CondensateTank...Why?

vaporvac

I think this question may go for all WetBased boilers, but it certainly applies to the SF Intrepids.

They suggest a condensate tank of some sort (mine would unvented, attached below the water line and just be gravity fed).

I believe Dave Bunnell has done installs without one and it got me thinking. Why would one need it? Isn't the boiler rated to make enough steam to fill the radiators, so shouldn't that amount of water fit in the boiler? I understand that the WB boilers are smaller, but are they just built needing a tank ,and thus work as a sort of on demand water steamer? I'd really like to avoid the added complexity of one, but I'd hate to flood the boiler.

Thoughts...experience?

JiminWorcester

Boiler Feed Tank

I'm assuming this is an older system with a replacement boiler? The boiler should be sized to meet the demands of the system and the system to keep pace with the heat loss. A modern boiler can do this with a lot less water in the boiler (and a lot less fuel) than the old tube boilers. If it's a big system then it will hold a lot of steam (and make a lot of condensate) so if the cycle time from a cold start is, say, half an hour, you will need to have enough water in the boiler or condensate in reserve to prevent the water line from dipping below your autofeed unit for that period of time. The boiler might be sized properly to the EDR of the system and still need a boiler feed tank, because what matters is the size of the system--it's capacity to hold steam, and the rate at which it sheds heat. If you don't put one it you will run the risk of eating your system alive with all that fresh water coming in, and if it is a gravity return then you will certainly flood the boiler.



Then again, I don't know enough about this stuff to speak about various installations, but I'm not sure how you would install a reserve tank that supplies the boiler via gravity--it seems to me that it would require a pump of some kind, but if there is a way I'm sure someone on this forum knows.

Rod

Stick to Gravity if Possible.

Hi- I would avoid a tank and pumps if I could. Both Dave Bunnell and Gerry Gill have done multiple boilers with gravity returns. Check Gerry's website as I believe he has pictures of multiple boiler setups. If you run out of water you can always add a reservoir setup.  If I was you I wouldn't be in too much of a hurry till I got every thing figured out. The vent(s) to the chimney probably one of the primary considerations as to the placement and orientation of the boilers. You then need to figure out pipe sizing and control configurations.

- Rod

nicholas bonham-carter

Gravity return

My 55 rad, 1,050,000 btu system works fine with gravity return. There is plenty of water in the peerless 211a to fill the pipes with steam. I do not have an auto- feed, but I do have a reservoir tank.

If you put an auto-feed on, it should be valved off to reveal any system leaks.--NBC

The Steam Whisperer (Formerly Boilerpro)

I think....

that vaporvac is talking about a pumpless reservoir tank piped at the water line of the boilers, equalized between the supply and return.  It may be a good idea, as these boilers do hold a small amount of water.  I have found they run right on the edge of water capacity, especially if you are downsizing the radiation with orifice plates or pushing the capacity limits by using small pick up factors.  I'd suggest at least provide the connections for it (a couple of plugged tees) and add it in later if you need it.  If the water starts getting dirty, the  boilers will throw water up into the system, and then you start having overfilled boilers.  A tank should provide a nice sfety factor for less than optimal operating conditions.

jumper

shoes too big

An plant engineer with decades of hand on experience explained it this way.

If my feet feel good in size nine shoes imagine how roomy size eleven shoes feel .

Assuming you have the room and budget, the ideal is lots of big tanks.

A condensate tank above a receiver tank so that there always an abundant supply of water to boilers without adding any fresh water. A nice touch is degassing facility. The goal is to set it and forget it.

vaporvac

Righto!

TSW nabs it again! I think that is exactly what SFs referring to. (They do mention a pumped return, but not for my VV system) I did not downsize my boiler in any way as I plan on adding a HW loop to an attached space to make it usable in the winter, so I may be good without one? I will plan for it in case that doesn't work out. I'm interested in Jumper's ideas...these tanks aren't pressurized so hopefully aren't too expensive. However, what is the de-gassing facility? I'd definitely like to set it and forget it.



