Hydronic system calculations

My guess is that it might be related to pump curves, efficiency, positive vs variable displacement, viscosity, valve bore, Reynolds number used, radius of els, length of run, to name a few. Both numbers are right, and both are wrong. For differing flow rates and pressures.

Don't forget your wier plate.

Rich

how many miles of straight pipe?

I think the right number is somewhere between those two. Unless you are using really heavy walled pipe, you should have minimal pressure drop going through the pipe and fittings. I see the heat exchanger as the big unknown. Can you borrow a 5 gpm pump and measure the pressure drop through it?

butterball valves, like the turkey?

You don't have a whole lot of selection when you're down that small. My sense is you'd just like to be directed in the sensible path to the cheapest effective circulator that will do the job.

If you want to purchase NEW equipment, a Taco 007 or Grundfos UP-15 is the right pump for the right price.

You can also do just as well with a circulator found at a garage sale.

BUT ! If you're pumping fresh water, ( drinking water ), you'll need the same HP pump, (approx 1/16 hp) but with a STAINLESS or BRONZE BODY, otherwise it'll grow shut with rust.

If you're still bent on doing some math, look up the pressure drop curves of similar looking plate exchangers as yours and choose a pump that will give you the GPM you desire while overcoming the plate exchanger's pressure drop. ( I'm assuming that the exchanger's CV is well in excess of local piping, if not count the CV of other major pressure drops.) PS. stay away from butterball valves, they'll gook up the impeller.

Yea, the copper system requires a bronze pump or there will be damage. Taco 007 or a small Grundfos are likely the size I need, but I am trying to balance the pump with the right psi loss so I have a built-in flow regulator: the back pressure.

I have looked at a lot of bronze pumps and even have a request in with one supplier for info, but they do not appear to be too eager to provide the answer to my friction loss question.

Too bad... without that information, I cannot purchase their pump, whichever it is.

By the way, Sniccus, if not butterball valves, what does your experience suggest?

That was as "tongue in cheek" reply. Valves are either BALLVALVE or GATE VALVE or BUTTERFLY VALVE or STOP and WASTE.

Don't get off on a rabbit trail here. You're building a widget to move heat from one place to another. There are fundamental formulas for doing this.

The amount of heat (in BTU's) you needed determines the size of the heat exchanger. It also begins to tell you how strong of a pump you need.

Determine your BTU requirement

Choose a heat exchanger with more than enough BTU's required

Add up your friction losses (in ft. of head) of the heat exchanger, fan-coil and interconnecting piping, (mainly elbows).

Choose a pump that meets or exceeds the GPM needed while meeting or exceeding your perceived friction loss.

Now, you can get same btu delivery with a SMALLER exchanger and a BIGGER pump, or with a BIGGER exchanger and a SMALLER pump. ( Remember if you use an exchanger just big enough, you'll need to force the water through at a high velocity requiring a much stronger and EXPENSIVE pump. I like really oversizing heat exchangers and using smaller pumps for a variety of reasons.

Also, size your pump so it is operating in it's "sweet spot" which is approx. 80%. Don't ever use a pump where it is operating at the TOP of its curve or the BOTTOM of its curve , you'll burn it out.

ALWAYS....put your expansion tank as close to the suction side of the pump as you can.

You forgote globe valves.

Rich

To resolve the unspoken question, I should mention that the "Butterball Valves" are butterfly valves manufactured by Milwaukee Valve Company.