RADIATORS
www.heatingandventilating.net Balancing act
Heat pumps can produce some of the best efficiencies of any heating technology, however, achieving them depends on more than just the appliance. Griff Thomas, managing director of GTEC, looks at some of the specific challenges of selecting radiators for low-temperature systems, dispelling common myths and helping installers design heat pump systems that work efficiently and fit the customer’s brief
T
o achieve top efficiencies, heat pumps need to run at a lower flow temperature than oil and gas boilers. The higher the temperature the less efficient the heat pump becomes and this is not a linear path – going
from a target temperature of 50°C to 55°C will typically increase the electricity consumption more than an increase from 35°C to 40°C. Specifying the right radiator for the job will make all the difference. Generally,
radiators with a greater surface area will be more effective at a lower temperature, that’s why underfloor heating is ideal for heat pump systems. It does, however, require a change of mindset for consumers who are used to radiators that are boiling hot.
All radiators are suitable for use with a heat pump
To bring forward mass heat pump deployment we should first look at what is installed in a property and not immediately jump to replacing all radiators, as this can dramatically increase the cost. Some radiators will provide better outputs than others and heat pump
installers will need to be able to accurately calculate the various pathways. If old cast-iron radiators are installed, for example, it will be tricky to achieve the desired output, while at the other end of the scale, aluminium radiators (or similar) can offer better results than traditional steel panels.
Get a specific brief
Ask the customer if they have any specific needs for an increase or decrease in “typical” target temperatures, for example, do they want any food storage areas such as pantries heated or unheated? Or do they want any rooms heated above the typical 21°C or 22°C? Be clear about what can be achieved – I recently heard of someone complaining because their system wasn’t designed to get their front room to 25°C.
Start with room-by-room heat loss calculations Calculating heat loss on a room-by-room basis is the only place to start if you want to be sure of keeping the room and property warm. With these calculations to hand, you can check the existing radiators and pipework to see how well they will work with a low flow temperature. Heat loss calculations are of paramount importance for low temperature
systems. If you need to brush up on your knowledge then a training course that covers basic heating and hot water system design and specification will ensure the best results.
To replace or not to replace?
It’s then a “trade off” between having to increase the flow temperature to suit any existing radiators – and therefore decreasing the efficiency of the heat pump
- or replacing/adding additional radiators to that room. Radiators that have to come out may be suitable for another room, so don’t
discount reusing them if costs to the consumer are an issue. Don’t forget to power-flush the system before first use, especially when reusing existing radiators and pipework. When selecting a new radiator, it’s possible you will need to adjust the manufacturers standard output tables to correct the output for lower flow temperatures (although some do provide look up tables for lower flow temperatures now) – something we cover in detail on our heat pump training courses. Replacement radiators will almost certainly be bigger than previous systems so don’t be afraid to have that conversation upfront with the consumer – explain that the larger the radiator the more efficient you can get the heat pump to run (and lower electricity costs). Safety tip: Be careful lifting large radiators into place, the weight of double panel double convector and even triple panel radiators is much more than a regular rad.
Choose the right training
MCS is a must for heat pump installers – customers will be looking for quality workmanship, customer care and competency. If they are applying for any funding from the government, which will probably be the case for most over the next few years, they will require an MCS certificate. Our recently launched ‘MCS Made Easy’ online learning platform helps installers navigate the MCS process. There are a lot of choices and decisions to make when retrofitting a heat pump
system, both for the consumer and the heating engineer. Heat pump engineers need quality practical and theoretical training and accredited qualifications to enable them to provide sound advice and install efficient systems.
26 February 2022
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