I have a situation and I'd like to expose my diagnostic to see if I am finally starting to think like hydronic pro. Emphasis on starting...
I have an inadequate heat supply from an air handler that covers the 1st floor of our house. It consists of:
- a 20" x 30" heating coil in my air handler. https://www.firstco.com/documents/ProductDocuments/hwc209.pdf
- connected via a janky 1" copper to 1" pex to 3/4" copper to 3/4" ID header on the coils (10' away so WTF, I know)
- supplied via a Grundfos UP 26-64 F
- as one of 4 zones on the secondary off a 200K BTU boiler (nominal; 160 MBH)
- [edit: @ 22 PSI]Inadequate = not warm enough given Chicago winter and best efforts to improve insulation / mitigate heat losses and sufficient "layer up" feedback to wife / children. Manual J and square footage questions - you can ask, but I'll refer to "inadequate." Demand for heat is not met by supply.
I kept water supply temp at 140 last winter and this air handler ran the entire months of Jan and Feb, never satisfying the call for heat on our first floor. The fact that our bedrooms on 2fl / 3fl were warm (via a separate handler / coil / supply line / pump on same secondary) seemed to me to prove that I was rate limited somewhere on the supply side of this 1st floor handler.
Where is my rate limiting factor?
This coil set has some moderate head, with the instructions PDF not giving data beyond 9 GPM (7.5 ft of head). 9 GPM at deltaT of 20 gives me 90K BTU. The PDF says that higher supply temperature will give me more BTU, but my hydronic mind says that is only possible with higher delta T, not a higher supply temperature per se. Thus, I'm going to declare these coils maxed at 90K BTU.
Looking backwards from there, 3/4" copper and 1" pex, respectively, have max GPM of 6.5 and 7.5. Very short run from boiler to unit (10 feet away), but let's assume we are rate limited in the pipe at 6.5 GPM. That gives me 65K BTU. That feels right, but I don't have enough experience to justify my gut on that.
Then there is the Grundfos. The Grundfos literature says that at 7.5 feed of head, it will try to pump at 22 GPM. I'm not sure that is happening through the 3/4" pipe, though. But I can't declare the pump as the rate limiter at all.
So my analysis would be that the limiter in this system is first the 3/4" supply and second, the head of the coil set.
Thus,If I can plumb a big fat 1 1/4 pipe the whopping 10 feet to the handler, and find a new coil set that can handle a 1 1/4" connection, I will have eliminated my first rate limiter. I need to make sure the internals of the coil set still work -- big tubing, in parallel, inside the coils, so that the head stays under, say 12, I'll be able to keep using my Grundfos pump.
Am I on the right track?
Most gratefully, TC