Pumping Awa Question

tom3holer

Thanks Chris and Eastman

Thanks guys for taking the time to explain this stuff to a hydronic dummy.

I am beginning to get it finally. So if my boiler is running steady state with, just say, all zones on and extracting the exact amount of BTU's the boiler is putting out it would measure, at the boiler in and out ports, whatever rise I had set the flow for.  

As we want to keep the input returning water as low as possible having a secondary flow greater than the primary is the way to go. So choosing a high D/t on the primary will give the best chance of this. So why would anyone choose lower D/T?



Tom

Eastman

What is your thinking here?

"As we want to keep the input returning water as low as possible having a

secondary flow greater than the primary is the way to go.  So choosing a high D/t on the primary will give the best chance of this."



Why would would you want a primary dT greater than what is on the secondaries?



Quoting myself: "We can infer from this information that the boiler setpoint must be 170, even though the fintube system only requires 160." 



If the primary dT was set equal to the secondary dT, one could lower the boiler setpoint temperature by 10 degrees.



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Can you see that, either way the return temperature is the same? (140)  It has to be since the assumption from the get go was that a secondary system supply of 160 was required, and the system delta was set at the maximum allowable of 20.  But one way requires a higher setpoint (170) versus the case when the two deltas are equal (160).

CMadatMe

Because

They are the same guy that installed your boiler. Don't know nor care to know the math. Hook it up, turn it on and away we go. Trick is you better measure those emitters and make sure the mixed water supply temo will get you where you need to go.



The only thing I do not agree with Eastman on is that boiler supply water temp is more important to boiler efficiency then boiler return water temp factoring in rate of modulation.



By the pics you have 5 Zones. You say the heat loss is 60K what are each zones heat loss? Can't be more then 10-12K a zone. That's a 1 to 1.2gpm system side flow rate. How many of the zones are operating simultaneously for the majority of the heating season? The majority of the time maybe a 3gpm, 4gpm flow rate, maybe 20% 5gpm and 5% all 6gpm.



Here is is both ways. Alpine 80 running on the 7.3gpm and 4.2gpm flow rate. What is more important boiler supply or boiler return water temp? Now if I reduce the system flow rate it gets more interesting. The 40 boiler rise flow rate gets you to condensing much quicker then running the boiler on the 20 rise flow rate matching the system side. The majority of the heating season the system side will rarely be at full gpm need. Overall seasonal efficiency in my opinion would be better with the boiler running on the 40rise flow rate and the system side running on the 20.



There are 2 pages on the attached PDF.

hot_rod

your original question

if you are re-piping I would change the pumps to "pump away" Without knowing all the details and dimensions it is tough to say if your system will have problems pumping towards the PONPC.



How it performs depends a lot on things like pump spec, fluid temperature, system elevation, fill pressure, pressure drop through the circuits, etc.



Graphing a simple piping circuit with a very common off the shelf circ capable of adding 8 psi you can see clearly what happens throughout the circuit. Adding gauges to your system would show this.



These drawings are from Modern Hydronic Heating third edition by John Siegenthaler. a great book you should consider adding to your collection And your installers!



If in fact you have a noisy, air bound, tough to eliminate air problem, then the PONPC could be the issue.