SWIMMING POOL HEATING

HEATING YOUR POOL

Pool heater, whether heat pump, gas, electric, or oil are fitted with a thermostat to keep the pool at a controlled temperature. Solar panels are controlled by a different temperature control to activate the system whenever solar heat is available for collection. It is important that you identify the temperature you require in the pool, the available fuels on site, and therefore the best system to suit your requirements.

Whether you have an oil or gas-fired boiler or heat pump, remember that these units require servicing and winterisation in the autumn by your swimming pool manufacturer/maintenance company to keep them in good condition.

Pool temperature
Temperature is very much a matter of personal preference, but diligent use of the heat retention cover, couple with the very efficient modern heaters available enables the pool to be kept at an acceptable temperature, economically.

HEATING VIA A HEAT PUMP

A heat pump is quite simply a refrigerator, which is trying to cool the atmosphere and put the heat collected into the pool water, as opposed to the domestic refrigerator which is cooling your butter, milk etc. and putting the heat from these items into the atmosphere in the kitchen.

For the technically minded, the operation is achieved by a large cylindrical fan in the heat pump which moves air through the unit. The air which is relatively warm, passes over an evaporator containing liquid, which boils at very low temperature. When the liquid boils, it turns to a vapour. This vapour is pumped into a compressor and compressed which increases its temperature by five or six times.

This hot gas is then pumped into a heat exchanger where it heats a metal coil as it passes through it, the pool water circulates through the heat exchanger on the outside of the coil, picks up the heat and takes it back to the pool. Therefore the pool water cannot be heated unless the filter pump is circulating the water and, of course, the heat pump switched on.

The heat pump is very efficient and depending on the outside air temperature can return 3 to 5 more units of heat per unit of electricity than if an electric heater on its own were used.

This method of heating is classified as “low grade” heat. This means that to heat the pool water you will, at the beginning of the swimming season, have to run the heat pump, and consequently the filter pump, for 24 hours per day until the desired temperature is achieved. Thereafter the running time can be cut back to 10 to 12 hours per day. It is important to have a heat retention cover on the pool to conserve the heat otherwise the heat pump efficiency is lost particularly at night.

During the heating process the heat pump will produce condensation which will drip out of the discharge pipe outside the plant room. This is a good indication that the machine is working. However at the beginning and end of the season air temperature can get quite low even to the point when this condensation will freeze. No harm will come to the heat pump, as it will sense this. However in doing so the compressor will switch off and the fan will continue so move air through the heat pump trying to warm it up and de-frost itself.

It is important that the circulation of air is not restricted in its passage through the plant room, the heat pump, and thereafter out of the plant room. That is to say the air vents or windows must always be open and wheelbarrows, bushes, chairs etc. must not block the discharge vent.

The front of the heat pump should not be covered but kept clear, periodically dust debris, flies etc. should be brushed off.

Remember the indications that the heat pump is working are:

• The main indicator lamp is on and the filter pump is running.
• There is a cold draught coming out of the discharge vent.
• There is condensate dripping out of the drain tube.

HEATING VIA ELECTRIC HEATER

The heater works in the same way as an electric kettle although very much larger. Most have a series of “status” neon lights, which indicate whether or not the elements are working. They also have dedicated neon to indicate whether the power supply is on. This will stay on even when the filter pump is off.

The heater is controlled by an on/off switch on the pool control panel and also by the large switched fuse isolator alongside. The heater will have on it a pool water thermostat. Once the pool water is up to the required temperature the heating elements will be switched off.

There heaters are neat, clean and easy to install, although obviously a registered electrician must make the electrical connection. Depending on the connection, they may be able to function either with or without a cheap rate tariff. The electrical supply into the property must be competently checked before installation to ensure adequate supply is available. If the electric heater does not contain a flow switch then one must be installed to operate the heater on/off switch with water flow through the system.

HEATING VIA HEAT EXCHANGERS

The heat exchanger has an outer shell which contains a multitude of small bore tubes; imagine a kitchen mug on its side and full of children’s drinking straws. The hot water from the house boiler circulates between the “mug” and the “straws”, the pool water flows through the “straws” and is heated by them. The two waters do not mix.

