Danfoss one pipe thermostatic valve problems

Jim_108

HELP! I,am a contractor in Washington D.C. been in the trade for 40 + years hold several masters and a 3rd class steam licenses. I was brought into a old building (the Ontario] and was asked to install some thermostatic radiator valves for the condo owners as requested. I installed probably around 40 of the valves and have been having a lot of problems with them either overheating or like today not heating at all. As an example the one I examined today was not heating at all because the vent was completely filled with water and not allowing any air out of the radiator therefore causing a no heat call. I emptied the water out of the vent and the radiator started heating again. I think the vacuum breaker inside the valve was preventing the water from running back down into the radiator somehow but not sure. I have had this happen on several of these valves. I have also been been getting service calls for overheating because the valves don't seem to close completely. At first on those calls I thought the boiler pressure was too high (4/5lb) so I replaced the cheap Honeywell 15 psi on/off control with the 4psi oz control and replaced the 15 psi proportioning pressuretrol control with the l91B control and I am now running about 7 to 8oz in the building. I have gotten a lot of complements on that re control as far as noise overheating etc. but still having a lot of issues with these Danfoss valves. By the way today on the valve with the flooded vent I installed an eight inch street tee and Macon 3901 vacuum breaker between the radiator and the Danfoss valve. Hope it works.

nicholas bonham-carter

Those TRV’s can only work properly on a balanced system, so how is the main venting?
What radiator vents are on the TRV’s? Slower vents would be better.—NBC

Danny Scully

TRVS on 1-pipe systems can be tricky. Pressure is key. It needs to be extremely low and you need to confirm this. Master venting the radiators is something to consider as well when using 1-pipe TRVS. What vents are on the TRVS?

Jim_108

NBC, thanks for responding. This building is six stories and has around 230 condos. The boiler room is in the basement and delivers the steam from there up to the attic and is distributed thru large mains running horizontally to each riser that go down to the basement again branching off to each radiator on the way down. When I was up in the attic the other day the only vents I found were on the main line shortly after it turned horizontally. They were piped in parallel on 3/4 black pipe. They were about 3" in diameter and when I tapped on the they sounded kinda hollow. The steam was off at the time. There is also Barns and Jones RK 2015-6 traps in the basement.

Inliner311

Does the boiler(s) cycle off? All TRVs need the boiler to cycle.

Also check if the TRVs tilt toward the radiator and back to the pipe, maybe the 1/8" hole was drilled and tapped at a slight angle. That could cause the water to pool in the body and the vacuum break wouldn't be able to pull all the water out.

nicholas bonham-carter

A down feed system, designed to heat the upper floor first, in the days of coal boilers, when the first steam was made in November, and continued until the spring. Now with modern fuels, and their on again off again operation, air has to be removed with every call for heat.
I think you need good big mouth vents on the drops in the basement, so the supplies are filled with steam first, and then the radiators. As it seems now, the radiators are providing the main venting for the system. When the main venting has been made right, the TRV’s may not be needed, or will finally certainly work.—NBC

Jim_108

NBC, When I went by there yesterday and found the vent flooded I installed (as stated above) the 3901 1/8 vacuum breaker on a small 1/8" street tee between the radiator and the Danfoss valve. As I was observing the radiator the boiler actually did cycle off and for the first time I could hear air being drawn into the radiator thru the vacuum breaker at a high rate. With the danfoss valves I never could hear anything close to that. As mentioned above I have installed the Honeywell L91b control on the boilers so I can control the boilers cycle rate with ease by simply reducing the time when the boilers will go into low fire and eventually cycle off on the pressure control but I believe (correct me if I am wrong) the building will be paying the price due to a cool stack having to come up to operating temperature. I am hoping the 1/8" macon 3901 vacuum breaker will help correct the issue. That's the beauty of one pipe steam as it's so easy to make these adjustments. I could change or increase the size of the three vents up in the attic because they are completely exposed but I can't touch any of the old piping because it is all covered in asbestos and it is actually in very good shape. Looks like it was put in yesterday.
DC Jim

EBEBRATT-Ed

@Jim_108
An overhead steam supply is the old "Mills System" invented b John Mills and described in @DanHolohan book LAOSH.

I realize your sending the burner to low fire with the L91B that seems the way to go for best efficiency but if your fix doesn't work skip the modulating and try cycling.

Mike_Sheppard

Fairly certain I have worked in that building before as well. Long time ago.

