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GARVEY MN

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Posts: 10
Reply with quote  #1 
I'm in the early stages of designing my first solar project. I have been using a kerosene heater in my wood shop, but with the smell and depletion of oxygen I get headaches.
I have a 6'x12' exterior wall that points directly south that I will be mounting the heater to. I was planning on building the heater 6'x10', but, after reading through this forum, now I am wondering if that is just too large for my 12'x16' wood shop.
Currently my design has a 2x6 frame, double screen absorber, and clear corrugated polycarbonate panels.

I guess my first question is, simply, Is the size too big for the area I plan to heat?

I'll try to get a picture of the cross section of my design. But I'm not the most computer literate person out there.

Any suggestions would be great.

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KevinH

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Posts: 554
Reply with quote  #2 
Part of it would depend on how well the shop is insulated.  If you can get an idea of the current heating requirements, that would help.  For example, if you plugged in a small electric heater (like 1500W) in the morning would it keep the shop warm enough during the day?  1500W is about 5100 Btu/hour.  Or if you knew how much kerosene is used during the day and the efficiency of the heater, you might be able to estimate it that way.  From there, we could estimate how much collector area is needed.

You could always design in a way to get rid of excess heat when needed, especially since it is a small shop and not a house.  Maybe a way to partially shade the collector, a way to mix in cold outside air, or a way to partially vent excess heat outside.

Looks like you are in MN, so if you have access to a Menards they carry the twinwall glazing that a lot of us use.

Kevin H
GARVEY MN

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Posts: 10
Reply with quote  #3 
The heater i am currently using has a 23,000 btu/hr. But it's actually way too much, because after 4 hours running, my shops temp is at 90°+.

The shop is well insulated. R-13 walls and R-23 ceiling. And like I implied, it's air tight. I do have 2 small windows I could open if need be.

And yes, Menards is my home away from home. Some weeks it seems I'm there more than I'm at home. The twin wall is special order, but that's not a big deal, since I will not be building the collector till spring. I work outside all day, so it's tough for me to work outside when I get home on these figid days. I'm just trying to get most of my ducks in a row before I start building.

I was planning on just cutting rectangular holes for the inlet and outlets, is that a problem? Or should they be circles? I was thinking 3 inlets on the bottom spaced out across 10 feet, and 4 outlets at the top. Again not sure if that's too many.
gbwillson

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Reply with quote  #4 
Welcome Garvey!

Is this going to be a passive unit? Or will it have a fan to move air? A 4'x8' collector similar to what you have drawn will supply you with roughly 4,000-5,000BTU's per hour, if it has a fan. Your design is roughly twice that size, so figure 8,000BTU's if it has a fan, or less if no fan. This should be fine for maintaining the heat in the wood shop. It might be slow to warm up the shop, but you can always fire up the big heater to get the shop warmed up quickly and the solar heat to maintain the area during the day. Overheating shouldn't be much of a problem as you can always find ways to reduce the heat in your shop. But you will be glad you have the extra capacity. 

With so many duct openings, I'm guessing you are looking at a passive design. In general, air will flow better with more intake space than at the exhaust. Duct shape should not matter. 

Greg in Minneapolis[wave]

GARVEY MN

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Posts: 10
Reply with quote  #5 
Greg,
Yes, I am shooting for a passive system, to start with anyway. I figure I can add fan/s at a later date if I need to. If I understand correctly, I should have more intakes than outlets? Which does make sense now that you mention it. I'm just really green when it comes this project.

I haven't even started this build yet and I'm already thinking where else i can utilize the sun for heating.

Are twin wall panels better than corrugated polycarbonate? If so what are the main pros/cons?
GARVEY MN

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Posts: 10
Reply with quote  #6 
Greg,
Yes I'm shooting for a passive system to start, anyway. I figure I can add a fan layer if needed.

If I understand correctly, I should have more intakes than outlets? That makes sense I guess. I'm really green when it comes to this project.

Are twin wall panels better than corrugated polycarbonate panels? If so what are the main pros/cons?

Gordy

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Posts: 137
Reply with quote  #7 
Quote:
Originally Posted by GARVEY MN
Greg, Yes I'm shooting for a passive system to start, anyway. I figure I can add a fan layer if needed. If I understand correctly, I should have more intakes than outlets? That makes sense I guess. I'm really green when it comes to this project. Are twin wall panels better than corrugated polycarbonate panels? If so what are the main pros/cons?


Passive collector's run at a hotter internal temps than collector's with fans. So you will loose much more heat through the insulation and glazing, than with a fan unit. Twin wall gives you some insulation and rigidity, at the cost of blocking a tip of sun from getting in.

If you want to get the most out of your collector go with fan's. There is more $$ in putting fans in, but you will get heat out of the collector earlier and later in the day, than with passive. As well as more BTU's in general. By lowering the collector's internal temp with fan's you slow down / reduce the heat loss through the glazing. 

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Gordy,
Minnesota
gbwillson

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Reply with quote  #8 
Having more intake area than exhaust on a passive heater helps with the airflow. I can't say how much more is ideal as every build is different. Maybe you could simply increase the size of the intake openings a little at a time until you find the sweet spot for maximum airflow. But you should also plan out how and where to install fans at a later date. Passive units also perform better if they have a vertical configuration, like a chimney. But you will still get lots of heat. 

As Gordy mentioned, passive units tend to run hot, and therefore lose a lot of heat out through the glazing. In cold climates like ours, twinwall adds a bit of R-value compared to single layer glazing. Twin wall also goes for less than half the price of UV coated single layer polycarbonate sheets. Menard's has it on sale quite often. I've seen it for as cheap as $30 per sheet after rebate.

https://www.menards.com/main/building-materials/roofing/specialty-roofing/tuftex-reg-4-x-8-polycarbonate-clear-twinwall-panel-6-mm/1594351/p-1496848120528-c-5819.htm?tid=-8878523335437952900&ipos=2

They are changing vendor for this product, but the above is the new product.

Twinwall is also far easier to install than corrugated panels. It's easy to cut, lightweight, and easy to seal. 

Greg in MN
GARVEY MN

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Posts: 10
Reply with quote  #9 
First off, thank you guys for all the insight.

I would like to get the most out of my collector as possible. What kind of fans are used and where would I find them? Do you suppose I could just hook them up to a timer, so they turn on/off at a specific time each day? I'm not exactly sure how to go about rigging them with a thermostat. Can you guys point me in the right direction for that?

KevinH

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Posts: 554
Reply with quote  #10 
There is a lot of good info on passive on builditsolar.com such as this one on Gary's workshop.
http://www.builditsolar.com/Projects/SpaceHeating/solar_barn_project.htm

Includes testing on the vent sizes.

Kevin H
MN


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