How hot is the air in the plenum that you are going to draw heat from? I think that is the biggest issue. If you have 120 degree plenum air, over time, lots of time, the water in the heat exchanger would eventually get there. If the bottom of the tank is higher than the top of the exchanger you will have decent circulation, but this process would be very slow. The tank would also need to be very well insulated to retain the precious little heat you can capture.And, the drumroll - I think from what I've seen, I CAN heat my water with the output air. I ordered a heat exchanger today, and once the many inevitable delays have run !their course, I should have info for you on how it worked out (going where no-one has gone before - and all that!).
Timely reply, as it's time for an update. After a bit of time to get everything installed, the last few days have been snowy, giving a good opportunity for some testing.…My guess: If the plenum air is running continuously at about 120 degree and you inlet water is about 50 degrees and the system is very well balanced with the tank high enough to allow natural circulation you will be able to produce about 20 gallons of 105 degree water a day. Less if the room is cool the tank is in or if the plenum air drops lower than 120 degrees. There are a lot of variables that affect this, most would lower the amount of water or the temp of the water. A few would increase it.
Post your results, please. I would like to be wrong. I personally had a coil screwed against the outside of my woodstove, with a pump that was controlled by a solar temperature differential controller, and when the stove was real hot I got less than 5 degree rise in my 50 gallon tempering tank.
The temp reading for the tank is at about the top third line. I've found that readings taken near the bottom of the tank are somewhat meaningless in this application, as the 30-40 something degree water that comes in with usage causes huge variations at the lower levels.Where are you taking the temp readings in the tank? Near the top or bottom? I am surprised that you have 200 degree air temperature coming off the furnace. If that is being produced I would agree there is plenty of heat available. Are you using the water in your system currently? Were you able to get this gain during normal household use? I am curious about the drop pipe in the cold loop, if that helping or impeading heat gain. My understanding is that any part of the tank or piping below the heat source will impede the curculation.
The main reason I see for a pump is because his heat exchanger is sitting too high. It should be lower than the bottom of the tank for proper thermosiphoning. If he adds a pump the return to tank loop needs to be moved to the cold water inlet so that it is not adding "cool" water 2/3 of the way up the tank as it is being pumped. Is should be pumped in near the bottom, moving in the tank and the heat will then rise up. If the pump is moving the warm water out of the plenum faster, drawing in cooler water it would raise the delta T allowing the water to absorb BTUsAdding a pump may not help much. If you increase flow, your DT will decrease, and you might not see temps as warm. But sometimes things like this are hard to accurately predict.
The coolest water is going to be at the lowest point in the system (without a pump). If the coil is half way up the tank the coldest the water will be is as cold as the water in the middle of the tank. There will be a cold bubble of water sitting at the lowest portion of the tank. A pump will fix this issue because you are not relying on convection to move the water.I don't think it could draw in cooler water than what it is now? Also not sure the advantage of outputting the heated water into the bottom of the tank? Ideally it should be inputted into the top area, since that is where the hot water is being used from and I would think you'd want he hottest water in the spot it would be used from?
Might need more temp readings to get a full handle on how useful this will be - mutliple tank temps at various levels, and/or temp readings in & out. It would at least supplement the 'other' water heating some, so there should be some value to it, but not sure about cost vs. benefit here. The biggest uncertainty might be how will that big coil in the airstream affect the house heating & furnace perfomance in heating season. I don't think any design & engineering work on it was done with something like that in the airstream, but not sure what effect it might have.
How cold does it get where you are at in the winter ? It was 106F at our house yesterday with the heat index.The rest of the house is at 62 and cooling with the doors and windows open and a breeze blowing the 58 degree outside air in. I'll vent the heat from the furnace room in an hour or so when I unplug the circ pump. I'd just let it warm the house, typically, but we're expecting a small heat wave - supposed to get to around 80 the next couple of days and I don't have A/C, so I'm storing some cold .
It can get pretty cool here in the winter. I guess I don't really know how cool because the digital thermometer I can watch from the safety of my warm bed stops working at -42 or -46 or something. After that it just displays OOR for out of range. If I had to know, there is a weather station here I can pull up online, but really, if it says OOR, that's all I need to know!How cold does it get where you are at in the winter ? It was 106F at our house yesterday with the heat index.
I've done it both ways...started out in series, then switched to just letting the speed control do its thing...I have it all torn apart right now (well, almost back together again now) to remove the old Yukon furnace and install the Kuuma in its permanent home (it was installed as an add-on last winter due to time, and the lack of) just need to finish the wiring on the Kuuma and install the stove pipes for the Kuuma and oil furnace both.I thought I recalled that you were using a variable fan control. If so, do you have the variable wired in series with the fan control switch?
That is cold. A couple years ago I had to feed the cattle in -10F with the windchill temps and I thought my face was going to freeze off. I even had a face mask on. I don't mind the heat nor the cold, I just don't like when the temps are extreme.It can get pretty cool here in the winter. I guess I don't really know how cool because the digital thermometer I can watch from the safety of my warm bed stops working at -42 or -46 or something. After that it just displays OOR for out of range. If I had to know, there is a weather station here I can pull up online, but really, if it says OOR, that's all I need to know!
That would be nice. Ohio is the 7th most populous state in the union. I could get use to less people for sure.Winter here keeps the place from getting crowded!