Plate heat exchanger threads

Buzz Saw Posted By Buzz Saw, Oct 1, 2017 at 11:18 PM

  1. Buzz Saw

    Buzz Saw
    Feeling the Heat 2.
    NULL
    

    Jan 18, 2014
    477
    78
    Loc:
    Attica, Ohio
    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

    Sent from my SM-G950U using Tapatalk
     
  2. maple1

    maple1
    Minister of Fire 2.
    NULL
    

    Sep 15, 2011
    7,497
    1,311
    Loc:
    Nova Scotia
    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.
     
  3. Highbeam

    Highbeam
    Minister of Fire 2.
    NULL
    

    Dec 28, 2006
    13,490
    2,520
    Loc:
    Mt. Rainier Foothills, WA
    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?
     
  4. jebatty

    jebatty
    Minister of Fire 2.
    NULL
    

    Jan 1, 2008
    5,460
    760
    Loc:
    Northern MN
    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.
     
  5. Buzz Saw

    Buzz Saw
    Feeling the Heat 2.
    NULL
    

    Jan 18, 2014
    477
    78
    Loc:
    Attica, Ohio
    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.

    Sent from my SM-G950U using Tapatalk
     
  6. maple1

    maple1
    Minister of Fire 2.
    NULL
    

    Sep 15, 2011
    7,497
    1,311
    Loc:
    Nova Scotia
    You really need to consider your reserve capacity also. Bigger tank = less HX needed.
     
  7. Buzz Saw

    Buzz Saw
    Feeling the Heat 2.
    NULL
    

    Jan 18, 2014
    477
    78
    Loc:
    Attica, Ohio
    I'm not following. If the domestic water only passes through the HX once how does storage effect HX size?

    Sent from my SM-G950U using Tapatalk
     
  8. Bob Rohr

    Bob Rohr
    Minister of Fire 2.
    NULL
    

    Jan 9, 2008
    1,153
    167
    Loc:
    SW Missouri
    It is all about temperatures and flow rates. You can find a free calculator online at www.flatplateselect.com, 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

    \
     

    Attached Files:

  9. maple1

    maple1
    Minister of Fire 2.
    NULL
    

    Sep 15, 2011
    7,497
    1,311
    Loc:
    Nova Scotia
    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.
     
  10. Buzz Saw

    Buzz Saw
    Feeling the Heat 2.
    NULL
    

    Jan 18, 2014
    477
    78
    Loc:
    Attica, Ohio
    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.

    Sent from my SM-G950U using Tapatalk
     
  11. Buzz Saw

    Buzz Saw
    Feeling the Heat 2.
    NULL
    

    Jan 18, 2014
    477
    78
    Loc:
    Attica, Ohio
    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?


    Sent from my SM-G950U using Tapatalk
     
  12. maple1

    maple1
    Minister of Fire 2.
    NULL
    

    Sep 15, 2011
    7,497
    1,311
    Loc:
    Nova Scotia
    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.
     
    Buzz Saw likes this.
  13. peakbagger

    peakbagger
    Minister of Fire 2.
    NULL
    

    Jul 11, 2008
    3,193
    753
    Loc:
    Northern NH
    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).
     
  14. Bob Rohr

    Bob Rohr
    Minister of Fire 2.
    NULL
    

    Jan 9, 2008
    1,153
    167
    Loc:
    SW Missouri
    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
     

Share This Page