one pipe steam with air handler

Dave Grabowsky

I have a situation where I have hooked up 3 small one pipe steam coils to an air handler. There is lackofheat transfer and considerable banging in the lines. I will use one of mycoils as an example. This coil is sized for 1600 cfm and 80,000 btuhs through the coil. This should be a delta tee of 45 degrees. The most I can reach is delta tee of 25-30 degrees. In addition the banging of the piping is so bad I have replaced the air vent after 2 days of use. I have the coil installed with the headers above and below the coil.Th Online Store | Find a Professional | Heating Q&A | Steam Problems | Questions | Dan's Reading List | Virtual Trade Show | Library

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I have a situation where I have hooked up 3 small one pipe steam coils to an air handler. There is lackofheat transfer and considerable banging in the lines. I will use one of mycoils as an example. This coil is sized for 1600 cfm and 80,000 btuhs through the coil. This should be a delta tee of 45 degrees. The most I can reach is delta tee of 25-30 degrees. In addition the banging of the piping is so bad I have replaced the air vent after 2 days of use. I have the coil installed with the headers above and below the coil.The piping and the connections are 2'. I have a full port 2" belimo slow acting modulating valve below the headerwhich takes appoximately 3 minutes to open. Of corse this should allow steam up into the coil as wellas condensate to fall into the pipe.I also have 2 connections at the top of the coil. One side has an air vent. The other side of the top of the coil has an 1/2 " connection with piping running parallel to the coil with a 1/2" Belimo valve in line and the piping connecting upstream (or below) the coil and steam valve. This 1/2" valve is considered an on/off valve but will take one minute to open.As the min steam valve begins to modulate open it is approximately 1/3 rd. open when the 1/2" valve is fully open. As the main steam valve opens halfway there is minimal noise. From halfway to full open there is considerable hammering and shaking of the coil. The steam pressure entering the coil is 3#'s.My steam consultant had me remove the air vent and in its place put an Armstrong rv4-s one pipe steam valve with an sv-12 air vent and lv-4 operator. This didn't seem to help much. His advice to me is to better synchronize the 1/2' secondary valve to open quicker in relation to the 2' steam valve.
I need help ASAP.I have an area that cannot heat properly and is being water hammered to death. What should i do?
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e piping and the connections are 2'. I have a full port 2" belimo slow acting modulating valve below the headerwhich takes appoximately 3 minutes to open. Of corse this should allow steam up into the coil as wellas condensate to fall into the pipe.I also have 2 connections at the top of the coil. One side has an air vent. The other side of the top of the coil has an 1/2 " connection with piping running parallel to the coil with a 1/2" Belimo valve in line and the piping connecting upstream (or below) the coil and steam valve. This 1/2" valve is considered an on/off valve but will take one minute to open.As the min steam valve begins to modulate open it is approximately 1/3 rd. open when the 1/2" valve is fully open. As the main steam valve opens halfway there is minimal noise. From halfway to full open there is considerable hammering and shaking of the coil. The steam pressure entering the coil is 3#'s.My steam consultant had me remove the air vent and in its place put an Armstrong rv4-s one pipe steam valve with an sv-12 air vent and lv-4 operator. This didn't seem to help much. His advice to me is to better synchronize the 1/2' secondary valve to open quicker in relation to the 2' steam valve.
I need help ASAP.I have an area that cannot heat properly and is being water hammered to death. What should i do?

Ken_40

Dave,

The first thing you should do is check out the dis-combobulated message we see, and are having a tough time deciphering.

Without understanding exactly what you are explaining, I'd bet lunch the pressure and dimension 'A' are excessive. If you run more than 3# of pressure, the unit heaters bottom(s) better not be lower than 10-feet above the boiler water line!

We can help, but not without a brief, intelligible narrative.

ttekushan_3

Single pipe air coils

are a bit dicey if you expect a counterflow set up to work.

PLEASE POST A PHOTO OF THE CURRENT ARRANGEMENT. A picture's worth a thousand words. Especially those words :-)

The rv-4 is going to act virtually identically to the original air vent. The problem is with either with the way its piped or the length of time it takes for the valve to open in a counterflow (steam and water flowing in opposite directions) set up due to the increasing turbulence as the valve opens with water stack up above it. Probably both.

I'd prefer to see the 2" inlet and modulating valve at the TOP and the 1/2" increased to 3/4" or 1" exiting the BOTTOM and run into a wet return (below boiler water line). This acts as a condensate drain that prevents the turbulence of counterflow. The vent should be placed on a riser coming off this 3/4" drain line. Include a check valve on this line in the direction of condensate flow to the wet return, being sure that the air vent is before the check valve. DO NOT USE THE THERMOSTATIC VENT IF IT DOES NOT INCLUDE A VACUUM BREAKER. Closure of the modulating valve can literally crush the coils under vacuum.

The long and short of it is, that coils of this type must have the condensate drained separately from the steam inlet or you get the problems you have. Coils generate huge amounts of condensate for the size of its passageways. You want to get the steam, condensate and air moving in the same direction, top to bottom, through the coil.