As a side note, concerning the sizing...good thing I have some wiggle room as I just realized TODAY that I missed including a radiator in the EDR because I had never even noticed it before!!! It's in the Chauffeur's quarter's bathroom and I'm probably going to turn it on to help heat the basement a bit and also radiate some heat towards the floor above. I've read these new boiler heat the house instead of the basement so it might not be so toasty warm down there anymore.

Dave in QCA

Here is an excellent drawing

Colleen, Weil-McLain offers a design for a condensate reserve tank, for exactly the same reasons that you may need one.  That is the water volume in the boiler is small compared to the time that it may take for the condensate to return on a big old cast iron heating system.  It shows how it is connected and the location relative to the water line.  That is a critical point.



Some boiler feed tanks are set up with feed pumps for the boilers and also offer the capability to drive off volatile gasses such as O2 and CO2, thus helping to protect the boiler.  The plant that I managed many years ago had a large deareator tank as the feed tank.  I performed an important function on a process steam application, but also consumed a fair amount of energy in doing so.  Such systems are generally not used on heating systems and pretty much never used on a residential system.



Click on this link and go to page 19, figure 20.

 http://www.weil-mclain.com/en/assets/pdf/eg_boiler_manual.pdf 

nicholas bonham-carter

Another new idea

What about this solution for a condensate tank?

Suppose the tank is completely below the waterline with the connections to the return on it's bottom. A small air compressor feeds into it's top.

When the lwco calls for more water, the contacts energize the air compressor. Air being pumped into the tank top will force the water out of the tank, raising the level in the returns, and boiler. Most of the time the makeup tank will be idle as the gravity returns will function normally, however when the boiler is steaming hard in a cold snap, there may be a drop in waterline as the returns struggle to return enough water back to the boiler. Then the tank system helps out with a bit of extra water.--NBC

Rod

Reservoir Tank

Hi- Gerry Gill has a good article and pictures on reservoir tanks on his website.

Here's a link to it: http://www.gwgillplumbingandheating.com/webapp/p/640/adding-extra-water-to-an-existing-steam-boiler.html

- Rod

vaporvac

Thanks for link...

Thanks for the links, guys. Haven't had tome to study the WM as I got completely engrossed in GG's site. I'd like to say I'm inspired, but intimidated is a better description. There is a lot going on in some of those installs. Geez.



What I found of interest was that he talks about adding low-firing rates to the burners as if it's something to add-on.  Is this possible? They looked like atmospherics. I don't know why there aren't more options for stage-firing at the lower btus.



BTW, Riello is looking to offer their G400 series #C8554115 in a stage-fired configuration in the next year.  I'm 90% sure this is the burner I'm getting, so I'd be thrilled if one can add the controls to modulate later. I'm hoping so.



On to read the WM diagrams before taking down the ceiling around the boilers.

vaporvac

Thanks for the clarification...

Thank you, MarkS! The ones Gerry intalled could do hi and low firing depending on demand, but I'm assuming not infinite modulation.I know some burners have two firing rates, but  once it's set, one can't change it. That's not what I'm referring to, but I could be misinterpreting what Gerry wrote.

Powerflame has one they call a modulating burner (x400m) which does h-l-h, as opposed to the x400HDT (high turndown), the latter having much more modulation. Talk about confusing...I only found out about the first option last week! that's why I'm only 90% sure of the Riello. I don't feel I would need a huge turn-down, since I'm already stage-firing my boilers, but I'd like a little something since I hope to operate as a vaporvacuum system. It was designed that way originally.and there might be a marginal difference in efiiciency, delivery and comfort.



