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Sizing a Heater And Other Considerations

Heating a pool quickly is more efficient than heating it slowly, because of the heat losses. If it takes 8 hours to heat a pool, you get 8 hours of heat losses. If you use half the size heater, it may take 20 hours rather than the implied 16 hours, to heat the pool to the same temperature as it will suffer 20 hours of heat losses.   Simplistically, it is more efficient and more convenient to buy a bigger heater than a smaller one.   However, you must not exceed the capabilities of your existing plumbing and pumps.


There are some special things to consider in choosing a new heater:-

Heated water need to mixing thoroughly on returning to the pool

All heater outlets should ideally be situated near the bottom of the pool at the deep-end and angled down at 30 degrees but also inclined in the direction of circulation of the water from the filter.  If you use the normal Return-to-Pool outlets to return heated water to the pool, you may well get a shallow, rapidly-cooling layer of warm water on top of quite a lot of cold water.  You need to mix the heated water near the bottom of the pool. Warm water rises and so you need to inject it as deep as you reasonably can.

If the heater is used intermittently, as are most heaters, and if it uses water from the filter, as most do, consider purchasing an automated valve to switch the heated water flow to the heater return deep in the pool when heating, and use the normal Return-to-Pool for normal filtration.

Gas Heaters – Location and Plumbing

The flue exhaust from gas heaters is hot and can damage any electronics that are directly exposed (including the Pooled Energy Intelligent Pool Controller (IPC)), melt plastic and kill trees and shrubs.  Please mount the heater accordingly and leave about 1 meter clear from the exhaust to anything that can be potentially damaged by the hot exhaust.

Typically gas heaters require the use of Class 18 or higher PVC plumbing for at least 2 meters in and out of the heater or you may have pipe failures due to pipes overheating while under pressure.  Use 50 mm diameter if you can. Gas heaters need high flow and if you restrict it with narrow pipes, you may need a larger pump.

You should allow the IPC to control the heater if it is in the filtration circuit so that the IPC can shut the heater down correctly and cool the pipes so that they do not melt.

Try to avoid putting the heater more than 1 meter higher than the pool water level as you can have plumbing crushed by atmospheric pressure if the pipes get hot. If you use the IPC for control and class 18 plumbing, you can locate the heater higher but please check with us.

When the Operating Plan requires it or you request it via the Pool App, the IPC switches the heater power on to enable the heater. Modern pool heaters are designed for this approach. (Note: Some older heaters may require modification to achieve this type of operation).     Select the temperature you want on the front panel of the heater itself: say 27 degrees. If the water temperature is lower than this, the IPC will turn the heater on and the heater will operate to heat the water. The heating period needs to be sufficient to reach the desired temperature.

For shut-down, the IPC uses a special interface to make sure the heater shuts down correctly.

A correctly sized gas heater will heat a pool about 1 degree C per hour

Heat Pumps

Heat pumps work by transferring heat from the air. The efficiency with which they do this is determined by the Coefficient of Performance (COP). A reasonable COP for a pool heat pump is typically 5 to 6.  A COP of ‘6’ means 6 units of heat are transferred for 1 unit of electricity used.

COP falls with air temperature.  Some vendors of heat pumps recommend that you only run heat pumps during the day, when the air is warm.  This is generally incorrect.  It is true that energy transfer is more efficient from warm air than from cold air, but the electricity to run the heat pump during the day is 2-4 x more expensive than running at night if you have Time-of-Use metering for your electricity.

The critical item therefore is the graph of the COP?  What is the COP in the daytime and what is it at night when you are likely to use it

Ideally a Heat Pump should have a COP of at least 4 down to an air temperature of preferably 5 degrees C.  Here is a set of curves showing this for a Toyesi heat pump.

Clearly, it is far less expensive to run this heat pump using off-peak electricity at night, even at 0°C air temperature with a COP of 3+, than to run it at 2x or 4x the cost of electricity at a COP of 6, at 25 degrees air temperature…assuming that it gets that warm during the day.

The way the IPC works with heat pumps is that it enables the heater using a contactor.  If your Heat Pump does not have a control contactor, Pooled Energy can supply and install one for an additional fee. To operate the heater, select the temperature setting you want on the front panel of the heater, say 27 degrees. The IPC will turn the heater on within times permitted by the cost of electricity and other settings. The heating period needs to be sufficient to reach the desired temperature.   The IPC will also enable a correct shut-down and cool-off sequence.

A correctly sized heat pump will heat a pool about 0.5 degrees C per hour. A pool blanket is a good idea with a heat pump.

Solar Heaters

The best arrangement for solar heaters, is to have them independent of the filtration circuit with their own suction and return-to-pool plumbing. If they use water from the filtration circuit, then they are ‘in-line,’ and require special management to ensure that the pool filter provides sufficient water flow when the solar heater is running.

Conventional pool filters with in-line heaters often incur unnecessary, additional electricity charges because the filter usually runs at full speed all the time, in case the heater controller ‘decides’ to turn ‘on’. Pooled Energy’s IPC on the other hand, adjusts the speed of the pump as required and synchronises the operation of the filter and the solar heater.

The IPC will run your filter at an efficient filtration speed when the heater is off, and speed up to an efficient heating speed whenever the heater turns on and requires higher flow. This optimises overall energy use and improves filtration.

Choice of Type of Heater

The choice is individual but, at present fuel costs, if you have set-times when you swim, maybe gas is best.  You heat the pool only when you need it.  If you want the pool warm all the time, a heat-pump running off-peak and a pool blanket are a good idea.  If you don’t mind heating varying with the weather, solar and a blanket may be the better choice.