JUGHNE

How are the basement traps vented?

ChrisJ

TRVs need cycles, preferably 2 or 3 per hour.
Without them, the radiator will heat until the steam supply stops.

Jamie Hall

As has been said -- main venting. Only in this case, the "mains" which need to be vented are those downfeed risers -- they have to be freely venting at the bottom, which is the end. And being large, they will need lots of venting.

Then -- pressure. Absolutely no more than 1.5 psi at any time. Ideally, you would want the pressure to simply hold around 1 psi, varying slightly up and down. Never down to 0 if you can help it, never more than 1.5. If you can do that consistently with timers and switching in and out of off, low fire and high fire, wonderful. If you have to use a couple of pressuretrols (or, more accurate, 4 psi vapourstats) to do it, so be it. But do it...

ChrisJ

> @Jamie Hall said:
> As has been said -- main venting. Only in this case, the "mains" which need to be vented are those downfeed risers -- they have to be freely venting at the bottom, which is the end. And being large, they will need lots of venting.
>
> Then -- pressure. Absolutely no more than 1.5 psi at any time. Ideally, you would want the pressure to simply hold around 1 psi, varying slightly up and down. Never down to 0 if you can help it, never more than 1.5. If you can do that consistently with timers and switching in and out of off, low fire and high fire, wonderful. If you have to use a couple of pressuretrols (or, more accurate, 4 psi vapourstats) to do it, so be it. But do it...

Doing this will make TRVs completely useless on a single pipe system.

Jamie Hall

Oh? How so? How Is adequate venting and low pressure in a downflow system like this different from adequate venting and low pressure in any other system? I need to know, so I won't make the mistake again.

nicholas bonham-carter

In our neck of the woods, the installer, can remove a small amount of asbestos insulation in the course of repairs without having a specialist do it. Certain procedures need to be followed, especially with regard to disposal. Maybe there is not such a possibility in your area.
This would make it possible here to move the main venting to a location after the last radiator (lowest floor), where it would vent the whole main, and the upfeed-downfeed riser. This would get those pipes filled with steam before all radiators began to fill simultaneously.—NBC

Jamie Hall

nicholas bonham-carter said:

...
This would make it possible here to move the main venting to a location after the last radiator (lowest floor), where it would vent the whole main, and the upfeed-downfeed riser. This would get those pipes filled with steam before all radiators began to fill simultaneously.—NBC

That's what I was thinking, @nicholas bonham-carter , but @ChrisJ tells me it won't work.

ChrisJ

> @Jamie Hall said:
> Oh? How so? How Is adequate venting and low pressure in a downflow system like this different from adequate venting and low pressure in any other system? I need to know, so I won't make the mistake again.

Well, at least on my system once some steam gets into a radiator it will continue to heat until the boiler shuts down and stops feeding it. Even if you shut the trv it will keep heating the amount that is currently filled, pulling fresh steam in. The vacuum breaker has no effect. Remember, the steam is above atmosphere so the radiator has no reason to pull air back in through the vacuum breaker at this point.

Once the cycle ends and the system empties the TRV will control the next cycle. Be it not venting at all, or throttling the venting, or full venting

The TRV can stop it from heating from the start, or stop it from advancing but it cannot go backwards.

Again, this is the experience I have only on my own system but it's accurate.

JUGHNE

I worked on a '33 school with attic main, though a 2 pipe.
All air had to be vented thru 1/2" rad or drip traps into dry returns some which may have turned into wet returns because of bad new install.

Finding the ends of the largest branches in the drops, I added 5 B&J-BM air vents in 3 places, as NBC suggested above.
They are up on 4' risers with ball valves below in case a lot of water shows up. Now a 4' riser in an old classroom with exposed piping is acceptable....maybe not so in a Condo.

If you have access to the basement drip traps and do major venting there it may improve steam delivery.
The attic vents sound like they just vent the vertical riser.
I imagine there would be a F&T at the base of that riser.

On first start up of the school, I had the ball valves closed.
As the pressure just started to build and each venting valve was opened the amount of air released was impressive and the speed that the steam arrived was just amazing.
And this system still had the original air venting scheme in place.
(1/2 traps only--think coal fired boiler)
This has oversized NG boiler that short cycles much less than it used to.

I was fortunate to have the prints for this with attic piping shown. You might have access to prints for your building somewhere?

