CI radiator demo high and low connections

hot_rod

Broke my heart to cut out this decorative plug.. but in the interest of research. Cast plugs don't come out easily like steel nipples. So I chose to tap the inside to 1". I think I can braze the flowered plug cut off back onto a 1" steel plug.

So feeding the bottom at 4 gpm, return from top same side. 45 minute run time.
Delta T started at 12, closed to 8 at 45 minute run.

BTU output at start, cold radiator 25.8K BTU, 500 X 4 X 12.6= 25,200 BTU/ hr

BTU output at 45 minute 19.4

So the BTU meter reading and the hydronic formula, in italics, pretty much square.
Also, no question the connections on the same side, top and bottom does allow the radiator to heat just fine. It differs from the bottom to bottom flow path by the heating profile, a small amount.

Getting toasty in here, I'll run it to thermal equilibrium, supply and return temperature stabilize.

Big Ed_4

What about supply on top and a bottom return with a lower GPM ?

hot_rod

some gravity design data that Larry W  posted in 2018

Looks like 3/10- 1 fps velocity. So 1 fps in 3” pipe would be how many gpm?

Steamhead

hot_rod said:

Broke my heart to cut out this decorative plug.. but in the interest of research. Cast plugs don't come out easily like steel nipples. So I chose to tap the inside to 1". I think I can braze the flowered plug cut off back onto a 1" steel plug.

So feeding the bottom at 4 gpm, return from top same side. 45 minute run time.
Delta T started at 12, closed to 8 at 45 minute run.

BTU output at start, cold radiator 25.8K BTU, 500 X 4 X 12.6= 25,200 BTU/ hr

BTU output at 45 minute 19.4

So the BTU meter reading and the hydronic formula, in italics, pretty much square.
Also, no question the connections on the same side, top and bottom does allow the radiator to heat just fine. It differs from the bottom to bottom flow path by the heating profile, a small amount.

Getting toasty in here, I'll run it to thermal equilibrium, supply and return temperature stabilize.

Well, that rad is definitely in a partial short-circuited state. Note how the hottest water is in the first section, even after a 45 minute run. I'd be interested to see the FLIRs of when the feed is at the top, with the return at the bottom of the same side.

Also- note the very small friction losses in the charts you shared- 0.001 to 1 pound per square foot EDR, per running foot of pipe. This was needed to allow gravity circulation since the motive force was so small, and also explains why the pipes were so big.

Big Ed_4

A near gravity flow would work better ..

hot_rod

Big Ed_4 said:

A near gravity flow would work better ..

What would near gravity flow be? In gpm.

I reversed flow, supply at top, got flow set to .4. The radiator is still warm from earlier testing, I'll run it tomorrow.

I suspect if flow goes laminar at low flow like .4 gpm heat transfer will go down.

I would say these cast columns look to be 1-1/4 or maybe 1-1/2" pipe equivalent. So calculate The Reynolds number based on 1-1/4 and 1-1/2" schedule 40 pipe.

LRCCBJ

Something is in error regarding the BTU output. A rough estimate of that radiator results in an EDR of 32. With 150F supply, at equilibrium, the output is 3520 BTUH. It cannot be anywhere near 19400 BTUH. Of course when the radiator is cold, a considerable amount of energy is demanded to warm it but this is not at equilibrium.

hot_rod

Another run at .3, 3/10 of a gpm flow rate.

The delta at 5 minute run was 83°. 500 x .3 x 83 = 12,450 btu/hr. The BTU meter showed 12.2 btu/hr
After a 60 minute run, delta was 48°. 500 x .3 x 48= 7,200 btu/hr.

I run this at 4 gpm, merge the IR slide for a side by side look at the heat output profile.

PeteA

@hot_rod
really cool test and interesting images. This is a great visual for me now that I see the reason why after 15 minutes my thermostat is satisfied yet my returns are still very cool compared to the output. I'm really glad to see that it looks like the water doesn't short circuit through the first couple of ribs since it looks like it shoots over the top of the whole radiator and then gets pulled down through the radiator body.

Thanks for the great work running these tests

hot_rod

Comparing a .3 gpm and 4.1 gpm flow, boiler running 180 SWT
8 section cast iron radiator 2" connections top and bottom

At the end of 45 minutes the higher flow run was 165 - 170° across all the sections.
The .3 gpm run showed the radiator temperature from 57- 155° at the top

You could certainly smell the higher temperature radiator in addition to the IR view.

Larry Weingarten

Hi @hot_rod , Nice research! Is there any TRV that would be compatible with gravity flow? That could make for a simple and comfortable system.

Yours, Larry

realliveplumber

And to think all these new mcmansions and multi million dollar houses, all with scorched hot air.

Every once in a while,you see one from 10-15 years ago with a boiler and fan coils in an air handler.

People will never experience the comfort of a hydronic or steam system.