I built my system with a loading unit instead of a separate circulator and thermostatic valve for temperature protection on the return side.
I got the Termovar model with the "backflow preventer"; which not only is supposed to keep the system from leaking heat out of the storage tanks after the boiler has finished firing but will allow the boiler/storage tank to thermosiphon heat from the boiler to the tank in case of power failure. This last feature is not guaranteed but depends on a lot of factors. No way to know until you try it.
So last night while the boiler was hot and ripping right along with a nice charge of very dry hardwood I yanked the electric plug out of the wall. Then (according to strict Utube experimental protocols) I opened a beer and pulled up a chair.
The blower on my Tarm Solo 40K is not all that loud but it's very quiet when it's not running. So I could hear the torch still running down in the afterburner chamber. I have a tall masonry chimney up to the attic and metalbestos up and out through the attic. The draft runs about -.05" on the manometer when fully at play. Within a few minutes the draft dropped to -.02" and stayed there for the rest of the test. And by that time the torch was no longer audible but still visibly burning a dull orange.
At the time of the power cut the supply temperature out of the boiler to the storage tank was running about 160F: normal for the 1st cycle through with a cold tank. Supply was mixed through the thermostatic element in the loading unit and coming into the boiler at 140F: again, normal. Without trying to guess what would happen I was surprised to see the supply temp DROP a few degrees after 5 minutes. This didn't make sense until I looked at the return temp to see that (without the circulator running) the thermostatic mixing part of the loading unit was no longer mixing and the supply was straight out of the storage tank at 80F. So the "backflow preventer" does work. Let me say here that this is probably entirely dependent on the tank being higher than the boiler. In my case the top of the tank is 3ft. above the top of the boiler but the bottoms of both are close to the same level and only 2ft. apart.
The most dramatic thing is that the water temperature coming out of the boiler didn't increase but the temperature difference between supply and return increased from 20F to 75F. Things went like this for an hour... 80F in and 154F out, 12.5PSI to 13 PSI at the end of the hour. The boiler was actually charging the tank (Yeah, I know, pretty slowly). That's when the dinner guests showed up and the fun was over. I plugged it back in, started the draft fan and it was back to normal fire within seconds.
I now need to try this same thing with the tank full of hotter water to see if it maintains the same deltaT at higher return and supply temperatures.
Anybody else out there with loading units try this yet?
I got the Termovar model with the "backflow preventer"; which not only is supposed to keep the system from leaking heat out of the storage tanks after the boiler has finished firing but will allow the boiler/storage tank to thermosiphon heat from the boiler to the tank in case of power failure. This last feature is not guaranteed but depends on a lot of factors. No way to know until you try it.
So last night while the boiler was hot and ripping right along with a nice charge of very dry hardwood I yanked the electric plug out of the wall. Then (according to strict Utube experimental protocols) I opened a beer and pulled up a chair.
The blower on my Tarm Solo 40K is not all that loud but it's very quiet when it's not running. So I could hear the torch still running down in the afterburner chamber. I have a tall masonry chimney up to the attic and metalbestos up and out through the attic. The draft runs about -.05" on the manometer when fully at play. Within a few minutes the draft dropped to -.02" and stayed there for the rest of the test. And by that time the torch was no longer audible but still visibly burning a dull orange.
At the time of the power cut the supply temperature out of the boiler to the storage tank was running about 160F: normal for the 1st cycle through with a cold tank. Supply was mixed through the thermostatic element in the loading unit and coming into the boiler at 140F: again, normal. Without trying to guess what would happen I was surprised to see the supply temp DROP a few degrees after 5 minutes. This didn't make sense until I looked at the return temp to see that (without the circulator running) the thermostatic mixing part of the loading unit was no longer mixing and the supply was straight out of the storage tank at 80F. So the "backflow preventer" does work. Let me say here that this is probably entirely dependent on the tank being higher than the boiler. In my case the top of the tank is 3ft. above the top of the boiler but the bottoms of both are close to the same level and only 2ft. apart.
The most dramatic thing is that the water temperature coming out of the boiler didn't increase but the temperature difference between supply and return increased from 20F to 75F. Things went like this for an hour... 80F in and 154F out, 12.5PSI to 13 PSI at the end of the hour. The boiler was actually charging the tank (Yeah, I know, pretty slowly). That's when the dinner guests showed up and the fun was over. I plugged it back in, started the draft fan and it was back to normal fire within seconds.
I now need to try this same thing with the tank full of hotter water to see if it maintains the same deltaT at higher return and supply temperatures.
Anybody else out there with loading units try this yet?