Brad White

Let's step back a bit

The use of one-pipe steam and heating coils is one of mis-application in my opinion.

One pipe steam cycles on pressure (as to all boilers of course) and run best on the lowest pressure you can control to. They also down-cycle, meaning go to zero pressure in mild weather, especially if connected to higher mass cast iron radiation.

In-Unit coils tend to be copper tubes and aluminum fins, decidedly low mass. With air blowing across them especially, the volatility of heating control is extreme. They cool off almost instantaneously when steam is removed. Thus you find yourself running the system at higher pressures fighting it's desire to be low pressure and to aid in condensate return. Is there ever enough "A Dimension?" he asked, rhetorically.

The correct application for air coils in my experience is 2-pipe steam for a number of reasons:

1) You may have control valves and probably should if individual units. Control valves and one-pipe steam have an ongoing feud dating back over a century. Don't use them.

2) Given the need for control valves, the pressures required are higher to overcome the valve authority pressure drop. Generally at least 2 PSIG is needed in the coil to allow room above vacuum production and to meet the coil rating. Some manufacturers want to see 5 PSIG in the coil. Add the valve pressure drop to that and you need to operate the boiler at 5-7 PSIG. Not a good thing with a one-pipe steam boiler trying to return condensate reliably and quietly.

3) The separate path of condensate return in two-pipe steam makes this all come together. A high demand (control valves open) and the need to return spent steam (condensate) to not have to wait for one-another to finish.

I would suggest a re-pipe to 2-pipe steam. Otherwise you are polishing a sneaker.

ttekushan_3

Brad--you say, \"

you are polishing a sneaker."

very diplomatic ;-)

BTW, lots of good info in your post. I presume some of these issues are why a check valve is always shown in manufacturers piping instructions.
-Terry

HWK

one pipe steam w/ah from 1-6-07

MR GRABOWSKY,S SITUATION IS SOMEWHAT ABNORMAL IN TODAY'S WORLD OF 2PIPE STEAM. BUT I THINK IT CAN BE SOLVED.
PROBABLY THE EASY THING TO DO WOULD BE TO CONVERT IT TO A 2 PIPE SYSTEM. HOWEVER IF THE REMAINING AREAS OF THIS BUILDING ARE SINGLE PIPE STEAM THEN I WOULD THINK HE PROBABLY WOULD LIKE THIS APPLICATION TO BE ONE PIPE ALSO.
IF THE REMAINING AREAS OF THE BUILDING ARE RADIATORS AND ARE LOCATED ON DIFFERENT LOWER FLOORS THEY AT ONE TIME WORKED FINE AS INSTALLED AS SINGLE PIPE. IT SOUNDS LIKE WHAT HAPPENED HERE WAS THAT THE TENNNANT WANTED TO ADD AN AIR HANDLER SO THAT COOLING COULD BE ACHEIVED. IF THIS IS A/H IS ON A TOP FLOOR THEN THE PRESSURE WOULD NEED TO BE THE GREATEST AT THIS POINT TO GET THE STEAM TO THESE 3 ZONE VALVES.

HWK

one pipe steam w/ah from 1-6-07

MR GRABOWSKY,S SITUATION IS SOMEWHAT ABNORMAL IN TODAY'S WORLD OF 2PIPE STEAM. BUT I THINK IT CAN BE SOLVED.
PROBABLY THE EASY THING TO DO WOULD BE TO CONVERT IT TO A 2 PIPE SYSTEM. HOWEVER IF THE REMAINING AREAS OF THIS BUILDING ARE SINGLE PIPE STEAM THEN I WOULD THINK HE PROBABLY WOULD LIKE THIS APPLICATION TO BE ONE PIPE ALSO.
IF THE REMAINING AREAS OF THE BUILDING ARE RADIATORS AND ARE LOCATED ON DIFFERENT LOWER FLOORS THEY AT ONE TIME WORKED FINE AS INSTALLED AS SINGLE PIPE. IT SOUNDS LIKE WHAT HAPPENED HERE WAS THAT THE TENNNANT WANTED TO ADD AN AIR HANDLER SO THAT COOLING COULD BE ACHEIVED. IF THIS IS A/H IS ON A TOP FLOOR THEN THE PRESSURE WOULD NEED TO BE THE GREATEST AT THIS POINT TO GET THE STEAM TO THESE 3 ZONE VALVES.

HWK

con,t from earlier

it also sounds as though the coils where installed vertically with a 2"main w/a modulating valve at bottom inlet of the coil and also a 1/2 on /off valve piped with a vent at the top of the coil.i'm thinking outloud but i wonder if it would make any difference with the open timing of the 2 valves?. ridding the condensate from the coil here is the problem with the amount of steam pressure required to this point.i also wonder if his valves are piped in the horizontal or vertical? this is an interesting situation. i'llkeep watching for solutions

Christian Egli_2

Oh, it's the same post

Check out one pipe steam revisited, same post, but clearer

http://forums.invision.net/Thread.cfm?CFApp=2&Thread_ID=43874&mc=4