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Post by jonnoh on Jan 22, 2021 7:51:27 GMT -8
Ha! I thought the group would take a big dump all over that idea for sure! Well, maybe this one is worth exploring further.
Regarding the condensing concern, your point about needing to pre-heat the water is well taken. I've got a PV system that should have no trouble heating 40 gallons of water up to a reasonable starting point (maybe 80F?) using a small on-demand water heater and circulator pump. I would consider this the 'primary loop' of my radiant system.
Need to think about this option a bit more and draw it up to see exactly what it would take to make it work.
Thanks for the feedback!
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Post by Solomon on Jan 22, 2021 8:48:00 GMT -8
Starting to get unnecessarily complex.
If it were me, and it may be some day, I think I would build a simple tube in tube stainless steal gas to water heat exchanger which would be put in parallel with my water heater. Or find something at the scrap yard that would work reasonably well as one.
Like I said, water heaters are designed to be inefficient, the gas flows the wrong way. I would be concerned that you couldn't control it enough. Water absorbs a massive amount of heat and I doubt you can get the gas flow and temperature right to prevent condensation. It's a materials problem.
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Post by jonnoh on Jan 22, 2021 9:00:21 GMT -8
Starting to get unnecessarily complex. If it were me, and it may be some day, I think I would build a simple tube in tube stainless steal gas to water heat exchanger which would be put in parallel with my water heater. Or find something at the scrap yard that would work reasonably well as one. Like I said, water heaters are designed to be inefficient, the gas flows the wrong way. I would be concerned that you couldn't control it enough. Water absorbs a massive amount of heat and I doubt you can get the gas flow and temperature right to prevent condensation. It's a materials problem. Yeah, probably way too complex, considering my skill/knowledge level... For your recommendation of a 'gas-to-water' heat exchanger, I assume the gas would be the flue gasses. Do I have that right? Where would you locate the exchanger? Above the riser? Would you be trying to approximate the CSA of a 6" stove pipe, and 'funnel' all the flue gasses through it at some point in the system? Sorry if I'm completely miss-understanding your recommendation. |
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Post by Solomon on Jan 22, 2021 11:38:21 GMT -8
Yes, a gas to water heat exchanger is basically what a propane water heater is (I'll use propane rather than "gas" to avoid confusion). It's tubes that carry hot gas through a container of water.
Optimally, you might use a condensing water heater, just attaching your stove output to the bottom and letting the blower do the work.
But a simple, perhaps less efficient one could be constructed with stainless sheet metal and a high temp blower.
I would locate the heat exchanger near the water heater to heat water with a thermosiphon, no pumps.
I would not use the entire gas flow of the rocket mass heater. A water heater size system only has a 4" flue.
I would extract a portion of the exhaust gases from the top of the bell, run them through the heat exchanger, and then probably vent them back into the system after the mass. At least that's what I would try first. They might need to be vented outside because cold air might stop your chimney draw. Would need to incorporate a high point or a low point so that the system would not auto draft without the blower being on.
My idea in the past has been to create a water jacket attached to a portion of the bell or barrel. However, there's no way to run the system without heating water and that could be dangerous. Need to be able to run the RMH without heating water, or at least use an open system where the first tank can boil off in case of overheat.
Another hurdle is 4" high temperature insulated piping to carry these hot exhaust gases to the heat exchanger unless perchance they are sitting next to one another.
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