Hey guys. After a couple weeks of dreaming, I think I've decided to take the plunge and install a backup boiler in my basement. Got my fingies on a Lochinvar Knight 94% condensing boiler with a 5:1 turndown. The plan is to pipe a 50 plate into the OWB loop, before my A/W exchanger in the furnace plenum, and yes, I do already have an LP furnace for the house but it's more complicated than that. My shop is 3 feet from my OWB and is heated with the OWB. I do have an electric boiler in there as backup but the stupid thing costs $400/mo to run, thanks to the astronomical electric rates here. So the ultimate plan is to basically use the Knight to heat up the entirety of my OWB water to still be able to heat the shop in the event of a wood outage, vacation, etc. Essentially the return line to my OWB would now be the "supply" from the gas unit when running. Does anyone see an issue with dumping hotter water into the return ports on top and continuing to draw from the bottom ports to serve both buildings? I'm wondering if stratification is going to be an issue from dumping the hot water on top from the LP boiler but still dumping colder return water in the other top port from the shop? I am flowing about 16 GPM total with both loops so I should have a full exchange every 13 minutes or so, in theory.
I've installed a lot of these Knight units and have a pretty good understanding of them from a hydronic standpoint, but given my commercial nature, I don't touch the electronics. Now it seems to me that if I strap an aquastat on the incoming line to the plate from the OWB to activate the pump/boiler on the LP side when the OWB falls behind, it's going to want to run 100% until the aquastat is satisfied. Given the 5:1 turndown in this particular unit, I would like to utilize the turndown when possible to keep efficiency up a little bit if possible. Say I set that aquastat to kick the LP boiler on at 130 degree water temp from the OWB, but want it to maintain maybe 160 degrees while the Knight is running, how does one go about making the controls function? I'd ultimately like it to run 100% until it reaches 160 and then just maintain it at 20% fire or whatever. Seems like the aforementioned aquastat route isn't going to allow that to happen, but I'm electrically challenged so maybe I'm looking at it wrong.
Many questions, sorry. Some insight would be greatly appreciated. Thanks!