Sizing flat plate heat exchanger

Jpurdy647

I have 230k BTUH worth of baseboard in a sperate building from my boiler which needs to be heated, however, it needs to be filled with antifreeze since that building is only used in the summer spring and fall, and turned off during the winter.

To handle this I plan to use a flat plate heat exchanger and a buffer tank off the main boiler (in the adjacent building which is always heated) which is sized for both buildings.

I'm running into trouble sizing a plate heat exchanger though since specs are typically for radiant low temp, snowmelt, or domestic uses. How would one calculate or determine the necessary size heat exchanger for this purpose?

Tinman

https://espthermal.xyleminc.com/ESPLogin.aspx

This is what I use. You'll need to create a login ID and username.

Jpurdy647

I've seen that calculator, there seems to be no way to register though. How did you?

Tinman

Let me go back and check. It's a good tool.

Tinman

https://esp-systemwize.com/heat_exchangers

Here ya go. You need to email a request for your login. They're quick about it, as I recall. If you send it tonight, you'll probably be up and going tomorrow.

Jpurdy647

A google search brought me to a registration page, although there is no link to it. Trying this tool out now.

Jpurdy647

Thanks! I sent an email and was in immediately, it must have been automated.

I used the tool, I'm not positive I'm reading the output correctly though:

https://i.imgur.com/QMV6zhW.png
https://i.imgur.com/evrL6Wp.png
https://i.imgur.com/zWmWO6n.png

Result:
https://i.imgur.com/zE1gEnP.png

How do I determine which heat exchanger will transfer enough heat from this? Sorry if this is a silly question!

Tinman

All you have to do is make absolutely certain that information you're inputting is correct...fluids being used and their actual and/or necessary temperatures. The app does the rest. If you're uncomfortable with the result, call Xylem tech support to double check your work.

Tinman

Your results are all over the map. Something isn't right.

hot_rod

Here is an example with the Flat Plate program. Maybe it clears up the inputs. It has a close approach, 10° for instant DHW production.

i have a few spare plate HX if you need a good deal, on a good brand,and the size works.

Jpurdy647

Better result

https://i.imgur.com/iDiFN2T.png

Figured out how the program works somewhat, tuned my inputs and think I have the model I need. I'll call Xylem for a double check tomorrow, that's a good idea. Did not know they offer support but definitely want to be sure what I purchase will truly be able to handle what I'm using it for. Looking like the BP415 - 60 will do it for the cheapest.

Reading Dan Holohans on primary secondary piping has cleared up a bunch of questions as well. That man is a God send!! Haha

GroundUp

I'm sure I'll catch hell for this, but:

Not that I'm against B&G or anything, but for the cost of the 415-60 one could purchase 6 of the knock-off HX with the same performance. Quite honestly I have been having better luck with the knock-offs; 0% failure rate in the 4 years since I switched which is more than I can say for a few "reputable" exchangers such as Xylem and Kelvion. If you're interested in saving a few bucks, I may suggest shopping around

Zman

@Jpurdy647
Make sure to keep an eye on the pressure drops. The first 2 in your last post were pretty high. If your circs can't handle the pressure drop, it will change the GPM and whole calc goes out the window.

Jpurdy647

Yea, I discovered that some of those results were unrealistic for that reason. I looked further into this sizing situation, dug for some prices, and it looks like the kind of heat exchanger I would need would be on the order of over $2,000. I probably have a budget of $500-$600 for this heat exchanger before I decide it's not worth the separation and I'll just combine the systems.

Ironman

I hope this doesn't violate the rules about pricing, but I can sell you a 100 plate 5 x12" HX in that price range.

P/M me if your interested.

GroundUp

The aforementioned knockoffs that I buy typically come from a store called Badger Pipe in Wisconsin and all specs are listed on the site. A plate with similar flow/pressure drop numbers to the 415-60 can be had for well under your budget. I've got hundreds of them out there with zero callbacks so far. 3 this past month alone have replaced failed Xylem plates, 2 of which were less than 3 years old and the third 6 years old. My parents have one of the Badger 20 plates heating their DHW off a wood boiler and it's 14 years old right now; never been cleaned or struggled to keep up to a 4 person DHW demand

EYoder

And Badger is a great company to work with. I've used them a lot.

Paul Pollets

Remember that the FPHX will need it's own fill, drain, relief valve and expansion tank. ASME may be required.

Jpurdy647

There isn't much information available for selection of badger plate Heat exchangers. How do you determine which size fits? I'm not sure what they base their BTU measurement off of since that changes for every application

hot_rod

I noticed that also. Most of those software sizing programs are developed by the manufacturers. Perhaps they source from multiple off shore plants that have not developed software or have any certifications?

I would not trust performance spec from one brands software to cross over to another brand.

In other words not all 5X12-30 plates are created equal, or would perform the same. You can sometime see that just in the square footage of surface area, if that info is provided.

