One pipe steam system with Danfoss controls

Calpac1

Hey Fellow Steamers, I'm in need of some advice. Currently installed Danfoss valve w/breaker #013G0140 and Danfoss 1 pipe steam air vent #013L8011. I've already lowered the system to 2 PSI but the heat to the radiators does not turn off despite the danfoss in off position. The radiators are still hot. I've reached out to Danfoss and what they suggested is for the boiler system to have an off cycle. During the off cycle vacuum will break and air will enter back in. With that said does anyone know the minimum time the cycle needs to be off? 2hrs? 6hrs? 8hrs? It's a 32 unit apt building. Each unit has one radiator.

Jamie Hall

It just has to be off long enough to drop to zero pressure and the main vent to open. A little longer won't hurt -- but it doesn't have to be that long.

EBEBRATT-Ed

chances are you don't need 2psi. the lower you run the pressure the better they will work

Mad Dog_2

I ran in to this exact problem over 25 years ago. Dan pointed that out to me.  Another large commercial, multi-tenant building. I would up installing a Torque clock for hourly off cycles of about 30 minutes. What I found is that TRVs are often used as a Panacea (Magic wand attempt) for messed up systems. There are usually much larger issues that need to be fixed first. TRVs should be used very sparingly...a Cherry Ona Sundae...Mad Dog 

Sylvain

For a TRV to work, it must trap air in the radiator to limit the radiator heat output.
To trap air, air must first come in the radiator.
Air will come in the radiator if the pressure drops. (I guess your TRV have a vacuum breaker.)
To have regulation, that is to say to adapt to the heat losses variations due to outside temperature/solar input/wind variations along the day, the pressure has to drop regularly.

Mad Dog_2 said:

[...] I would up installing a Torque clock for hourly off cycles [...] Mad Dog 

Jamie Hall said:

It just has to be off long enough to drop to zero pressure and the main vent to open. A little longer won't hurt [...].

If all the rooms have their TRV closed because it is warm enough in the rooms, then, when the boiler starts again, it might short cycle on pressure. So the off time should not be too short.
If the off period is too long, the room temperature will drop too much and the TRV will be wide open. The radiator vents mounted on the TRV must vent slowly enough. So there is some tweaking to do to take thermal inertia into account.

Mad Dog_2

Sometimes DAYS of tweaking....Mad Dog 

Sylvain

I have read a comment about adjusting TRVs: Have an unmounted one aclimated in a room with the target temperature, blow into it and turn the button such that it will just shut. Now there is surely some variation between different TRVs and it depends how/where they are located.

Thinking again about the off time, it should be longer in mild outside temperatures and maybe down to zero at design day. But then this strategy can be used even without TRVs.

Calpac1 said:

Hey With that said does anyone know the minimum time the cycle needs to be off? 2hrs? 6hrs? 8hrs? It's a 32 unit apt building. Each unit has one radiator.

Jamie Hall has answered about the minimum off time to allow the air to fill the radiators. If the off time is too long, the tenants will complain about the temperature drop between two heating cycles.

If the 32 units are the same, the tweaking should be easier.

ChrisJ

Sylvain said:

I have read a comment about adjusting TRVs: Have an unmounted one aclimated in a room with the target temperature, blow into it and turn the button such that it will just shut. Now there is surely some variation between different TRVs and it depends how/where they are located.

Thinking again about the off time, it should be longer in mild outside temperatures and maybe down to zero at design day. But then this strategy can be used even without TRVs.

Calpac1 said:

Hey With that said does anyone know the minimum time the cycle needs to be off? 2hrs? 6hrs? 8hrs? It's a 32 unit apt building. Each unit has one radiator.

Jamie Hall has answered about the minimum off time to allow the air to fill the radiators. If the off time is too long, the tenants will complain about the temperature drop between two heating cycles.

If the 32 units are the same, the tweaking should be easier.

I adjusted mine by letting them sit in the room at the temperature I wanted and then blew thru them and adjusted it so it was throttling the flow. Not fully closed, not fully open.

It seems to give the perfect starting point and can be slightly tweaked from there. It's probably best to let it sit in the location or close to the location it's going to be installed in, in case the wall is usually cold etc.

They need to be vented correctly to work well and as has been said cycles are important. It'll keep heating whatever amount it was when the TRV closed until you stop feeding it steam and let air back in. Venting is important because if you vent it really fast it'll cause the radiator to fill too much and the TRV won't have time to react. You'll still get an overheating room. Too slow and the opposite happens.

The more cycles the better. Honestly I'd recommend 2 to 3 an hour but I have no clue how practical that is in large buildings. All of my experimenting has taken place in a small single family house. 1 cycle an hour works, 2 works extremely well, significantly better than 1.


TRV's don't fix broken systems but they do make good systems better.