Programmable 1-pipe Thermostatic Radiator Valve (TRV)

HBH · September 2020

My house has a 1-pipe steam heat system with 14 radiators - and only one thermostat. In other words, the entire house is one zone. I would like to subdivide the house into zones using TRVs. Some rooms have multiple radiators so I'm looking for TRVs that can be controlled wirelessly by a programmable thermostat located in the room that has the radiators it controls.

The house's existing thermostat can control the base level of heat, say 68º during the day (6am to midnight) and 63º during the night (midnight to 6am). In the rooms that we seldom use, I can increase the radiator vents resistance to minimize heating - except for the radiators nearest the thermostat. In frequently used rooms, the programmable thermostats can adjust the vent resistance to allow or limit the amount of incoming steam, thus creating sub-zones in the system.

Does this make sense? And are there wireless TRVs that can be controlled by programmable thermostats?

Jamie Hall · September 2020

Sort of. Keep in mind, though, three things. First, a thermostatic radiator vent can only reduce the heat produced by a radiator, and can only do that while the radiator is heating up -- once the radiator is reasonably full of steam, it will continue to heat quite happily until the boiler shuts off.

Second, keep in mind that the vent can't turn the boiler on -- only the thermostat (or a timer, in some applications) can do that.

Third, remember that steam boilers operate in conjunction with their connected radiation. If you TRVs effectively shut off a significant part of that radiation, you will get short cycling, just as though you had an oversize boiler.

hvacfreak2 · September 2020

I looked into this a couple of years ago. Honeywell does have an actuator that MAY fit a couple of brands of TRV's. This actuator ( I don't remember the model number ) may or may not be available in the US , I'm not really clear on that. I just didn't have the cash to experiment with it either.

If I ever hit the lottery I'll experiment with making my own using a motorized ball valve between the radiator and the vent. I'd have a mesh of ( Enocean or other wireless frame ) controllers that control each valve ( Easyio has a tiny wireless controller with an analog output ). Bury that mess in a decorative enclosure or in a recessed wall enclosure.

I'd have priority zones that would open first. Based on the main temperature the other zones would open. As the main temperature reaches maximum all zones would be open for a minimum run-time. After that they would be released to control to room temp , or something like that , lol.

Yeah , I have thought about it , lol.

mattmia2 · September 2020

Another way to go about this, especially if you can get some t-stat wiring to each radiator from a basement or behind a baseboard or even powered locally from a receptacle and through a wireless receiver of some sort, would be to put a 1/2" motorized ball valve in a vertical section of pipe off of the vent tapping with a reducing ell and connect a straight vent on top of that. As long as you do your reduction in the vertical section, the condensate should return to the radiator properly.

mattmia2 · September 2020

You might want some sort of a communicating and configurable thermostat system that you could make it only fire the boiler if over a certain number of zones were calling or make it ope some dump zones if enough zones were not calling or something like that.

KC_Jones · September 2020

While this doesn't answer your question, I feel these points are valid.
1. How balanced is the system now?
2. What exactly are you trying to accomplish with this endeavor?

My reasons for asking are this. If the system isn't balanced as good as it can be first, then TRV's of any kind can end up being a disappointment. Second if you are trying to save energy by keeping some rooms cooler I will suggest you will probably spend more money keeping them cooler than the amount of energy you might save. Remember, those rooms are still in the house, so if you cool them down they now become a partial load on the surrounding rooms. The cliché of "there is no free lunch" is valid here.

Now if the desire to be cooler in some rooms relates to comfort (I do this without TRV's in my house), then I can understand what you are going for.

Regardless of all that, it is an interesting idea.

HBH · September 2020

Thanks everyone. In response to Mr Jones:
Years ago, I balanced the system based on the size of the radiators in the rooms (Dan Holohan's method). When we were a family of 4 and occupied the entire house, this worked well.

Both kids are now out on their own (must have done something right) so the house is now twice the size we use. I've increased the vent resistance in the unused rooms and balanced the remaining radiators. Overall, this probably makes the boiler a bit oversized for the working system, but it works.

I use a Nest programmable thermostat and the system responds well on a day/night schedule. Now, I'm curious if I can create sub-zones in the system so there's more control of how much steam goes to the radiators in different rooms at various times of day. It doesn't sound like there's a 1-pipe system TRV that will do this on a programmed schedule.

Plan B -Install regular TRVs and adjust them manually. This will be more hands-on since it means adjusting the TRVs over the course of each day.

Or Plan C - Check the balance on the smaller system and live with it. It doesn't feel like I'm getting the most efficiency out of the system though.

Programmable 1-pipe Thermostatic Radiator Valve (TRV)

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