Tweaking the BioWin's Buffer Tank

[bdud]

Yep, aquastat.
The sensor for turning off the boiler is on the buffer tank, and then, after that event, the aquastat on the boiler supply pipe keeps the pump running until it (drops?) to a certain point.

 

[velvetfoot]

Can you tell me where on the tank sensor and aquastat are located?
I really have a hankering to have the boiler turn itself off rather than a tank sensor.

 

[bdud]

A picture of my aquastat that controls my pump for the buffer tank.

A picture of the aquastat controlling the boiler on and off.

I took out the original mechanical aquastat and put this one in. This one seems more precise, with an easy to see display. The probe is in the stock location where the old aquastat's probe was installed, maybe 2/3rds up from the bottom of the tank.
I have the boiler temp set at 167 and the buffer tank is at 170. If there is a call for heat on any of the zones and the boiler is on, the buffer tank does not reach the 170, hopefully running more economically rather than the boiler having to keep powering itself up.
I had considered rewiring so if any zone was on the boiler would not turn off, but this works well.
Might need some more tweaking in the colder temps.

I am not sure what you mean by "I really have a hankering to have the boiler turn itself off rather than a tank sensor."
If there are no zones calling for heat and the buffer tank is up to temp, not sure what you want to achieve.

 

[velvetfoot]

Thanks.

I am not sure what you mean by "I really have a hankering to have the boiler turn itself off rather than a tank sensor."

I just did it. I changed the wiring so that the heat demand from the tank is turned on by a temperature controller with a sensor 1/3 of the way from the top, and turned off when the boiler draft fan stops. The heat demand is kept going by a relay that gets its signal from the running draft fan. The tank got to 179 top and 176 bottom. The guesswork is eliminated and the heat transferred is maxed.

As a side benefit, the heat purge on shutdown timer can be eliminated, because the pump continues to run throughout the burnout stage, which is about 10 minutes, I think. Although I didn't time it yet, the tank's top and bottom temps were the same 179/176 after running 10 minutes after the end of burnout, so I think that running the pump through the burnout phase does the trick.

The oil backup is also simplified, and a timer eliminated, because it is wired to come on if the 1/3 from top tank temp is somewhat less than the temp triggering the pellet boiler and the pellet draft fan is off. It will also stay running until its built in aquastat is satisfied.

What stays the same is the pellet boiler pump won't run unless the boiler temp is above 130, and the zone pumps won't run unless the tank top is above 130.

Deering noted a situation where his backup boiler came on because the tank sensor temp was below that of the boiler while it was in standby. I'm hoping that's not a problem for me, but I can always lower the oil boiler's kickoff temp.

 

[velvetfoot]

Well, I tested it, and everything seems to work! Anyway, everything seems to work! The backup oil boiler came on with the tank top -1/3 Ranco set at a little less than the pellet sensor and stopped with the boiler aquastat, the pellet boiler came on and stopped in a similar manner. Pellet boiler pump ran throughout the burnout stage (which was at least 13 minutes-I think I caught it near the start when I went downstairs, lol). Pellet boiler pump and zone pumps do not run at less than 130. Another side benefit is that the setup is a lot more compact with fewer stuff. I believe my tweaking has come to an end!

I should note that during my testing the Froling Energy Tank top sensor got below 130, as I recall, and was providing good hot water for the shower.

Here is what the new setup looks like.