There are a lot of ways to install a radiant system. However, radiant systems can be broadly split into low mass radiant systems and high mass radiant systems. The difference between these is important because it can significantly affect the best design for your next project.
What does low mass and high mass mean?
Regardless of where radiant systems are installed, they can either be low or high mass.
This is a term that describes the thermal mass of the system – mainly the capacity to store heat energy. Low mass systems have a very limited capacity to store energy, while high mass radiant systems have a large capacity for energy storage.
The 4 major differences between low and high mass radiant systems
1. Energy retention
Low mass radiant systems, typically lightweight aluminum panels, do not have the ability to retain energy for a long time and have to be constantly functioning at the time that the radiant heating/cooling is required.
High mass radiant systems, typically concrete building elements, retain energy for an extended period and can provide radiant energy transfer long after energy has ceased being added/removed.
2. The speed of response
Low mass radiant systems respond quickly to desired changes in the thermal environment. Essentially, once set to the desired temperature, they will heat up / cool down instantaneously to reach that temperature. High mass systems, in comparison, are very slow to reach the desired temperature, typically taking a few hours.
3. Choice of material
Low mass radiant systems are commonly tasked with higher performance requirements than high mass systems. Therefore materials with high conductivity such as aluminum are chosen. However, low mass systems sometimes are also required to address additional features simultaneously, such as sound absorption. Gypsum is often chosen as a trade-off, providing lower heating/cooling but better sound absorption capabilities. High mass systems almost exclusively use concrete as it is the most common material to build floors and ceilings.
4. Physical construction
Low mass systems are commonly applied when the majority of loads should be addressed by the radiant system, and auxiliary systems will be used to address remaining tasks, such as fresh air supply, regulate air humidity and cover peak loads. The physical installation of low mass radiant panels can also take into consideration a lower or higher convective part by turning the panels from horizontal to vertical. The latter being able to increase the performance of the system.
High mass radiant systems will use a dense, heavy, low conductivity material such as concrete. These systems are commonly used to cover base loads so auxiliary systems can be down sized and designed to just address the peaks.
Overall, the main difference in high and low mass radiant systems is in their ability to retain heat energy. However, this apparently simple difference has a lot of important implications for building design, construction, energy budget, and ultimately the thermal comfort of occupants.