High Mass Systems, Low Mass Systems, Radiant Cooling

Should You Use A Low Mass Or High Mass Radiant System For Your Next Project?

In a previous blog, I covered the differences between low and high mass radiant systems. In short, there are four major differences; energy retention, the speed of response, the materials used, and the physical construction. In this blog, I will cover what these differences mean for the building project, and what the merits and challenges of each system are. Hopefully, this will help you decide which radiant system, high or low mass, you should use for your next project.

Energy retention


This is essentially the fundamental distinction between low and high mass radiant systems.

Low Mass

Low mass radiant systems do not have the ability to retain energy for a long time and have to constantly function at the time that the radiant heating/cooling is required.

high mass

High mass radiant systems can absorb a large amount of energy, and transfer energy relatively slowly over a long period. The cooling/heating capacity of low mass systems is commonly higher than that of high mass systems.

The main advantage of high mass systems here is that they can be heated or cooled outside of peak hours. The system can then run at a minimum capacity during occupied, peak hours, and still, provide the requisite radiant cooling/heating.

In climate zones, or seasons, that experience large swings in temperatures between the day and night, a high mass system can be beneficial as it will buffer the range of the swing. The temperature will be maintained in between the extremes, in a more comfortable range. Moreover, high mass systems can make use of solar heat gain during the day, and retain that energy for release overnight. Or, high mass radiant systems can take advantage of cool nights to passively cool down, and cool the space during the heat of the day. Either way, high mass systems will reduce the amount of energy input needed during peak hours in these climates.

The speed of response


The rate of response follows directly from energy retention, as they are inextricably linked. Low mass radiant systems have a much shorter response time than high mass radiant systems. Low mass systems will typically reach the desired temperature instantaneously, compared to over high mass systems which can take hours.

This difference in response times means that high mass radiant systems cannot be used to match short-term fluctuations in cooling/heating requirements. Short-term occupancy fluctuations over the space of an hour or two cannot be adjusted for. For instance, some spaces within building complexes, such as conference rooms, may not need to be temperature regulated at all times but do need to be able to be used and temperature controlled intermittently throughout the day. Low mass radiant systems, on the other hand, can be adjusted at a much finer scale to match requirements throughout the day and night.

Physical construction and material


The main difference between high and low mass radiant systems is in the materials they are made out of. This difference is the underlying cause for the difference in energy retention, and therefore the difference in response time. However, it also has significant consequences for design and construction.

It is important to consider before the construction stage, for example, whether any decoration material would be covering the concrete surfaces later on, which might prevent the system from functioning to its full capacity.

In the case of high mass heating / cooling, the radiant system will normally have to be incorporated into the initial construction process.

Low mass radiant systems are light weight in comparison and tend to be more manageable, as well as flexible in design and installation. Ceiling panels, for example, can be retrofitted. They can also feature various other functionalities, such as ventilation outlets, sound absorbing surfaces, lights, fire fighting equipment, or loudspeakers. Depending on whether they are installed horizontally or vertically, they design engineer can also increase or decrease natural convection around the panel varying the cooling/heating capacity of the system.



The apparently simple difference between high and low mass radiant systems has a lot of important implications for building design, construction, energy budget, and ultimately the thermal comfort of occupants. However, whatever radiant system you select, it will provide the energy and comfort benefits you are looking for.



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