Welcome to the Solar Collector
Brainstorming and Development Page!


 

Home

Hot Air Collector

Hot Water Project 1

Hot Water & Space Heating

Solar Electric

Solar Construction 101

FAQs

Best Collectors

Simply Solar
Register Calendar Latest Topics
 
 
 


Reply
  Author   Comment   Page 1 of 2      1   2   Next
Dave

Registered:
Posts: 3
Reply with quote  #1 
Hello everyone.

I am new to the forum and solar hot air, but not solar electric. I built my own solar house the past three years all by myself and did not hire a single thing out. I poured my own slab, framed, ran electric, plumbing, and did all the finish work all by myself. We are off grid and only get propane trucked in once a year for our cook stove and a back up heater.

I want to look into solar hot air for both my home and my small workshop. I plan to build a screen type of hot air collector for the workshop to test it out and then want to build a large unit for the house.

I am looking for what would be a good recommendation for how to size a collector for my area. I am in northern Minnesota, with only 4.2 peak sun hours. My workshop is just a small well insulated 12x16 building that currently I heat with a small 14,000 btu Williams propane heater. I use about a gallon a day just keeping it at 55 deg F. I would like to cut down on propane usage and also as I said above, test it our for building a unit for the house. Our temps regularly get down to -25F in the winter.

Is there a way to calculate what size I should use? I am fine with it getting very warm in the day so that it will hold the heat into the evening when I will be out there working. I have a south facing wall that I can put up to a 4'x16' collector. Is this too large for this workshop space of only 192 sqft? Would this be enough?

I also do not have power in the shop, but plan to move the small solar system from our rv to it this winter and from this I could run a 12v fan for the collector.

Any help would be appreciated.

Thanks a lot,
Dave

Bert

Avatar / Picture

Registered:
Posts: 522
Reply with quote  #2 
If you regularly get down to -25 and use it mostly in the evenings I would make it 4' by 16'.
It may be hard to find a 12v fan that would be strong enough. Maybe someone on here might know for sure.

__________________
Bert K.
Michigan

https://www.youtube.com/user/1thinkhealthy/playlists
gbwillson

Avatar / Picture

Registered:
Posts: 2,249
Reply with quote  #3 
Dave-

Welcome!  You say the workshop is well insulated, but how high is the ceiling? And is the 14,000BTU heater big enough for your needs? There are several people on this site that have used solar heaters as the primary heat source for their workshop. Let me give you a couple of examples. My friend has a 600sf workshop here in Minneapolis that has a furnace/central air unit. He's retired, so he spends most of his day in the shop, even in winter. But like you he was spending a small fortune operating the furnace. While the shop is mostly insulated, with an 8' ceiling, the 16' wide garage door is not. It has two layers, with a hollow core. For fortunately it's a dark green and faces south. A couple of winters ago I helped him build a 4'x16' ZeroPass heater which puts out between 16,000-20,000BTU's every hour while the sun is out. And since that time he has not had to use the furnace even once! He has a small electric heater for very early and late in the day, but it is rarely needed. Most mornings, the shop temp is about 52˚F. With the heater running he can work in a T-shirt. Here is a like to his heater:
http://simplysolar.supporttopics.com/post/kraut-man-craig-and-his-zeropass-collector-7957395?pid=1291128089

Another member, Matt, built a ZP heater for the back of his 24'x24' workshop out in rural Wisconsin. Like my friend, he rarely has to use any supplemental heating in his workshop. Here is a link to Matt's ZP build:
http://simplysolar.supporttopics.com/post/my-version-of-a-zp-7939709?&trail=10

Again, roughly the same size and performance as my friend's build. If you didn't need quite so much output you could build a smaller unit, or simply turn down the output fan speed for less BTU's. You'll collector less through heat loss, but can always adjust the unit for maximum BTU output as needed. 

I always suggest building bigger, and for more BTU's than you think will be needed. You can always open the door or work in shorts if you get too hot.

Greg in Minneapolis[wave]
Dave

Registered:
Posts: 3
Reply with quote  #4 
Thanks guys. Yes the 14,000 btu heater does fine keeping it warm. I suspect it runs about 6 hours a day as it is using around a gallon of lp a day. If I could cut that down to half a gallon a day I would be happy. It is just a small 12x16 workshop with 6ft sidewalls going up to 8'6" in the central portion that is 4ft wide. Basically it is a cathedral ceiling with a 4ft flat at the top. It heats up really fast, but needs to stay above freezing all the time.

I guess the biggest issue will be if I will be able to have enough fan to run a longer collector. No electricity in the shop and will only have a small solar system added in the next month or so. Will just have two 6v Trojan T105 225Ah batteries for lighting and powering this collector. This system is one we used in our camper rv for power when we were building and it is sufficient, but not sure how large of a fan I will need. If I could get away with a couple large 12v computer fans that would be nice.

Seems like if your friend is heating 600 sqft with a 4x16, I should be able to bake myself out of my little 192sqft workshop. [biggrin] Would a few large computer 12vdc fans work for this? I had thought about maybe using one on the intake pushing air in and one on the exhaust pulling air out.
gbwillson

Avatar / Picture

Registered:
Posts: 2,249
Reply with quote  #5 
Dave-

If I recall my friend Craig had roughly 440CFM blowing through is collector via two 350CFM fans with one pushing and one pulling. He needed this much to keep the unit from getting too hot. His bottleneck was the 6" ducting. With 8" ducts he could likely not only move more air, but run more efficiently. 

Matt's collector used a furnace fan. He used 8" ducts. He didn't have any issues with the glazing bulging as he used 1/4" tempered glass he had laying around. 

Since you have no power you might consider something like a solar gable fan. They are often rated with CFM over 1,000, but I'm not sure how well they would handle static pressure. But if you don't likely won't have long duct runs, it might be something to consider. But you will also likely need a small, booster-type fan. Otherwise the glazing can bow out quite a bit, leading to air bypassing the screen gap. 

Another idea you might consider is to use 12v computer fans in parallel. Again, you'll need some pushing and few pulling to ease the pressure a bit. You want to purchase fans that handle static pressure and have the needed CFM. Here is a link where you can purchase such fans:
https://www.digikey.com

Remember that while a fan may be rated for a given CFM, this rating is always unobstructed. 

The good thing is that the workshop sounds like it holds heat well. So any heat collected will save you $$$.

Greg in Minneapolis
Rick H Parker

Avatar / Picture

Registered:
Posts: 753
Reply with quote  #6 
Dave - before you follow the Tim Taylor philosophy, is the workshop insulated?
__________________
Rick H Parker
Kansas, USA
Electronics Engineering Technologist
stmbtwle

Avatar / Picture

Registered:
Posts: 2,747
Reply with quote  #7 
Post #1
__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
Rick H Parker

Avatar / Picture

Registered:
Posts: 753
Reply with quote  #8 
Post #1

Ah! missed it first time.

__________________
Rick H Parker
Kansas, USA
Electronics Engineering Technologist
SDJunkMan

Registered:
Posts: 13
Reply with quote  #9 
If powering a fan is a concern, why not go with a passive system for the shop to get started? It may not put out as much heat, but your space is relatively small, and you have room to build a fairly large collector. If power becomes available later, you could possibly convert the collectors to active solar.

Jeff
Black Hills of South Dakota

__________________
Jeff
Black Hills of South Dakota
Dave

Registered:
Posts: 3
Reply with quote  #10 
Would a passive system do very much? Would it still be better to build a collect like I was originally thinking about but with smaller fans? Thanks.
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics