Well, I'm sitting hear on the couch recovering from a very satisfying Turkey Day. I hope that you all had a great Holiday too. Time to update the BoilerMate project!
Well, this system worked pretty well when we were using the Van Wert in the basement. 2 weeks ago, we switched over to the Axeman in the garage and that caused problems.
The reason this caused problems has to do with my overly complicated heating system. A couple years ago I realized that I could run a reduced temperature loop for my heating system (radiant floor and radiators) by flipping a few valves, running the pump in the Van Wert 24/7 and using the Van Wert aquastat to control the loop temperature through a zone valve. This passes heat from the Axeman in the garage into the heating loop when needed.
This heating system works GREAT for the radiators. They are PERFECT for sitting on when they are about 110 degrees.
It DOESN'T work that great for DHW. I never intended to run the system like this when I built it so there were compromises.
The DHW compromise is that there was no direct DHW return line to the Axeman in the garage. The return path was through the house heating loop. This was not a problem when the BoilerMate was functioning properly because the DHW heat calls were only 20 minutes or so.
When the DHW zone is ON for a long time it pushes loads of 120 degree water out of the heating loop, into the Axeman in the garage. This drives the heating loop temperature up over the set point and crashes the supply temperature to the DHW zone.
To solve this problem I installed a bypass line and a shut off valve so that the DHW zone now has a direct path back to the return side of the Axeman in the garage.
Then I got back to the convection loop / thermosyphon problem. I figured I could make this work by putting a Swing Check Valve in the thermosyphon line.
The Blue PEX loop on the left is the new thermosyphon line.
It is Tee'ed into the cold water inlet to the plate.
On top of the BoilerMate I connected the Swing Check Valve and a shut off on the left side.
This is where it got complicated.
Lightning wrote: ↑Sun. Oct. 31, 2021 9:14 pm
That's the backwards convection happening that I illustrated in the diagram posted earlier today
Lee is right on the money about this. I was counting on a forward convection loop! This didn't happen.
So I did something completely unorthodox.
The Swing Check Valve should be mounted vertically and this would have worked IF we had forward convection. It didn't work so I started cranking the fitting to get the swing check closer and closer to horizontal. Once I got it a little below horizontal, it started working!
This leaves the door on the swing check hang open just enough to get the backwards convection Lee is talking about.
Luckily, the plate heat exchanger provides enough of a pressure drop that when you open a hot water tap, the pressure on the plate inlet forces the swing check closed keeping cold water out of the hot water.
It's been a couple days and it is working perfectly now. The DHW zone stays OFF. In fact I rarely see it come ON. Plenty of hot water and the zone rarely runs.
It didn't work out like I expected it to, but it does work very well!
-Don
