Pop Can / Downspout Solar Heater...

[GoFish_Tony]

I have started construction of my Pop Can Solar Heater and have a question for you all.

I will duct my cold air in through the bottom and hot air out the top.
My question is; "Should the Hot Air Plenum be larger/smaller/same size, as the Cold Air Plenum?

I admit I know nothing about HVAC or Ducting air flows.

Any help would be greatly appreciated,
Tony

[Daox]

I don't see any reason to.

[Ryland]

On the other hand, shouldn't the bottom inlet be larger because it's under a slight vacuum and the air out the top would be under a slight pressure?
I would say size the ducts a little larger and if it's not enough you can put a fan on the inlet.

[Daox]

I'd put a fan on it regardless. You'll loose a lot of heat due to the collector heating up so much if you don't have a fan.

[creeky]

if hot air expands and cool air is denser, a slightly larger plenum at the top might be a good idea.

[Daox]

Actually, if you're going to rely on natural convection, the largest openings on each end would be best to reduce any minor restriction. I doubt plenum size has much to do with it vs inlet/outlets from the plenum.

[GoFish_Tony]

I've come to realize that my projects isn't all that different then many of yours (in one respect anyways...) And that is; it really come down to "efficiency vs practicality".

For me, I am in this to learn some basic fundamentals of collecting Solar and transferring that energy to heat. (Probably the simplest use of the Sun but still it befuddles me in how to do this in the most efficient yet practical way.)

I am patterning my Solar Heat Collector after what I have seen so many others do. It's simple and practical and I'm sure theirs all worked to some degree. But following their plans does little to help me in my education. I wish to learn as much as I can and improve upon their ideas. But I need your help.

OK, time for another question.

My first column of cans is temporarily installed between the Bottom Plenum plate and the Top. I will use some sort of adhesive/sealant where the corner of the downspout transitions to the round shape of the can. Inside these downspouts I have 11 cans stacked and taped together with adhesive backed foil tape. Each can has one end cut out, and on the other is a series of slots and fins. (Supposedly to create turbulence and to slow down the air so that it can get heated.)

My question is: Do I gain anything by filling these downspouts with cans, over just having one can at the top and one at the bottom?
I've considered even shoving steel wool 1/3 and again at 2/3 of the downspout length.

I believe there are many factors here that I don't fully understand. Like, time Vs heat transfer, material thicknesses, heat chambers and air flow.
My head is starting to spin. HELP!
(I don't mind experimenting, but would like to get at least one of these built ASAP. And I would like to get the first one as close to my design intent as possible.)

Thanks in advance for all your input.
More pictures and details at:
https://sites.google.com/site/tonysf...pop-can-heater

Tony

[Daox]

The cans will probably make your collector throw off less heat.

What you have in a solar collector is pretty simple. You have a window X by X large. Sun hits the material inside the collector and heats it up. What you want to do is efficiently move the heat away from that material. In this case you're using air to remove the heat. So, you essentially want some form of heat sink which means lots of surface area. But, you also don't want to restrict airflow. I see your cans restricting airflow. IF they had good surface contact with the downspout, they could help spread the heat out and give more surface area for the air to pick up heat off of. But, since they're just sitting inside the downspout I don't see them transferring much heat away from it and into the air.

[GoFish_Tony]

Ahhh... More surface area. That's good!!!

I think I agree with you about the cans. It would sure simplify the design a lot.

Do you still think that I should try and do something inside the downspouts to slow down the air? Maybe one can midway, and one at the top and bottom?

This is the kind of input that I need. (I can tend to over-think things at times.)

Thanks again,
Tony

[Daox]

I would not try to slow the air down at all. Faster moving air will keep the panel cooler and that will increase the efficiency of it because it will be loosing less heat to the outside environment.