Like most tuning in, I'm anxious to hear how your MidcoLN500 install goes. I really liked everything about that burner, but it was too many pennies, especially as I would need two, and I wasn't sure it would add much more to the overall efficiency. I think it's quite a different case when using a single large boiler.

vaporvac

Linkageless

Interesting...when I spoke to Midco they say the RE4400DS HTD was also linkageless so it must be something they do for all their modulating burners. At least that's what I remember, so don't quote me on it.  I had read about that feature and they explained what it meant, but I don't have my notes with me. wonder why the other manufactures don't go that route?

vaporvac

I think you've got it!

I think you're right, Mark. Right about now I'd be very happy for that configuration, but the Reillo is only on/off . I think it works on pressure

Noone has returned my calls again today so we'll see what tomorrow brings concerning the burner and the piping.

Trying to drywall the ceiling. filthy job taking it down, but if I ever want to show the finished job it would be nice if it weren't too embarrassing!.

The Steam Whisperer (Formerly Boilerpro)

RE4400

I believe it has a standard motor and uses 2 belimo actuators to operate the gas valve and air shutter.  I think they get programmed from a computer.

Dave in QCA

2 Boilers = 2-Stage

Colleen, I just wanted to reiterate what has been said before.  Your new system with its two separate boilers, set up in a staged configuration is by definition, a 2-stage system.  Lo = 1 boiler, Hi =  2 boilers.   This will give you a LOT of control.  In fact, more control than probably 98% of residential systems.



I can certainly relate that you want the system to be the best that it can be.  Infinitely variable firing would be a great thing, but also a challenge to regulate with off the shelf components.   Someday, somebody other than yourself will be called to service your system.  You want to keep in mind that making a system that is unnecessarily complicated may not a good idea.  I worked for a CEO a long time ago who often repeated a mantra   "KISS!"  or, "keep it simple, stupid."  HA!



Pressure is one way to control your two, staged boilers.  However, keep in mind that upon EVERY call for heat from your thermostat, they will both fire until a "set" pressure is established, at which point one boiler will drop out.  During a long firing cycle, the lag boiler may start and stop several times to maintain that pressure.  Keep in mind that maintaining that pressure probably has little to do with a varying heat load.  A varying heat load results from changing outdoor temperature.  Following that thought, one possibility, but not necessarily the best or the most simple, you could install an outdoor stat that would lock out one boiler when the out door temperature is above a certain point.   Another option, and I think it is the best, because of its simplicity and the fact that it will allow the 2-stage system to respond directly to the heat demand in the space, is a 2-stage thermostat.   This is exactly how TSW set up a pair of Slant-fins he installed in a large old home.  I am trying to recall what he said, but I am thinking it might have also been a Trane system.  It was not an orificed system and at first was a little prone to imbalance when firing on one boiler.  But, this was easily remedied by partially closing all of the inlet valves, thus simulating to a small degree, the operating of an orificed system.



Two-stage thermostats are not a complicated thing.  I think that the highly favored  Honeywell Vision Pro is available with 2-stage heat control.   The way I look at it, TSW has probably considered every possible control combination that could exist and he opted for simplicity with a 2-stage thermostat.  There must be a reason.

vaporvac

Riello it is!

By George I've go it! Did it take long enough? It's Two (2) x Riello #G400 series

#C8554115 gas power burners! I already ordered them from the rockin' Karen at simplyplumbing.com

I'm giving them a big shout-out again for their absolutely stunning customer service. They've done exactly what they said they would when they said they would. I'm still waiting for some info from the local reps at Powerflame for the umpteenth time, but now it's a moot point.

Plus, for me this was by far the least expensive option. I love it when the best option is also the cheapest as it rarely seems to work out that way! In fact, that's the way it's worked out for this entire boiler/burner combo. Maybe we'll have the boiler installed by the time they arrive. Thanks all for helping me with that decision. I don't know why I got so hung up on the turn-down issue. I'll have to investigate the Honeywell Tstat.;that's the brand my current programmable one is, but not sure if it's the VisionPro.

Great to have finally made that decision.

C