Wednesday, June 20, 2012

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.

Friday, June 8, 2012

Water to Water Heat Pumps

Another option for Commercial/Industrial Heat Pump water heaters is the Water to Water - or hydro sourced Heat Pump.   Water source heat pumps (WSHP) are specialized types of heat pumps that can also be used as reverse cycle or multi function units that use water as a heat source when in the heating mode and as a heat sink in the cooling mode. In the Water to Water HeatPump, heat is absorbed or rejected in a fluid medium rather than from the ambient air. Water loop heat pumps (WLHP) use a circulating water loop which could be from a chiller/cooling tower system as the primary heat source for the liquid refrigerant causing it to vaporize before moving it to where it is upgraded by an electrically-driven compressor and is then subsequently delivered at a useful super heated temperature for heating potable water via a suitable heat exchanger.

A typical schematic of a multi function Water sourced Heat Pump shown above indicates how in some cases a single Water to Water Heat Pump Unit can be used to provide hot water, air conditioning, as well as under floor heating if required.   In the schematic layout above the primary heat source can be provided by any medium (ground, lake, sea water or hotel cooling tower circuits) where heat energy can be captured (transferred) in the primary evaporator in the Heat Pump Unit.   These types of Heat Pumps can also be used very effectively for just the hot water output function depending upon the project requirements and still have the capability of delivering a very high Coefficient of Performance (COP) outcome of over 370% more than the actual energy consumed.   However, when used as a multi function unit for example, delivering hot water and air conditioning in an ambient temperature environment of around 24ÂșC the combined COP’s for both functions can be as high as 700% more than the energy consumed for the operation of the system.