In last month’s column, we discussed individual zoning controls. It is a known fact that the majority of people like a cooler sleeping environment. With a radiant ceiling in the bedroom area, recovery from overnight setbacks can occur fairly quickly if desired. This is due to the fact that the resistance value of the emitting panel is very low, as is the mass of the panel, so reaction time is fairly short.
There is a class of thermostat on the market that, when used for heating, can create a proportional flow control system, which is very conducive to energy savings and occupant comfort. This thermostat is proven on the European market and is known as a nonelectric thermostatic radiator valve, commonly referred to as a TRV.
To the best of my knowledge, they are only available for use in a heating application. There are some battery-operated power heads on the European market that can be used for a programmable setback condition, but none of them offers a wireless programmable ability, which does limit them to manual operation. I am controlling my mountain home with this type of system, and have actually set it up such that I can have remote setup control. I do this by using the TRVs to limit the upper end of temperature control. When my home is in setback condition (40°F), that condition is being controlled by an electronic thermostat that can be remotely manipulated.
Basically, the solid state thermostat controls the home below the TRV’s normal operating point, and when in normal or recovery mode, the TRVs cycle the flow back as the home approaches the TRV’s set point. Bear in mind that in this scenario I am using a modulating boiler, a modulating circulator and modulating thermostats.
During deep setback conditions, modulation is completely out of the picture because the boiler and fluids are relatively cold, all restricting valves are mostly open — causing the circulator to operate at maximum capacity — and the TRVs are typically wide open, so when the system fires to maintain the setback condition, it is running full out at an extremely high efficiency (approaching 96%).
While this is a hybrid system, I did it this way to prove that the control accuracy of TRVs can be interfaced with a deep setback control using state-of-the-art, Internet-enabled electronic controls. It is not the norm, but it is simply an option that contractors can and should keep in their bag of tricks.
Some of these TRVs can come with a remote capillary tube controller that comes in 10 meter (33 feet) lengths. This requires a little bit of advanced planning to ensure that the control valve and the thermostat location are within 33 feet of each other, but the benefits are well worth the effort. Others have a box that the TRV sits in that is recessed into the wall, requiring the zone’s supply or return line to be flow controlled from this static point.
One important note: These TRVs are not conducive for use in radiant cooling applications. Their valves would be mostly closed due to excessively warm conditions, choking flow and interrupting cooling fluid delivery. It would require that all TRVs be manually turned up to their maximum heating set point in order to allow them to have flow.
If cooling is an option, it is recommended that a conventional low-voltage (24 volts or less) control logic be used, and that numerous dew point sensors be used through the building to monitor the dew point and control the possibility of a panel producing condensate, and to take necessary actions to avoid this potential.
This will also require the use of a heating and cooling thermostat. To my knowledge, there isn’t (yet) a thermostat that can monitor and control the dew point on an individual basis, but I suspect that the market will alleviate this condition in the near future as the demand for radiant cooling increases. The thermostat that you choose can be either a remotely controlled WiFi thermostat or a conventional manually adjusted thermostat. The use of a WiFi thermostat requires a relatively stable Internet connection and, obviously, a secured wireless system.
There is a plethora of WiFi thermostats that have begin hitting the market in the past few years. Some of them can be set up to control and monitor more than just the heating system, and most of them come with the ability to graph monitored conditions, as well as send out an e-mail or text alarm if controlled conditions are outside of a given set of parameters or if recovery is taking much longer than it should.
Tune in next month as I help you continue to evaluate your options in delivering good radiant comfort from alternative surfaces using state-of-the-art controls. In the meantime, Happy New Year from the Radiant Professionals Alliance! Do something good to start the year, and join our organization!
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