Return on steam coils

Mike

I'm in the process of replacing a rather large steam coiling a church. A/C also. Very little room anywhere. My concern is getting the condensate back to the return main. Iso there a recommended drop from the coil outlet, to the F&T trap? I have very little room from walls and ceilings.

AMservices

Do what EBEBRATT-Ed says

EBEBRATT-Ed

You need to come out of the coil with a full size elbow. The elbow inlet must be the same size of the coil. The outlet should be the same size. Drop down 1' minimum and put on a tee the branch of the tee should be trap size. Size the trap for a 2:1 safety factor. Put a nipple and a cap on the other tee connection.

If you can drop more than 1' do it. There is no maximum, more is better. If you need to extend farther out from the coil with a nipple and a coupling you can. Make sure to put a vacuum breaker on the coil. The vac breaker (I use a 1/2 or 3/4 inch Y pattern check valve) should be installed either between the control valve and the coil inlet or between the trap and the coil outlet. Either way point the tee straight up and use a long nipple or pipe and get the vac breaker up high away from any condensate. Use 45s to get around obstructions. Put the vac breaker up high.

Most important if this coil will EVER handle air below freezing use a freeze stat which should OPEN the control valve wide open and shut down the fan and close the outside air damper.

a trap will lift condensate to a return but this should be avoided if at all possible and absolutely do not lift condensate if the coil handle air below freezing temps. Doing this helps prevent frozen coils

Mike

Thanks Ed, you confirmed what I was thinking. Unfortunately, I don't have the 12 inches, ceiling and doorways. I'll get it as low as possible, but the condensate line is a real mess, full of water, back, pitched. Can only touch so much, had to twist boss's arm about the vacuum breaker. Thanks again for your input.

EBEBRATT-Ed

Best bet would be a condensate pump. They also make pumping traps and steam powered condensate pumps. $$$$$unfortunately but sometimes you have too. Unfortunately if not done right you could have a potential freeze up. LOL Boss"s what do they know??

Mike

Yeah what does he know. Well it worked before. Did it? The chuchs building super showed us the t'Stat, and how he turns it on. Found the air handler (with outside air), and a control panel with a billion wires disconnected, and no wiring diagram. But notes of zone dampers. God help us. It's a chuch, he should hear our prays. It's gonna be interesting.

EBEBRATT-Ed

Steam coils follows Murphy's law (doesn't everything hvac related) If it can freeze it will.

DanHolohan

Mike, air has to vent beyond the F&T. If that condensate line is constantly filled with water you're going to need a vent between the outlet of the F&T and the return line.

I'm also thinking that F&Ts don't need a cooling leg since they discharge on a mechanical float not a thermostat, so you can place it close to the outlet of the coil.

GBart

begs the question..........why are we replacing the coil? did it freeze? did it freeze so many times and get repaired so many times it is now useless? you can't repair a steam coil anyway you can patch it but you loose output each time

if it has froze up that has to be adressed

side note: the reason you want to drop out of the coil to a trap is so that coil is full of steam and no condensate, if the trap is close to the outlet you'll have condensate in the coil and the rated output will be lower

DanHolohan

@GBart, I'm thinking that when the control valve is open the condensate will drain from the trap because there will be enough pressure differential across the trap. When the control valve is closed, the vacuum breaker is open to allow air into the coil. At that point, the only differential across the F&T will be the static weight of the condensate above the trap's inlet, but there shouldn't be that much condensate in the coil to cause a water-hammer concern or a derating of the coil.

Unless I'm missing something. Thanks.

GBart

There should be, when I worked at sub base Groton we had a ton of steam coils and many had froze at one point and people tried to patch them. Some were mixed air, some 100%OA, some had bypass dampers, all had different issues for freezing.

DanHolohan

I agree with you when it comes to outside air. Absolutely. Thanks.

EBEBRATT-Ed

Height of the coil outlet above the trap is important. Most recommend a minimum of 12-14". In my opinion more is better the more drop from the coil to the trap the better

Mike

I have to thank you all for your feedback. You reenforced, what I was thinking, and learned from this site. To update, we replaced a Westinghouse horizontal cased coil section, steam coil and 30 ton cooling coil, in ceiling. Fan section in another room. System serves either the church, or a meeting hall, by motorized zone dampers. Just started up the cooling, having air flow problems. Some of the dampers aren't working. It was supposed to be a exact a exact replacement. Not. A little taller, longer, and not quite as deep. Start the team side tomorrow. Connections are close, off by a inch. With only about 12" to the wall, not sure how I'm gonna get up there. The outside air, looks sealed off. So that shouldn'the be a issue. Old coil looked solid. I believed the cooling coil had leaks. It's in such a place, one can't work on it. I just have to make it work, and properly. Thanks again for your comments. Really helps when one doesn't with steam every day.