too many layers of control on this steam system?

Craig_8

thats exactly what I've been thinking, the Tekmar is unnecessary in this application.


more info about the system

there are two 1.6 million BTU Kewanee boilers with two stage Webster power burners. the pressure is controlled by a Heat Timer SEQ sequencer for up to 4 stages of heat (two stages each boiler. however 1 boiler enough to heat the building, so they alternate them weekly.

The zone valve for the west wing is a full port 4" valve on a 4" pipe.

the zone valve on the east wing is a reduced port (globe valve style) 1.5" valve on a 3" pipe (reducers on either side) I honestly don't know how this valve allows enough steam through and thought it was the reason for running at 9 PSI, but it still works alright at 3 PSI.

the pneumatics control individual radiators and are mostly used for (and work great at) turning off the heat to vacant rooms

[Deleted User]

too many layers of control on this steam system?

We've been working on trying to get the energy bills under control at a church that has not had proper maintenance in over 20 years.

I tested the steam traps ultrasonically and found 1/3 of the radiator traps bad and all of the F&T's bad. after replacing them i was able to drop the steam pressure from 9 PSI to 3. i have not tried going lower yet.

now im trying to get the controls in working order. building is layed out with an east wing and a west wing.
The east wing was a zone valve controlled by a digital thermostat.
the west wing has the same, but also has pneumatics in most rooms.
on top of that, the boiler has a tekmar boiler controller that runs the boiler based on outdoor temperature, time, and condensate return. it does not read indoor temperature in any way.

So for the west wing to get heat, the tekmar must be calling, the digital stat must have the zone valves open, and the pneumatic system must have the radiator valves open.

previously it was possible for the Tekmar to run the boiler even when no zone valves were open. i rewired it so that a zonevalve must be open for a boiler to run.

Im thinking that there are too many levels of control in this building and either the Tekmar or the thermostats and electronic zone valves need to go. there are occasional times when they need more heat than what is programmed into the controls, and it is too confusing for them to turn up the thermostats and turn on the override on the tekmar.

what would you do in this case?

Jamie Hall

cute

Hopefully you will get several replies on this one; we've got some really good control people on here...

But to start: the only time the boiler needs to run is when something, somewhere, is calling for steam. As I understand your description, you have two zone valves: one for the east wing and one for the west wing (I do hope they are full port valves; reduced port valves raise havoc with saturated steam). If either zone valve is open, then, either the west wing or the east wing is asking for heat: turn the boiler on. The boiler should -- and I presume does -- have either a Vaporstat or Pressuretrol; this will cycle the boiler in accordance with the steam demand. Unless I am missing something, I see no need for the Tekmar at all. One layer gone...

What do the pneumatics in the west wing do? Control individual radiators? That's OK, except all they will accomplish will be to lower the temperature in the space they control; since they don't open the zone valve (and therefore turn the boiler on!) they can't call for heat.

The only real problem I see here is that either the boiler is undersized if both wings are calling, or way oversized if only one wing is calling. Need to know more about that.

So in summary -- zone valves controlled by digital thermostats which also ask the boiler to run. Steam pressure controlled by Vaporstat or Pressuretrol. Done...

Jamie Hall

That globe valve

is killing you. a 3" gate or plug (motorized,of course) isn't cheap, but you will be able to drop the pressure -- probably to a pound or so and maybe less if you put one in, and that should make the whole thing work better.

The Heat Timer sequencer should be able to run at the lower pressure -- just set it to start at high fire and switch to low on the operating boiler at say half a pound or so, then shut the whole thing down at a pound until the pressure comes back down, cycling on low unless the pressure drops below half -- which it probably won't.

Have fun!