Ways to further boost boiler efficiency levels

With modern condensing boilers delivering similarly high efficiency levels, controls are fast becoming the definitive way to improve system performance. Martyn Bridges, Director of Marketing and Technical Support at Worcester, looks at the various options.

Boiler manufacturers are constantly looking at new ways of improving boiler efficiency, and the positive changes brought about by the ErP Directive have provided a further incentive to advance performance levels. For example, it has almost become an expectation that a new condensing boiler will operate at efficiency levels of either SAP 2009, >88%, or ErP Band A or B. But while a boiler’s individual performance is key to system efficiency as a whole, the right controls can add an uplift of between 1 and 5%.

As the industry continues to make technological strides in this area, the onus is placed on the installer to help educate their customers on the options available in order to continue to promote the benefits of increased efficiency within a system.

Controls upgrade

With the ErP Directive, we have an authenticated piece of European legislation which states the overall upgrade in efficiency offered by each different type of control. As said, these contributions vary between 1 and 5% to the overall energy efficiency of a heating system. In other words, depending on their classification, the percentage efficiency benefit is added to the efficiency of, say, a combi boiler, to form an overall figure for system efficiency.

It’s important to note that although the efficiency uplifts vary between 1 and 5%, the efficiency improvement does not necessarily correspond with the numerical classification. For example, although category 1 offers a 1% improvement, category 3 grants an enhancement of 1.5%. Although we expect each category to become relatively familiar over time, it is important for installers to note this subtle observation when getting to grips with this new system.

Class system

Class 1 gives a 1% uplift in efficiency to a system that simply has an on/off room thermostat, which remains the most typical form of thermostat seen in UK homes. Presently, that type of room thermostat is one part of the minimum set of controls a house in the UK should have, and through the 1% uplift in efficiency under the ErP Directive, the benefit this solution now brings to the heating system is finally being recognised. It should also be remembered that some of the ‘all-singing and all-dancing’ smart or internet enabled room thermostats are still just an on/off thermostat and therefore receive just a 1% point uplift.

We then move up the scale a little further to class 2, where a weather compensator is given a 2% uplift in efficiency when used in conjunction with a modulating boiler. If attached to a modulating boiler, the weather compensator will vary the flow temperature leaving the boiler in accordance with the outside weather temperature via a variable signal from a sensor sited on a north-facing wall.

Class 3, which offers a 1.5% efficiency improvement, entails a weather compensation for use with on/off boilers. Much like the solution in category 2, the controller will act in line with the outside weather temperature, but effectively turns the boiler on and off when the appropriate figure on the desired flow temperature is reached. It is worth noting that due to the classification being affected by the burner technology of the boiler, it is feasible for one control to be in multiple classes.

By class four, we’re looking at a Temperature Proportional and Integral (TPI) room thermostat, which boasts a 2% efficiency uplift and is used alongside on/off output boilers. This solution works via an electronic thermostat which turns the boiler off at a point slightly before the desired room temperature is reached. The circulating pump will continue to run, but the thermostat anticipates when the temperature will be reached to ensure the boiler doesn’t run for any longer than is absolutely necessary, avoiding any form of overshoot. The idea is that the residual heat sat within the building fabric and furniture for example, will prove just enough to raise the temperature to a sufficient level.

Class 5 offers a 3% enhancement to efficiency and takes the form of a modulating room thermostat for use with modulating boilers. This form of load compensating thermostat works with a modulating boiler to adjust the flow temperature upwards or downwards depending on the measured room temperature.

Class 6 involves the use of a weather compensator and a room sensor, when connected to a modulating boiler. Although there are very few examples of this solution installed in homes around the country, we expect that to change. Here, a temperature reading is taken from the outside and the inside of the property in order to calculate the optimum time and temperature for the boiler to fire at. This form of solution offers a 4% efficiency improvement. Our new Worcester Wave smart controller falls into this category, making it more than double the efficiency of most other smart thermostats on the market. Combined with the premium efficiency levels of the boilers available this addition uplift is all that is required to achieve the 98% heating efficiency necessary for an A+ rating.

The type of device within class 7 is a weather compensator alongside a room sensor, but this time used with an on/off boiler. Because of the slight limitation, whereby the flow rate cannot be altered, the reward is a marginally reduced, yet a still attractive 3.5% uplift.

Finally, class 8 – the best classification available with a 5% efficiency benefit – takes the form of a multi-sensor room temperature controller. This is effectively a device that monitors the temperature in three different rooms within a property and gives a much more accurate average temperature than any of the other solutions available. Thanks to this more precise operation, the boiler can be notified of the temperature it needs to fire at, and when it needs to turn on and off.

Any percentage gain under a given classification is then added to the efficiency level of the boiler to give an overall system efficiency level.

Property rating

As of yet, the ErP system label will not affect the energy rating of a house. However, given that controls have a definitive impact on the boiler’s performance and, consequentially, the property’s energy consumption, the industry as a whole is presenting a case to the Government to show that these Europe-regulated figures are a fair and accurate way to record the a property’s energy performance.

Should the system come into force, it could lead to wider consequences on a homeowner’s pocket. End users will want to improve efficiency, and a new, high-performance condensing boiler alone is only as efficient as the intelligence of controls installed. With ErP labelling now in effect, installers will have to be aware of the various classifications of controls and the different efficiency benefits they offer.

Despite controls forming part of Building Regulations for the last ten years, at least around six million homes are without a room thermostat, and over one million do not have any controls at all. Only when temperature controls are utilised to their full potential will a heating system be able to achieve the highest possible efficiency rating it is capable of.


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