Air assist for a steam pre-heat coil
Air assist for a steam pre-heat coil
(OP)
Yes, I'm thinking way out of the box here.
The air handlers serving our new lab supply 100% outside air and use steam preheat coils. A face and bypass design was somehow discarded during design and modulating steam valves were used instead. At lower temperatures (10-50degF), the coils are at atmospheric due to the opening of the vacuum breaker downstream of the steam valve. With so little head, condensate sits in the coil waiting to get out the tiny trap orifice. Meanwhile the steam/air mixture above the water cools and the freezestat trips.
My idea before resorting to more expensive options, is to tap into the pipe downstream of the steam valve and add a 5psi or so compressed air supply. The coil already gets induced air from the vacuum break, I'm just trying to give it some oomph to clear the condensate. Crazy??
The air handlers serving our new lab supply 100% outside air and use steam preheat coils. A face and bypass design was somehow discarded during design and modulating steam valves were used instead. At lower temperatures (10-50degF), the coils are at atmospheric due to the opening of the vacuum breaker downstream of the steam valve. With so little head, condensate sits in the coil waiting to get out the tiny trap orifice. Meanwhile the steam/air mixture above the water cools and the freezestat trips.
My idea before resorting to more expensive options, is to tap into the pipe downstream of the steam valve and add a 5psi or so compressed air supply. The coil already gets induced air from the vacuum break, I'm just trying to give it some oomph to clear the condensate. Crazy??





RE: Air assist for a steam pre-heat coil
RE: Air assist for a steam pre-heat coil
RE: Air assist for a steam pre-heat coil
Another solution would be a 'pump trap' that uses steam to pump the condensate. I'd go this route first, deliberately adding air to a steam system sounds like the wrong solution to me.
RE: Air assist for a steam pre-heat coil
The piping needs to be absolutely correct on installations like this. The condensate MUST - in short order - flow from the trap to a vented receiver. The trap itself MUST be sized for very little pressure drop across it.
Spirax Sarco's publication "Hook-Ups" explains "stall", and provides an excellent explaination and diagram of exactly how the system needs to be laid-out.
RE: Air assist for a steam pre-heat coil
I'd go the REAL Safe route - I'd consider a small shell&tube heat exchanger on a wall nearby (I am sure you can figure out some space, even ceiling mounted if need be) and use a small pump with a glycol per-heat coil. You've got steam right there anyway.
Ultra Safe and fairly cheap. Somehow, we in the mechanical trade, we only get noticed when things go wrong, when things go right, everyone take it for granted.
Instead of you losing sleep each time the weather goes below freezing, why don't you go out and spend some of that Preventive maintenance money.
RE: Air assist for a steam pre-heat coil
Only air temps at or just below freezing are the problem. Once the air is several degrees below freezing, the steam control valve is open sufficiently to keep the vacuum breaker from operating.