Thinking ahead about cutting carbon

There are significant changes ahead for the installer as we move to a more technology agnostic industry over the next 10 years. However, we should not ignore the fundamental core theory and skills that are required to successfully install low-carbon technology.

Education does not solely fall into the hands of the installer – it is the responsibility of the whole industry to ensure the consumer and the future installer fully understand the benefits and opportunities of low-carbon heating. However, without clear, long-term government policy and a collaborative approach between branches of government such as the Department for Business, Energy and Industrial Strategy (BEIS) and the Ministry of Housing, Communities and Local Government (MHCLG), industry will struggle to adapt.

With the potential forthcoming amendments to Part L of the building regulations, we hope to see changes such as the mandating of low-temperature heating systems and hydraulic balancing. However, it is important not to forget the importance of tasks such as pipe sizing, especially when installing a heat pump, as they typically require higher flow rates and low temperature differentials between the flow and return pipework. If we are to future-proof our heating systems to enable a smoother transition towards a low-carbon future, then the system needs a more rigorous assessment from the outset.

What is low-temperature heating?
Low-temperature heating in this article refers to the water leaving the heat generator at a temperature lower than that of a traditional radiator heating system. For example, a heat pump flow temperature may be as low as 40oC, whereas traditional radiator heating systems deliver a typical flow and return temperature of 75ºC to 65ºC. The use of the term ‘low temperature’ in this article does not refer to LST lower surface temperature heat emitters, which are used in areas where vulnerable people are present; however, the use of low surface temperature radiators can help reduce the risk of burns.

When designing low-temperature heating systems, it is imperative that the heat emitter and the associated pipework are sized sufficiently to deliver the same amount of heat as the equivalent high-temperature radiator. The low-temperature heat emitters are generally oversized to accommodate for the lower water temperatures being supplied to the radiator, which can result in a radiator being increased in size by a factor of three or more. A more suitable low-temperature heat emitter is warm water underfloor heating, which delivers a more even temperature to the room, typically through a series of pipes embedded into a floor screed.

Increasing efficiency through lower temperatures
As we move towards a low-carbon future, the installer needs to recognise the importance of future-proofing the heating system for a wide variety of low-carbon technologies, such as heat pumps. Figure 1 demonstrates how reducing the flow temperature of the heat pump can significantly increase the heat pump’s efficiency. The same principle applies to condensing boilers whereby reducing the return temperature from 65ºC to 45ºC can significantly improve its efficiency (figure 2). Unfortunately, when designing a system to incorporate lower temperatures, it is inevitable that the cost of the system will increase and impact on the consumer.

Determining emitter size
Before starting the design of a low-temperature system, it is important to carry out a room-by-room heat loss assessment to ascertain the correct size of the heat emitter required.

Radiator manufacturers supply their products with published heat output data tables based upon the EN 442 test as can be seen in figure 3. This published output data is based upon the following temperature parameters demonstrated in figure 4:

Radiator mean water temperature (70ºC) – air temperature (20ºC) = ∆T 50ºC.

Adjusting radiator output for a lower water temperature
In simple terms, once you have calculated the heat loss for the room, you then need to decide what flow temperature and ∆T that you require. For example, when installing a heat pump with radiators, you may typically install the system to run with a flow temperature of 45ºC (figure 5) with a mean water temperature of 40ºC { (45 + 35 )/2= 40ºC }; although heat pumps typically run at a lower ∆T of 5ºC .

Referring to figure 6, using an example radiator output of 1,200 Watts from a published output table at ∆T 50ºC (line 1) , the equivalent radiator output at a ∆T 20ºC, (line 4) drops to as low as 365 Watts. Therefore you would need to increase the installed radiator surface area almost fourfold in certain circumstances. However, it becomes increasingly obvious that warm-water underfloor heating is the perfect low-temperature solution compared to radiators, as it not only frees up wall space, but offers a much greater surface area than radiators with the whole floor becoming the heat emitter.

One of the crucial determiners that ensures the efficient operation of a heating system is that it is correctly commissioned and handed over to the customer with full operating instructions. Simple tasks, such as correctly hydraulically balancing the system, are often overlooked at the end of the job when it’s time to put the tools back into the van.

Where next? While stakeholders focus on the next steps for low-carbon heating, installers and engineers can start to adapt to the rapid change that our industry faces by seizing the opportunity to carry out CPD in this area.

This article first appeared in the Jul/Aug 2019 issue of P&H Engineering, the magazine for members of the CIPHE. Find out how to join here.

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