still trying to get my head around a possible power failure

[sweetheat]

I've been reading all the threads on power failure for the tarm 40, please correct me if I'm wrong. a dump zone is the first line of defence in a power failure. what is the difference between a dump zone and a gravity feed zone with an automag? are these both the same things? If I understand it correctly the gravity zone has to be installed without any bends or changes in elevation, restrictions, and placed above the boiler. some have a cast iron radiator in use for there dump zone, seems like there would be restrictions in a cast iron radiator. others talk about a thermo-siphon loop to a tank above the boiler for an overheat situation. 25' of fin tube seems to be what everyone uses. or possibly a pressure hot water tank. a heating zone will not work because of the restriction ? can a heating zone without restrictions be used as a dump zone? or is this impossible. what to do about a pump failure? automag to the overheat loop which is the same as a dump zone??? it's my lack of plumber terminology. please get me straight on the different words and what they mean. thanks sweetheat

 

[MrEd]

Here is my understanding. You actually need two "dump" zones, but they could be the same thing with some clever planning and piping. The first dump zone is where you want the heat to go when the power is on, but nothing is calling for heat, but the boiler needs to dissipate the excess heat to prevent from overheating. In my setup I have about 80' of baseboard in my cellar that will be my place to throw excess heat when I have no other place to put it. On my setup a honeywell L4008B will force open the zone valve to that loop, even if that zone's thermometer does not want it to open. The circulator will push hot water thru that long run of baseboard and the cellar will get hotter than I would like, but the boiler won't overheat. Its a good use for excess heat in my setup since a toasty cellar tends to keep the floors warmer upstairs, so the heat is not wasted. Worst case is I crack open a window if it gets to hot.

The second "dump" zone I have is a gravity dump zone which will only get used in the case where the boiler is running and there is a power failure. Right off the top of my tarm (I go to a "T", and the up leg of that tee is going to go to an automag zone valve and then approx 40 feet of baseboard I have mounted high up on my wall in the garage (right above the tarm). The automag zone valve will normally be closed, if the power goes out, that zone opens by default. Circulators will not be running, so this loop will depend on gravity to push the hot water up into the loop and thermosiphon itself around. Since I am always home when the tarm will be running, I will also open up the large doors to the cold outside temperatures to help those baseboards cool down even quicker.

I am not sure about the no changes in elevation and no bends...any loop is going to have elbows/bends and probably at least some elevation changes. I think as long as the beginning of the loop goes "up", that the constant flow of new hot water pushing "up" will cause the loop to circulate.

 

[webbie]

Consider that a tarm solo will also likely not produce a lot of BTU's during a quick power failure - that helps a little!
I worry much more about power-out with very low water vol. boilers such as Seton, etc. - it seems these could almost instantly convert the water to steam in such a case.

Another simply trick I often used was...in the colder weather, to leave a check valve partially open - or even a mixing valve (you can set the baseline) - this allows a little heat to leave the boiler by gravity - at least when the boiler is below the living area.