The increasing use of renewable heating systems has led to widespread debate about their compatibility with radiators. Nick Whitwell discusses the issues and explains why ‘high and low’ is the golden rule when choosing radiators for renewable systems.
Developers of new homes, local authorities and homeowners are all considering renewable energy sources as their preferred method of heating buildings to reduce energy bills and help meet carbon reduction targets.
Over the coming years, as energy prices rise still further and the Government’s commitment to reduce carbon emissions by 80% by 2050 starts to impinge on our lives, installing renewable technology in homes will increasingly become more urgent. Already there are local authorities piloting schemes where people with solar panels on their roof or ground source heating, benefit from lower
council tax bills.
This increasing focus on renewable heating systems has led to widespread industry debate about their compatibility with radiators due to lower flow temperatures.
Lower temperature
As installers will know, traditional boilers will produce water flowing into the radiator at a temperature of between 70°C and 75°C, whereas air source and ground source heat pumps, for example, provide water at a much lower temperature – typically between 45°C and 50°C. Therefore heating systems driven by these types of heat pumps will usually only operate at a Delta T of 20–25K compared to a traditional boiler system that would run at around Delta T 50K. Effectively this means that the water in the radiators doesn’t get as hot with a renewable system so the heat output is less, and it is argued that you need a larger surface area to get the room to the right temperature.
There is, then, a myth that the only solution is to significantly oversize the radiator or use a different type of heat emitter with a larger surface area, such as underfloor heating. To be effective with renewables, the radiator needs to make optimum use of the water’s energy content.
High and low
In fact, the answer is actually to use a high (heat output) and low (water content) radiator, which means that, while there may still be a small degree of oversizing, installers don’t need to go up to such a large radiator or install other expensive heat emitters.
High output, low water content radiators are made to deliver top heating performance, no matter what energy source is warming the system – traditional boiler, condensing boiler or renewable source. In fact, the higher the heat output and the lower water content you can get, the more efficient it will be.
For example, Quinn’s new Hi Lo radiator has just been launched specifically for low temperature systems and has the highest heat output and lowest water content of any product in the market, meaning it uses less energy and is faster to heat up.
Space-savers
Another good idea with renewable systems is to get more radiator surface area in less wall space by using a triple panel or vertical radiator. By doubling up or tripling up on the number of panels, it is possible to achieve higher heat levels from shorter radiators.
There are many benefits of installing radiators rather than underfloor heating as the main heat emitter for renewable systems. First of all, assuming the heating system has been properly installed, no maintenance is required. Being on the wall, the heat emitted by radiators isn’t affected by coverings – unlike underfloor heating where the heat emitted can vary depending on the floor coverings used.
Evidence also suggests that buildings heated by low temperature radiator systems consume less total energy than underfloor-heated buildings, even when using renewable energy such as heat pumps. Last – but certainly not least – is cost. Fitting an underfloor heating system is much more expensive than installing radiators, particularly as most underfloor systems won’t provide a total heating replacement anyway.
There are still urban myths about renewables and radiators not giving optimum energy performance, when in fact renewable systems can be three times more efficient than a standard boiler system, providing they are combined with the right radiators.
Full efficiency benefits
The mistake that homeowners often make is to install a renewable system without replacing old radiators. This could potentially be more of an issue with the introduction of the Green Deal, which gives financing for microgeneration technologies but not for radiators. There is, then, an opportunity for installers to educate customers that unless old radiators are replaced, they won’t see the full efficiency benefits of a renewable system and might be disappointed by the heat that is emitted from their new system.
Online calculations
It is important that installers consider not only the Delta T factor but also the space constraints of the property they are working in. Using an online heat loss calculator allows the installer to change the Delta T factor to enable installers to calculate the right size radiators needed for both renewable and traditional systems.
With all renewable systems, there will need to be some degree of oversizing – potentially width, height or depth – but there are different options available. As long as installers remember the golden rules of high (temperature) and low (water content), heat emitters with huge surface areas aren’t needed and any oversizing can be kept to a minimum.
