windyhill4.2 wrote:We enjoy endless hot water from our water to water plate exchanger,no matter if the heat is also running.
How big is your reserve tank that has the exchanger in it? And how much water does your boiler have in it?
My boiler only has a paltry 27 gallons of water in it, and each of my 4 zones probably have about 5 gallons of water in them. Dropping 5 gallons of cold zone water into 27 gallons of hot boiler water can drop the boiler temp noticeably, and if two or three zones (let alone 4) are open at once it can really bring the temp down. But I set it up where my circulator shuts off whenever the calling zones bring the boiler down to 150 degrees (turning on again at 160 degrees), so it rarely goes below 150 degrees. I had considered getting a 27 gallon reverse/indirect HWT at one time to double my boilers water capacity. That would most likely give me endless hot DHW.
For one cold (60 degree water) zone calling and the boiler at 180 degrees:
27(180) + 5(60) = 32(x)
32(X) = 5,160
X = 161 degrees boiler (entire loop) temp
For two cold (60 degree water) zones calling at precisely the same time and the boiler at 180 degrees:
27(180) + 10(60) = 37(x)
37(X) = 5,460
X = 147.5 degrees boiler (plus both loops) temp
But double my boilers capacity and all 4 cold zones firing simultaneously suddenly looks like this:
54(180) + 20(60) = 74(x)
74(X) = 10,920
X = 147.5 degrees boiler (plus all 4 zones) temp
Suddenly my worst case scenario is 147 degree water. And I have almost never seen all 4 zones firing at once, let alone having them all initiate their call for heat at the exact same time.