Posted by Dave Bull at 2:49 AM, November 30, 2011 [Permalink]

OK, before I can tell you about today's WONDERFUL events, you have to get up-to-date on something that happened back in the autumn of 2003. This page (from October 2003) on the Studio Construction section of the site will do that ... I'll wait here while you go read it ... :-)

The duct didn't work. As I wrote on a subsequent page back then: "The air duct was not so successful; it did pull a stream of air from the warm attic, but 12 meters is a _long_ way, and very little of the warmth made it to the bottom of the pipe. And what was worse, because the lower room was so cold, any moisture in that warmish air instantly condensed at the mouth of the pipe, and the room became damp. Cold is OK ... cold and damp is unbearable. So it stayed off. Perhaps in the future, once this room is properly insulated, thus negating the large temperature differential, it will be possible to move the air around without the condensation problem ... we'll have to wait and see."

Did you notice that phrase 'perhaps in the future'? Well, the future is here!

The basic reason for the failure of the original project had been the weakness of the fan that I had used. I should perhaps have searched for a stronger one, but the additional problem with the condensation - not to mention the lack of insulation in the lower room - combined to kind of kill my enthusiasm for it, and I just didn't bother.

But now that we have done most of the insulation, I have started to think about giving this another try, and hunted around for a reasonably priced strong fan. A chance comment by Sadako the other day, when she mentioned that she had been having trouble with a little leaf blower she was using in her garden, led me to search the 'net for other such products, and I found this on a Yahoo auction listing - a Ryobi 'blower':

It at first looked like nothing more than a little toy, but the specs said that it could move 3.5 cubic meters a minute (a lot of air!), with a pressure of over 5.5 kiloPascals (also pretty impressive). And it was cheap.

I put in a bid, won it, and it arrived yesterday afternoon. Today - a moderately clear day with quite a bit of haze in the sky - I took it upstairs, opened up the wall for access to the attic, and put it in place at the top of the long duct (replacing the earlier weak fan).

The attic was not actually all that hot today, just low 20s (although as we will see a bit later, this is not the most accurate thermometer in town!) On a day of full sunshine - in mid-winter - I've seen this thermometer pushing close to the 40 mark.

Here's one of the photos from that old web page, showing the outlet of the duct down in the (then un-insulated) workshop:

And here we are, ready for today's test:

When I built the duct all those years ago, I wired it with a two-way switch, one at the top of the stairs, and one down here in the workshop. I now switched it on for the first time in eight years, and was rewarded immediately by a very strong stream of air coming out of the opening. This was of course cold (just as when you turn on the sink tap and hot water has to come from the tank ...), but a few seconds later it felt a bit warmer, and over the course of the next few minutes heated up dramatically.

I twisted the duct to point towards the room thermometer, to give me some idea of the temperature of the air coming through:

Look at that! Can you read it?

26 degrees, and a low humidity! Success!

And this is on a semi-overcast day! What will it be capable of on a really sunny day?!

I'm very much looking forward to seeing how this is going to work in practice. I have no idea how early in the mornings we will be able to turn it on. This test was happening in early afternoon just after I had my lunch. That'll be fine for getting the room warmed up for the afternoon/evening work, but it would be nice to be able to use this during our morning 'shift' too.

Another question is how long it might take for the fan to 'exhaust' the heat from the attic and start blowing cold air down the duct. My guess - after running this for over an hour today and finding that the thermometer upstairs hadn't changed at all when I went up there to check - is that the attic can supply far more than we can draw ...

Eight years ...

Do I win the procrastination prize? Or - now that I think about it - I guess I'm disqualified from membership in the procrastinator's club; after all, this is finally up and running!

Following comment posted by: Dave on November 30, 2011 9:21 PM

And wouldn't you know it ... nothing but clouds and rain in the forecast for the next few days (most un-seasonal!)

Following comment posted by: Marc Kahn on December 1, 2011 1:09 AM

Wow! An (almost) passive solar heating system for the workshop. Very nice!

Following comment posted by: John Becker on December 8, 2011 11:08 AM

Dave, there's another thing to consider... is it possible that the blower itself is heating up the air a bit? If so, you could bypass the duct and just have it close to the room (though the noise might be reason enough to keep it all the way upstairs).

Also, what kind of wattage does the blower eat up? More than the space heater you have in the studio, or less? Remember, normal hair dryers are around 1500 watts. That "free" heat might not be so cheap.

Following comment posted by: Dave on December 8, 2011 1:19 PM

I rather doubt that there is any heating effect in the blower itself - any given molecule of air is only inside that thing for the merest split-second. It's an extremely fast moving thing ...

But your second point - the power consumption, is a major consideration. This is clearly not 'free' heat, and I understood that from the beginning. We're not talking about anywhere near 1500 watts for this fan; it's just over 500, which is the same as the little heater I've used for these first tests.

I think - this is anecdotal, and not scientific - that I'm getting a lot more bang for the buck with the fan. After running it for about an hour in the early afternoon, and getting the room thermometer to run up to 25c, I shut it off, and do not need to supplement with the space heater for the rest of the day ... the temperature holds pretty well right into the late evening.

On the days where there is no sunshine, I have to use the heater off and on all through the afternoon and evening, and it can't get the temperature up over 20.

So yes, certainly not 'free', but at this point I don't see how I can get all that much more efficiency out of this system. The funny thing though, is that this is going to increase my electricity consumption. For years, I've simply shivered and put up with the cold conditions, because I couldn't bring myself to waste energy partially heating a room that wasn't insulated - it simply felt morally wrong. But now that I have all this wonderful insulation in place, I have no qualms about using these two heating tools. So my bills are going to go up, as is my 'impact' on the planet, etc. etc.

Following comment posted by: John Becker on December 11, 2011 10:51 AM

After all those years that you made do on the heat of a single 500W bulb, I don't think the planet has any room to complain.

Following comment posted by: Margaret on December 11, 2011 2:35 PM

I always love a good problem solving story.