"on demand" aquahot burner control?

[oneknight]

Has anyone succeeded in doing this?

I've toyed with putting in a second thermostat to trigger the burner at a lower temp than the electric (as used by older aquahot units) but can't find a spot to screw it in or a thermostat that will fit any existing taps into the tank.

I've read here about an idea of using heat demand from any zone to trigger the burner, but never seen anything concrete.

My thought is to leave both switches on, but only let the burner run when actually needed to keep up with demand.

[dbircky]

Not sure what your trying to do. Aquahot is an on-demand hot water & heating system. I leave my electric switch on all the time but before taking a shower flip the diesel switch on for unlimited hot water. If I’m not on hookups, the diesel burner is let flipped on. The electric provides plenty enough for the washer or for doing dishes.

[RayandWendy]

I think what Jim is talking about is the ability to automatically turn on the burner when the electric isn't able to keep up. Like when the temperature drops lower than expected during the night.
It's definitely an interesting idea.
Later...
Ray

[Bobby Dowdle]

You should be using the electric and diesel together currently to maximize efficiency. The unit uses a control thermostat to tell it when to activate on heat and uses a snap disc on the water line to sense when to active the unit for water as well. I would contact aqua hot before you do anything. And if you ever take it in for service, you need to make someone aware of your changes.

[oneknight]

Originally Posted by Bobby Dowdle

You should be using the electric and diesel together currently to maximize efficiency. The unit uses a control thermostat to tell it when to activate on heat and uses a snap disc on the water line to sense when to active the unit for water as well. I would contact aqua hot before you do anything. And if you ever take it in for service, you need to make someone aware of your changes.

Earlier versions used 2 thermostats. Electric would come on first, alone. If it couldn't maintain temp, the burner would fire. Automatically. Without me having to go out and flip a switch. Without me even having to be home. That's what I'm looking to achieve.

The second thermostat (and a separate stir pump) have been cost reduced out of current aquahot models.

My coach is in outside winter storage, plugged in, the electric maintains a "warm enough so nothing freezes" temperature until/unless it gets really cold or stays there for a couple days. Then someone has to flip the switch.

I hope I've adequately explained why I want to do what I want to do?

[96 Wideglide]

I think you would need both a hi-temp, and lo-temp just for the electric element.

From what I've read, the older units that worked the way you (and I) want, had 4 thermostats.

[oneknight]

Originally Posted by 96 Wideglide

I think you would need both a hi-temp, and lo-temp just for the electric element.

From what I've read, the older units that worked the way you (and I) want, had 4 thermostats.

My boiler has 5 taps for thermostats (that I've found so far) One 1/2" pipe for the main, and 4 small ones for the Hi-Limits. I'd gladly sacrifice one or two Hi-Limit breakers to do this, If I could find a thermostat that would screw in.

[FIX-IT-BOB]

Like this...... thought the same thing.. It be helpful in a resort in that the diesel burner firing up always stinks out the neighborhood.. Having it turn on as a required or if the 120VAC was off be a great addition.

AND furthermore.... Id like a better heat exchanger in the aqua hot so that while driving down the highway in the cold the engine could heat the coach better..... The small heat exchanger is at its best good for hot water when washing hands at fuel stops ,,

CHEERS !!

[96 Wideglide]

It would be nice if a manufacturer made screw in thermostats in 5deg increments, so you could experiment until you got your system just the way you want it !

[oneknight]

Originally Posted by 96 Wideglide

It would be nice if a manufacturer made screw in thermostats in 5deg increments, so you could experiment until you got your system just the way you want it !

I put one of these in my Aquahot to replace the original thermostat after the second failure.
It's been solid for 3 years. Available in 10 degree increments.
2 parts so if it ever does fail I can swap it out without dumping boiler fluid all over.

It is "backwards", open until it reaches the set temp. I wired in a relay to reverse the logic, make it closed until set point.

https://amzn.to/3EPWHoA

[96 Wideglide]

I'll have to look into that next year!

I'd like to reduce the frequency of the on/ off burner cycles, even if the burner needs to run a couple of extra minutes when it does run.

[voltdoc]

Jim, saw your PM, here is the diagram from the EasyTouch thread that you said didn't show (some issue with google, hopefully it works now) speculating on a possible way to turn on the AH burner if any zone calls for heat. Caveat emptor its just a concept and untested.



