Domestic Hot Water Priority
- Lightning
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At some point in the near future I may incorporate DHW priority with my setup. My goal would be to shut off the circulator (I only use one circulator) while the hot water is running so that the boiler is only doing one or the other. Meaning it's either heating DHW or it's heating the house and outbuilding, with priority on the DHW.
Could anyone give some details on how to do that?
Would I just have the circ shut off if the boiler went below a specific temperature?
Could anyone give some details on how to do that?
Would I just have the circ shut off if the boiler went below a specific temperature?
- hotblast1357
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How are you making DHW? Plate exchanger?
And I have to ask, why? Axeman can’t keep up?
And I have to ask, why? Axeman can’t keep up?
- Retro_Origin
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A standard setup with a triple aquastat runs the circulator thru the c1 and c2 terminals so that the domestic takes priority over the heating system by not powering the circulator unless low limit is met
- Lightning
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I'm using the internal DHW coil in the boiler. Yes the Axe keeps up just fine, but if I slow the fan down I'll want to split up the duty.hotblast1357 wrote: ↑Sat. Feb. 04, 2023 9:07 pmHow are you making DHW? Plate exchanger?
And I have to ask, why? Axeman can’t keep up?
- hotblast1357
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easiest way would be to mount a strap on aqastat onto your DHW line, either cold in or hot out, and have it cut power to your main circulator. I couldn't imagine giving DHW priority, in my house keeping it warm is more important than a hot shower at that moment.
- Lightning
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I ran that thru my thoughts. It would work to initiate a circ pause, but what happens when water stops flowing? It would sit in the pipe at it's current temp until ambient temperature influenced it, which would take way too much time.hotblast1357 wrote: ↑Sun. Feb. 05, 2023 8:08 ameasiest way would be to mount a strap on aqastat onto your DHW line, either cold in or hot out, and have it cut power to your main circulator.
DHW use is relatively short bursts with the exception of a kid taking a 30 minute shower, so it might not be hugely noticable in the house heating, or maybe it would, I don't know for sure.hotblast1357 wrote: ↑Sun. Feb. 05, 2023 8:08 amI couldn't imagine giving DHW priority, in my house keeping it warm is more important than a hot shower at that moment.
I'm thinking that using another Inkbird to measure boiler temp would be easy. I'd have it cut the circ if it went below a certain temp, like 150 for example so that the boiler could catch up.
- hotblast1357
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I guess ill ask it here as it was overlooked in the other thread... this is all because you want to slow the combustion fan so that it runs longer... but currently you have the hysteria set to like 2 degrees or something crazy small so that the fan cycles a lot, why not just set it to 10-20 hysteria like "normal"? you fan will run longer and everything will be just fine.
- Lightning
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If I were to assume on demand water heating at a flow rate of 2 gallons per minute, is the following calculation correct?
8.34 pounds per gallon x 2 gallons per minute x 75 degrees (delta 50 to 125 degrees) x 60 minutes = 75,060 BTU per hour
I need 75,060 BTU per hour minimum for 2 gallons of 125 degree DHW per minute?
Did I do that right?
8.34 pounds per gallon x 2 gallons per minute x 75 degrees (delta 50 to 125 degrees) x 60 minutes = 75,060 BTU per hour
I need 75,060 BTU per hour minimum for 2 gallons of 125 degree DHW per minute?
Did I do that right?
- Lightning
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I intended to answer that but I get scatterbrained sometimes lol. It's not that I want the fan to run longer, but of course it will... . I'm very curious if better matching the boiler to the heat load will improve fuel usage. I have a lot of data for pounds of coal used per HDD. It averages 1.5 to 1.6 pounds per HDD most of the time during normal wintertime weather. If I see a dramatic drop or increase due to fan speed, I'll know it was a contributing factor. Some of the things I do are for learning and just general curiosity.hotblast1357 wrote: ↑Sun. Feb. 05, 2023 9:59 amI guess ill ask it here as it was overlooked in the other thread... this is all because you want to slow the combustion fan so that it runs longer, but currently you have the hysteria set to like 2 degrees or something crazy small so that the fan cycles a lot, why not just set it to 10-20 hysteria like "normal"? you fan will run longer and everything will be just fine.
- Lightning
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So if I need 75,000 BTU per hour minimum for DHW, and I have the boiler doing one or the other (home heating being the other). I could theoretically cut the fan speed to the point that the boiler produces 75,000 BTU per hour instead of 130,000.
- Lightning
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On my coldest day I'll use around 100 pounds of coal. That is less than half of the Axe's current capacity. A lot of wiggle room there to slow it down.
But if I want to go under 75,000 BTU per hour output I'll need to spread out the DHW heating. That would be the next bridge to cross after this one.
But if I want to go under 75,000 BTU per hour output I'll need to spread out the DHW heating. That would be the next bridge to cross after this one.
- hotblast1357
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i would say you dont need anywhere near 75,000 BTU/H for heating needs, and for the DHW usage, correct you need around 75,000BTUs for one hour, the other 23 hours of the day you need nothing.
at 100 pounds of coal per day, thats only 37,500 BTU/H. 100X9,000 BTUs= 900,000 BTUs / 24 HRs is 37,500 btus per hour.
at 100 pounds of coal per day, thats only 37,500 BTU/H. 100X9,000 BTUs= 900,000 BTUs / 24 HRs is 37,500 btus per hour.
- Lightning
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Yeah, that's what the boiler would need theoretically so it wouldn't fall behind. An easy work around would be to run the boiler a little hotter to store some heat as a buffer for DHW heating.