Jamie Hall

That makes sense, @ChrisJ -- so it isn't the venting but the idea that the pressure never drops to zero. I'll buy that -- thank you!

nicholas bonham-carter

No silver bullet in TRV’s, I guess. Maybe a timer to cycle the boiler to provide the needed vacuum would enable them to work.—NBC

Jim_108

Everyone that has taken their time to help me on this I just want to say I really appreashite this. Basically from what I am taking away from this conversation is that I am possibly not cycling the boilers enough and I have noticed that I have been getting more complaints on colder days. I did install the 4lb oz control on the boilers but at the same time I installed the pressuretrol L91b so I could have a long cycle by firing the boilers on low fire therefore keeping my stack hot for higher efficiency. I have the boiler cycling long on cold days but they do cycle even on the colder days but only after a rather long on cycle. They shut down at around 9 or 10oz. It would be easy for me to cycle the boiler more often by simply delaying the modulating control some which should cycle the boilers faster. When I installed the new boiler controls they were in fact cycling much faster until I watched and adjusted the burner mod control further and further down until they had a long cycle.

Jamie Hall

Have to admit that I'm fascinated by this -- since we so often try to make the boiler run as long as we can without cycling! It would seem, though, that a thermostatic regulating vent can only exercise control if it happens to be closed when the boiler cycles on. This almost suggests that if we want to have TRVs exercising reasonably close control of a room temperature, we need to have the boiler cycle off and drop to at least atmospheric -- preferably a slight vacuum at the radiators -- at somewhat frequent intervals. Like 10 to 15 minutes? (Maybe there is a use for a Cyclegard?)

Thoughts? Comments? Could this partly explain why sometimes we hear complaints that the TRV isn't controlling the space temperature -- that it overheats?

JUGHNE

There is a Danfoss tech bulletin from 12/91 concerning this problem.
"Sufficient boiler off-cycle time with negative system pressure or vacuum must be allowed to draw air back...."
"for larger installations with reset etc, a typical off cycle of at least 15 minutes per hour must be provided....or overheating could occur…."

So it seems the boiler must shut off and drop to 0 PSI.
For ChrisJ, do these work if your t-stat does the cycling?

ChrisJ

> @JUGHNE said:
> There is a Danfoss tech bulletin from 12/91 concerning this problem.
> "Sufficient boiler off-cycle time with negative system pressure or vacuum must be allowed to draw air back...."
> "for larger installations with reset etc, a typical off cycle of at least 15 minutes per hour must be provided....or overheating could occur…."
>
> So it seems the boiler must shut off and drop to 0 PSI.
> For ChrisJ, do these work if your t-stat does the cycling?

It doesn't matter what does the cycling as long as there's enough.

To me, the tstat is a little on the low side for number of cycles. It works, but they're too long both running and off for perfection.

Jim_108

Ok guys, Am I not seeing the forest thru the trees? How about I go over there tomorrow and simply lower the 404 pressure (on/off) control lower to shut down the burner at a lower pressure causing the unit to cycle more often. I have watched this boiler and it goes to zero in about 30 seconds or so.

ChrisJ

Jim_108 said:

Ok guys, Am I not seeing the forest thru the trees? How about I go over there tomorrow and simply lower the 404 pressure (on/off) control lower to shut down the burner at a lower pressure causing the unit to cycle more often. I have watched this boiler and it goes to zero in about 30 seconds or so.

I heat my small house with as little as an 1/8 of an ounce.
That doesn't mean your system will heat that low. You should run it as low as you can, as long as all radiators heat reliably and as long as it doesn't cause a lot or short cycling.

That being said, you want the system to cycle around 2 or 3 times per hour, including when it's cold out.

I don't know how your system works or what tricks you can do to cycle the system.

Gordo

Is it just me, or does it seem that too often one pipe steam TRVs are a solution looking for a problem?

That said...

I've noticed that the vacuum breakers on the Danfoss single pipe steam TRVs leave something to be desired and fail quite often, sometimes right out of the box. I've pulled them (easy to do, fortunately) and replaced them and solved a few annoying failure-to-control-the-heat issues.

More often, we've simply pulled the TRVs altogether and installed Vent-Rite adjustables.