As shown the idea is it would turn on the burner if any zone called for heat. An additional thought is to modify this by adding in a simple thermostat (the kind that closes a contact when the temperature drops to the setpoint) between the diode cathodes (the pointy end) and the relay. That would create logic where the burner would be turned on IF BOTH the zone was calling for heat AND the temperature had fallen below the thermostat setpoint.

That might work, however, I think what you might really be trying to do is trigger the burner if the fluid temp drops below a certain threshold. I'm not 100% clear on the existing temp sensor logic on the AH but it seems like it would be feasible to use that sensor to trigger the burner in a similar fashion.

I expect you don't want to get this hi tech, but for me, I monitor the outside temp (and other temps) and based on that turn on the AH burner when needed via eRVin. On a related note, I have been looking into converting my circa 2017 Aquahot to use the new Reporter Module which theoretically would provide various status like boiler temp and many other parameters to the RV-C network. I have found that one difference between my older AH and the reporter module versions is they use a thermistor sensor which can report actual boiler temp instead of a simple temp switch - see page 1 here under "Basic Features". The old thermostat was part ELE-015-011, the new thermistor version for use with the Reporter 2.0 or newer is ELE-014-711. My research into this is very preliminary and I'm not sure yet if it is feasible to convert and older AH to use the new reporter module.

Regardless, I think there is a much less complex way to trigger the AH burner to come on if certain conditions are met as discussed above.

[oneknight]

Rob,
I am not seeing the picture.
Just a blank box containing a gray circle with a line thru it. Some sort of permissions issue. I don't see any of your links on any posts.
Can I get the pic from your blog? or directly from your google drive?
Jim

I am mostly just trying to maintain boiler temp without intervention, emphasis on the without intervention part, tho if using heat demand is the easiest way...

Originally Posted by voltdoc

Jim, saw your PM, here is the diagram from the EasyTouch thread that you said didn't show (some issue with google, hopefully it works now) speculating on a possible way to turn on the AH burner if any zone calls for heat. Caveat emptor its just a concept and untested.



As shown the idea is it would turn on the burner if any zone called for heat. An additional thought is to modify this by adding in a simple thermostat (the kind that closes a contact when the temperature drops to the setpoint) between the diode cathodes (the pointy end) and the relay. That would create logic where the burner would be turned on IF BOTH the zone was calling for heat AND the temperature had fallen below the thermostat setpoint.

That might work, however, I think what you might really be trying to do is trigger the burner if the fluid temp drops below a certain threshold. I'm not 100% clear on the existing temp sensor logic on the AH but it seems like it would be feasible to use that sensor to trigger the burner in a similar fashion.

I expect you don't want to get this hi tech, but for me, I monitor the outside temp (and other temps) and based on that turn on the AH burner when needed via eRVin. On a related note, I have been looking into converting my circa 2017 Aquahot to use the new Reporter Module which theoretically would provide various status like boiler temp and many other parameters to the RV-C network. I have found that one difference between my older AH and the reporter module versions is they use a thermistor sensor which can report actual boiler temp instead of a simple temp switch - see page 1 here under "Basic Features". The old thermostat was part ELE-015-011, the new thermistor version for use with the Reporter 2.0 or newer is ELE-014-711. My research into this is very preliminary and I'm not sure yet if it is feasible to convert and older AH to use the new reporter module.

Regardless, I think there is a much less complex way to trigger the AH burner to come on if certain conditions are met as discussed above.

[alank]

I don't understand what is going to be gained by having the diesel burner come on when any zone calls for heat. It sounds like the boiler fluid thermostat is going to be bypassed as a control of the diesel burner, and the activation of a/all zones is going to be the control that activates the diesel burner. Why would you want to do this?

The diesel burner produces 50,000 + btu's of heat that gets introduced into the Aqua Hot. If my bedroom cozy comes on calling for heat, it will remove 5,000 to 10,000 btu's of heat from the Aqua Hot while the diesel burner is introducing 50,000 btu's of heat into the Aqua hot. How long do you think it will take before the Aqua Hot area becomes heated to the point, you'll have a fire?

If you say no, the boiler fluid thermostat will shut off the burner before it gets that hot, isn't that the way it works as manufactured? Aren't you bypassing that by having the burner come on and off with the zone demand?
Either the boiler fluid thermostat, or the zone switch, will have control of the diesel burner, they both can't control the burner at the same time. I just don't see what the advantage would be.

I originally thought that the intent is to keep the boiler hot with the electric element, and only have the diesel burner come on when a zone calls for heat. It seems to me that having the diesel burner controlled by zone demand rather than thermostats/thermistors is just a design for disaster.

Explain to me what I'm missing.