Curious insulation exemption mentioned in the NYC Article 321 filing guide

ariccio

On page 30 of the Article 321 filing guide, under "Selected best practices and other guidance", they included the following bullet point:

"It may not be advisable to insulate condensate piping in pumped-return steam systems, as overly hot condensate can increase the risk of cavitation and thereby damage the pump(s). As such, this measure is NOT mandatory for pumped-return steam piping"

This wording seems like a mistake to me. My gut tells me that this is to continue letting certain buildings with removed condensate pipe insulation as a hack continue with said hack….

(i.e. that have blown steam traps that heat condensate pipes to 205°F to leave parts of the condensate return piping insulation removed so that the wasted steam has a chance to condense (my building))

But, I'm not sure, so I'm asking here: are there legitimate and reasonable reasons why a building would be designed to have condensate returns used as waste steam radiators?

pecmsg

It legitimately reasonable.

Code is vague at best and minimum standard.

ariccio

https://forum.heatinghelp.com/discussion/comment/1836005#Comment_1836005

That's what's curious about this - it's part of the prescriptive route where they're a lot less vague on purpose!

Pumpguy

High condensate temperature will indeed damage condensate pumps.

That said, there are special pumps designed specifically to handle high temperature condensate. The ones I'm familiar with are called TWO FOOT NPSH PUMPS. These are of conventional single suction centrifugal design but have an additional axial flow prop and intermediate straightening vanes just upstream of the centrifugal impeller.

In cases where a building is heated with district or "street" steam, the condensate is frequently just sent to the sewer. In these cases there can be temperature limits, so a condensate cooler is employed. I often see the cooler on the discharge of the pump.

I sometimes see this arrangement where vacuum pumps are used as part of the pumping equipment. In these cases, it is recommended to put the condensate cooler upstream of the vacuum pump so the vacuum pump sees the lower temperature condensate. For best performance, vacuum pumps always want the lowest possible condensate temperature.

The heated cooling water from the condensate cooler could be pumped to hot water radiators or for pre-heating domestic hot water.

I've had operators tell me "we want the condensate to come back as hot as possible so we don't have to add so much heat to make steam again".

What they don't realize is the amount of heat needed for change of state; to change 212*F water to 212*F. steam is 970 BTUs per pound. To heat a pound of 160*F water to 212*F. takes 52 BTUs. That's a very small percentage of the additional 970 BTUs needed to turn it into a pound of steam.

Jamie Hall

Interesting. And understandable. For two reasons. First, the heat loss from condensate return lines should be — and in a properly operating system will be — astonishingly low. It should be minimized, yes, but how much return are you going to get? Related, if the condensate lines are hot — never mind steam hot — you have other problems which are much more important.

Second, and related, the first sentence up there in the bullet point is absoutely correct: if the condensate is hot enough to think about saving money or energy as a good thing, it is also hot enough that the risk of damage to the pumps is, economically, far more important. Much more intelligent to not require something which is almost certain to damage something else.

Perhaps if somewhere else in the code there was a section which mandated that buildings with condensate hotter than some convenient figure — let's say 150 F or so, open to debate — MUST examine and repair or replace all steam traps. Now that would make sense…

ariccio

Yeah, undoubtedly these lines are way too hot from bad traps - it's been part of the long saga to try to cajole management and the coop to do something about it even though they're fine with spending $400k+ on a new boiler. The other day I captured an image that perfectly illustrates that problem:

You can see that dropping return joining with a larger one. Care to guess which parts of the buildings have the most failed open traps? 😆

I do indeed suspect that at some point someone removed much of the insulation because the condensate was too hot. Instead of, y'know, fixing the traps, this could have been an ok temporary hack. I'm not quite sure when it happened, but as long as this is the case current relevant personnel do not accept that there are blown open traps in the building - then there'd be steam damaging the condensate pump, right?

Where this gets very interesting - no such exemption is actually in the code! This seems to only show up in the filing guide. As part of this article and the filing guide, buildings are already supposed to fix their traps. What's the backstory here?

pecmsg

are you a tenant?

ariccio

Yes. See some of my previous posts.

Dealing with a building that classically never manages steam traps, but with the added fun that neither the staff nor the engineer accept even the concept that a steam trap can fail open. The fact that the garage can reach the 80s on a cold day due to the massive heat coming off those pipes, and the fact that the fan coils in the garage haven't been used in at least a decade, and the fact that half the building is too hot with their heat off, and the fact that there are still apartments that are cold even with a new boiler that is like 20% larger than the original one from 1960... Doesn't seem to spur curious thinking.

I got started thinking about this ten years ago when I noticed that on a night when it was below freezing my apartment was 77 degrees with the radiators shut off. Somehow the usual response to complaints of uneven heat include reference to the side the sun shines on, y'know, even when it's night.

pecmsg

ok