RowCropRenegade said:
Jim, I meant a mixing valve for protection of the garn. Keep cool water at end of manifold from re-entering garn below 120. The 3 loops after my house loops could potentionally be radiant loops, you are saying put mixing valves on the secondary S&R of each of those loops. Which doesn't do much for protection of the Garn, or does it?
Apparently, no one has put their primary pump on return side with a Garn. I asked a question that apparently Martin alone has the answer for. Jim did you get your pump moved lower? If so, where did you put it?
If Russ is watching, I'm reviewing how his system is Teed into his boiler room. Looking very similiar to mine, except his future barn loop is my future in house radiant loops.
Every day this project changes a little. Added another Tee to bring in new cold water to the manifold, mount the filter and all. Be nice way to clean out manifold after piping.
Hopefully someone with more Garn expertise will tell me if I'm wrong, but my understanding of the reasoning behind return water temp protection and the way a Garn operates, is that a Garn really doesn't need that sort of protection, and you are going to get the best performance if your return water is as cold as you can get it (from using the BTU's to heat with, of course, not just running the water through a cooler...) In theory at least, and possibly in practice if your loads were mostly low temp radiant circuits, you could cycle the Garn tank down to around 90°F or so, well below the normal condensation temps, and get really high efficiency on the reheat burn...
In a standard gasser or other cast iron boiler, the return water pretty much blasts against the inside wall of the firebox, and if it's cold, can cause concentrated flue gas condensation at that one point, with subsequent corrosion, and so forth. Thus protection is needed to ensure that the return water is above the condensation temp, about 140°F...
With the Garn, the cold water just flows into the giant tank, where hopefully it stratifies and pushes the warmer water towards the top of the tank for use - when the entire tank is cold the unit is fired, and the firebox and exhaust tubes get heated, and are mostly surrounded by a layer of the water they are heating, which keeps them above condensation temperature... Any cold water returning to the tank during the firing still mixes into the bottom layer, and doesn't impinge on the firebox, so there is no condensation issue - if no condensation, no need for protection...
Gooserider