Solupro Renewable Energy » Heat Pumps

When you think about cooling a hot building, you probably don’t think of heat pumps. In fact, the term “air conditioner” is likely the first to come to mind. As it turns out, a heat pump can both heat and cool, and in some applications, it’s preferred to separate heating and cooling systems.

Simply put, a heat pump is a device that uses a small amount of energy to move heat from one location to another. Heat pumps are typically used to harness ambient heat from its surroundings and, under the principles of vapour compression refrigeration, uses a refrigerant system involving a compressor and a condenser to absorb heat in one area and release it at another (in this instance to heat water).

A heat pump’s economic efficiency manifests in the fact that it simply transfers heat, rather than burn fuel to create it, although the fan and compressor do require a minor amount of electricity to operate albeit approximately 25% of that which a conventional electric element (in relation to geyser size and paired heat pump) would have required.

Comparison of Heat Pumps vs. Solar Water Heaters:

FactorHeat PumpSolar Geyser
System ComponentsSince a heat pump is a free standing mechanical component, it is not a comprehensive water heating system. For this reason, a water storage tank needs to be added to this assembly to which the heat pump will be connected. A heat pump replaces the function of a conventional electrical element.A solar geyser serves as a comprehensive solution boasting a tank and collector panels. A solar geyser tank is usually fitted with a conventional 2kW electrical element, serving the purpose of boost or back-up heating, ensuring that water will be heated in the event of unfavourable weather conditions or excess demand, and is controlled by a pre-set timer unit.
System ApplicationA heat pump delivers an output efficiency of 1:4 under favourable ambient conditions. In essence, a heat pump consumes 1 unit of electricity and 3 units of ambient heat to heat the same amount of water which would have been heated by an electrical geyser that would have consumed 4 units of electricity. For this reason, a heat pump can deliver similar results to an electrical geyser by consuming 1/4 of the electricity.The effective and economical application of a solar water heater requires that the unit capacity be sized appropriately and sufficient for the family’s demand. Under average circumstances (where a reasonable hot water consumption pattern prevails), a general rule of 50 litres of hot water per person per day applies. The ideal is to heat a sufficient amount of hot water to provide solar heated water for the entire demand, so as not to rely on electrical back up to heat the excess demand, in which case the saving will be compromised.
Renewable source availabilityA heat pump boasts the benefit of being able to function 24 hours per day, since ambient heat is always present in the atmosphere albeit to a lesser degree during night time and cold spells or cold seasons. Therefore its function is not limited to solar yield and demand can be supplied indefinitely.
However, since a heat pump is reliant on electricity, this benefit is dependent on the availability of conventional electricity.
A solar geyser's core function is of course limited to solar hours and favourable weather conditions, which justifies the importance of heating a sufficient supply during these times. Although a solar geyser is equipped with a back-up element, this element is not key to its primary function.
Efficiency in terms of Thermal AbilityA heat pump is designed to heat potable water up to 55°.The temperature reached by a solar geyser depends on
  • the solar collector area, since the energy absorbed holds direct relation hereto. An aptly designed system that have been married with a suited collector panel assembly, will aim not to reach temperatures whereby overheating will occur since this can damage the system; and

  • the system type - an indirect system will typically reach a slightly lower temperature than a direct system, however direct systems are not suited for frost prone areas.

The average temperature obtained under favourable weather conditions in an aptly assembled system, can vary between 55°C and 70°C.
Aesthetical consideration A heat pump may, in certain circumstances, be the most viable solution from an aesthetical point of view, since there are little requirements for its placement. Though a heat pump should be placed in a well ventilated area, it can easily be mounted out of view but preferably within close proximity to the water storage tank (or geyser). Since a solar geyser's placement is required to be within ample solar exposure; on an angle no lower than 22° and orientated as close as possible to North, aesthetics are often compromised. The possibility exists that the tank may be placed in-roof and thus out of view, provided that certain specifications are met in terms of the roof slope length, angle and orientation in order to gain thermo siphon whereby the tank is placed at a higher elevation than the panels. Should the latter not be possible, the addition of a Photovoltaic circulation pump eliminates the limitations in terms of the placing of the tank, often making it possible to place the tank out of view.

However, should a pumped system be utilized, the following need to be taken into consideration:
  1. The addition of a pump component will increase the cost of the system as a whole;

  2. Being a mechanical component, a pump in itself will boast a much shorter lifespan than the passive solar geyser system, and

  3. A mechanical device requires regular maintenance.
Maintenance, Servicing and Expected lifespanMaintenance required on a heat pump entails servicing and replacement of mechanical components and energy efficient coefficients. Since a heat pump is a mechanical component, it's function entails the movement of parts which are subject to wear and tear, the expected lifespan of such system in 10 to 12 years, dependant on regular maintenance and servicing.
Solupro offers a Solserve service plan for Heat Pumps ensuring that your heat pump system is serviced 12-monthly.
Maintenance required on an indirect solar geyser, mainly entails a minimum of bi-annual glycol replacement, as well as the visual inspection and, if required, the replacement of energy efficient coefficients; the element and sacrificial anodes. The expected lifespan of a Solartech Solar Geyser is 15-20 years, dependant on regular maintenance and servicing.
Solupro offers a Solserve service plan for Solar Geysers ensuring that your heat pump system is serviced 12-monthly.
Basic TechnologyA heat pump is, in every practical sense, a mechanical component that constitutes the inversed cycle of a conventional air conditioning unit, consequently expelling cold air as a by-product. The primary function of a heat pump is to:
  • harness ambient heat from the atmosphere;

  • inverting and compressing the energy (during which the heat is concentrated / increased);

  • where after a heat exchange process results in the potable water being heated.
A solar geyser, when installed in thermo siphon configuration, is for all practical purposes a passive system; i.e. moving processes occur naturally and are not mechanically induced. An indirect system, which is essentially frost resistant and therefore best suited for Gauteng and its climate, boasts a heat exchange process whereby:
  • the heat transfer fluid, a propylene glycol solution (AKA anti-freeze), is contained within the solar collectors and heated by harnessing solar energy;

  • the heated glycol siphons into the heat exchange manifold surrounding the water storage tank, where heat is exchanged to heat the potable water
Accredited by Eskom on the Solar Water Heating Rebate Programme