Plate heat exchanger threads

[Buzz Saw]

I'm going to be ordering two plate heat exchangers. I've noticed that you can purchase the plates HX with male(MPT) or female(FPT) threads.

Is there a preference on what type of threads to get? Pros or cons? Different situations that it would matter for install purposes?

Also, would 20 plates or 80k btu be enough for domestic hot water?

Thanks

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[maple1]

20 plates should be enough, but might depend on your setup. E.g. if you have a smaller tank & depend more on fast recovery during heavy use, you might want a bigger one. I have a 20 and it's lots with my 80 US Gallon tank.

I think I went with female threads, thinking the female side on the plate would be stronger than a female copper adaptor I would have been using if I had gone with male plate threads.

 

[Highbeam]

The plate exchanger rating depends on a specific temperature for each fluid. Then what is it, 1 btu raises 1 lb of water 1 degree?

 

[jebatty]

Not only temperature of each fluid, but also desired approach temperature, temperature rise, flow rate, and pressure drop.

Also, would 20 plates or 80k btu be enough for domestic hot water?

What is the 80k btu based on for each of these factors? As an example, 80k btu = a 75 degree temperature rise 50F to 125F at 2.1 gpm. Think through your application, look at the charts and specs carefully, and then size appropriately to get a satisfactory result.

 

[Buzz Saw]

Not only temperature of each fluid, but also desired approach temperature, temperature rise, flow rate, and pressure drop.

What is the 80k btu based on for each of these factors?

Good question. The 80k btu came from how it's marketed. I guess I need to look at the charts to see what works best. I would rather be over sizes and run the pump slower.

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[maple1]

Good question. The 80k btu came from how it's marketed. I guess I need to look at the charts to see what works best. I would rather be over sizes and run the pump slower.

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You really need to consider your reserve capacity also. Bigger tank = less HX needed.

 

[Buzz Saw]

You really need to consider your reserve capacity also. Bigger tank = less HX needed.

I'm not following. If the domestic water only passes through the HX once how does storage effect HX size?

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[Bob Rohr]

It is all about temperatures and flow rates. You can find a free calculator online at (broken link removed), you do need to register. Here is an example with a 5 gpm A side flow rate. Properly sized they can provide instant DHW production if you have some boiler capacity or a buffer tank.


I have a couple nice new plate HX for sale, 3X8- 30 plate, they are in an insulated shell, have 3/4 union connections and bleeder on A side.

Union connections are nice so they can be serviced. With hard water you may need to de-lime them from time to time. Radiator shops can "cook" them out inexpensively.

If not unions, add flush valves on both connections on the B port, like Webstone's

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[maple1]

I'm not following. If the domestic water only passes through the HX once how does storage effect HX size?

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OK - sounds then like you are wanting to do this on-demand? You didn't say that before - in that case, the bigger the better and it should likely be bigger than a 20 plate. Mine is not on-demand. It recirculates the tank DHW until the tank gets up to a setpoint.

 

[Buzz Saw]

Sorry for the confusion. I didn't even consider putting a pump on the domestic side. This can be done pretty easily as I have a hot water circulation pump for the entire house already in use. I would just habe to route the return loop through the HX.

As far as storage I have a 40 gallon electric water heater. The plan was to go from the HX into the water heater for storage.

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[Buzz Saw]

Mine is not on-demand. It recirculates the tank DHW until the tank gets up to a setpoint.

What sort of circulation pump do you have? Is this where you use your alpha pump? Flow rate? What controls the set point? Aqua-stat?


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[maple1]

What sort of circulation pump do you have? Is this where you use your alpha pump? Flow rate? What controls the set point? Aqua-stat?


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The boiler side of the HX uses an Alpha, my main load circ - it is just plumbed in as another zone. I have 4 rad zones and this DHW zone on it.

The DHW side uses a B&G Ecocirc. I forget the model number now. It's variable speed, adjusted with a dial. So I can vary flows on both sides of the HX to tune it in - boiler side by throttling with a ball valve, DHW side by turning the dial. Once I had things where I liked them I didn't have to touch again.

