Can air heater

[bucketboy]

Im new to solar and i m interested in the can heaters. we built one (4x8 feet and 240 cans) it generates 120 to 140 degrees during sunlite hours. is there a secret for output? or are they limited? i have a old furnace fan pushing air through it. i cut the bottoms out and left the tops on with the hole i can only get 60 degrees in a 20 x 20 room where it is. or am i expecting too much? thanks

[russ]

Hi Bucketboy - Welcome to Solar Panel Talk!

What was the outside temperature when your room reached 60 degrees?

How well insulated is your home?

Leaving only the original small opening in the top is a great restriction to the air flow.

Russ

[bucketboy]

the outside temp is usually less than 0 or 32 F but the reviews i read before building may not be accurate. reviews claim they heat their homes with a panel. i felt if this was sucessful attempt i have room to build several to heat my home. the home is 5 years old and well built. I can find a real testomonial as to how much heat is actually produce from these type of heaters.

[russ]

Hi Bucketboy - The testimonials are totally useless unless you know the person offering them. Some are misunderstanding while others are totally BS.

Your collector has a little under 3 m2 of surface area.

In the winter you may be getting 500 watts/m2 insolation - probably less but I will use 500.

Note: In January where I am we received a daily average of 2197 watts/m2/day with very few hours over 500 watts (only 14 hours had greater than 500 watts/m2. Possibly the 4 hours in the middle of daylight you will collect all the heat and other hours will cool your hose unless you have a stopper of some sort (check valve).

I do not know a good efficiency number for a can heater - it would depend on many things but I seriously doubt it would be over 50%.

So, 3 m2*500*50% efficiency*4 hours per day = 3000 watts per day - at best.

Solar thermal is great but the total surface is important - there is only so much sun available to capture.

[bucketboy]

it is just about lunch time here outside temp is 12 F and the units out put is 105 F so it does have temp rise but i feel it isn t enough output for the size of the room it is in. russ you may be right i need more panels to increase the surface area to be able to blow more air through and turn or circulate the air faster in the room.

[russ]

Search for posts by Mountain - he built one of the heaters he was happy with - he lives near a ski resort in the Canadian Rockies so they can certainly use the heat.

Russ

[flyingdog]

at 32 sq ft of collector surface area (actually a bit more since the surface is curved/wavy), you're definitely generating some good heat there, but airflow is definitely an issue with the can tops still on. I'm wondering if there's a good amount of space between your can surface and the glazing as you could probably recover some of the excess heat (that's currently radiating out through your glazing) by venting the air heating up there.

My personal rule of thumb is if the temperature of the air coming out of a panel is more than 30* warmer than the space (room) I'm trying to heat, the panel needs more airflow

Can-type panels are supposed to be more efficient at producing heat than a flat panel collector, but they seem like far too much trouble to me, between the additional effort in building one and it adding more factors to think about for the overall efficiency of a panel.

[bucketboy]

how would you build a flat panel solar heater?

[flyingdog]

how would you build a flat panel solar heater?

check out this threat I posted earlier today - it's an article I put on my blog a few days back that I reposted here...I talked a bit about construction and provided a few photos

http://www.solarpaneltalk.com/showthread.php?3285-Simple-Solar-Heating-for-RVs

[bucketboy]

i have experimnented with hanging black coreplast in the south facing windows and had a little sucess. not the temperature i thought i would get from a thermal siphon. i have fooled with different types of passive heaters. the one thing i am really disapointed with is there is really no exchange of information on the net. we can t learn from someone elses mistakes. i had a difficult time finding plans to anything. what i have built is just a self made copy of what i seen on utube. i look forward to trying to exchange ideas on this site.
cheers

[LucMan]

A quick guesstimate.
A 20 x 20 room with 18 sq ft of windows and one exposed wall has a heat loss of approximately 6000 BTU per hr at 10 degrees outdoor.
I think your going to need more cans.

[bucketboy]

i have another 4 x 8 on the go i told my wife i thought we would need 3 panels when i started.......now it going to be more like........more lol

[CarrieTaylor]

anybody have calculated an optimal length for the heating circuit ?.................... Would longer can ducts give higher volume efficiency than parallel conducts for a same exposed area?.....................................

[Naptown]

Most likely higher temps at the outlet however the efficiency drops off as the temps rise in the collector so probably less BTU output. You would most likely have to increase velocity through to compensate.

[Wy_White_Wolf]

Gary at www.builditsolar.com has done some testing to document how much output you can get from air heaters.

WWW