Improvised hydro fan coil?

Gordan

So, I've got a need for something that will produce about 8000 BTU/hr, give or take, with 120 F water, in a small footprint. Basically, a temporary heater for a room that will be in the process of getting redone. I have a mess of fin tube elements ripped from recessed convectors that I could apply to this purpose. The enclosure is already there, say 4' x 3' x 6" deep. Has anyone done something of this sort?

JStar

Okay.

The numbers...



An average convector that is 4ft x 3ft x 6in will produce about 50 sq. ft of radiation.

At 120 degree supply water, a 20 degree delta, makes the average water temperature in the radiator 110 degrees.

The radiator will produce 150 BTUH.

So for your 8000 BUTH heat loss, you'll need roughly 54 convectors.



My math is estimated, not taking into consideration how multiple convector elements would combine into one single enclosure.

Gordan

Thanks

Average "unforced" convector, yes. But I was thinking more along the lines of forced convection. So, for instance, a toekick heater with 90 cfm across a three-row coil might produce 3500 BTU/hr with 120F supply, at 1 gpm. I'm paraphrasing specs from a Turbonics toester T6/8. I could rig up a four-pass arrangement of fin tube elements (counter-flow, of course) with a row of DC fans across the outlet for a much much larger fin surface, and hopefully bigger delta-T, so I think my question primarily boils down to:



1) can I move enough air through the elements cost-effectively, and

2) is there some dark art (or high science) element that I'm ignoring, that would render this not only crude, but completely ineffective?

Rod

Jaga?

You might want to take a look at Jaga for some ideas. http://jaga-canada.com/Low.aspx

http://www.jaga.co.uk/Uploadedfiles/jaga/DBE_Info.pdf

Gordan

I guess I'll try and see...

I just picked up a cooling fan tray from a big network switching chassis for small change. It's got nine 5" fans and is supposed to be able to flow enough air to keep a 7 kW heat source (that being the switch) at 20 F above ambient... It also has a controller on it that modulates the fans up or down based on the temperature inside the cabinet. Could be the greatest thing since sliced bread, if I can wire it up!



So, another experiment about to happen. Modulating ECM-based forced convection!

Gordan

Ah, our posts crossed!

Yes, I was thinking along those lines but couldn't remember the name of the manufacturer that I'd seen people mention here.

Rod

Fan Coil

Please let us know how it works out.  Modulated fans with adjustable heat control has lots of possibilities.

Gordan

I surely will.

The way I was thinking of rigging this up, a TRV would respond to low indoor temperature by proportionally increasing water flow, which would in turn cause the temperature inside the cabinet to rise, which would cause the fan controller to kick up speed. The controller is not programmable - at least not by me - so this will be a bit of a hail Mary, but I'm hoping that a favorable balance will be struck.

Roland_18

Improvised Hydro/Air

I made this change in order to pull a few more B.T.U.'s out of this convector.

It's strictly low-tech, just 6 recycled (12vdc)  plasma TV fans, a 130*F fan thermostat, and a wall wart power supply.

Gordan

So how well does it work? :-)

That's more-or-less what I had intended, only with full fan coverage up top, and a few fin-tube elements stacked on top of each other in a staggered-fin fashion, to break up laminar air flow.



So the fans are on full blast whenever they are on?

Roland_18

DIY Hydro/Air

Hi Gordan,

The room that this unit is in never felt comfortable in winter. I first did some air sealing which was more than half the battle. In my own estimation, the convector was too small for the size and open plan of the room. The only other option was to replace the convector with a larger one. This was not in my budget, hence, the DC fan idea.

The fans run at 9Vdc so they are a bit quieter. The increase in heat output was just enough to make the room comfortable. The air sealing made the biggest difference. And yes, the fans run full blast ( if you can call it that) when the snap disk thermostat kicks them in.

I have included a picture of the mission-style cover I had custom made by a local crafts-person. Not too shabby.

Rod

Cabinet

Very Nice!

- Rod

Gordan

Very pretty!

