steam system piping

hvacdmia2

A couple of months ago I posted here about converting a steam system to hot water, the decision has been made, finally, going back with steam. It’s a 2 pipe system with mostly cast iron radiators and traps. The owner complains of very high heating bills and some areas not heating at all. This is a 10,000 sq. ft. 3 story house in Iowa. I’ll try to explain how the piping is now.
Steam main goes to a T, 4” branch A makes a loop around the basement feeding 90% of radiators, aprox. 200’ long and down to 2” turns down and has a drip leg with an F&T trap on it. Brach B of the main also 4” goes about 15’ turns down and connects to a wet return. The F&T trap from branch A connects to the same wet return. Because of a lower floor in part of the house, off the bottom of branch A there is a 2” main that feeds half a dozen radiators. This main turns down at the end, has a drip leg with a ¾” thermostatic trap. The radiators and end of main trap have a ¾” return that runs back and connects to the same wet return as branch A F&T. After the ¾” end of main trap is a ¾” air vent. There is only 1 other air vent and that is after a trap for 1 radiator.
Each radiator has it’s own pneumatic valve within a couple of feet of the steam main.
I know it’s hard to picture how this piping arrangement looks from such a brief description but it looks to me like there is no way for the air to get out, except for the main and radiators on branch C. Most of the radiator traps go to a dry return that turns down and connects to the wet return. Some of the radiator traps connect directly to the wet return.
My plan is to install a condensate pump, there by changing the wet return to a dry return and putting F&T trap on end of branch B. Repair or replace all steam traps. This should give me some place for air to vent and hopefully all radiators will now heat.
Opinions and suggestions are welcome.

Matt Undy

What were the pressure controls set to? If they were high that would make the fuels bills high and make the steam not move around the systme very well.

I am not an expert but my guess would be the venting is inadequate. I'm not sure that ading a condensate pump is needed, it seem that more venting is needed and possibly some of the steam traps need repair. The air should be pushed through the radiators and be vented.

I think a condensate pump is needed when either the volume of steam is too great too keep the boiler from flooding on the off cycle or the boiler can't be moved low enough to arrange for gravity return. Of course with a new smaller water content boiler the volume of the system may be too small where it wasn't on the original system.

I think if you could sketch the system and post it that would help others comment.

BTW, I only knwo what i've read here..jsut sounds like classic problems related to lack of/uneven venting and pressure contorls set way too high. Somewhere off the wall there are a number of storries of people installing condensate pumps at huge costs to cure porblems that a condensate pump won't cure.

Matt

Matt

Steamhead

I agree, you don't need a condensate pump

to vent that system. This would complicate things to a degree that is not necessary. Most likely you just need more vents.

It's hard to tell from the photo, but if the drip fron the end of a steam main goes straight down into a wet return (below the boiler water line), a trap is not needed on the drip. What is needed is a way for the air to be vented from the main, sized to let all the air out of the main in about a minute. This could be done by removing the trap and piping in a main vent on the drip above the waterline. If you tell us how much of each pipe size there is on each main we can size your main vents for you.

The air from the radiators goes into a dry return, above the boiler water line. You say there is a 3/4-inch vent on the dry return- I assume this is the size of the pipe connection. However, all 3/4-inch vents are definitely not created equal. If you tell us what vent you have we can get an idea if it is adequate.

Also, are all the dry returns connected together above the waterline, so this vent can serve them all?

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hvacdmia2

condensate pump

Went to the job site again yesterday to look things over again. Replacing existing leaking boiler with a low water content boiler and a combination receiver feed pump. Because of the way the piping is arranged it is going to be less work to do a little repiping and change the wet return to a dry return and put a trap on end of steam main. That should solve the air venting problem. The dry returns hook to the wet return several different places and I need the pump anyway. Most of the existing traps are Webster Sylphon. Took one apart and on the trap element it said Fulton Sylphon. Anyone know if repairs are still available for those traps

Matt Undy

Zone Valves and Boiler Sizing

Here's another question. You will size the new bioler to the EDR of the system. But is this the correct approach with zone valves. Is the heat output of the system way oversized such that much of the system will be closed off(or throttled down, those look liek pneumatic modulating zone valves) by the zone thermostats most of the time so the boiler will only be seeing part of the total EDR of the system at most times? Is a combination of EDR and a heat loss needed to size the system? Can some sort of controls be put on the zoning system to prevent the enire system from being opened all the way when it is turned on to a cold house?

Even better, is there a modulating steam boiler out there? I know there were coal boilers with pressure controled draft regulators that modulated....

Maybe I'm thinking about this too much but if the system is oversized won't the boiler short cycle as most of the zone valves are closed at any given time? What is the solution to this problem.

Matt