Most efficient method to heat multi-unit building with steam boiler?

GBC_illinois

I'm wondering what advice people have to most efficiently and comfortably heat a 15-unit coop building with a 2-pipe steam boiler. Through other threads, I've heard about completely different control schemes that I had no idea existed, so I feel like I'm starting from 0.

Here's the system setup:

• 15-unit, 3-story + basement, owner-occupied coop building.
  
• Weil Mclain "LGB-9 Series 2" 2-pipe steam boiler was installed in 2011, replacing an older steam boiler.
  
• When they replaced the boiler in 2011, before my time, they replaced the old gravity feed with a condensate tank and pump (unfortunately).
  
• Boiler is probably oversized by 25%+, with estimated total radiator EDR of 2062.
  
• Boiler currently operates on a Vaporstat that I have set to between 4oz - 12oz of pressure, and this effectively heats all radiators silently without water hammer issues.
  
• There are no separate heating zones in the building.
  
• Every radiator has a Danfoss RA 2000 thermostatic radiator valve
  
• Radiators DO NOT have steam traps (not even the pinhole kind for vapor systems). The only steam traps are F&Ts at the end of the main lines immediately before they return to the condensate tank. We do not plan to install steam traps as I believe this would be prohibitively expensive, and the current scheme results in the basement being pleasantly heated by the condensate return lines.
  

Here is our current control setup:

• A simple Ranco thermostat, set to keep the indoor temperature in a common room at 74-76 degrees.
  
• There is no timer function.
  

Here are the problems we are trying to solve:

• In an ideal world, we would be able to keep all the radiators in the building warm (if their individual Danfoss RA 2000 valves are not satisfied) from late fall through early spring. Currently with the indoor thermostat setup, the boiler will fire for a period of time until the thermostat is satisfied, then shut off for hours until the indoor temp drops enough. During this down time, the radiators turn cold. Note that we would not pay more in gas usage to achieve this "always warm" state. If we can't keep the radiators always warm in a cost-efficient way, then having them warm at specific and predictable times would demystify the boiler operation for the unit owners.
  
• As far as I know, the current boiler setup only allows 1-stage firing, which because of how oversized the boiler is, results in short cycling. The off cycle is less than one minute before it reaches the cut-in pressure threshold and fires again. Once the 12oz pressure is reached, it would be great if the boiler could fire at a "simmer" to just maintain that pressure, rather than the flame going out and firing again at full blast a minute later.
  

So my main questions are:

• Is 1-stage firing all that my boiler can do? Is there a method to put it on "simmer" once we reach pressure, and if so, what controls or components are necessary to achieve it?
  
• Some people like @pedmec and @Long Beach Ed have mentioned heat-timer products, rather than a thermostat, to control the boiler, but I do not understand how these work, or how they would be any more efficient or comfortable than a thermostat, even after reading their web pages. It sounds like they keep the boiler on for a certain number of minutes each hour, depending on outside temp? Can someone explain what that is like in practice? I.e. are the radiators then "always warm", but hotter if its colder outside?
  

I really appreciate any answers you experts can provide!
-Flynn

GBC_illinois

Here are some pics:

EdTheHeaterMan

As far as I know, The LGB boiler's burner design does not make allowances for lower firing rate. The combustion side of that boiler is only On and Off operation. Weil McLain tech support may have some information that might help in determining if there is a minimum firing rate for the LGB 9 that is somewhat lower that the standard firing rate, however, I do not believe it will be enough to get to your desired "Simmer" firing rate.

Pumpguy

I can only comment on the condensate pump and tank. Is this a boiler feed unit or condensate return?

The difference being a condensate pump is "dumb", running start/stop on demand of a tank mounted float switch while a boiler feed runs on demand of low water controls on the boiler.

There is a good possibility that with piping changes, this pump set is not needed. Others will provide more details.

Jamie Hall

A rather difficult control problem. However, by no means insurmountable. You are fortunate that you are using steam heat with radiators, since you can take advantage of the fact that the radiators take time to cool off.

Others will have other thoughts, but I would approach this (in terms of boiler control) by controlling the boiler on time with a timer governed by the outdoor air temperature, such that as the temperature dropped the on time would, correspondingly, increase and the off interval would be shorter. I'd select a total time (on plus off) so that the radiation which was on at the time would be still warm, but not hot, even with the longest selected off time. Then I would control the cycling within the boiler itself with the vapourstat, as you are doing. This is necessary (in my view) because of the completely random nature of the actual connected load at any given time,

GBC_illinois

Pumpguy said:

I can only comment on the condensate pump and tank. Is this a boiler feed unit or condensate return?

