Page 1 of 5 Heat Pumps for Swimming Pools This factsheet provides members with invaluable information about heat pumps and their use for heating swimming pool water. There is a consumer factsheet already available that details the various types of heat pumps and so this Member factsheet focuses on air source heat pumps, as they are typically the most popular type of heat pump for swimming pools. What is a swimming pool heat pump? A swimming pool heat pump is a self-contained renewable energy heater that is specifically designed for heating indoor or outdoor swimming pools. Purpose built swimming pool heat pumps are designed to directly take the flow of swimming pool water from a pool filtration system by using materials that are compatible with swimming pool water. They are able to extract heat from many different sources, but in swimming pools primarily, they collect heat from ambient fresh air and use this to heat the swimming pool water. The heat pump will need a mains electricity supply, a free and unobstructed flow of fresh air, and pipe connections into the pool water filtration circuit. The heat pump also produces condensate which needs to be drained away. The heat pump will normally be completely automatic in operation, incorporating a pool water thermostat to switch the heat pump on and off as required. It will only work when the pool filtration pump is operating and so should be interlocked with the pump by a flow switch, a pressure switch, or via auxiliary contacts on the pump contactor. Heat pumps are available in different capacities, and the correct output must be matched to a particular size of swimming pool. There are also different de-frost methods available depending on the required swimming season. Note a summer de-frost heat pump will not generally function during cold weather and winter season heat pumps should incorporate a means of keeping the drip tray free from ice. The heat pump will often be located externally in the same general area as the outdoor pool or, alternatively, within a plant room or shed etc. providing adequate free air flow is maintained. Correct application guidance It is imperative that the selected heat pump has enough heating capacity and is fitted with the correct anti-icing or defrost control for the season required.
Page 2 of 5 1) Application criteria: To avoid misunderstandings, installers should establish the design criteria with both the end customer and their heat pump supplier, making sure it is documented in writing. Key criteria include: - Surface area of the pool (the cubic capacity of the pool alone) is inadequate information. - How many hours per day a surface cover will be used. - The target pool water temperature. - The intended swimming season e.g. May to September. - If there is any possibility of ground water being in contact with the pool shell and the associated implications. - If the client requires the pool water 'heated up' within a specific duration of time. - If there are times, e.g. at night, when the client does not want the heat pump or pool filter pump operating. It is strongly recommended that heat pumps are sized against a particular swimming pool size by the manufacturer/supplier and not merely by comparing stated heat outputs, produced by competing manufacturers. Manufacturer/supplier selection guides and charts may provide an initial indication of sizing for their heat pumps, but this should be followed up with documented confirmation of the selection by the manufacturer / supplier. Equally, installers must appreciate that if the heat pump is to be installed in the UK, then any selection guide used must be based on UK climatic conditions, as many are not. The selection criteria may represent part of the installer s legal contract with the end client in respect of demonstrating that the heat pump supplied is fit for purpose. 2) Heat output: It is important to appreciate that there is no industry standard when it comes to rating the output capacity of a swimming pool heat pump. Consequently, the installer should avoid being drawn down the route of a 12kW heat pump or a 15kW heat pump. One brand may be rated on a completely different set of operating conditions to another, e.g. ambient air temperature, humidity, or pool water temperature.
