At the end of last month's column (Hydronic Radiant Heating Options, Part 4), I promised I would tell you about the results of the operational efficiency tests of radiant glass. What Kansas State University found was quite interesting. They determined that at 115°F room glass temperature and an outside air temperature of 10°F, roughly 85% of the energy produced came into the room, and the balance was lost to the outside environment.
On the outset, that does not appear to fare all that well. We have natural gas powered hydronic heating systems with sources approaching 99% efficiency. Why would someone want to employ a system that was less efficient than other methods with an inherent energy cost that is two to four times as expensive as a natural gas alternative? Keep reading.
Bear in mind, this test was performed at the maximum allowable worst-case operating conditions. Under normal circumstances, here in the Rockies, that occurs about 2% of the time. So, if the glass is treated like a hydronic heating system and the heat emitting surface temperature is changed to consider the room's real need for heat and indoor versus outdoor temperature, it is possible to reduce the glass surface's operating temperature significantly.
This reduces to a minimum the back losses of the glass, all the while making the window thermally opaque to the transfer of heat from the inside of the room to the outside. By raising this normally cold “heat sink” surface, the mean radiant temperature within the room to which the window is “looking” is raised significantly. So much so, that KSU estimates that the room air temperature will have to be lowered in order to maintain the delicate balance of human comfort.
The potential energy savings associated with this product are significant. There is the ability to make the window virtually disappear as it pertains to heat loss, which typically is between 25% and 50% of the average building heat loss. The product also has the ability to significantly raise the room's MRT, resulting in a possible reduction of the operating air temperature, all the while raising the human comfort factor significantly.
I don't know about you, but I really don't know anyone who can put a price on comfort. But I do know some lawyers who have put a price on discomfort. People don't buy “BTUs.” People buy comfort, and comfort can be priceless. I've said it before, and I'll say it again. We're not in the heating business. We're in the comfort business. And my definition of being comfortable is not being aware of your surroundings. You are not hot, you are not cold, and you don't hear your comfort system in the background. You are simply comfortable. Hence, I will not address the calculated BTU per sq. ft. output factors found during the testing at KSU because research on its overall impact on the human comfort factor is still ongoing. Therefore, the 85% efficiency number is irrelevant at best.
Suffice it to say it appears that the glass saves much more energy than it consumes due to its overall effect on the people inside the building.
Research is a never-ending proposition. They continue to discover new things about this technology and as they fine-tune these discoveries, test them and confirm their thoughts and findings, it continues to impress me as one of the greatest energy saving human comfort devices available on the open market today. It holds the potential of being coupled with solar PV, hydrogen fuel cells, wind generators and virtually anything that can generate DC power, up to and including 48 V under the current listed approval.
Take for example a hydrogen fuel cell. The cell generates electricity from a device called a PEM, which stands for proton exchange membrane. This voltage varies as a function of the amount of hydrogen being moved through the PEM. At its peak, it will be about 48 V DC for most residential sized hydrogen fuel cells.
Normally speaking, in order to use the power produced, it has to be run through a DC to AC inverter. This will cost a minimum of 5% of the electricity originally generated due to inverter inefficiency. If the windows are allowed to use the DC electricity directly off of the PEM, it avoids the 5% efficiency loss, thereby boosting the efficiency of the hydrogen fuel cell by 5%, which is huge in the world of hydrogen fuel cell efficiencies.
Tune in next month as we continue to discover the intricacies of a see-through diodic resistor and make an earth-shaking announcement.
Until then, keep your hands off the glass and on the steering wheel.
Mark Eatherton is a Denver-based hydronics contractor. He can be reached via e-mail at [email protected] or by phone at 303/778-7772.