heat exchangers - steam to water

Mark Crisafulli

We manufacture a Shell & Coil Heat Exchanger on Long Island ,NY. We have small sizes that are around $500.00 that are used in residential in fact we sold two last year that were installed on burnham boilers. the customer loves them. These units can do up to 360,000 BTU. The size is 2 1/2" round and about 2' long. we also make larger ones that can due 3.6 Mbh that are 16" round and 54" high sell for about $10,000.00(small & cheap Box car you got there Tony). With our water to water like the ones District Energy St. Paul, MN Have been buying for over 30 years have a approach temperature of 5 degrees F. I was in NH at a Holiday INN doing a start-up when we found the actuactor was broken during shippment. We had 3 of the small Shell & Coil heat exchangers package together piped to 3 - 200 gal storage tanks outlet to a hobly valve. They needed the hot water so I let the valve run full open. We got 175 Degrres from the boiler and 175 out from our heat exchangers to the tanks. I saw it and so did Frank I Rounds Company as well as the hotel engineer. That joye is what we call 0 approach temperature. or perhaps 98-99%.
Subcooling in steam to water means you take as much energy as possable out of the steam. like our shell & Coil heat exchanger I tell people "you give me 5 PSI steam and I will give you 90 Degree Condensate in a DHW application".

To end we can stamp our Shell & Coil heat exchangers for 400 PSi @ 600 Degrees. Standard Stamp is 250 PSI @ 400 Degrees. Just wanted to add my input.
Thank you for your time.

Best Regards
Mark Crisafulli

Joye Chizek

Heat Exchanger - Steam to Water

I know boilers and I know steam, but I just heard about a shell and coil heat exchangers that claims 98-99% and can take condensate and squeeze the heat out of it to provide domestic hot water. I might be dumb, but I don't see how this can be true. It's some swedish technology. Anyone heard of this? Anyone able to explain to me how this could work? Thank you...Joye

Tony Conner

Ask Them...

... exactly how the efficiency is being calculated.

Actually, "efficiency" isn't a very good term to use for heat exchangers. You can just keep adding surface area to get the approach temps closer and closer. But the more area, the bigger the HX, the more $$$ it costs.

If the condensate is being sewered, then the more heat you can pull out of it before it hits the drain, the better. If the condensate is going back to the boiler, then essentially, the heat you pull out of the condensate by subcooling it, just has to be put in again by the boiler. Beyond a point, it's a zero sum game.

Tony Conner

Ask Them...

... exactly how the efficiency is being calculated. That's usually good for several minutes of sputtering & stuttering nonsense.

Actually, "efficiency" isn't a very good term to use for heat exchangers. You can just keep adding surface area to get the approach temps closer and closer. But the more area, the bigger the HX, the more $$$ it costs. I could say I've got a HX that's 99.5% eff for a given application. It's for residential domestic hot water. The downside is that it's as big as a boxcar...and only slightly more expensive. Somehow I don't see it being a very popular model, though.

If the condensate is being sewered, then the more heat you can pull out of it before it hits the drain, the better. If the condensate is going back to the boiler, then essentially, the heat you pull out of the condensate by subcooling it, just has to be put in again by the boiler. Beyond a point, it's a zero sum game.

I rep a line of HXs, including shell & coil. They really do a nice job. But they're not universal (no HX is), so it depends upon what you need to have happen. The great bulk of the shell & coil units I deal with are far better suited to high temp hot water systems, or steam (they do a really good job with high pressure steam), but tend to get priced-out of the picture pretty quickly on small residential space or domestic hot water applications. (They're an industrial grade unit - ASME rated for 300 PSIG steam service.)

Joye Chizek

Thanks, Tony

How exactly do you define "approach temps"? I come from a boiler/ steam trap background and don't understand that term. How do you "subcool" condensate? Do you take the heat out somehow to use for domestic water and then feed it back to the boiler? If you take something at one temperature and put it through a process and even get 99.5%, I guess I'm not sure why you put it through something else(especially if it is expensive) and get something tangible - bottom line fuel savings out of it. In my experience any "industry "efficiency" number is "commercialized - which means that someone probably attained it for a fraction of a second once when all conditions were beter than perfect. Most products would be hard pressed to come with 4% of published numbers in the field. A heat exchanger that could do so seems to good to be true, but then I'm struggling to understand it. Sorry to be so dumb...thanks for your help. Joye

Joye Chizek

Thank Mark

Can you give me a breif "woman's" explanation of how you accomplish this? and how you can do it in such a small space? Do you have any proof of your claims? Thank you Joye

Tony Conner_2

What was the rest of the data on the hotel HX installation - the inlet & outlet temps on both sides, and the flows? Can you show us the values and calculation method that was used? What's the surface area of the HXs that were in service at the time? I'm not at all sure that an "efficiency" of 98 - 99% can be claimed, solely on the basis of the hot side inlet temp matching the cold side outlet temp. To me, that's like a hot water boiler (at it's simplest, all a boiler really is, is just a heat exchanger) manufacturer having a 175*F flue gas temp, and an outlet hot water temp of 175*F, and claiming a boiler efficiency of 99%. Without the BTU/hr input of the fuel, and the inlet water temp, combined with the GPM, it can't be done.

