So how does this relate to radiant cooling and heating systems?
Well, it just so happens that relative to the industrial quality temperatures we create with combustion and compression, the non-industrial temperatures we need for buildings are readily and freely available in radiant dependant renewable energy systems. You see the biggest radiant cooled and heated surface known to mankind is the one we walk on every day – it’s called earth; and just below and above the earth surfaces in relatively short distances one can find all the low-grade thermal energy we need without having to generate industrial-grade temperatures.
In order to engage these readily available non-industrial grade temperatures, we need to detach from our traditional use of small surface area heat exchangers and engage the use of large surface area heat exchangers. Why? Because relative to the energy flux in buildings (Btu/hr/ft2 or W/m2), in heating, a high flux served by a small exchanger needs a high source temperature; and in cooling, a high flux served by a small exchanger needs a low source temperature. Mankind to the detriment of earth’s ecosystems has found it convenient to obtain these high and low temperatures through the burning of fossil fuels. However, with large surface area heat exchangers we only need tepid temperatures similar to those found on and in the human body – and these low-grade tepid temperatures can be found in renewable energy systems.
So where can you find large heat exchanger surface areas which only need low-grade heat? Well, of course the floors, walls and ceilings of spaces. As it happens, controlling the surface temperatures of interior spaces falls directly into the health sciences of thermal comfort in a subset study defined as the mean radiant temperature. According to exhaustive medical research the human body exchanges 50% to 60% of its sensible energy with the surrounding environment via radiation; ergo it only makes sense that we control the radiant exchange; and we can do this with a combination of building enclosure performance, interior design and radiant-based HVAC systems.
At the end of the day, radiant floors, walls and ceilings enable the use of low-grade heat, which supports thermal comfort with energy systems that are nurturing, supportive and dependable…and, to me, that has always made so much sense.