Boiler feed tank

EBEBRATT-Ed

I usually size the feed pumps for double the boiler steaming capacity @ twice the boiler operating pressure.

As for the tank size Brad is correct about 20 min. before the condensate comes back howeaver, you should figure the tank size so that the tank does not overflow when the condensate comes back and does not take on any feed water during the warm up time.

The legenth of time before the condensate comes back depends on several factors including the building layout. A verticle 6 floor apartment building will probably bring condensate back quicker than a one story school that is spread out. A little math, a little guestimating.


Ed

FRANK_24

boiler feed tank

FRANK_24

boiler feed tank

I did a survey of a school, came up w/5090 sq.ft. installed. Existing boiler is a wm 1088, rated for 7933 sq. ft. No big deal, we can down fire the Carlin oil burner. However, upon calling two mfg reps for a boiler feed tank, one told me 50 gal Hoffmann receiver, the other a 183 gal Shipco tank. I guess I'll keep calling other mfgs and wait till I get two guys agreeing on one size.

Brad White_9

Old Confucius Say....

Man with one watch know time. Man with two never sure...

Rule of thumb (FWIW) as I learned was that a boiler feed tank should hold at least 20 minutes of condensate return storage ("surge" capacity during morning warm-up unless you have a separate surge tank). Given that the boiler feed pumps respond to boiler low water versus tank high water, you need a bigger bladder so to speak.

Your radiation at 5090 EDR, let's say that there is another 20% for piping and pick-up? Call it 6100 EDR equivalent.

That is 1525 lbs. per hour [(6100 x 240)/960]

Divide that by 8.33 lbs. and you have 183 gallons per hour or a bit over 3.0 GPM maximum condensing rate. (Your figures may vary; void where prohibited. Not valid in Puerto Rico.)

Twenty minutes at that rate means 60 gallons minimum. (What do you know, a third watch...)

Here is where it gets dicey: Suppose what feeds the tank is a mixture of gravity (has to be some) but also some remote condensate return units? The pump and receiver volumes have to be known. If they start full near the beginning of a cycle and discharge at once back home to the Boiler Feed Tank, can you handle the volume?

If the Shipco rep can back that up, buy him or her lunch.

Now, your boiler feed rate should be 3 x condensing rate by my experience so you would have a 9.0 GPM feed pump but that is another story.

Let me know the final answer, would you?

Hope this helps.


Brad

Christian Egli_2

One size fits all?

The boiler feed tank only needs to be related to the speed at which the condensate returns to the boiler. If you don't get any juice back before a half hour has lapsed, you need an accumulating tank that can feed the boiler on its own for at least a half hour.

Ball park figures indicate you need a supply of 1 pound of water for every 1000 BTU of power you consume within the time delay, and add some margin.

Is it a sprawling one floor fifties style school with miles of pipes or is it one that has steam to air coils just a foot away from the boiler? The latter needs no delay storage tank. The most elegant solution is always to do without complex pumping schemes, except for giant vacuum pumps.

Is it a private school or a government run one?

Christian Egli_2

Too slow for you

Man, my watch says you beat me by three minutes. You win.

Brad White_9

Great Minds, Christian...

Always a pleasant association with you! But man, are my fingers tired...

Steam: The Ultimate Condensing Boiler! Just had to get that out...

Cheers!

Brad

Christian Egli_2

That's one great slogan, I like it I like it,

Brad, you came up with another good one,

Steam: The Ultimate Condensing Boiler!

Let's see, if I find a watch that has stopped a few minutes ago, can I go back and steal your credit? One day, a movie will have to be made of this Wall. Best reality ever.

Steamhead (in transit)

Frankie, do you really need a feed pump/tank?

If the system was originally gravity-return, you probably don't. If this is so, I bet you can run it on less than a pound of steam pressure.

