Gas boilers can be combined with other technologies including renewables to create a high performing heating system that has a low impact on the environment. Mark Northcott explains.
Condensing boilers are incredibly versatile heat generators. They can be used with a whole host of emitters including radiators, underfloor heating systems and convectors to produce efficient heat at the right time and the right temperature.

However, their flexibility can be boosted still further by joining them with renewable technologies such as heat pumps or solar thermal heating systems. This sort of arrangement combines the best of both worlds - not only is heat always guaranteed, but, in the summer, when less heat is required, you can take advantage of the outstanding coefficients of performance (CoPs) of renewable technologies to lower fuel bills dramatically, cut emissions and raise energy efficiency.

So specifying and installing a system that combines the best of renewable and conventional heating technologies in the form of a 'bivalent' system makes perfect environmental and economic sense. Bivalent systems combine two heat generators - say, condensing boilers and a renewable heat source - in order to maximise the operating efficiency of the system as a whole over the course of the year. These systems are relatively simple to retrofit and work by taking advantage of each form of heating - for example, the condensing boiler's effectiveness in supplying heat and the heat pump's high CoP.

Offsetting disadvantages

The arrangement also makes perfect sense because each heating system offsets the disadvantages of the other. For example, although they can offer impressive energy performance figures and they are low maintenance because they have few moving parts (something which, incidentally, contributes to their lack of operating noise), heat pumps are less good than condensing boilers at heating water to higher temperatures. The higher the temperature the less efficient they become.

This is where the well-established and proven condensing boiler comes in; not only is it a powerful heat generator, but it is also energy efficient and produces few harmful emissions.

That is why I believe that specifying a single heating technology may be close to an end. For me, the future lies with mixed technology. Bivalent heating systems work particularly well on refurbishment projects because older buildings often enable the designer to take full advantage of the renewable source. For example, many Victorian buildings already have an old coal bunker that would be perfectly suited for storing the fuel for a modern biomass boiler.

With the right controls - such as weather compensation or sequencing controls in a multi-boiler configuration - retrofit systems can be made pretty much as efficient as a bespoke new heating system.

In a nutshell, producing a combination system in which both elements work effectively and efficiently together offers the best opportunity to ensure excellent heating performance at the lowest cost and producing the least environmental damage.

However, I would urge installers and designers to be cautious. A bivalent system using two separate manufacturers for the two elements is more likely to fail because of lack of compatibility. It therefore makes sense to employ the same supplier for both systems. That way, you can be certain that the two elements will have been designed to work well together to produce their optimum performance.

• The author is commercial director of Remeha