Combination boilers are by far the most popular boiler type amongst installers, accounting for over half of all boilers sold so far this year. Combi boilers are particularly suited to smaller households and offer a number of benefits, not least because they allow for mains pressure at all hot and cold water outlets, as well as taking up less room in the house as there is no need for a hot water cylinder or cold water tank feed system. Also, from a cost point of view, they are potentially much quicker and easier to install as there are fewer system components.
However, the fact that combi boilers do not require a storage cylinder has led to some concern in terms of integrating renewable technologies such as solar thermal. All renewable technologies require some form of hot water storage, as the amount of natural heat varies depending on the time of day, month or, in some cases, the weather conditions. Fortunately, the industry has now developed a solution that means a solar thermal system can be used to ‘pre-heat’ the water entering a combi boiler, thereby reducing the amount of energy required to raise the water temperature to the desired level for the household.

How a Combi Pre-Heat System Works

A typical solar thermal system consists of solar panels, controls, pump station and a hot water storage cylinder. However, although a storage cylinder is required for a combi pre-heat solar thermal system, it is much smaller than the type of cylinder used in traditional storage water heating systems, thus saving valuable space. The heat from the solar panels is transferred into the hot water storage cylinder, in exactly the same way as a regular solar thermal system. In this instance, though, the heated water then passes into a mixing valve before entering the combi boiler directly via its cold inlet. The mixing valve is an essential component of this system, as it ensures the temperature of the water entering the boiler is not too high as to damage the boiler’s hydraulic controls. It achieves this by combining the preheated water from the storage cylinder with cold water from the mains, if required, to create the ideal water temperature for the boiler. This means that when the pre-heated water arrives at the boiler, its temperature is never high enough to cause damage, yet it still reduces the difference between the ‘target’ temperature and the temperature of the water entering the boiler. So if, for instance, the water in the storage cylinder is pre-heated through solar gain to 40°C and the required water temperature for the household is 50°C, the boiler only has to raise the water by 10°C, thus saving energy.

When installing solar thermal to provide preheat for a combi boiler, the installation is nearly exactly the same as for any other combi, except for the addition of the mixing valve connecting directly to the boiler and an option to install an electronic card that plugs into the boiler instead of an external solar controller. This card updates the way in which the product works, opening up the parameters for solar thermal. It will also give an error code for the solar system, should a problem arise. These two straightforward additions to the boiler means installation is virtually ‘plug and play’.

Ariston’s GENUS HE and CLAS HE combi boiler ranges are perfect for use as part of a combi pre-heat system and can be used alongside Ariston’s new range of solar thermal solutions.