Swimming Pool and Spa Heat Pump Sizing Information

Heat pumps provide higher output power during the summer months - it is not uncommon for output power to be 60% higher in summer compared to winter.  However, the serious heating is required in winter.  Many manufacturers provide output power and COP figures showing the performance of a heat pump on a hot summer day.  This can make distributors, dealers and customer believe that the heat pumps are a lot more powerful than they really are.  This can result in customers paying additional money for a heat pump because they believe that it is more powerful, or an undersized heat pump being installed.

THERMOswim and Accent provide output power and COP figures for indicative winter operating conditions, and THERMOswim provides a wide range of other operating temperatures, so that distributors, dealers and customers have the correct information to make the right choice.  We hope that the tables below will provide you with some additional information so that you can properly compare systems, and so that you can choose the model that is truly best sized to your needs.

Sizing Factors

Heat Load

The heat load is the amount of heat that a pool or spa requires at a given time of the year to maintain a desired temperature.  Many factors affect the heat load.  These include:

• Adequate heating is available to achieve the desired temperatures

• The heat pump has not been over specified - a common approach which causes customers to spend more money than necessary

• The customer has a reasonably accurate indication of monthly heat pump running costs

Other Factors

The heat load provides an indication of the heat which the pool or spa requires over a 24 hour period.  Other factors which now need to be considered include:

The above calculations and considerations, if performed professionally by properly trained consultants, will give a fair indication of the output power required from a heat pump for a unique installation.

This is now the time where you have to rely on truthful and accurate heat pump performance data from the manufacturers.

Example. A 40 square metre pool has a calculated heat load of 7.6kW per hour (182kW per day) to maintain a temperature of 30 degrees in the coldest month of the year, assuming that a pool cover is used for 20 hours of the day.  For this installation, the hours of operation need to be restricted to 14 hours per day. This means that 13kW per hour is required to provide the 182kW required to heat this pool per day. The consultant then needs to look at the performance graph to determine the heat pump size that is most appropriate for the actual air temperatures during the coldest months of operation.  In south east Queensland the average air temperature in the coldest month would be around 13 to 15 degrees (average over whole day).  The THERMOswim TSC14 would provide the required heating for a high proportion of the time.  It may not quite get the pool to temperature during prolonged periods of unusually cold weather. This is not generally an issue for a domestic pool. The THERMOswim TSC19 would be recommended when maintaining the pool temperature is more important, or when a pool cover is used for fewer hours of the day.