Page 3 of 5 Unlike a fossil fuel boiler, heat pumps have limited surplus heating capacity so installers should never be tempted to undersize a heat pump in order to appear more price competitive, this will invariably result in a lot of issues, and cost, for everyone involved. Installers should always operate on the side of caution if they want happy, satisfied customers. The selected heat pump must be able to generate sufficient heat to at least match the normal heat losses from the pool during the coldest month of anticipated operation. The heat output of a heat pump falls as the ambient air temperature reduces and, obviously, the heat loss from an outdoor pool increases. Therefore, greater capacity heat pumps are necessary if operation beyond the normal summer season is envisaged. 3) Efficiency comparisons: In the absence of any independent certificated testing or effective policing, it is unwise to draw any reliable conclusion that any particular brand of heat pump is any more efficient than another, simply from published data and claims. There is a great deal of unrealistic performance information in circulation, much of which cannot be relied upon. 4) Anti-icing or defrost control: If the fresh air temperature drops below approximately 10 C, then ice may start to form on the heat pump's evaporator, obstructing the passage of air and impeding performance. A typical 'summer use' heat pump may simply switch off under such a scenario, indicating the end of the client's swimming season. However, if the heat pump is equipped with a de-icing facility, then it will be able to clear the ice and heating can continue. The de-frost is usually activated automatically and typically the heat pump will operate in a 'reverse or bypass mode, using a small amount of heat from the pool water, or the electrical input of the device, to melt the ice. When ambient air temperatures are close to freezing, ice protection of the condensate tray and drain are also needed. A heat pump equipped with reverse cycle de-frost facilities can operate successfully at fresh air temperatures well below freezing. You must be aware however that the heat output will be severely limited at such cold conditions. 5) Positioning the heat pump: Installers should assess where the heat pump can best be positioned:
Page 4 of 5 Fresh air flow It is generally irrelevant whether a heat pump is positioned in direct sunlight. The heat pump needs an unrestricted supply of fresh air and the 'cold' exhausted air must not be allowed to recirculate in to the inlet of the heat pump. Consequently, the discharge air path should not be obstructed by walls or bushes etc. If the heat pump is positioned within a plant room, then a free flow of fresh air must be accommodated. Typically this is via a louvered door or window, with a route needed for the exhausted cold air back to the outside, without any recirculation. Many heat pumps will need a special air ducting kit and an under-base tray to collect condensate, if located in a plant room. Noise All heat pumps produce noise due to the need to pass a large quantity of air through. The noise levels between different brands of heat pumps, processing a similar amount of fresh air, are unlikely to vary greatly, regardless of what may be optimistically claimed. Be wary of the 'tricks' used in promotional literature, the distance away from the heat pump at which the noise reading is taken is critical, it is possible to reduce the noise figure by 3dB simply by doubling the distance the sound is measured at! The focus is likely to be night time operation, when there is minimal other background noise, and particularly during warm weather when bedroom windows are likely to be open. The primary consideration is to ensure that the client is aware that the heat pump will produce a level of noise and, therefore, avoid positioning a heat pump near a bedroom window or neighbours' boundaries. If there is an unavoidable conflict, the possible options should be considered at the design stage. Electricity supply Consideration should be given to the availability of a suitable mains electricity supply. It should be appreciated that, in order to avoid voltage problems, the electricity supply cable must be of sufficient size to cope with the large starting currents, comparatively high power consumed, and the cable length. If installers are connecting into an existing consumer unit, it is possible that the existing supply cable may be insufficient. Installers should not rely upon the rating of any existing switch gear but involve a qualified electrician as necessary.
Page 5 of 5 If the available electrical supply is restricted, then it may be possible to specify a heat pump equipped with an electronic soft start, which helps limit the peak starting currents that occur. If a site is already subject to a low or erratic voltages, use of soft starting devices should be discouraged as these will generally exacerbate an already poor site voltage. Other considerations Installers should: - Try to avoid long pool pipe runs between the heat pump and the pool filtration equipment, and insulate exposed pipe work where appropriate. - Ensure there is sufficient space around the heat pump for routine maintenance access. - Be aware that for much of the normal swimming season, the pool water filtration pump may need to operate 24 hours per day to enable the heat pump to meet the heating requirement. Warranty commitments and after-sales The exact terms of any warranty should be confirmed in writing with both the heat pump supplier and the end customer. The retailer normally holds contractual responsibility for providing the end client with the described warranty so appropriate caution is needed. Manufacturers offer a host of differing warranties, with some particularly long-term parts-only deals. Distributors of imported heat pumps usually only provide a parts only guarantee, so clarification may be necessary regarding potential costs of a refrigeration engineer s attendance and exactly who will attend site in the event of an issue. Operation, maintenance, and winterising On 'hand-over', the installer should ensure than the client is familiar with the normal function of the heat pump, of the benefits of routine maintenance, and the need to protect the product from frost damage in winter. SPATA reminds its members that no responsibility can be taken by SPATA, its employees, or agents in respect of any errors or omissions from this factsheet. This version of M23 dated 1 September 2015