To just state a HX is 150, 200,000 or something BTU is a bit misleading. There needs to be some flow and temperature numbers included in a rating.

If you want the engineering data to back up the decision....

Jpurdy647

The volume of water between the plates would be a critical factor is my thought. Badger provides a BTU/H rating, but I'm not sure under what conditions they measured that because the rate of BTU transfer depends on the fluid temperature on both sides. In my case in this post, it was high temp to high temp which required a MASSIVE heat exchanger.

That wasn't going to work out so my next phase is to size a heat exchanger to produce instantaneous hot water through a mixing valve off of the boiler. Like an external tankless coil. I'm going to pipe it as a bypass on a primary loop system so water is always bypassing through it when the boiler circ is on, so it will be ready for heating (flow switch to call the boiler on when there is HW demand)

GroundUp

Well I'll be dipped, I can't find the data either now. It's not often I have a unique job that needs to match temp, so it's been 8-9 months since I dug up that data. Seems to me now that I may have called and had it sent to me? Can't remember now. But their plates are not to the same spec as, say, Xylem. Seems the numbers on the Badger 80 plate 5x12 were almost identical to the 415-60, but don't quote me on that. I'll dig through my disaster of a desk and try to locate that paperwork from last fall

hot_rod

Jpurdy647 said:

The volume of water between the plates would be a critical factor is my thought. Badger provides a BTU/H rating, but I'm not sure under what conditions they measured that because the rate of BTU transfer depends on the fluid temperature on both sides. In my case in this post, it was high temp to high temp which required a MASSIVE heat exchanger.

That wasn't going to work out so my next phase is to size a heat exchanger to produce instantaneous hot water through a mixing valve off of the boiler. Like an external tankless coil. I'm going to pipe it as a bypass on a primary loop system so water is always bypassing through it when the boiler circ is on, so it will be ready for heating (flow switch to call the boiler on when there is HW demand)

That is called "close approach" sizing where the A & B sides are within a few degrees. Corrects it does take more surface area.

Interestingly enough my DHW is produced from a large, 500 gallon solar, wood boiler tank, instantaneous via a plate HX. . I still get a comfortable shower with my A side down to 110F.

The HX is a 3.5 x 8" 40 plate. Pumped with B&G Vario, mid speed range, piped with 3/4" solar flex stainless. A flow switch on the domestic water line feeding the HX triggers on the Vario, so only a few second delay to warm up the small HX. One low flow shower head running.

Keep in mind for a shower typically under 105F.

JUGHNE

I had this dilemma over 25 years ago as I had a Weil-Mclain GV boiler with a 120 gallon WH tank with a single 4.5KW element.
I wanted some heat exchanger to use the gas boiler for HW.

One weekend visiting the father-in-law's farm I noticed a 3' length of 6" pipe with a 8 bolt flange on one end sticking out of the scrap heap. It just looked like a tube in shell exchanger I had seen in our power plant.
I pulled it out of the scrap iron pile and he closed up the open end with a plate of square steel. Then he went to the factory where he used to work and had them make a flat closure plate for the flanged end. They drilled the plate for three 3/4 holes and welded 3/4" couplings in both sides of the plate. One 3/4" coupling is for the pressure relief valve. The other 2 are for the DHW flor. The 6" pipe shell had 1" couplings welded into the sides of the pipe, one high and one low for the boiler water to circulate thru.
I had my 12 Year old son solder up a copper bundle with 3/4" nominal type L. We used 8X30" lengths of copper. 90's and street 90's made the return bends. So we have 20' of copper inside the shell. Dielectric unions are used on each side of the custom built closure plate. (today I would use SS unions).

The science and math calculations that went into this project were such: It was a free 6" X 30" scrap of pipe with the flange already welded on one end. We could only fit 20' of tube bundle inside the 6" tube. The FIL was a very good welder with connections to an excellent metal fabrication factory.

So my out of pocket was 20' type L copper, 90's and st 90's.
4 dielectric unions, pressure relief valve, 3 3/4" couplings that they cut in half , one 1" coupling, cut in half also. Not knowing better I gave them steel merchant couplings for these connections.....no problem with them so far.
I suppose if I had to purchase everything outright I might have 300-400 buck involved.

Back in my DA youth days, I used the pump that came with the 120 gallon tank.....it was a solar tank and the pump was high head. Twice I had to pull the bundle to repair pinholes from high velocity water flow thru the bundle before I realized this would happen. Thankfully the Pop valve started to dribble for warning...…..a reason to have one on a separate vessel.

This is still in use in my basement.

Years I had to install a "proper" tube in shell. It cost well over a grand and looked to have only half the capacity of my homemade HXC.
BTW, the 3' length is just right for FG insulation sleeve.

hot_rod

Another DIY solar HX was to slip a 20' stick of 3/4 copper inside a stick of 1". Drill the stops out of a 1X 3/4 3/4 tee for the ends.

A 20' long tube in tube HX.