TRVs on a two pipe steam system with radiators

swflood

I am renovating a Victorian that has an old steam two pipe radiator heating system. I would like to install TRVs on each radiator. Do you have any suggestions on which TRV I should use?

nicholas bonham-carter

Has there been a problem with unevenness of heating in the house?
TRV's will require the removal of the old valve, and spud, in order to install the new set, which is a chore.
Two-pipe systems can usually be balanced very well so that steam will arrive at all radiators simultaneously. Check all the radiator, and crossover traps, and replace the innards as necessary.The inlet valve to any radiator can be slightly closed down if there is over radiation in any room. The system can then be controlled by a remote sensor on a Honeywell Visionpro thermostat placed in the most exposed room.
I expect that in your renovation, you will be tightening up the building envelope/windows, etc.--NBC

Jamie Hall

Before you consider TRVs -- which are expensive and make control of the heating system as a whole very difficult indeed -- follow up @nicholas bonham-carter 's suggestions. Make sure that all your traps are functioning properly. Make sure that the main vents on the dry returns are functioning properly and are big enough. If you don't have crossover traps, make sure that the main vents on the steam mains are functioning properly and are big enough.

Then, adjust the inlet valves on radiators which provide more heat than is desired for the spaces they are in to cut down on their output.

Then. Live with it for a bit. Then, and only then, consider the possibility of installing some TRVs -- but be aware that they will almost certainly cause the boiler to short cycle on pressure, Further, remember that a TRV will reduce the heat output to a space -- but cannot increase it.

Paul_11

HERE IS WHAT I DO ALL YEAR LONG YEAR AFTER YEAR

If you don't have a condensate or vaccuum pump and all condensate returns by gravity to the boiler, then what I always reccomend for my customers is the following.
MASTER VENT THE OVERHEAD STEAM LINES
MASTER VENT THE STEAM SUPPLY RISERS.
MASTER VENT THE CONDENSATE RETURN RISERS.
INSTALL A VAPORSTAT & A 5PSI PRESSURE GAUGE
INSTALL MEPCO TRV WITH ADJUSTABLE ORIFICE RADIATOR VALVES & ADJUST THE STEAM SUPPLY TO EACH RADIATOR
ADJUST YOUR VAPORSTAT SO IT IS AT THE LOWEST POSSIBLE SETTING THAT HEATS THE BUILDING
It is the utimate in efficiency and comfort.

If your boiler short cycles when you are done, it is proof that you just made your steam system so efficient that your boiler is now too big.
To me this is just an opportunity to work on the boiler/burner so it can operate as if it was smaller.
This is easier on bigger burners, but still possible on smaller atmospheric boilers.

nicholas bonham-carter

Not sure what you mean by "master Vent" the risers, but I would think all the main venting should be at the end beyond the crossover traps.
If you space out the vents on the supply chain, the close ones, (riser vents) close too early, as steam hits them first. When they are all at the end, they stay open until all the air is out.
I like the manual adjustable orifice valves for derating any oversized radiators.
If I had a Two-Pipe system, I would be experimenting with natural vacuum, sub-atmospheric operation.--NBC

Jamie Hall

If you have crossover traps, remember that they will try to vent into the dry returns at a very very high rate -- well up to a couple of BigMouths or better, depending on the exact trap.

In my humble (?) opinion, if you have crossover traps and they are working (if they aren't fix them!!!) there is no need to vent the steam mains or the risers. However, you do need to vent the dry returns. This can be done with main vents at the ends of the dry returns at the boiler. How much main venting do you need there? Depends on the system, eh?

If you are interested in playing with vacuum, you can use Hoffman 76 vents as your main vents.

Now if you don't have crossover traps, then yes indeed, you do need to vent the steam mains beyond the last radiator takeoff, and you need to be generous with that venting. Again, in my humble opinion, risers and runouts should not need venting unless they serve several radiators -- in which case, they should be treated like, and vented like, mains, which they are.