Why Radiant is Considered “Greenest” of the Green Comfort Delivery Technologies
For many years, radiant heating – especially hydronic-based radiant heating – has been recognized as the most comfortable means of providing heat for human comfort. Clear back when hydronics first made its appearance on the market, its vapor-driven predecessor steam had already been recognized as the most comfortable heating system in the world. Radiant heating was understood by the engineers and scientists of the day but not really by the end user, other than the fact that steam and hydronic homes were much more comfortable than their counterparts.
As time went on, the scientists and engineers realized that numerous components affect ahuman’s feelings of comfort. All three of these major players are invisible, so it is still hard for people to grasp the concept until they have had a chance to experience these comfort conditions or, worse yet, the lack of these comfort conditions. These three invisible factors are the mean radiant temperature, air temperature and relative humidity. When all three of these components are in perfect alignment, the human comfort level is at its highest.
The largest influencing factor for overall human comfort is the mean radiant temperature, or MRT for short. Simply stated, this invisible force is the average of the surface temperatures surrounding the human body. If it is not controlled, it can also negatively affect human comfort on both ends of the comfort scale (heating and cooling). The human skin has 165,000 (plus or minus a few thousand) temperature sensors built into its surface. It can detect minor changes in MRT, which may eventually affect human comfort. Anyone who has walked down a frozen food aisle in a grocery store has experienced what is commonly referred to as “Cold 70.” We Americans are so focused on air temperature that we have forgotten to pay attention to the MRT. As you are walking through the store, grab an air temperature-sensing thermometer from the hardware aisle and note the air temperature. Also note your comfort conditions. Are you hot? Are you cold? Are you comfortable?
Now, go to the frozen food freezer aisle and stand there and do the same thing. I think your brain will tell you that although the thermometer tells you should be comfortable, in reality, it feels rather cool. Now, you have experienced “Cold 70.”
In order to attempt to control the MRT with heated air, the rooms becomes insufferably warm, so using air temperatures to influence the MRT is out of the question without creating conditions of significant discomfort. Controlling the radiant energy and the MRT are the primary keys to delivering a good human comfort experience, and not all humans are the same. Some prefer a lower MRT, and some people prefer a higher MRT depending on numerous variables including, but not limited to, physical activity, age and the type of clothes being worn.
The key to utilizing these known radiant factors and using the alternative energies available from alternative energy sources is controlling the MRT. Although it might be feasible using the Solar PV system along with an electric radiant panel, the better alternative would be to use hydronics to affect and control the MRT within a given space. And don’t just focus on the floors as your radiant heat-emitting surfaces. Any reasonable surface (walls, floors, ceilings, countertops and even windows) can be used to influence the MRT within a space, and all of the alternative energies (solar, ground-source heat pump, hydrogen fuel cell, combined heat and power) have the ability to generate fluid temperatures that can be used with these fluid delivery systems.
In order to utilize these low-temperature fluids (120-140 degrees Fahrenheit range) it will be necessary to use one of many heat transmission plate systems currently available on the open market. Every hydronic radiant tube manufacturer provides some means of directing the fluid temperatures to the heat-emitting surface using conductivity as the primary means of energy transfer. And if you didn’t realize this before, conductivity is the king of primary heat transfer methods.
Lower operating temperatures must be handled with tighter tube centers/tube density, but can still be configured to positively and significantly affect the MRT within a given space. It all starts with proper design and eventual application. If you are interested in learning more about radiant heating, cooling and ventilation, go to www.radiantprofessionalsalliance.org and become a member today!
We are in the process of helping to restructure and amend the Uniform Solar Energy Code to include hydronics. We are also preparing to provide certification programs for designers and installers based on our 20-plus years’ worth of experience, and we want you to become a participant in our effort to deliver excellent comfort and efficiency. Don’t delay, join today! We are also making snow-melting systems green where possible by grabbing the free solar energy that falls on these large, hard, conductive surfaces during non-snow-melting seasons, and utilizing this free resource for the preheating of DHW, pool and spa heating, as well as anything that can use temperatures in the 120-to-140-degree Fahrenheit range.
The RPA is a 20-year-old nonprofit organization dedicated to the use of radiant and hydronic heating and cooling systems on residential, light commercial and heavy commercial buildings.