I hadn't realized that one can "modulate" these using input voltage... most references I'd seen were to PWM inputs to the built-in drive circuitry on the fan. So, was the larger convector out of your budget, or was it the matching large custom convector cover? :-)

Roland_18

Hydro/Fan

Did I mention that the covers are made from quarter-sawn solid oak with a hand- rubbed finish?



Really, replacing the convector would have caused damage to the wall under the window as the metal convector cover would have to be replaced. Comparing that to plugging air leaks and adding a few fans it was a no brainer.

Quater-sawn oak,  Mmmmmmmmmm!

Roland_18

Hydro/Air

It is possible to vary the speed of these 2 phase fans (somewhat) by varying the input voltage. Frequency control would be the right way to go, but, I chose the expedient.

Gordan

Hand-rubbed finish...

I hope you left a big tip!

Paul Rohrs_14

Clever

Nice job Roland.

Gives me all kinds of ideas.  I might try this with some even number of fans but wire an aquastat with two temp settings to stage separate fans.  (2-stage based on Delta T)

Did some work for my Brother-In-Law last year by putting radiant in his wood shop.  Yes, he's a cabinet maker.   Mmmmmm....

Quarter sawn cover is beautiful.

Paul

Gordan

That may be problematic

Unless you devise some sort of backdraft damper for the fans, the fans that are off could make a short-circuit path for air. Better to have some sort of voltage staging, where you run the fans at, say, 7v for low stage and 9v for high stage?

Paul Rohrs_14

Good Advice

Thanks Gordon, that is good advice.   I guess I am guilty of a zoning with circs mentality with fluid instead of moving air.



Thanks,



Paul

Gordan

Now I'm thinking...

I might go with an Arduino-based solution, and PWM-controlled BLDC fans (4-wire.) This would give me full control over fan behavior. I looked at some Jaga docs and I think I can do better. For one, my multi-pass design should result in better water-to-air heat transfer than their single-pass design, even if they do have corrugated fins. (Yes, clearly they have more constraints on material than I, so that's not really a fair comparison.) But, also important, I think I can devise a better fan speed control strategy than theirs.

Rod

Fan Coil

A couple of comments:

1 . It would seem to me for longevity that the electronics and fans should be positioned on the intake (cool) side of coil.

2. While you might get more heat transfer,  I'd be a little concerned about a multi pass design in that it might clog up quickly with dust etc. This has always been a problem toe kick coils so easy cleaning is a must.

Just some thoughts.

- Rod

Gordan

Good comments

The fans tend to be rated for higher temperatures, considering their typical function in ventillating hot electronics, so I think they'll be fine, but I'd keep other electronic components out of the air stream alltogether or on the intake side. I think it would be far too noisy and inefficient to try to blow air at the fins rather than suck it through them. Yes, dust is a concern, and I was thinking that I would position the intake a few inches from the floor to avoid the worst of it, and then put some sort of filter on the intake. At the air velocities we're talking about here, a pleated filter of some sort shouldn't create very much pressure drop. What do you think?

Jean-David Beyer

then put some sort of filter on the intake

I have a thin foam filter at the input of my computer to filter out dust. It does a pretty good job, but I assume not as good as a pleated filter. I find I must wash the filter monthly. The computer is on a desk top, so 30 inches or so from the floor.



Once a year I open the computer and vacuum out the grit that seem to deposit at the bottom, and clean the fan blades.



If you use a filter, you should check often to gauge how often the filter needs changing.

Rod

Filters

My thinking is that I'm not generally all that in favor of using a filter as I think that would inhibit natural convection when the fans were off.  JDB's idea of a minimum foam filter would probably work best but I think you would still have to rely more on easy cleaning to keep things going. My experience with toe kicks is they are a "dust magnet" and need constant cleaning (especially if you have animals) to operate to the optimum .

- Rod

Gordan

I'm not really counting on natural convection

For this project, we're talking 120 F supply MAX. I really don't think that I could get any natural convection going at those temperatures.