• The water from the house heating comes through pipes, which are connected to the heat exchanger.
• The pool water thermostat controls the pool temperature.

If the pool water requires heat, than s signal sent by the thermostat will operate the boiler and a circulating pump turns on and draws water from the central heating system to the heat exchanger. When heat demand to the pool water is satisfied, a further thermostat signal will turn the boiler off.
Therefore to heat the pool the following must happen:

• The filter pump must be running.
• The house or pool boiler must be turned on and available to provide heat.
• The heating switch on the main control panel must be on.
• The pool water thermostat must be set at a temperature greater than that I the pool.

HEATING VIA GAS HEATERS

Gas heaters, whether they are fuelled by natural gas or propane must be installed by a registered GasSafe fitter in accordance with current regulations. These include the size and position of the flue, the gas supply and the ventilation. Some gas pool heaters are designed to stand outside a building in the open in this case this is no flue. However siting is important and again must be in accordance with regulation.

Three separate switches control the heater:

• A control panel isolator.
• The on/off switch on the heater itself.
• The thermostat on the heater.
• A gas cock on the gas supply.

The heater has three safety devices:

• A high limit thermostat, which will shut down the heater if it gets too hot. Once it has cooled down the stat will automatically reset itself.
• A safety gas valve, which will cut off the gas supply if the flame or pilot light goes out. In this case the heater will have to be re-lit.
• A pressure switch which will turn the heater off if the pool water stops flowing and automatically re-set itself when the flow is resumed.

With modern technology, thermometers are very accurate with a digital display, so simply set it to the desired temperature. With older models, the easiest way to get your desired temperature is to turn on the filter pump to run constantly, until it has reached the desired temperature. Turn the heater ON, both on the main control panel and the heater, turn the thermostat to maximum. Put your pool thermometer into the pool water and when that reaches  your desired temperature return to the plant room, turn the heater thermostat down to the position where the heater just goes out, the thermostat setting will then match the pool water temperature and will maintain that temperature in the pool.

Most new gas heaters have electronic ignition, but on older models, should the heater pilot light go out, re-lighting instructions are usually set out on the inside of the front door, or in the appropriate instruction booklet. Always ensure that all air vents are clear and/or the ventilation is not hindered.

HEATING VIA OIL HEATERS

Oil heaters have long been used to heat swimming pool water. A few are available that have the pool water flowing directly through them and operate in a manner similar to the gas heaters as described. In some cases, they are standard domestic or commercial boilers which are connected to the pool water via a heat exchanger.

In this case the oil heater can either be the main house boiler with the heat exchanger added to the system in a manner similar to an additional radiator, or as a stand-alone boiler. In the latter case the boiler will need to be fully installed with either a header tank or expansion vessel and connected to the heat exchanger with a set of primary flow and return pipes.

As with the gas boiler the flue and ventilation requirements are critical but at present are not covered by direct legislation. However care must be taken when siting the boiler to ensure thet flues do not terminate close to windows, to boundaries etc. Additional stand-alone boilers will require connection to an oil supply whether existing or a dedicated tank.

HEATING VIA SOLAR PANELS

The concept of the solar heating system gathering free heat from the sun is attractive and will work. However in this climate it is unreliable at maintaining a constant temperature in the pool. The usual heat input from a correctly sized solar panel; system is 2-4oC (35-39oF) above the natural temperature of the unheated water, the higher rise occurring at the hottest part of the season.

The panels are controlled by a differential controller that is set to measure the temperature of the water and the temperature of the air. When the air is sufficiently warmer than the water the pool water flow through the panels will be started. (Otherwise the heat from the pool would radiate to the air).

Standard pool solar collectors require a bank of panels’ equivalent to approximately 75% of the surface area of the pool depending on the geographic location. Ideally the bank should be angled at 15° to 45° degrees to the horizontal and be facing south. The distance between the filter pump and the panels must be taken into consideration when designing and siting such a system. Solar panels are most effective when combined with another fossil fuel heater or heat pump.

See our range of swimming pool heaters here