The difference being a condensate pump is "dumb", running start/stop on demand of a tank mounted float switch while a boiler feed runs on demand of low water controls on the boiler.

There is a good possibility that with piping changes, this pump set is not needed. Others will provide more details.

I am not familiar with the difference between the setups you mention, but I can say that the pump is controlled by the boiler water level. Even though I am not educated enough on the matter, my hunch is that you are right that we could ditch the pump with piping changes. I am almost certain that with our old boiler, there was no pump, and our overall system gets condensate draining very quickly back after the steam starts being produced. If I knew enough about this subject and could be confident I wouldn't mess our system up, I would love to return to pure gravity feed. The local HVAC contractors here (and I've spoken with 3 of them) do not seem to understand enough about how the old systems work to be confident piping a gravity return.

veteransteamhvac

I help maintain an LGB-8 that is equipped with a dual stage valve that permits hi/low firing and operates as such. It's my understanding that the boiler was not originally configured this way and WM was involved in the change. WM should be able to advise you and your technician how to proceed.

This boiler is in a large, single family dwelling and is also significantly oversized. The hi/low firing requires adding an additional pressuretrol/vaporstat to control the drop to low fire. I see from one of your pictures that you already have installed an additional pressuretrol, are you certain you are not already set up for this?

The boiler tends to short cycle (still) as well, but the owner has devised an external timer scheme that extends the time between cycles. As WM coordinated the hi/low fire change I assume they are comfortable with the stack temps on low fire.

veteransteamhvac

Fdarby82 said:

Pumpguy said:

I can only comment on the condensate pump and tank. Is this a boiler feed unit or condensate return?
....
There is a good possibility that with piping changes, this pump set is not needed. Others will provide more details.

....... I would love to return to pure gravity feed. The local HVAC contractors here (and I've spoken with 3 of them) do not seem to understand enough about how the old systems work to be confident piping a gravity return.

The LGB-8 I help maintain also has a similar condensate/feed tank situation. I was just there today cleaning the feed float opening as it had clogged. The tank itself is rather gunked up with sludge as it has not been drained in quite a long time. Keep this in mind that regular flushing of your return/feed tank is necessary, though I like the design of your tank much more in this regard.

Certainly you could return to gravity piping as long as the delay in condensate return doesn't cause low water situations which will cause overfilling. The WM LGB installation manual has an entire page devoted to proper return/feed tank sizing and capacity. In some instances city building code specifies the need for a receiver tank.

pedmec

Found the thread. The heat timer control is basically an advanced thermostatic control that uses an algorithm to determine the length of time to run base on outdoor temperature. Because it doesn't read internal space temperature (your in a building, hard to measure a true central temperature) it uses a temperature initiate/ time run cycle. Depending on the outdoor temperature it will run longer as the outdoor temperature gets colder. When set up correctly, it has a warm up period that allows the steam to reach the farthest radiator of the building before starting the heating cycle. It also automatically turn on for the winter season and shutdown for the summer.

The good thing that you have going for you is thermostatic radiator valves. You should be able to tweek the boiler set up as the season progress's to determine the best settings for the control if you were to install. you state out with more than you need and then start reducing the run time until you reach sort of an best case scenario. The thermostatic radiator valves will prevent overheating provided they are functioning properly. The draw back is that if you have bad thermostatic traps it will create a problem on setting the control. this just a short summation of the control. It is so much more involved.

pedmec

i just notice that you said there is no thermostatic traps on the radiators. disregard that last line

Long Beach Ed

Flynn -

You seem to get into this stuff, so let me direct you right to a Heat Timer installation manual. This will tell you all you need to know. You can go to there site for the sales fluff... You should enjoy this. Check out the wireless averaging indoor temperature sensors with 10-year batteries.

https://www.heat-timer.com/wp-content/uploads/2022/09/Heat-Timer-Genesis-Manual-Rev.C.pdf

Of course there are different models with different features and prices...

