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solar panel & fan connections - direct connection OK?

(11 posts) (8 voices)

Started 12 years ago by Popolydopoly
Latest reply from CunningPlansDept

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Popolydopoly
Member
I need to provide some airflow to reduce ground moisture levels in some dead areas in my subfloor (think old double brick house with single brick internal walls that extend all the way to the ground ... built when noone really cared much for subfloor ventilation) and was thinking it would be reasonably appropriate to power some fans with a solar panel but wasn't sure of the pros and cons of a direct connection between fan(s) and panel.

I was thinking of something like a 12V 7W 12cm axial fan (or, perhaps 3 for a 20W panel) (similar 4.5W version) to connect to a solar panel (eg 10W for $50 or 20W for $100).
- Does anyone know what sort of voltage / current variation these sort of DC fans can happily withstand? ie can I directly connect to a solar panel?
- How well matched would the panel and fan power ratings need to be to prevent damage?
- If I need to regulate voltage to something the fan is happier with, is there a decent hack that lets me do it cheaply or reuses parts from other broken things?
I've researched myself into thinking that I should be extracting the air from the subfloor, but can't help thinking that if I can draw dry air in that would be better (since removing air implies replacing with air from various locations/moisture levels). I know hot air can hold more moisture so perhaps there's a risk of condensation or increased moisture forming when the air is cooled as it enters the subfloor...but if this argument really holds, then I should be looking to move air on cold days.
- Should I extract the air and continue to let most replacement air enter from the cool south side of the house?
- Should I force in air from the likely driest location? I guess that just because the air is hot doesn't mean it will have more moisture (if it hasn't had a chance to pick it up). The north side of our house has a cement/tile patio and there air here is much warmer than on the south side, but I would assume much the same (or possibly lower) moisture content) ??? Any expertise appreciated here.
We have a pretty old house (1930?) and, apart from insulation problems especially on the south side, if we can solve this moisture / rotting problem we will have increased its longevity by another 20 years.
Posted Thursday 22 Jul 2010 @ 2:50:51 pm from IP #
munter
Member

Strangely enough I was doing just what you describe a few weeks ago. After a period of heavy rain I was concerned that the sub floor of our double brick 1940's house was damp. I had a 10w solar panel sitting around and so hooked it up to a brushless pc cooling fan (12cm I think). The Voc for the panel was about 20v and it seemed to run the fan quite well. I ran it for two afternoons and the packed it away as the whole setup was only intended to be temporary. It's hard to know how much additional drying happened but it did seem to work as I could smell that underfloor smell coming from other vents around the perimeter of the house.

Posted Thursday 22 Jul 2010 @ 10:25:48 pm from IP #
ghostgum
Member

I have one damp area under my house, in a corner with inadequate subfloor ventilation. The subfloor area got extremely wet during house construction, and wasn't drying out quickly enough. At the moment I am using a 90mm muffin fan to blow air from the garage into the subfloor area, through two conduits that I had placed in the garage slab for future cabling. This has been effective at reducing moisture under that corner of the house. I need to crawl back under there and see how dry it is in winter 2 years on. Longer term I am hoping I can turn the fan off, or at least just run it during winter.

Posted Thursday 22 Jul 2010 @ 11:47:59 pm from IP #
rockabye
Member

Matching the solar module to the fan as you suggest should work fine. No regulator is really necessary as the voltage will not rise above 14V when loaded as long as the module power output is similar to the fan power consumption.

Posted Friday 23 Jul 2010 @ 12:32:09 am from IP #
gully
Member

Is it worth pointing out that in winter, when it's most damp and wet (and cloudy) that the fan will be running the least if it's on solar power?

Posted Friday 23 Jul 2010 @ 9:37:36 am from IP #
ghostgum
Member

But it will only be running during the warmer times of the day.

Posted Friday 23 Jul 2010 @ 10:58:42 am from IP #
Eco
Member

There are subfloor vent systems available as a package that directly connect a solar panel to a subfloor fan. I had one in my last house. Seemed to work well.

Posted Friday 23 Jul 2010 @ 11:15:22 am from IP #
Popolydopoly
Member

Yes, some good responses here.

gully, that the fan would be running less in winter is a point I'd considered, but I honestly don't know if that's an issue. Sure, there's more moisture in summer air, but I think it would still have more capacity to absorb moisture. In any case, this looks like it's been a problem for many years, so drying it out in summer(s) will be OK - ie it mightn't actually be a winter problem. Any atmospheric genii here?

It's encouraging that others have had success with 90-120mm fans as I thought there was a decent risk that these just wouldn't push enough air. My installation space is so tight I don't know if I'd be able to get a 15cm fan in (they start to get noisy as they get bigger anyway).

I notice a few went for the instinctual approach of blowing air in rather than sucking it out - any reason for this? Perhaps a question for atmospheric genii again?

Maybe I'm just trying to find some sort of useful solar project now that I have my own place. Perhaps a fan on a solar thermal collector to blow warm air into the house? Or perhaps I'll just look into using a tiny panel to flip a switch when it's sunny - then connect this to the fans or other things that

Thanks heaps for your responses all. Gotta love ATA folk!

Posted Friday 23 Jul 2010 @ 12:16:50 pm from IP #
gully
Member

I certainly think it's better than nothing. You should consider removing a brick and adding some vents in though (do it right and make it naturally ventilate itself with the prevailing wind direction).

A 9-12 cm fan will not displace much air at all. The cfm goes up exponentially as the size of the fan increases (and rpm speed usually decreases with size). Eg a 12" fan may displace twice as much as an 8/9" fan.

As you say blowing air into the area should be easier and almost as effective as moving the air out, as long as it's warmer air and less 'wet'.

Posted Saturday 24 Jul 2010 @ 7:39:01 am from IP #
Diver
Member

Have you tried to determine the external source of the dampness? Altered topography, new paving, recent vegetation including lawn removal, a neighbours new driveway, even water tank overflows all come to mind. Also check for rising damp, dry rot and recent termite activity. The little critters love damp conditions!

Posted Saturday 24 Jul 2010 @ 8:05:45 am from IP #
CunningPlansDept
Member

I've been going through this myself the past 5yrs. Unfortunately geography worked against elimination of the water source so ventilation was the best option, with some opportunistic drainage to help the free water get out once it had surfaced.
I've got 3 suction fans, 2 cheap 4-fan vent mounted units and 1 ducted unit. The ducted unit does most of the work (and half of the cheap fans have failed).
When the duct got installed it really wasn't ducted to the appropriate places to create cross flow, so I extended it myself.
Positive versus negative pressure is a decision that should be based on the layout of your sub-floor. The aim is to create flow of air across the entire space, with air taking the path of least resistance.
In my case the ducts that terminated at the entrance to a dead end, were only sucking air from behind themselves.

I've spent a lot of time under the floor and have noticed that external wind has a significant effect on the ventilation despite the inadequate vent slots. I can hear the fans surging as the wind changes, so it is something to consider in the design too.

If you want a second opinion on your layout, I'm happy to have a look

Posted Saturday 24 Jul 2010 @ 9:14:55 am from IP #

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