Gravity circulation option on new primary loop

Quercus

Hi,
I was going to install a thermostatic valve as a system bypass to act as boiler protection, but have instead decided to go with primary-secondary. I feel that I would have the greatest flexibility in the future since I may want to add heat to a sun-room and an indirect water heater.

During our last two major October snowstorms we lost power for a week and were without heat. So I am thinking of installing bypasses from the primary loop around the pumps with shutoffs. The idea being if I could muster enough backup power to fire the boiler I could keep the house from getting too cold in a prolonged outage.

Original system was gravity and I am keeping the piping at 1-1/4 near the boiler. Boiler is an atmospheric CI with the supply on top.

Am I nuts? I am hoping that this will be like the effect of a new snowblower on snowfall rates.

Steve

JUGHNE

Some water will migrate by gravity thru pumps if there is not a flow check built into the pump or one added downstream.
You could just fire the boiler with the pumps disconnected from power and see what happens. The old gravity piping might induce enough flow for minimal heat delivery. It might take hours. Something to do while you monitor short cycling of boiler firing of course. Interesting project, let us know if you try this, please.

Quercus

Thanks for responding.

I haven't piped it up yet and don't know if I will be installing the flow check in the pump or not. There is no primary loop at this time. That's why I thought there was no time like the present.

Regarding gravity flow through the pumps, I originally planned on installing the secondary loops on the upper part of the loop and felt that would be prone to unwanted flow. When I made the diagram for the post I moved the secondary taps to the lower part of the run and would shunt from the top of the run to help the gravity flow. My thought was to embrace the gravity flow for any reason I would need it. Cost is not bad if it saves frozen pipes some day.

Original piping had the whole house directly above the supply but I never fired it in a power outage.

I plan on testing as you described and will post results. It's mighty tempting to fudge the results to get the "Quercus Shunt" published in boiler manuals.

hot_rod

I know for a fact you can get thermal migration up the secondaries, especially if they are vertical like that.

I'm not sure the heat energy will get in and out of the boiler and warm the primary loop without that circulator running?

What drives gravity circulation is vertical piping and temperature differential. If little heat energy, mainly temperature, leaves the boiler, you may not have much differential to drive the heat up the secondaries. The closely spaced tees may complicate that further.

Then old timers knew how to calculate that gravity driven flow based on the bouancy provided by the delta T.

Or you could install ecm circs and get a few deep cycle batteries and an inverter to run the system during power outages.

Gordy

Or ditch the batteries, and inverter just get a little 2000 watt Honda for 900 bucks. 13 amps will run near 4-6 hours on a gal of fuel under load. Of course it would have to be outside..........gotta say it.

Quercus

hot rod said:

I know for a fact you can get thermal migration up the secondaries, especially if they are vertical like that.

I'm not sure the heat energy will get in and out of the boiler and warm the primary loop without that circulator running?

What drives gravity circulation is vertical piping and temperature differential. If little heat energy, mainly temperature, leaves the boiler, you may not have much differential to drive the heat up the secondaries. The closely spaced tees may complicate that further.

Then old timers knew how to calculate that gravity driven flow based on the bouancy provided by the delta T.

Or you could install ecm circs and get a few deep cycle batteries and an inverter to run the system during power outages.

I noted in the drawing that the turnaround at the start of the loop was level but since I have thought elevating into the part of the loop for the secondaries would be better to move the water up. I drew the shunts to draw from this high section of the loop and join the secondary above the pump. So that would alleviate concerns about close spaced tees unless you are talking about the two circuits being too close to each other.

Not enthused by generators with the gas sitting in them for years between uses. I'm holding out for NG residential fuel cells. I'm gonna skip the whole modcon fad.

Oh yeah, I forgot to show the shunt around the return pump.

I was thinking only enough power to drive the damper. I am unsure of the power draw on the circs and don't know how long I could run them. Usually you can tell if the power is going to be out for a little while or a really long while.

Quercus

I'm halfway through the job. Here is a pic of the progress. Next boiler gets a wall panel. Space and tubing seems to get consumed at an alarming rate.

Quercus

I managed to finish without messing too much up. Got all but one leak found and fixed before powering up. Forgot an isolation valve for the main zone - DOH!

Anyway, I put in 2 bumblebees and left a baseboard loop with the 007 on it. I put the boiler pump in setpoint mode with 140* target and the main house on delta T of 45*

The baseboard pulls off the primary first and returns cool water to the primary before the main zone. The main zone ends up returning water around 85* (while I was watching).

The numbers may not be totally accurate because I had to do a second radiator bleed. Anyway my goal of having gradual heat with a long heat call has been achieved. The pumps stay running and the boiler works off its 180 high limit. It's interesting to see the 2 bumblebees adjust there flow rates to do their jobs. You can see the flow in the primary and secondary circuit to see how much supply water is being sent back to the boiler for protection.

I am pleased with the pumps. If only the programming was simpler. If I did it every day I could get used to it but the touch switches are hard to tell if you are making contact or not.