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Solar pool heating systems are becoming more and more popular due to their simple design and since they are very cheap to operate as the suns energy is free.  In addition, since they don't use fossil fuels for heating and have a fairly long life expectancy due simple design.  In Part 1 of the Solar Pool Heating series we are going to discuss the basics of how these systems work. 

Open Loop Heating System

The simplest and most common system for seasonal pool heating or for heating in climates with high year round temperatures is an open loop system.  In an open loop system your pool water, as needed for heating, is pumped through unglazed solar panels where the suns energy, in the form of heat, is transferred to the pool water being pumped through the panel.  Below is a basic diagram of an open loop system.

Closed Loop Heating System

A closed loop system is more commonly used on indoor pools that require year round operation and is located in a colder climate where the risk of freezing is possible.  Closed loop systems operate similar to many Solar Domestic Host Water heaters in that a mixture of propylene glycol and water (50/50 mix) is pumped through the solar panels to gain heat from the sun.  Unlike the open loop system, in a closed system the pool the water is not pumped directly through the solar panels but instead it is heated via a heat exchanger.  The heat exchanger transfers heat from the solar heated glycol solution to the pool water.  Essentially the glycol solution is cooled (passes heat to the heat exchanger) as it passes through the heat exchanger and the pool water is heated (takes heat from the heat exchanger) as it passes through. 

Unglazed Solar Panels

Unglazed panels are the most common for solar pool heating are very basic in design compared to some other solar panel technologies.  They are often made from a special rubber compound that is designed to withstand constant exposure heat and UV from the sun or they are often plastic tubes with similar characteristics to ensure long life in outdoor applications.  Water is pumped through the panels, picking up heat from the sun along the way.  Plastic tube panels resemble a parallel manifold in which cooler pool water is distributed evenly across the panel, picking up heat, and then heading back to your pool.  Panel sizing for an open loop system is generally done by having a panel surface area equal to about 40-60% of your pool surface area depending on your geographic conditions, your desired temperature, and the specific product.  Closed loop systems which operate all year round will likely require a larger panel area due to the reduced solar energy available during the winter months in northern latitudes.  If you have a lot of daytime shade, poor directional exposure on your roof, or want warmer water, you can also add more panels to increase the panel surface area to provide additional heating capability. 

Keep The Heat In Your Pool

It's always advisable to ensure you use a solar cover to retain heat within your pool as over 90% heat loss from pools is from the surface.  Additionally, anything you can do you stop wind from blowing over your pool (which increases heat losses) is advisable and will help to maintain your pools temperature (i.e. fences, plants, shrubs etc.). 

Pumping

In an open loop system your pool water is pumped via your existing pool pump, or if necessary due to long runs or a very low power pool pump, via an additional booster pump.  With an open loop system you are pumping your pool water directly through the panels and as such you will need to drain the system prior to the winter months to prevent any damage that could occur from water freezing in the lines and panels themselves.  In a closed loop system an additinal pump is needed to circulate the glycol/water mixture through the solar panels.

Solar pool heaters certainly offer a great alternate option to the traditional fuel based heating systems so don't overlook them if you are looking at installing a new pool this season or it's time for an upgrade or heater replacement.

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