Will This Boiler Have Slow Cond Return? Want to avoid a Pump.

JUGHNE

1920's 3 story, 2000 sq ft per floor schoolhouse---
Presently this 1 pipe parallel flow system is zoned off of a 1M+ BTUH, 1955 Kewanee.
The other zone is for a 2 pipe system discussed in my other posting.

The 1 pipe system has only 414 EDR connected. There are 8 capped take offs on the steam main.
The steam main has 12' of 6", 100' of 4" and then 35' of 2 1/2" dry return before dropping in the boiler room.
(Presently thru F&T then to cond pump to existing Kewanee)
There are also 3- 2" rad risers about 14' high.

The boiler will be PB 63-04, 458 EDR. 10.8 gal of water for steaming. Evap rate of 0.23 GPM.
The plan is to pipe 2-2" risers 30" high into a 3" drop header.

It seems that with 147' of pipe, a considerable amount of water is needed to just "wet the pipe" before condensate water will return. The pitch on the piping has been checked and there is no water hammer on the system ever thru the entire cycle.
I will have the chance to time the return this winter as the old system will still be is use, but wanted an early heads up on if a condensate receiver/accumulator/tank might be advisable. Hoping not to need a feeder pump.

Plenty of "A" dimension. Water line will be approx 30" off floor and end of dry return is about 8' above floor.

The air vents will be at the end of the dry return. The 147' of pipe contain 12.45 cubic feet of air.
I planned to install 5 B&J Big Mouth vents. Hoping to run the system in ounces considering the now over sized piping. (2 1/2" steam main would carry the 414 EDR).

All of the NBP and 80% of the steam main will be insulated with 1" FG.
Garden level basement is now heated by boiler jacket losses and 4" piping.
Ceiling rads are long gone.

Need to put together a price for the entire project within a few more days.
If the simple gravity return might not work I would need to allow more in the budget.

Any and all comments welcome! TIA

Jamie Hall

Shouldn't really be a problem -- the pipes only contain the equivalent of a gallon and a half of water, filled with water -- which they won't be. Filled with steam -- a few quarts.

However. If you do find that it's a concern, why not put a tank at the water line of the boiler? Connect the top to the equalizer or steam main or header or whatever's handy, and the bottom to the wet return. Don't run the dry return into it! Make it as big as you like and gravity will take care of the rest.

Steamhead

With all that pipe and only 414 square feet, you'll need to increase the pick-up factor. In "Lost Art", @DanHolohan recommends using 1.5 as your pickup. So we need to ignore the usual 1.3 pickup and insert our own 1.5, like this:

414 SF = 99,630 BTU per hour

99,630 x 1.5 = 149,040 BTUH

Then select the boiler from the DOE (gross) rating. Assuming the Peerless 63 series, this would be just above the DOE of the 63-04 (147,000 BTUH). So I'd use the 63-05L, with a DOE of 171,000 BTUH.

Is there any way to tell how much radiation was removed (old radiator footprints, etc)?

JUGHNE

The floor has been covered, my best guess of what used to be there was 800 to 1000 more EDR than the remaining 414 EDR.
There are only 4 CI rads in use, averaging about 100 EDR each.

The room above the boiler room has it's 99 EDR shut off, often with windows and doors open.
That room is included in the 414 connected. There are 2 more CI rads off/stored/capped which may have to come into service when the jacket losses drop in the boiler room.
Also the garden level basement has only the piping for heat.

The last 75' is all dry return, 35' of 2 1/2" and 40' of 4" has no take offs. About 1/2 supply and 1/2 dry return.

I will consider the larger 63-5L boiler after an actual heat loss study is done later.

Just for entertainment purposes, this is an accumulator tank at a church that has 1218 EDR with 220' of 3" steam main and 200' of 2" dry return. Boiler is a Dunkirk/Bryant of 525,000 input.
This tank was built by a welder for the gas company which changed out the boiler. The old boiler was a large? fire tube, similar to the Kewanee I hope to change for the school.




The HL comes into the back end of the tank just below the water level.
The top equalizer (not even a drip)comes from the 4" header above that has the 2 3" mains connected.
The bottom of the tank has 2 connections that go into each side of the boiler return.
The fill valve puts water into both the boiler return and the tank.
That tank is a great sludge collector and I have used a pex type wand to clean it. FWIW.

This system runs on ounces and never any water hammer and certainly never runs out of water. 90 gallons to fill to water line!

EBEBRATT-Ed

Yes. Small boiler connected to a large (in comparison) system. I would be concerned with running out of water before the returns come back. I am sure the old Kewanees held a lot of water.

On a cold start I would expect a unstable water line

JUGHNE

The old firetube boiler is 7' tall 3 1/2' wide and 6' long...plenty of water.