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frank_25

A lot of questions and a lot of math!!! Here's the deal........A turn of the century church,with rectory and school built in the 50's. Two wm 1088 steam system. Each boiler with it's own header and equalizer, into a common header with three take offs. One of these is just for the school which has about 500' 6" welded steam supply in a tunnel. The return runs back from a condensate pump through the same tunnel and dumps into the common return connections at the boilers. There are four t'stats in the school, a five story building with convector rads pretty much wrapping two sides of the building. However, there aren't any motorized steam valves for the school! No one at the church/school/rectory knows why so many stats, or can answer any questions. The church & rectory returns, ( all gravity) are eventually twinned together into one common line dumping into a boiler feed tank, which feeds the common equalizer between both boilers. (Never liked that method. I always use spill traps in the equalizers dumping to a BFT.) There are two t'stats in the church, and one in the rectory. There are two zone valves in the mechanical room! Again, no one knows nuttin. The objective is to give the school it's own boiler 'cause it's being leased to the NYC Board of Ed. The Catholic school is no longer. Not enough registrants. I don't want to let the condensate tank feed the boiler. Never liked that scenerio. A second BFT is what I want to do. This system needs to be looked at with a magnfying glass as to it's control system,what is wired to what, etc. I believe all the t'stats in the school were installed to control cold spots. "You're cold on the fourth floor Sister? No problem we'll just install another t'stat. When you want heat, everyone else will get it also. If they're too hot, there are windows that open" The way it is now, it's either all rooms heated, or none. The piping for the church/rectory is another contract to investigate, then a price to repair. But back to my origional question, why does Hoffmann catalog show a 50 gal. tank, when that size appears to be too small??? I'll continue this whenI see more.

Christian Egli_2

Separation of Church and School

Essentially, everything works to everyone's satisfaction at present. However many thermostats there may be, my experience with catholic institutions is that they know how to be frugal with utilities and they are not ones to crank it up.

So now, the city school board is moving in and the bishop is rightfully worried those four thermostats will be set at 95F. Here are some thoughts.

I think individual thermostatic valves on each convector will do wonders to balance out occupied and unoccupied rooms. This type of ultra simple control works great on two pipe steam. It will rid you of overheat. There are many options for remote control and group control.

Then, you can control the boilers with a combination of outdoor reset and call for heat signals.

If everything is fine with the boiler's age and such, why not keep everything tied together? I suspect (even though it can under some circumstances cause erratic water levels) the two communicating boilers are more likely to give you a more steady demand for fresh condensate than all separate systems. Also, number crunching may show each separate boiler is not capable of heating each two new parts of the system.

The parish needs submetering.

The idea to separate the boilers really only came from the desire to control the utility bills, which is normal. Submetering is easy, one or two condensate meters will do the trick. Add a burner hour meter and you're all set to get fascinating operating data on the system; you'll also be able to track steam theft, and get reliable efficiency numbers.

Condensate metering is done all the time in district system, the concepts are no more complex than for a gas meter. It works on either gravity or pumped returns.

The advantage for you, is that you won't have to stick your neck out for dividing a system that works into two halves that may not both. It's not like you're redesigning and redoing the whole thing. And installing a condensate meter is still a nice job.

The advantage for the owner, two boilers provide redundancy that will keep a public tenant from screaming when something could go wrong with its own, single, separate but equal boiler.

Did you think of pushing for the all important trap repair / replacement work that may be needed?

About Hoffman, I don't know, just today, we gave a small Hoffman vacuum pump a good look over, and there are some manufacturing details I find disappointing. As you can guess, my hands were all over the thing.

Oh, and keep the thermostats, each, even if connected to nothing, has a way of exuding heat onto those who fiddle with it. But with secrets like this, we're getting into Da Vinci Code stuff.

Keep us posted. Photographs perhaps?

Brad White_101

Excellent point, Ed

about the feed water make-up coming on while waiting. That larger tank is looking pretty good now

Layout has lots to do with it. Having pumped satellite condensate units is another. You can tell I got burned on that point once!