Boiler manufacturers up their game
Paul Sands of Stokvis Energy Systems gives an insight into the technology that makes modern wall-hung boilers so efficient and how to ensure that system design maximises their capabilities.
Technological advances have increased the efficiency of commercial boilers to the extent that established, well-proven technology ensures high efficiency and reliable performance.
However, that does not mean the industry is resting on its laurels, because new developments continue to boost the energy efficiency and overall effectiveness of heating systems.
Great strides are being taken in boiler controls because the better the control the greater the energy efficiency, the higher the fuel savings and lower environmental costs of consumption.
Modern premix boilers can incorporate a temperature sensor linked to a temperature controller which, in turn, operates a frequency inverter that manages the speed of the fan. The gas is controlled by analysing the varying pressure created by the fan so that, for instance, on a higher pressure there is a higher requirement for heat and that opens up a pressure-controlled gas valve. This allows full modulation of the boiler, with all the energy-efficiency benefits that follow.
It makes sound environmental sense to modulate the gas and air from the primary heat source — the boiler — in accordance with demand because modulating to get the optimum gas/air ratio in the mix will save energy. If the water content of the boiler is also minimised, the user will also benefit from tight control of heat output and standing losses will be minimised.
Developments have also taken place in system controls such as weather compensation, which is designed to vary the boiler's heat output according to the outdoor temperature, thus minimising the amount of gas the boiler consumes.
With condensing boilers now the norm, the most efficient heating systems are designed for a higher temperature drop so that the return water is a lower temperature, which offers greater condensation opportunities and, therefore, higher boiler efficiencies.
More recently, condensing technology has meant that consultants have increasingly tried to design for lower flow and return temperatures to keep the condensing mode going. However, there is scope to apply more attention to system design to ensure the lowest possible flow temperature and higher temperature differentials on the system.
The onset of renewable technologies such as solar energy, biodiesel, biomass boilers, heat pumps etc., has meant that more-conventional high-efficiency condensing boilers are often used for ‘top-up energy’.
If renewable sources are starting to act, in effect, as the ‘lead boilers’, it follows that the boilers supporting them will get smaller. Indeed, as more commercial projects become renewable-based, the trend towards smaller boiler plant will accelerate. This, combined with further legislation that will improve the thermal properties of buildings, will result in less heat loss, which itself adds to the impetus for smaller boilers.
Another increasingly common sight in commercial settings is modular boilers packaged on a frame. These integrate system controls, manifolds, low-loss headers etc. and add to flexibility of design.
Factory produced packaged boiler systems and controls make it easier for consultants looking for efficiency in the system rather than just in the boiler. This is because they are able to obtain from the manufacturer ‘the points’ in terms of ratings for overall system efficiency. This in turn allows them to specify a complete and coherent system of boilers and controls — all in one easily rateable package. So it takes away the headache of specification.
Factory-produced packaged boiler systems improve on-site safety because fewer trades are on site for less time, and quality and reliability are guaranteed because the packages are produced in controlled factory conditions.
Paul Sands is sales director with Stokvis Energy Systems.
