Solar Heating

 

Solar heating is the most popular method of pool heating in Australia. It works by installing a large solar collector, usually on a roof, and pumping pool water through the collector to transfer the heat into the pool water. The system can be controlled with the use of a thermostat or solar pump controller. A correctly designed system will deliver summer type pool temperatures for up to 9 months of the year and even longer with the use of thermal pool water covers. The latest solar automatic control systems include cooling modes which run the system at night to cool the pools down during the peak summer months.

Solar pool heating has minimal running costs, it’s simple to maintain and has a very low carbon footprint. Solar heating will satisfy the needs of most domestic pool owners as it will double the use of the pool without large heating bills.

The solar collectors vary in material and styles, however they all are designed to do the same task and that is to collect the suns energy falling on a roof and to transfer it efficiently into the pool water. The most common is a strip collector which is a series of small extruded tubes webbed together to form a continuous strip. This product is typically made from PVC, TPR or synthetic EPDM rubber and is easily adapted to fit most roofs. Panel systems are usually made from polypropylene or polyethylene materials and are more modular in roof layout. 

Most solar collectors are black but the more recent products are offered in dark coloured materials, which are designed to blend with common roof colours. If a colour other than black is used then 10-15% additional collector area should be installed to compensate for its reduced ability to absorb the suns rays

Domestic household solar hot water panels and evacuated tube systems can also be used for solar pool heating, however no dramatic increase in efficiency will be experienced in the temperature ranges required for the average pool heating.

SIZE AND AREA

The recommended collector size is determined by the swimming pool surface area, as this is the major source of heat loss. Other factors will influence the overall efficiency but they are of secondary importance to the area of the solar collector.  Factors that should be considered when sizing the system, in order of priority are:

  • Solar collector area
  • Use of thermal cover
  • Pool shade
  • Shade on solar collector
  • Collector colour
  • Prevailing winds
  • Roof orientation
  • Roof type

SPASA Queensland recommends a minimum of 80% of the pool surface area for all solar collector designs, however increasing the size of the solar collector is the most economic way of gaining more heat into the pool. 
The collector area is referred to as the amount of collector to be installed and not the roof area which it is to be installed on; it should always be represented as a percentage of the pool and in total square meters.

LOCATION AND ORIENTATION

For best results the ideal orientation for the collector is north to north west, however  both west and east roofs can be used with excellent results provided additional collector is used to make up for the orientation short fall. Flat roofs are also a good alternative but again can result in slight loss of performance in the cooler months which can also be made up with additional collector. The overriding rule for all these options is finding a roof with good sunlight for the longest period of the day. Remember that 90% of all the usable heat is collected in the middle 2/3 of the day.

PUMPING REQUIREMENTS

Solar Pool heating systems can be run off the existing filtration system pumps, however this can create issues with varying or high filter pressure. Each site should be considered on its merits.

The most common and hydraulically safest way is to use an independent system where the pool is constructed with solar flow and return pipe work, i.e. Two designated suctions points with approved safety suction grates, at least 1.0 m apart.  The flow rate through these suction points should not exceed the latest ASA rulings to prevent the chance of suction entrapment.   At least one solar return point should be installed and care should be taken to position the solar suctions and outlets in the pool wall such that the flow of water does not work against the skimming action of the filtration water flow.

 The other option for pools constructed without solar provision, is the simultaneous running of a solar boost pump with the filter pump. The booster pump diverts some of the filtered water thought the solar collector and returns it back into the existing pool return outlets. In this case both the filtration system and solar pump work simultaneously to flow water through the solar collector. 

For both options correct flow rates through the collector are imperative to achieve good results and the solar pump must be sized with the following in mind:

  • Collector area
  • Pipe Size
  • Length of pipe run to the collector
  • Vertical lift to the collector

Pump selection should be based around a higher head / low flow rate than traditional filtration pumps which tend to be lower head and higher flow rates. The use of variable speed pumps is not recommended for solar pool heating as they are designed for filtration duty and do not deliver savings when running at the constant high speeds required to lift water up to roof heights. 
Balancing valves should be installed to control the flow and pressure through the collector.  Installing a pressure gauge at the collector is recommended to ensure the collector doesn’t exceed the manufacturer’s recommended working pressure.

SOLAR CONTROLLERS

As nobody can guarantee at what time of day the sun will shine, time clocks are of little use in controlling solar pool heating systems. What is needed is a temperature sensing control device which enables the pool owner to set and maintain the desired pool temperature. These units will operate the solar pump only when heat can be gained into the pool. Modern solar controllers have many extra features which monitor the systems functions and wherever possible conserve electricity.

HANDOVER AND COMMISSIONING

A formal handover and commissioning of a solar pool heating system should be carried out by the installation company, a full explanation of the workings of the product and setting should be explained with a full warranty pointing out conditions and servicing requirements for both the owner and the installation company, if a service schedule is in place to comply to the warranty, understand the timing and conditions.
Ensure the product handover and commissioning report states

  • Installation dates
  • Correct addresses and contact details  
  • Collector area and products used, this should match the quote/ sales order
  • All warranties, understand what product is covered by the installation company and by other suppliers/manufacturers. 

As the installation of solar pool heating in Qld is regarded as “Building Work”, ensure that your proposed Contractor is appropriately licenced by the Queensland Building Services Authority to perform this class of work. Licenses can be checked at www.bsa.qld.gov.au

Also, due to the nature of the work, Workplace Health and Safety “risk assessments” are required prior to the installation of solar pool heating; this should be readily available by the installation company.