I am trying to size my pump but I don't know how to figure out head loss for my heat exchanger. I know that in the description it says it is a 152,000btu and also that the gpm is 15.8. It is a 19x20 water to air exchanger. I am hoping to use one of those small 3 speed Grundfos pumps. It is going to be a pretty simple system with 100' of 1" pex each way maybe 4 pex 90 fittings the exchanger and that's it. I know that I want 10 gpm or less and a delta T of 20 to 40 across the exchanger. I assume since most all factory owb's come with the same pump I will be fine without running the calculations, but I just wanted to check.
head loss estimate for a heat exchanger
- Thread starter jwise87
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Where did you get the heat exchanger? What's the manufacturer? If we could find it we could help you find the pressure drop through it.
maple1
Minister of Fire
So I found a chart from a manufacturer. I don't know if that is who made mine or not but the specs match. They list a pd of 1.49 psi. Is that the number I need to know? Here is the chart, I would appreciate it if someone could enlighten me on how to read it.
![[Hearth.com] head loss estimate for a heat exchanger](https://www.hearth.com/talk/attachments/upload_2018-11-20_12-33-53-webp.233808/ "[Hearth.com] head loss estimate for a heat exchanger")
maple1
Minister of Fire
That' can't be the whole chart? But should be a start.
1.5psi I think is 3.5' of head. But that would vary with GPM - I would think?
1.5psi I think is 3.5' of head. But that would vary with GPM - I would think?
The wahx will add to the issue of 200' of 1" pex having about 28' of head at 10 gpm. Unlikely that "one of those small 3 speed Grundfos pumps" will meet your needs.
After more research and reading I am shooting for a 7gpm flow. If I keep my fittings to a minimum with 1" pex that puts my total head somewhere around 15. This rules out the Taco 007 pumps and their equivalents at that flow rate, but may not rule them out completely. What I am leaning towards right now is Grudfos 15-58. That will put m down around 3 or 4, which is minimum for turbulence on what I am using, and will probably leave me with a pretty high delta-T. If I am not satisfied with the heat output from that I will just plumb another one in series and that should put me close to where I need to be.
maple1
Minister of Fire
The 15-58 is a really good solid circ. I used to have one on my 5 zones, but I swapped it for an Alpha. An even better circ for that application. I still have a 15-58 on my loading unit, that's what came on it. And one on my backup electric boiler - which I pretty well obsoleted when we put our mini-splits in a couple weeks ago, but it will stay in place anyway. The flexibility of 3 speeds is nice. Given the price of them, having two instead of one shouldn't be a bank breaker. I have never used a Taco, but seem to have read about some failures over the years. Don't think I've ever read of a 15-58 failure.
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