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Use of radiators with low temperature systems


Choose the right radiator for renewable heat sources

In a constantly changing world and with an increasing focus on the environment, the government has set itself the goal of reducing CO₂ emissions every year until 2050. We are therefore looking into a future of more renewable energy with an increase in air, soil, solar and hybrid heating systems. However, the so-called 'low temperature systems' can cause problems when using traditional radiators. But it is possible to future-proof the system by making a few important considerations: Using the right heat loss calculations and choosing the right types and sizes of radiators for the project.


The difference between heating boilers and air source heat pumps

To get the best use out of a heat pump, you must think a little differently than with traditional boilers. Air source heat pumps work best with a steady and even approach. Since it takes some time to warm up and they run at a lower input temperature, it is best to keep the heat pump on for longer periods. This means that instead of letting the temperature fluctuate between a high and a low temperature, as with a traditional boiler, it is better to maintain a stable comfortable temperature throughout the day. This can be a challenge when replacing old with new technology. Let's look at one of the main issues when replacing a fossil fuel boiler with an air source or ground source heat pump.


Flow and return temperatures

For standard boilers, we use a standard format to calculate the required heating for each room based on the EN442 standard water temperature set of 75 ⁰C flow and 65 ⁰C return and an ambient room air temperature of 20 ⁰C (expressed as 75/65/20), giving a ∆ h 50 ⁰C. On the new low-temperature systems, the maximum supply temperature should not exceed 55 ⁰C. In addition to the building's material (insulation levels, windows, air tightness, etc.), selection and dimensioning of the radiators is therefore the second most important task.


A switch can result in a drop in production of over 50%

The difference between older, higher temperatures and the newer, lower ones can have a significant impact on the heat output of your radiators. Here is an example - using the EN442 standard - to meet a space heating requirement compared to a renewable heat source: Let's say a bedroom requires 900 W and the set temperature is 75/65/20 (∆t 50⁰C). This would require a radiator 600mm high x 1000mm long, with single convector. If we switch to an air source heat pump, the parameters change, as a supply and return temperature of 45 ⁰C and 40 ⁰C respectively are specified here. By assuming the same ambient room temperature as before of 20 ⁰C, the heat pump works at a much lower temperature with a ∆t of 22.5 ⁰C. Assuming no other changes, the heating demand for the room remains unchanged and still requires 900 W, but the radiator – a 600 mm high by 1000 mm long, single convector – as previously chosen, will only achieve 330 W at the new temperature set (45/40 /20, ∆t) 22.5°C). This is a drop in production of over 50%. In this case, a larger radiator must therefore be used to achieve the same performance.


Designed to perform

To satisfy the heating demand at ever lower supply and return temperatures and to obtain the greatest possible heating effect, Hudevad Radiator Design has over the years improved the efficiency of their radiators. This has been achieved by, for example, reducing the water content, increasing the surface area, increasing the depth or number of panels and the design of the convector fins. An installer can choose different types of panels from Type 10 (single panel, no convectors) right up to a Type 33 (triple panel, triple convector). To achieve 900W @ 45/40/20 (∆t 22.5⁰C) in the example mentioned, a 600mm high 1200mm long type 33 (triple panel, triple convector) would meet the requirement without significantly increasing the length.


Not all radiators are created equal

Hudevad's modern panel radiators, with their low water content and large surface, heat up faster than traditional cast iron radiators. This means they respond more quickly to changes in the environment, allowing the system to operate more efficiently and avoid potential waste of energy. Radiators designed for the greatest amount of convection heat (as opposed to radiant heat) perform better at low water temperatures.

How to choose the right radiator for renewable heat sources

The size - height and length as well as depth - are the most important factors when choosing radiators for low-temperature heating systems. With the large surface area of modern radiators, the heat output is maximized. By choosing the right design of radiators with a smooth flat front, closed sides and discreetly profiled top, you will e.g. a type 33 look less obtrusive in the room. Another way to maximize heating performance with low water temperatures is by using vertical radiators. With a vertical radiator, the "chimney effect", i.e. natural convection is maximized, giving impressive results at low water temperatures while using the least possible wall space.

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