The Ecocirc is controlled by a Johnson A419 controller. My DHW tank is bottom feed - the Ecocirc pulls from there via a T, and I also have the Johnson temp probe there - stuck in as far as I could stick it, on the tank inlet fitting. Wrapped with insulation. Actually, the Johnson also controls the Alpha - when it starts the Ecocirc, it also closes a separate RIB relay (coil is wired parallel with the Ecocirc) that has the Alpha circuit on the other side so starts that also, the same way an endswitch in a zone valve would. And the more I think about it the more I confuse myself - it has been a few years since I rigged it up. That relay actually opens a zone valve I have in the boiler supply to the HX, using 24v I pulled off my zone valve transformer. Then the end switch in the zone valve starts the Alpha, the same way one of my other zones does - I wired it into the same mess of wires in the junction box that my other zone valve end switches were wired into.

More or less.

That Ecocirc is a very nice compact circulator that is super quiet and uses next to no juice.

 

[peakbagger]

With respect to threads. I have seen several plate and frames with male threaded stubs welded directly to the end plate with no room to get a pipe wrench on the pipe. Especially with stainless, threads can gall no matter what you do and with this configuration you end up trashing the heat exchanger if the connection galls. Generally the female thread is a coupling so there is a place to get pipe wrench on the coupling. If the pipe that is screwed into the coupling galls you usually can cut it off and remove the pieces then retap the coupling. You cant do that with male thread. Ideally I like to use flanges on these connections as that removes a lot of stress on the connection (assuming someone doesn't "power pipe" the flanges by leaving a big gap between the faces and then forcing them together).

 

[Bob Rohr]

If it has male threads you can generally use a nut and tailpiece. Thisgives you a union connection and also seals with a gasket. Not much more than hand tightening is required if you use EPDM or silicone gaskets

In small dimension HX, those connections are very close to one another, and I agree stainless threads can be tough to seal. You can find Teflon tape made specifically for SS threads. Loctite is another options, just hand tight and the Loctite glues it all water tight. Use 600 series if you want a permanent connection

 

[Buzz Saw]

If it has male threads you can generally use a nut and tailpiece. Thisgives you a union connection and also seals with a gasket. Not much more than hand tightening is required if you use EPDM or silicone gaskets

In small dimension HX, those connections are very close to one another, and I agree stainless threads can be tough to seal. You can find Teflon tape made specifically for SS threads. Loctite is another options, just hand tight and the Loctite glues it all water tight. Use 600 series if you want a permanent connection

Digging this thread back out....My project got sidelined for a bit but I"m back at it. Bob can you direct to an example of a nut and tailpiece? I think I know what you are talking about, but I have no clue where do buy independent parts like this.

Thanks

 

[Buzz Saw]

Not only temperature of each fluid, but also desired approach temperature, temperature rise, flow rate, and pressure drop.

What is the 80k btu based on for each of these factors? As an example, 80k btu = a 75 degree temperature rise 50F to 125F at 2.1 gpm. Think through your application, look at the charts and specs carefully, and then size appropriately to get a satisfactory result.

The HX is rated at a Delta T of 20 degrees. Is it possible to get more out of the HX or is engineered Delta T the maximum capacity ? The chart in the link below is sort of confusing, as the numbers all apprear to be the same(unless I missed something).

Thanks

http://vi.vipr.ebaydesc.com/ws/eBay...descgauge=1&cspheader=1&oneClk=1&secureDesc=0

 

[maple1]

The dT must be for a certain rated flow though? All else being the same, if you increase flows you will narrow dT's.

OK, checked out the charts in the link. That's what they are showing. Well, not directly, as they are varying the dTs across each chart and comparing Btu output while holding flow steady.

 

[Bob Rohr]

Here are some examples of connections

You can get simple 1" copper to female adapters, solder the adapter on the tube first, thread it onto the HX and pipe from there.

Or a 1" nut with a tailpiece, probably 1" sweat. Caleffi 59834A. Or press NA16266

Here is a solar HX with a bunch of tailpiece angle adapters and bleeder, it came assembled this way.

That is not a very useful output chart. A simulation program lets you enter flow rates and delta T on both side to see various outputs.