Solar Thermal and Heat Pump systems to provide a reasonable “payback” period, and this can sometimes be linked to the expected life cycle of the system or probably more closely linked to the warranty period offered for the products involved.   If the capital cost can be recovered within the warranty period then it is worth being given further consideration. However, when assessing the value of adding Solar Thermal Collector Panels to a Heat Pump installation it must also be remembered that during the daylight hours when the Solar Thermal Collector Panels could be contributing to the energy input of the system, that is also the period of each day that the Heat Pump units would be operating at their highest efficiency as well so the amount of purchased (input) energy for the Heat Pump units during the day time period could be between 3½ to 4.0 times less than the actual output that is produced in the form of hot water depending upon geographical location, ambient temperature and humidity.

The thermal contribution to a Heat Pump system from Solar Thermal Collector Panels is governed by the amount of radiation that is available at any given time and this can be intermittent because of varying weather conditions.   Therefore it is important to recognize that the Heat Pump units must be considered as the primary heat source and sized accordingly to be able to meet the total hot water requirement of the project due to the reliability of Heat Pumps being able to produce energy efficient hot water in all conditions including daytime, night time, as well as cloudy or rainy periods.  The Solar Thermal collectors will therefore only provide supplementary energy input during periods when there is a favorable level of radiation available for collection.  A number of factors can influence the decision to add Solar Thermal Collectors to a Heat Pump installation or not, but generally it has been found that in Regions where Government or Utility incentives are offered for the inclusion of Solar Thermal Collector Panels and the value of that incentive covers the cost of the Solar Thermal Collector Panels then obviously the economic equation is positive however, when no incentives or subsidies are available then there are some questions that need to be asked as to the added value of the Solar Thermal Collector Panels fitted to Heat Pump Units.

By Mel Peatey

Heat Pumps compared to Solar Water Heaters

An Air to Water Heat Pump provides an ideal energy efficient hot water system alternative for both domestic household use, or for larger Commercial applications.  In reality a Heat Pump provides slightly less energy savings when compared to a domestic solar water heater, but there are a number of other significant advantages associated with the use of an Air to Water Heat Pumps.

One major advantage of the Heat Pump is the aesthetic appearance that is gained by not needing any thermal solar panels and in some cases a storage tank on the roof of the building to ensure efficient operation.  In some cases roof structures may have to be reinforced when they are required to support the weight of a domestic sized solar storage tank that can weigh in excess of 400 kg.  In addition, the installation cost of an Air to Water Heat Pump is very simple compared to the installation cost of a solar water heater, and this significantly lower installation cost for the Heat Pumps should also be taken into consideration when assessing the overall installed cost of either product alternative.

Another advantage of the Air to Water Heat Pump is the low energy input from the electricity supply that is required to operate the system, while at the same time producing an output of around 3 times more than the actual electrical input, when operated in average ambient temperatures of 20 degrees Celsius.  This results in an energy saving (reduction) of approximately 75% when compared to traditional electric water heaters.  In Regions where the average ambient temperature is higher than 20 degrees Celsius the actual energy savings can be higher due to the extra heat energy that is available from the ambient air in these locations.  Air to Water Heat Pumps do not require direct sunlight to operate efficiently because they collect free energy from the ambient air.    Contrary to popular belief, a solar water heater does requires back-up electrical energy to operate the booster element during periods of inclement weather, low radiation periods, and at night time when there is a need to supply hot water during those times.  When comparing similar volumes of hot water delivery the annual booster or back-up energy needed to ensure solar thermal water heaters provide a continuous supply of hot water during all weather conditions, or if hot water is needed during the evening period, is similar to what is expended annually for a Heat Pump to drive the evaporator fan and compressor.   A domestic sized Heat Pump could, in some cases, operate from Photovoltaic (PV) solar cell system due to the low energy input needed when compared to the actual output that is delivered in the form of hot water.  This makes the Heat Pump products ideal for isolated and heavily forested locations such as remote Eco Resorts.

By Mel Peatey.