Heat Exchanger Head Loss (pressure drop)

[allan]

I was looking at installing a brazed plate heat exchanger and used the software on www.flateplate.com to come up with the right size for the heating load. I also was interested in finding out the pressure drop of the fluid through the heat exchanger. GEA makes a low pressure drop heat exchanger. I talked to a supplier off the web and he seemed to think that a low pressure drop heat exchanger would not be as effecient. My thought was that a pressure drop of say .8 psi which would equal a head loss of approximately 1.9 feet would mean I could use a smaller pump, use less electricity etc. I'm interested in what different people has experienced. Also, if someone can give me an idea of the losses in the following pipe: 160 feet 1" pex (accounting for both supply and retun lengths) and 20 feet 1" cu and a 40 plate heat exchanger (depends on the pressure drop) I was thinking that the max gpm through the 1" pex should not be greatr then 7.5 gpm. Thanks in advance. Lots of good advice in the site.

Thanks

 

[heaterman]

I was looking at installing a brazed plate heat exchanger and used the software on www.flateplate.com to come up with the right size for the heating load. I also was interested in finding out the pressure drop of the fluid through the heat exchanger. GEA makes a low pressure drop heat exchanger. I talked to a supplier off the web and he seemed to think that a low pressure drop heat exchanger would not be as effecient. My thought was that a pressure drop of say .8 psi which would equal a head loss of approximately 1.9 feet would mean I could use a smaller pump, use less electricity etc. I'm interested in what different people has experienced. Also, if someone can give me an idea of the losses in the following pipe: 160 feet 1" pex (accounting for both supply and retun lengths) and 20 feet 1" cu and a 40 plate heat exchanger (depends on the pressure drop) I was thinking that the max gpm through the 1" pex should not be greatr then 7.5 gpm. Thanks in advance. Lots of good advice in the site.

Thanks

So far so good on your assumptions. What you have described should work provided your heating load doesn't exceed 70-80,000 btu's. Do a ;little experimenting with that software to see what happens to the head when you go to a 50 or 60 plate.

 

[allan]

Thanks heaterman. I will see if I can us the software to calculate the head loss through a bigger heat exchanger.

 

[in hot water]

How many GPMs are you trying to move through the exchanger? Pull out a pump curve and see what the GPM to head is for a small circ. Hard to finsd a medium flow low head circ. typically 8 gpm at 8-9 feet of head is a common circ.

If electrical efficiency is a goal an ECM circ like the Wilo, Grundfos Alpha, or Laing ECM would cut power consumption by at east 40% and do the same amount of pumping.

hr

 

[WoodNotOil]

In my experience you can run calculations all you want but the reality of your setup will likely be different. I would give three suggestions.

1. Use a 1" port flat plate and nothing smaller.
2. Get more plates than you think you need as the reality of gpm and headloss are very hard to predict. (more guarantees better transfer to a point)
3. Make sure to factor in the amount of btus you are trying to transfer.

There are good prices here: http://www.google.com/url?q=http://...t&cd=1&usg=AFQjCNE_dtHBerIpNk-54hoWV0vUdf9L-w

 

[allan]

Thanks hr and Wood not oil. I have rec'd the info for the heat exchanger calculation link from mjmotor sport. I noticed that the prices widely differ and so I talked to another site and that person suggested that a LP (low pressure) heat exchanger might not transfer the BTU's as effeciently. However, he could not give me any info on his exchanger other then to say you need this pump to run it. I don't like to waste mony on "use this and this and it will work" without som kind of backup. Guess it comes from my engineering background. He may well know what he is talking about, but I would like to hear what experience others have in real life situations. Wifes complaining that I'm getting married to this site, but I like reading the threads, some are very funny, but lots have good info.