Caleffi Heat dump zone

cutter

Hot Rod this is sort of directed at you, for you are the caleffi expert. I was sort of skeptical of the heat dump zone in Idronics #10. But I realized it is a gravity system zone that worked before some one discovered electricity, and then built electric driven pumps.

Idronics #10 has no information on how to build this heat dump. Back in the gravity era they used large supply and return pipes, so I was wondering what suggestion's you might have.

The supply on my boiler is 1 1/4", My idea would be to put in a 1 1/4" tee A little ways after the boiler and pipe 1 1/4" up to the 3/4" fintube and use a 1 1/4" X 1 1/4" with a 3/4 branch tee to supply the fintube. and have maybe 2 or 3 runs of fintube as pictured in Idonnics #10. All supply's sloped upward a little and returns all sloped and going down. In Idronics # 10 the return is shown going into the bottom of the return pipe, pictures of an old gravity system install I saw was the return went into the top of the return pipe.

Here are a couple of question if you are willing to give a little input.
Is there a reason the caleffi design has the return going into the bottom of the pipe?
Do you think the inch and a quater supply and returns I suggested are large enough?
How much fin tube should be run two six footers, three six footers?
Can fin tube be bought larger than 3/4 inch?

hot_rod

It is a bit of a guesstimate sizing for an arbitrary condition.

Many suggest sizing to dump boiler output for possibly 30 minutes. This should be enough to prevent over-heating in a power outage.

If for some reason the boiler does not shut down the air intake or blower tightly in a power outage it may need to run a dump zone for several hours worth of boiler output, until the fuel burns out?

Here are a few options. A large UPS could be tied into the current pumping arrangement to dump excess to zones or a buffer tank. The UPS would need to be sized to run all the pumps and possible open some zone valves depending on your piping.

This would involve the UPS sensing the power outage, a zone or zones, or a buffer tanks takes boiler output during outage. I'd consider this an active, powered heat dump system. With a power system the dump zone could be located anywhere. A garage, buffer tank, even a loop outside

A passive approach would be the fin tube piped to allow gravity induced thermosiphoning. I suppose one could calculate that pipe sizing with some of the old gravity design handbooks
I think a 1" loop with a few runs of 3/4 fin tube would work. No harm in oversizing the piping. Multiple runs of fin tube piped parallel would keep pressure drop low to encourage gravity induced flow. A gentle slope also helps encourage flow just like the old gravity systems were piped. This assembly needs to be above the boiler to operably properly.

The thermal trap at the bottom connection is to prevent ghost flow during regular, pumped operation of the system. The zone valve up top, NO normally open, (power to close) would open in the event of a power outage. The zone valve provides 100% shut off on one side, the thermal trap eliminates back end circulation aka ghost flow. 12- 18" deep for that drop.

Some example from the NYSERDA guide that Siggy developed for NY State.

cutter

Hot Rod, thanks for the suggestions. I have room above the boiler to put in an old gravity system. Or there is a small room next to the boiler room that does not get as warm that might be a better location. Where I am at we very seldom have a power outage. What I am more concerned about is the main pump going out. But that old series 100 bell and Gossett is being replaced with a Wilo Variable speed pump. Those B&G couplers go out when they want to.

I will most likely wire in two dump zones, one to dump into the largest zone when there is power and the gravity to dump, if power goes out in the middle of the night. I don't have access to old gravity design books but I will look around. The inside boiler I have does not have a blower on the supply draft side. The draft does shut down when hot but definitely not 100%.

The one picture that you posted that showed a dump zone just below the overhead had large headers supplying the fin tube, and looked to have large piping supplying the headers which would make sense. I wonder where they got a zone valve that large, or a valve that would open with no power.
Thanks again Hot Rod

hot_rod

Any brand of spring return N.O. normally open zone valve would work. When the power is on it is closed, opens when power drops off.

I'm not sure how much time and money you want to throw at this rare occurrence? New wet rotor pumps in good quality water seldom just fail.

I would think 1" would be plenty for the S&R. I have seen solar thermal systems run on just thermo siphons with 3/4" copper.

The elevation difference and the bouyancy of the hotter water drives the transfer.

Personally the UPS and a small ECM circulator would be the way I lean. It give you a predictable amount of energy transfer with simple off the shelf parts.
A small kickspace heater would move a lot more energy than bare fin tube and it could be located most anywhere in the building, to use the heat. You just need to move enough energy to keep the boiler from over-heating, not dumping the entire output. With the duper closed, you should not need to dump latrge amounts of BTUs?

So the pump kicks on in power outage, the kickspace heater sees a temperature increase and operates automatically via the snap switch included. Just power it from the UPS also. An ECM on low speed and a kickspace heater on low would probably consume less that 100W

cutter

In the 30 plus years of heating with wood in this house I have never had a power outage. The two biggest problems have been the coupler on the B&G pump and a Honeywell control that would not turn on the pump when it was supposed to. That was the main reason for thinking about putting in this dump zone. The pump is being replaced with a Wilo and the control is being replaced with a Caleffi control. So that will take care of the two biggest problems. I do have to have a dump for over loading the boiler, and that has happened more often than the pump and control failure.
When I re pipe this boiler this summer I will put in the extra ports for the dump.

I think you are right about this, I don't know what kind of maintenance the UPS would need. "Personally the UPS and a small ECM circulator would be the way I lean".