The Macon TRV vacuum breakers seem to be better built. Well, at least they're bigger, anyway.

nicholas bonham-carter

I have always thought that TRV’s were a bandaid-often on a gunshot wound.
I feel that large main venting, and small radiator venting will even things out, so that the:
Mains fill first, then
The risers and radiators fill finally all together, giving Miss Smith on the lower floor steam, at the same time as Mr Jones on the top floor-(I know he had been used to inviting Miss Smith up to his place for warmth before!). Now she can invite him downstairs!—NBC

ChrisJ

nicholas bonham-carter said:

I have always thought that TRV’s were a bandaid-often on a gunshot wound.
I feel that large main venting, and small radiator venting will even things out, so that the:
Mains fill first, then
The risers and radiators fill finally all together, giving Miss Smith on the lower floor steam, at the same time as Mr Jones on the top floor-(I know he had been used to inviting Miss Smith up to his place for warmth before!). Now she can invite him downstairs!—NBC

Sure.
Except that everyone has different preferences as to what temperature they're comfortable at.

That also doesn't take wind, sun, stack effect into consideration.

A system must be reasonably balanced before attempting to use TRVs. That's a fact.

But, it must also cycle enough.

A balanced system with TRVs cycling the correct amount will be far more comfortable for everyone than just a normal balanced system.

EBEBRATT-Ed

Again in a perfectly vented and piped 1 pipe system you shouldn't need TRVs.

But come on. The Op has a 250 unit condo. You can't go into every unit try different vents and screw with this forever to get it to work.

Needs a pratical soulution , not a perfect solution

TRVs are the answer to prevent overheating.

I don't like cycling but that probably what it is going to need.

@DanHolohan talks about this in the LAOSH. 1 pipe systems need "drop away" pressure or the vents and vacuum breakers can't work

JUGHNE

Who came up with the idea of the TRV's?

Maybe a better solution is increase the main venting and use Gordo's method of Vent Rite adjustables where needed.

ChrisJ

> @JUGHNE said:
> Who came up with the idea of the TRV's?
>
> Maybe a better solution is increase the main venting and use Gordo's method of Vent Rite adjustables where needed.

You need good main venting regardless of how the radiators are vented or controlled.

ChrisJ

Actually, there's something that I don't quite understand.

If I have a system with a bunch a adjustable vents and the system modulates, won't all of the radiators completely fill eventually making the adjustable vents useless?

This is exactly how my system behaved on colder days. On most days the different vents kept things good but on really cold nights the throttled radiators would catch up and overheat.

Inliner311

I researched TRVs alot trying to figure out where they work and don't. From reviews and post on here, it seems rare they don't work in a house because their boilers are oversized and will cycle alot.

The issue seem to come with apartment buildings especially the larger the building is.

I do think if you can figure out a way to tilt the TRV body back to the radiators slightly, it could help solve the issue. That ways if you can get it to cycle a bit more, when it does cycle more water will be removed from the body of the TRV.

I think the addition of the Macon vac break is a expensive bandaid. To me it just seems like poking a hole in the middle of a straw, it's just going to make it harder for the Danfoss vac break on the TRV to do it job properly.

Inliner311

I'm surprised this hasn't been asked but what exact configuration are you using with the Danfoss TRV? Like what straight vent and TRV head are you using? Danfoss now make electronic TRV heads that connect via Bluetooth. If you are putting a timer in on the boiler, syncing the TRVs up with a schedule so they open when the boiler cycles off might be solution.

Jim_108

Inliner, Thanks for responding. I went to the building today and brought the pressure troll down to about 7oz so they will cycle much more often now. I really would rather a long cycle but right now I am in "damage control in a big way". I found a one hour timer that i can interrupt the control circuit with on line and I plan to install them on Tuesday. I am thinking of interrupting the burner every twenty minutes for about a 2 minutes and with the post-purg etc. the burner should be off for around 3 minutes and then restart with pre-purg.
I did check in with the guy I installed the Macon vacuum breaker and that radiator was working fine however the one in the next room was not allowing any steam into it and the CHEMICAL straight vent did not have any water in it. So I removed the valve and blew thru it a couple of times and after reinstalling it it started working ? I am going to try to find some bi-metal vents and see if they work any better but I'm not even sure that is what was stopping the air from releasing or if the little ball/vacuum breaker was stuck closed. I've been around this trade a long time and haven't had a PITA like this in many years. I also installed a Macon TRV in another unit on the 6th floor but I am hesitant to call that lady beacause she was so upset about this issue I have been trying to stay away from her. I am going to get the building manager to contact her after I install the timers. I really like the vacuum breaker and vent (bi-metal) on that valve.
I didn't walk into that building selling these trv's they called me.
Thanks
DC Jim