Calculation for max primary hydronic pump gpm/pressure

[Alternety]

I need to replace a primary circulator pump in a hydronic system. It is a Grundfos UP-26-64 P. I am just looking for a correct max pump pressure and flow rate. I am not convinced that it is operating at the proper place on the pump curve. I understand the nasty variables in reaching this objective.

I have a couple of configuration programs, but they are too orientated toward a total system design. They require a whole bunch of detail I do not really want to recreate. I have not found a way around a full design. I just need to do a couple of iterations to see if the current pump is in the correct ballpark. I believe the loads below are too high, but the tools I have do not include loss parameters that match the design. I had a full design, but I lost it when a motherboard crashed. The installed system pretty much matched my design, but it was 10 years ago. And the details are lost. I understand the chance of everything demanding heat at the same time is fairly small. Most of the issues I have with the system are at low flow rates.

Here is what I need to be able to do. I am pretty much re-doing the piping for the main distribution assembly. I am doing this because of what I consider to be a serious failure of Viega compression fittings (i.e., they all leak and look really crappy, but not as far a Viega is concerned). In addition, the configuration is not compatible with an ability to properly flush the system or replace degradable components. I am going for a gross number. I just want to get a sense of whether the existing pump is too big/small. I want to use a variable speed pressure sensing pump.

- Assume 1/2" PEX, at a rational spacing, heating 2 X 3000 sq ft. (larger PEX to 5 manifolds)
- Assume 26 zones. Some are quite small, others large. Average is likely to
be a reasonable approximation.
- Heat loss max 40,000 BTU/hr. Too high, but a starting point for iterations.
- Fluid is 50% Polyethylene Glycol.
- Condensing boiler with a target of < 130 F.

If someone could point me to a suitable tool or set of calculations I would greatly appreciate it. I need to get this resolved. It is starting to get cold (Yeah, I know. But it was not that simple).

 

[Alternety]

I know this is a generally dumb question. But no actual information is available. The contractor no longer has his information. I did a parallel design, which matched his pretty closely, but as I noted above, my calculations are also gone. If someone can give me a rough idea of how many feet of 1/2" PEX would be used for this number of square feet in normal practice. I can then roughly distribute this footage to individual rooms/circuits from the manifolds. I should then be able to come up with an estimate of maximum flow with all of these estimated circuits in parallel and demanding heat. That should also yield an idea of the pressure needed at full flow.

So, if someone can just tell me how many feet of pex was likely to be used/sq ft, I think I can get where I need to go. I am just trying for a ballpark here.

 

[Sponsor]

 

[Alternety]

Got it. Really simple solution. The installer wrote down the length of each pex circuit in the manifold closets. Now I can figure out how much water is on the main floor and double it . Add some for the distribution pipes to the manifolds and the plumbing in the boiler room and buffer tank and I should have a pretty good idea of how much water there is for determining how much glycol I need and have a crack at doing flow. I can use the circuit info and use a design tool to determine the rest. I think I now have enough data points to get all the necessary answers.

 

[Tom Sawyer]

You could have just installed a VFD pump and forgot about all the calculations.

 

[Alternety]

This is rather n old post, but a finishing statement.

The only pump I thought would be a satisfactory device was the Taco Veridian series. They are a very nice piece of technology. I understood a small version was coming that would be suitable for residential and small commercial sites. I waited and waited. It came out and is way too big for the application. It is a shame. I think there would be a real market for a small version.

I also decided not to replumb the whole system. Too many $. I just had the really bad parts replaced. Including all of the %@@#$^% dielectric connectors.