Putting a DHW sensor on the outlet

Gordan

I've got a Turbomax 23 providing my hot water, and a Prestige Solo 60 is heating it. The tank has a hefty 1.25" outlet at the top, and an aquastat probe somewhere near the top of the tank. Having observed the whole setup in operation, typically it takes quite a bit of draw to get that aquastat to close, even when I dial the differential down as low as it'll go. I've been thinking about strapping the DHW sensor that comes with the Prestige to that outlet tube, making sure it's got plenty of thermal contact, and insulating the heck out of it. I would think that, when there is no draw, the measured temperature at the outlet should be the same as the temperature at the top of the tank.



The idea is that I should be able to detect the drop in the outlet temperature almost immediately and kick on the boiler (if appropriate - I get to control that with MCBA settings) minutes before the aquastat would have been able to respond - and long before the outlet temp drops so low that my mixed DHW supply dips - and maximize the ability of the boiler to keep up.



Am I howling at the moon here, or will the difference be insignificant? It seems like I should be able to squeeze about two more gallons of draw for each minute of reaction time that I shave off...

Mark Eatherton

Might give you a cold sandwich...

In the mountains, I have a FPHXer tied to my Knight for DHW. I have the sensor firmly mounted and insulated at the outlet of the heat exchanger. When I need hot water, say for a shower, I turn the water on a few minutes in advance, because if I don't and I turn it on and jump in, it goes cool before it picks up and kicks in, but YMMV because you have a considerable amount of mass surrounding the heat exchanger.



Won't cost much to try it and see if it works...



ME

Gordan

Yep, that's what I'm thinking, too.

So, regarding nuts and bolts - do you know of any strap-on wells for your average suppository-shaped thermocouple? Or will I have to McGyver it up?



Thanks again!

Mark Eatherton

Thermistor, not thermocouple...

Semantics, but you need to use the thermistor that the manufacturer recommends.



Just strap it to the pipes outlet using work gear clamps, and insulate it with some good pipe insulation.



ME