I have 2 thoughts on reserve tank, one is a standard compression tank with steam equalizer pressure entering the top and then the lower taps connected to the water return of the boiler.
Center of tank lined up with the normal water line of the boiler.
I removed one of these tanks from a steam system as my best guess was that it was not needed, that was correct.
Also there was no steam connection to the top of the tank, so it was ineffective for that purpose.....I kept that tank...fairly new...but it has only 1/2 FPT connections....seems small for any steam application??
And then is ASME rating coming into play with this tank...actually a water tank with max of 2 PSI steam pressure on the top of it?

The other idea was that I will most likely have to buy a 21' stick of 4" Sch 40 black and only need about 10 ' of it for other connections.
I was thinking that the remainder could be use as the reservoir pipe as shown by Weil Mclain drawings.
I will have the employ of a certified gas pipe welder for this project and he could put the appropriate taps on the pipe.
I would use 1" taps for this. Just getting the water lines set up might be critical. Any thoughts on that....long 4" pipe with reserve water in it?
Then the components are just pipe with welded fittings, not a tank.

EBEBRATT-Ed

@JUGHNE
I have used pipe for that purpose to avoid the ASME thing so that will work as long as it gives you the water capacity you need.

I am not so concerned about the condensate return being slow. With a 3 story building say 40 x 50 condensate return should be fine..........it's the low water capacity of the smaller boiler that I would be concerned with

JUGHNE

E-Ed, what size of pipe did you use for that accumulator?
I have seen the diagram that uses the 8" pipe, do you think the longer 4" would give the same effect?

From searching here and reading many old posts there were at least 2 postings of increasing water boiler capacity by over sizing the wet returns. Those were both de-bunked as not being effective. My understanding is that the larger return puts more water in the system but not in the boiler where and when it is needed.

Is there any variation of the increased return size that might be feasible?
In the pictures of existing church tank above, the entire tank is the horizontal "close" nipple of the HL.
The bottom connections hook right into the 2 boiler returns.
The equalizer from the steam header comes into the top.
The lines drawn on the tank show the boiler water line.
This system has only 3' of 2"wet return laying on the floor fed by 2 dry return drops. (first picture is before the returns were separated).
Why they did this as such I don't know....the only logic would be that the water of the tank would freely return to the boiler thru the double connection.

EBEBRATT-Ed

I haven't specifically used pipe for that purpose. Have used it for oil supply "day tanks" and buffer tanks and have made LL headers.

With a 3 story verticle building I would figure 20 min steaming before getting water back. So from a normal water level to the cut off level you would need enough water to = 20 min of evaporation including the boiler and any tank. If it gets too crazy you may need a boiler feed tank.

on another topic

I have also bought plain steel ASME air compressor tanks and used them for hot water or chilled water buffer tanks. The tappings are not always right but you can use pipe inside the tank with double tapped bushings. There cost is fairly cheap

Jamie Hall

The problem with oversized wet returns, @JUGHNE , is that the extra volume isn't where you need it -- at the boiler water line. This is why a nice tank sitting at the water line works.

EBEBRATT-Ed

agree with @Jamie Hall . Bigger returns below the water line do nothing. tank or pipe needs to be at the water line both above and below connected to the boiler return on the bottom and equalized to the steam on top

JUGHNE

I was pretty sure that was the case. I was just fishing for some other unique option....maybe not quite like the church tank shown above. Stir the pot a little and something might float to the top.
Probably on line with a 4" pipe tank for this project.
Have to measure cond return time this winter for the 1 pipe system. ....months away it seems but just around the corner.

jumper

EBEBRATT-Ed said:

@JUGHNE
I have used pipe for that purpose to avoid the ASME thing so that will work as long as it gives you the water capacity you need.

A good idea. Anything with ASME stamp invites inspector demands.

jumper

EBEBRATT-Ed said:

I

If it gets too crazy you may need a boiler feed tank.

on another topic

I have also bought plain steel ASME air compressor tanks and used them for hot water or chilled water buffer tanks. The tappings are not always right but you can use pipe inside the tank with double tapped bushings. There cost is fairly cheap

What do insurance inspectors say?

JUGHNE

This falls under the state boiler inspection domain.
That agency usually relies upon the building owners insurance inspector to make the final inspection.

The annual required inspection reports from the insurance company are shared with the State agency.
In the 10 plus years I have accompanied the insurance inspectors there was only one who inquired about combustion air and actually required something be done. (Added fan in a can type).
He also was the first one to test controls himself.

One of the first ones I was with required the 2nd LWCO-manual reset. He looked at the huge site built, unlabeled, cond water accumulator tank and commented "they said that couldn't work" and he took a picture of it. No inspector has commented or noticed it for the next 10 years as of yet.

This winter I can isolate that 1 pipe system and note the return time of the condensate. That will give me a better idea of the necessity.

I am reluctant to inquire to the state yet. This tends to stir the pot and throw up a possible red flag. However if it looks necessary I will then make a call.

This tank has been in since the boiler change out of the late 80's.