Welcome to the Solar Collector
Brainstorming and Development Page!


 

Home

Hot Air Collector

Hot Water Project 1

Hot Water & Space Heating

Solar Electric

Solar Construction 101

FAQs

Best Collectors

Simply Solar
Sign up Calendar Latest Topics
 
 
 


Reply
  Author   Comment  
dbc

Registered:
Posts: 265
Reply with quote  #1 
I have been thinking about running a hot-air collector with DC fans.  The other examples I have seen here all locate the fans inside the collector itself, which actually looks like the best place for them.  Neither of my heaters are deep enough for that, so I am looking at other options.

There is a wide selection of 120 mm (4.7 in.) diameter 12 VDC fans at Allied Electronics, other sources too.  What about mounting 4 of these on a plate inside a box, with duct stubs for in and out?  This would go in line with the input duct, ideally as close to the collector input as possible.  In my case, with my 4x8 ZP, there might not be enough room right behind the collector; I might need to put the fan box a little farther upstream.  Here is a rough drawing of the concept.  The fans would sit on a plate in a square box, with a tapered cross-vane to reduce interaction between the fans.  The box could have tapered sides to match:

1) Fan box, 112618.jpg 

One possible fan, $19 each, is the Orion OD1238-12HHB:

154 CFM @1.3A, 3800 RPM
Static pressure 0.57 in. water (142 Pa)

There are quite a few other 120 mm / 12V fans in the 120-130 CFM range as well.

I am presently using a 120VAC Suncourt TF106 Centrifugal fan, which is spec'd at 400 CFM (free air), static pressure 1.8 in. water @ 40 CFM.  Not sure how to realistically compare this to a grid of smaller 12V fans.

I'm also looking at another option, which is to modify the back panel of the collector to mount a row of 4 fans behind the intake plenum.  I would have to cut a rectangular hole for the row of fans, and build some sort of adapter to round duct enclosing the fans.  Something like this:

2a) Collector side view, DC fans, 112618.jpg 

3) Collector rear view, DC fans, 112618.jpg 

I apologize for the crude draftsmanship here; these are pretty rough.  Spacing and scale are not accurate either.  I hope the basic idea comes through.  The rear view represents a U-turn design, like my 4x8 ZP.

A little background to this idea - You may remember I experimented recently with running the Collector fan off my PV system, which has aged, marginal batteries.  The battery consisted of 4 ea. L-16, 6V / 370 A-H.  Turns out 2 of the 4 were beyond marginal.  Without PV input, they quickly dropped below 4V.  They each had one cell that wouldn't raise the hydrometer float at all.  The other 2 batteries looked like they might still be OK for some light duty.

So - I took the 2 bad batteries out, and rewired the other 2 for 12V.  Reprogrammed the Outback charge controller and Tri-Metric Battery Meter for 12V.  So far so good, but now I can no longer use the 24V inverter, so basically I have a 12VDC off-grid PV system with nothing to do, just keeping the batteries alive.  Only good idea I can think of is to run an easy 12V load, like a hot-air collector, which only needs power during daylight.  The PV array should be plenty big enough (48 V / 540 W STC), and it is charging the 12V battery OK, thanks to MPPT.

I could probably even remove 2 of the 12V panels and use them to run the heater PV-direct (no battery).  Don't want to mess with the array until Spring, though.

jjackstone

Registered:
Posts: 82
Reply with quote  #2 
I like the second idea better because it looks as though the duct reduction in the first plan would restrict air flow more, but of course I may be mistaken. I have recently been considering using heater/cooler blowers as fans. They can be bought at local salvage yards like picknpull for about $25 each. However several times a year there are half price sales on everything in the yards. Those are usually on holiday weekends when traffic would normally be slow for the yard. Has anyone tested or perhaps know just offhand what sort of cfm output an automotive blower might have. Obviously they're not all the same. Just looking for a ballpark figure.
__________________
JJ
stmbtwle

Avatar / Picture

Registered:
Posts: 2,907
Reply with quote  #3 
I acquired a heater fan from a Ford SUV a year or so ago.  It was a centrifugal blower and moved a LOT of air (but also pulled about 5 amps.)  A DC speed control would probably be in order.  The thing was built into the heater/ac ductwork and took quite a bit of creative cutting to get out in one piece.  Once I had it out along with the case I couldn't figure out how to install it, so I chalked it up to experience and scrapped it.

What I think would be easier to install would be an aftermarket radiator fan.  They're available in several sizes.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Bruce

Registered:
Posts: 137
Reply with quote  #4 
If you're pulling a fan at a reclaiming center (FKA:junkyard) try to get the fan speed switch and related capacitor module, if you can.
Bert

Avatar / Picture

Registered:
Posts: 541
Reply with quote  #5 
I second a radiator fan. I tried the smaller fans and just not enough power or CFMs. 
I had to hook my radiator fan right on the output or input vent inside the house because of the way mine happen to be set up. It should be okay for a 4x8' collector. 


__________________
Bert K.
Michigan

https://www.youtube.com/user/1thinkhealthy/playlists
jjackstone

Registered:
Posts: 82
Reply with quote  #6 
dbc. Sorry I kind of hijacked your thread. Which method have you decided to try first? I supposed you could build the first one and test it so you only have one small hole in the collector box. Then try the second one and test it. Or, build both and test side by side and publish your results here.
__________________
JJ
dbc

Registered:
Posts: 265
Reply with quote  #7 
Thanks everybody for the useful feedback.

I think I will look around for some automotive fans before I spend too much money on the 120mm computer-type units.

Bert - I remember you had some trouble getting enough airflow with the row of small fans in your tube collector until you added an outboard fan.

I should be able to handle 5 Amps OK, if that's what it takes (and it might with a ZP).  One of my 12V panels has Imp of 7.63 A (STC) ,and I have 4 to play with.  A hot-air collector would only be drawing power when it's (mostly) sunny, since the snap disc would still control when the fan runs.

I see a lot of 6 - 8 inch radiator fans that look like they would adapt to a round duct pretty easily, but I don't know about the static pressure part.  Radiator fans are usually out in the open.  A heater fan may have more oomph, although a lot of them have weird shapes.

I agree with jjackstone that built-in has an advantage over an outboard box with reduced cross-section in / out.  Maybe try this out on a new collector.

stmbtwle

Avatar / Picture

Registered:
Posts: 2,907
Reply with quote  #8 
Agree the heater blower will probably give you better pressure, if you're up to the installation challenges. The one I had was single-speed with a resistor pack for speed control.
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics