Baseboard Convectors

They will work, just at a greatly reduced capacity. I attempted to find you an idea of the heat transfer @ 110º F but none of my charts go below 150º F.

Want me to take an educated guess? I'd think < 100 BTU per foot.

Put in extra BB if you can

maximize the the amount of heat you get at lower water temps. If the room is well insulated, 120° might be all you need.

I was once told...

that fin tube convectors will not "convect" below 140.
If this is true how does the heat get into the room?
Am I being dense and missing something, or did I get bad information?

Bergy

I have that exact situation in my house

Craig:
My house has this exact setup. Mostly radiant, with some baseboard, with Mod-Con & reset. I'm using a Tekmar controller to acheive the reset curve, and injection to mix down to the radiant temps. As I don't have an indirect DHW heater, I set the it up so that when a thermostat controlling any of the basxeboard calls for heat, it triggers the DHW priority function which boosts the boiler temp to high temp. After the baseboards are satisfied, all goes back to normal reset running.

Here's the set up

435 sqft with 98 feet of wall, 88 ft is exposed. 14 triple glazed windows and super insulated. Heat loss @ -5 of 11,146 Btu/hr.

If I'm guessing correctly(The products paper work only shows temps down to 170) 120 deg @ 4GPM should give me
190 Btu/ft. I would need 59 ft of BB to cover the load @ design temp.

I could run the system at 120* even though I only need 110* for the bulk of it. Not the best solution, but it will keep down the cost and allow the mod/con to condense it's little heart out

Thanks for the help!

Bergy

Sure

Pipe it reverse return within the cabinet. Feed the top, first tee, and return from the bottom, last tee.

If you sized it and pumped it and piped it so that the supply pipe couldn't supply the flow rate to the (big enough) riser that you need to feed the (small enough) tube size within the convector.

To illustrate, you wouldn't CHOOSE inch and a half fin tube for 3 tier parallel flow, with 3/4" risers.

PLAN for flow rate, delta T, and fin tube diameter.

It's sold from 1/2" through 2", right off the shelf.

Noel

Counter-Flow

The term counterflow really comes from the colliding paths of the fluids, Mike. Air in the bottom going up meets hot water in the piping coming down.

If you ever come across cooling coils (chilled water I mean) piped backwards the difference is dramatic because of the low delta-T's involved. HW is more forgiving because there is more of a Delta-T hence wiggle room. Chilled water is much more demanding; success or failure is a degree or less away. You either dehumidify or you do not.

You grasp correctly, hot water below will retard the convection above. Sort of like the big brother taking the big piece of cake first...

My bad, Noel

Sorry about the mis-spelling, now corrected.

The BTUH output was below the selection criteria using Vulcan Radiator products; I do not have the data with me. But being a condensing boiler project and striving for high delta-T's overall, we would tend to have lower water flows.

We were not so concerned that we would lose significant heat but were scrambling for every BTU we could get. I will look at the charts tomorrow if I get a chance. But professionally we could not in good faith go counter to a manufactured product recommendation. They (Vulcan) have a minimum flow rate of 0.30 FPS below which laminar flow occurs. 1.0 GPM in 3/4" Type M pipe has a velocity of 0.62 FPS. Divide that by three and you are well below minimum. Most of our zones are in the 0.50 (minimum flow rate regardless) or 1.0 GPM ranges.

In point of fact the 3/4" tubing in series and the radiation flow rates were sized for a 20 degree delta-T flow rate (0.10 GPM per 1000 BTUH) but we allowed the owner latitude to down-balance to a 40 degree drop if they chose, to get colder return water. We were between efficiency and getting capacity out of the fins. The conservative side said go 20 degrees drop on radiation, 30 on unit heaters and no less than 40 on duct and reheat coils.

That all said, the key I see with condensing boilers and high delta-T systems is water balancing management given that flows are so low. With that comes the need for small tube sizes. Are manufacturer's listening?

BTW: Vulcan used to offer 1/2" tube then discontinued it. I was farkelmpt.

Noel

According to Vulcan (I=B=R actually), the laminar flow effect takes over below the 3.00 FPS rating standard (factor 1.000)

At 1.0 FPS the output can expect to drop to 0.957 x capacity. Where my design would have taken me if parallel, about 0.25 FPS, the rating would be 0.905, so roughly a 10 percent reduction. Glad we went in series.

I think you need your smoke detectors calibrated

designs

Good question, Noel, but there is a reason.
Originally I was going to make them in parallel, reverse-return for even flow but chose not to.
Reason? Laminar flow. By piping in series I have a constant velocity all the way through. In parallel even the 3/4" element tubing would drop below critical levels and I would lose output another way.

I agree, at a certain, low, flow rate. The flow rate is chosen by the designer. Should the designer use a flow rate to match the radiation, the radiation output would be as intended, and the higher average temperature would provide MORE btuh output; MORE load on the boiler, and contrary to your statement about lower return temperatures with the lower flow rate in the ZONE, more efficiency through the condensing boiler. This is due to less bypass water flowing through the boiler to make up for the slower zone flows required to lower the return temperatures, at the reduced output from the fin tube (that you get from the lowered average temperature).

More BTUH’s lost at the radiation equals a wider Delta T at the same RETURN temperature, measured across the boiler.

More BTUH’s lost at the radiation means a wider Delta T at the same SUPPLY temperature, measured across the boiler.

Lower return temperatures AT THE SAME FLOW RATE would indicate more efficiency, I agree with you there.

Agreed, pressure drop is less in parallel. If I had 1/2 tubing or smaller, or turbulators in the 3/4" I would be back going with parallel.


Why wouldn’t you use ½” fin tube, if that’s what you want to design your flow rates around?

You could size your 3 tier to work by gravity, if you chose to size the piping for it. You can choose any pump you like, to match your ¾” fin tube, so flow rate isn’t going to hold us back.
I also don’t disagree with your method, and haven’t yet. There’s more than one way to pipe things, and I think that you do a disservice to this board, by closing your mind to the multiple ways to pipe a system.

System size and room size obviously play a part in lengths of 3 tier installed, and that is more a factor in which method one would choose.

This was a hypothetical discussion in the beginning, without flow rates assigned to it. By assigning a specific job to it, which the rest of us haven’t seen, it takes it out of the hypothetical.
Hypothetically speaking, having a higher average temperature in EACH pipe in the 3 tier baseboard produces a higher output.

Smoke detector off.

Noel

It's predictable and published

under single tier and 2-tier ratings in the same cabinet.

1/2" fin tube is still made, in various brands. Not so much for commercial cabinets, but it's out there.

Noel