If you are curious about how all this came about and the basics, here's an ancient mechanical HeatTimer control on ebay that pretty much walks you through the electro-mechanical granddaddy of this stuff:

https://www.ebay.com/itm/265577795000?hash=item3dd5ab8db8:g:CGQAAOSw0VJhW8fG&amdata=enc:AQAHAAAAoLkYESjC87bnpmQnyfjCT8niJC8xxqYqSSoPEN4N7TAit6HaQ17XMuIEIe0ZE9H0PS/rAvmwq6YqdtrfQJ7cofhJqYhOWq6vtwtNU8xrRweb1OT/IITSTxP4I77YN7TUaxhxgNpb0Smf6Q1HelXzHJDF1qSCdZ3UMlLUPBT74cKcDWn+Nw2hUsONitYAlW5d4D9lMu8IhNsvshuSpab602o=|tkp:Bk9SR5Su96idYQ

Eddie

GBC_illinois

Long Beach Ed said:

Flynn -

You seem to get into this stuff, so let me direct you right to a Heat Timer installation manual. This will tell you all you need to know. You can go to there site for the sales fluff... You should enjoy this. Check out the wireless averaging indoor temperature sensors with 10-year batteries.

Eddie

This was very helpful, thank you. I have a good idea now of how it works and what the resulting experience would be if we installed it. I'm all for it, but we are presently considering whether or not to spend the ~$5k - $6k to get one and install it.

Steamhead

Sure that's not a Richardson or Kriebel system, with special return elbows instead of traps as described in @DanHolohan 's book "The Lost Art of Steam Heating"?

Where is this located?

clammy

How about a Honeywell t 10 thermostat using wireless sensors installed in each apartment ,you would then use them as a temperature averaging and have the t10 mounted where your ranco etc is presently mounted . You would disable the thermostats own sensor and use the wireless remote sensors . The only issue may be the danfoss trv and the few tenants who like it cold . If better control is needed at the radiators to control steam passing into the dry returns then possibly installing orifice plates in the supply spuds and of course size them for about 2/3 of the radiator edr which should solve any steam making its way through the radiator . Even though trv Does have a small orifice they are not the same as a real orificed valve or a orifice plate and they do not throttle there open or closed . I have seen them feed enough steam to pass to the dry return again on systems without traps and of course cause issues . If not placed in all apartments then the worse ones. I ve used them on similar applications as yours and had great results ,where I ended up just disabling the fairly new heat timer and within one month the building owner was amazed and his fuel reduction and no more open windows and short cycling on pressure due to run time initiated by the heat timer once heat was established stupid set up in my mind but it works fine for some . I find the indoor feed back from spaces being served as a better more realistic approach . The ranco could be re purposed and re programmed as a warm weather shut down control just move the sensor to the outdoors and mount in a box.
As for the condensate pump and receiver there could be issues as to why they installed like lose of water seals or possibly as a cure for low water content boiler and to reduce boiler cycling off on low water before the system has fully heated and started to return condensate . Who knows but in some cases having a boiler feed pump and tank isn’t the worse thing it does it job keeping the boiler w the correct water line and also prevents the boiler from cycling on low water while waiting for condensate to return by gravity . It s a slippery slope if gravity was in place originally I would think boiler water content might have been the issue in which case a gravity Reservoir tank sized and installed properly would have been the ticket . The biggest up side of the reservoir tank is zero moving parts no pumps and seals and for maintenance installed properly a good flushing and wanding and your done , just a matter of adding enough water volume .
It s all in a bag of tricks called experience
Peace and good luck clammy

GBC_illinois

Steamhead said:

Sure that's not a Richardson or Kriebel system, with special return elbows instead of traps as described in @DanHolohan 's book "The Lost Art of Steam Heating"?

Where is this located?

I am familiar with the Richardson system you refer to, but not Kriebel. We have replaced or repiped a few radiators, and I carefully inspected the return piping to see if there is one of these pinhole elbows. I have not seen one yet. Also, I haven't encountered a radiator yet where the condensate pipe (even a foot or more downstream from the radiator) didn't get to steam temperature. So, in short I'm fairly certain that we don't even have those return elbow traps, I don't think we have any at all.

This is a 15-unit residential coop built in 1920 in Champaign, IL.

Mad Dog_2

I think that TRV is in the wrong position on  the radiator.   The handle should be horizontal not vertical.   In that position. It may not shut off when you want it to. The Literature for Danfoss and Tunstall say that I'm pretty sure. Noel Murdough RiP one of the great Deadman, told me that And he explained the reason and it was something about The Steam continuing to be drawn up in to the open chamber.  An Engineer could 
'Splain.  Mad 🐕 Dog