"Effective" is a better term than "efficiency" to use for HXs. The better the design, the more surface area you can get into a smaller package. This needs to be balanced against the pressure drops for given flows, and of course, the cost. It's sort of like condensing boilers - will enough be saved on the more eff boiler to offset the significantly higher purchase cost? The payback isn't nearly always there.

It's not all that often over the course of a year that you can get the building heating load to coincide with the domestic hot water usage. Catching the waste heat is usually the easy part. Finding an ongoing home for it is the tricky bit. I used to run a steam district heating operation. I'm very aware of the challenges in this regard. When there's no condensate available, there has to be another source for DHW. I don't know of very many operations that will pop for the capital outlay on redundant DHW systems, even if one of them is pretty much "free" to operate.

Some process industries sewer condensate on nasty applications, because they don't want to take a chance on getting something ugly back into their huge, very expensive boilers. Others are on district steam systems that very often do not return condensate. For these relatively few applications, subcooling of condensate is an excellent thing to consider. For most installations, sizing them to big-time subcool the condensate doesn't pay back. We have a number of HXs that DO subcool on part load, but they normally weren't sized to do that. There's no particular energy savings to be had, as the boiler just has to make more steam to heat this cool condensate back up to deaerator temperature. Why would anyone deliberately do that?

Think of "boxcar" as a relative term. If somebody spends a lot more money than they should have, buying an oversized HX to subcool condensate for no particular economic reason, then it could be said that they have spent a "boxcar" more money than was justified.

Mark Crisafulli

Steam to water

Sorry Tony for the delay if you are still here I got the information you asked for. again sorry but things have been busy and I kept forgeting the file when I come home.

Anyway let see the rest of the data is

Primary side was based on 180 F but they were realy giving 175F. This information is from my sizing program and from being at the job site.

again 180 F in 115.7 out. although we did have our hands on the return and it felt cooler. (No gauge on the return side)with 47.2 GPM

Secondary 40F to 140F with 30 gpm

1,491,000 BTU
Velocity Prim/Sec (ft/s) 0.9/2.2
Pressure Drop 2.0 PSI both sides
As we have never measured the heating surface like the shell/tube and plate people do. these units are spun copper with heating surface all the way around if you saw one you would under stand completely.

Also the existing units were not very old and were leaking. made some place in nothern Texas!!!!!

We do alot with IDEA and district energy people so I am sure you know about our "Shell and Coil" design.

As I have been in this industry for a lone time and have bid and installed many and many redundant DHW systems. That why I have a pending patent on a system that has some redundeny in it. In some case you get one Package at about the same price as some other peoples single package.

In most cases the subcooled condensate is heated up by the outher condensate returning to you deaerator but on the way the subcooled is not burning up pumps. for the cost of pumps and unused vented steam it's better to use it up. No flash tank needed.

Anyway we can go back and forth untill our key boards ware out. Give me this if you please, time to show you each of the applacations we have talked about. When you see it you will understand. I say this because I have been thu this many times and after people see it they understand.

Tony I hope to hear from you and thank you for your time.

Best Regards
Mark

Mark Crisafulli

But

Tony.
But I do understand some of what you are saying and would enjoy showing you our product.

Joye Chizek

Sub Cooled Condensate

You guys are over my head - I was just trying to find out how you can exchange steam to water at +80% effeincies. But now I have another question - subcooled condensate? Does that mean you somehow are cooling the condensate? What temp to what temp? Why do you want to do that? Aren't you taking the heat out early? Mark, can you example this...in simple terms, please. Joye

Tony Conner

heat exchangers - steam to water

But I can plug your numbers into my sizing program, and get shown 100 heat exchangers that will do the job - plates, shell & tube, shell & coil... To be sure, some units shown have a very high (as in unacceptable) pressure drop, and others are grossly oversized, but they WILL all transfer the shown amount of heat. Does this then mean that they are ALL "99% efficient"? How could they not be? The only losses are a little bit to the surrounding air. Essentially all of the BTU/hr in, gets transferred out on the other side of the HX. I maintain that "efficiency" is a poor term to use when referring to HXs.

And if you've got customers who'll pop for redundant DHW systems, they must be paying a lot more for energy than anybody I've encountered lately. In the vast majority of installations that I've seen, the condensate is available when there's little or no demand for DHW, and for big chunks of the year, there's no condensate available at all. If you've got customers that can make this pay back, and have the capital to spend to make it so, what can I say? Party on.