The continuum of radiant myths
September 6, 2016 | By Robert Bean
Back in 2004 I penned an article called Radiant Mythology: 22 Myths about Radiant Heating. In the years since the first copyright of the article on www.healthyheating.com, that article has brought me the immense pleasure of watching tightly-wound individuals implode and explode through their nastygrams that arrive in my inbox. The myths continue and have expanded to well over 40 “myth-understandings” about radiant energy and radiant systems.i
Here are a few of my favourites.
1) Radiant floor heating was “invented by the Romans.”
This is not even close to being accurate. The earliest forms of radiant floor heating emerged well before the Romans ever showed up. Present day archeological sites in Asia and North America are uncovering forms of floor heating carbon dated back to 1000 B.C. That is hundreds of years before the Romans embellished the idea. But the application goes back even further with combination cooking and radiant space heating systems found in Korea and China dating back to 3000 to
It is time the radiant industry embraced its past and correct the sins of those continuing to distort history.ii
2) Radiant floor heating “creates the same feeling as sitting in the sun or in front of a fireplace.”
It is nice to think of floor heating in these terms but in reality if this were true you would bake to death. It is important to understand the sun and radiant floors operate on two completely different electromagnetic wave lengths.iii The sun or fires operate at high intensity short wave and floor heating operates at low intensity long wave.
Since the human body and floor heating operate in a similar temperature range they coexist within an almost identical long wave range. Translation: radiant heating systems do not heat you up in the sense of the sun or a fire, rather they enable you to retain more of your own heat by reducing the loss of body heat via radiation. Look at it this way–the temperature of your skin fluctuates and varies from your feet at approximately 85F (29C) to approximately 96F (36C) at your head. Remember, hot goes to cold. So what do you think is going to happen with heat transfer when your body is operating warmer than the floor? Feeling the heat of the sun from the floor? Not likely. Feeling the retention of your own heat–absolutely. Call it self-love.
3) Radiant floor heating “saves energy.”
Energy can neither be created nor destroyed, therefore it cannot be saved like the accumulation of coins in a piggy bank. Energy is always being preserved in its current state or converted with conservation to another state but it is never saved–not even by radiant systems. The concept of saving energy is likely the biggest disservice we have allowed to happen to mankind. It makes people focus on the wrong targets for sustainability.
4) Radiant floor heating “is energy efficient.”
This is going to shake some cages. First let me state unequivocally that radiant heating and cooling systems empower boilers, heat pumps, chillers and solar systems to achieve their maximum rated peak performance. Full stop. No one with a basic understanding of heat exchanger design can debate this principle. But an energy efficient machine does not equal efficient use of energy. For example, consider the combustion temperature of 3200F (1700C) in a 97 per cent boiler for creating 100F (38C) fluid temperatures just to maintain a space temperature of 72F (22C).
When the temperature generated at 97 per cent efficiency is approximately forty seven times hotter than the target temperature your brain should do mental gymnastics.iv Air only folks–do not get self-righteous, this also applies to furnaces. Neither appliance, regardless of its rating should be considered energy efficient if it wastes more than 90 per cent of the work potential.
This is a big broad topic but let me wind this myth up by stating radiant systems are first and foremost enablers. They allow cooling and heating appliances to transfer heat as intended by the manufacturer’s engineers and support the reduction in system power consumption used in motors.
5) Radiant floor heating “causes hardwood floors to crack.”
This myth still comes up. Consider that 100 per cent of all hardwood flooring complaints in buildings conditioned exclusively with air did not have radiant floor heating to blame. What is up with that? The number one cause of wood deformation is moisture changes not the operating temperature of a well-designed floor.
Control the absolute moisture in the wood and space and the differentials between the two and you control the deformation.v There is a caveat: if the floor heating system has to operate at such a high temperature as to be the cause for damage, the very ethos of low temperature floor heating has been completely ignored in the design process. Shame on the designer who ignores this first principle. We will hunt you down and put you in the stockade.
6) Radiant floor cooling “causes condensation.”
Along the same logic as above, 100 per cent of all moisture-related complaints in buildings conditioned exclusively with air did not have radiant floor cooling to blame. Understand all buildings with all types of HVAC systems need to manage moisture for controlling biologicals, dimensional changes in hygroscopic materials, to mitigate hydrolysis, to preserve artifacts, and for thermal and respiratory comfort. If you control moisture for these far more important factors, condensation on radiant cooling surfaces becomes a moot point. As with the hardwood floor myth, the problem is moisture not temperature; sweating the details on moisture control means no sweating on any cool surface.vi
7) Radiant floor heating “causes overheating with solar loads in high performance homes.”
Have you ever placed an ordinary thermometer in the sunlight on the floor inside your home on a winter day? What does it read and what does this tell you? In my highly-acclaimed, non-government funded research project at the international headquarters of www.healthyheating.com; using a meat thermometer from the kitchen cupboard–I measured floor temperatures up to 88F (31C) through double pane, lowE glass on a cool -8F(-22C) February afternoon in Calgary. Eighty-eight Fahrenheit is about 12F (7C) higher than the fluid temperature required in a high performance home heated with radiant. Again, hot goes to cold.
Now put on your thinking caps. If the floor surface temperature heated by the sun is hotter than the fluid in the radiant system, what mode is the floor system in? Heating or cooling? Also, if the floor warmed by the sun is hotter than all the other surfaces what do you think is happening to the radiant space temperature? The room does not feel hot as a result of the embedded tubes, you feel hot because your body cannot shed its heat fast enough since the room’s surfaces are not cool enough to extract sufficient body heat. The problem is not new and neither is the solution. Gain control over solar gains and you gain control over the overheating in all buildings with all types of systems.
You will hear the myths presented above and many more as you go about designing, installing and maintaining hydronic systems. Your clients will be well served if you keep an open mind and have the knowledge to determine fact from fiction.
Robert Bean, who is president of Indoor Climate Consultants Inc., is a Registered Engineering Technologist in building construction through the Association of Science and Engineering Technology Professionals of Alberta and a Professional Licensee in mechanical engineering through the Association of Professional Engineers, Geologists and Geophysicists of Alberta. He has served two terms as an ASHRAE distinguished lecturer, serves on ASHRAE committees TC 6.1 (Hydronics), TC 6.5 (Radiant), TC 7.4 (Exergy) and SSPC 55 (Thermal Comfort) and is a recipient of ASHRAE’s Lou Flagg Award.
ii Bean, R., Olesen, B., Kim, K.W., History of Radiant Heating and Cooling Systems, ASHRAE Journal, Part 1, January, 2010
iv Bean, R. 2010. Master Yoda – The E5 Jedi, HPAC January/February
v Wood Handbook, Wood as an engineering material. General Technical Report 113. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory
vi Bean, R. 2016. The logic of moisture management: Condensation is not the dark side of chilled water and radiant cooling systems. HPAC February