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
Sign up Calendar Latest Topics
 
 
 


Reply
  Author   Comment   Page 1 of 3      1   2   3   Next
Thor

Avatar / Picture

Registered:
Posts: 52
Reply with quote  #1 
Hi all- This is a great site, prevented me from sleeping last nite! I have some questions that I am sure have been discussed, but I find myself getting easily distracted by the many topics here...

1) thermal storage size to survive the nite? My house is 20x44 rambler in Minnesota, insulation is so-so, I guess average for a 1968 house. I am planning to spray foam the basement walls/rim joist and use hot water radiant base board heat... my thoughts are the heat will find its way upstairs.

2) Collector size/type to feed heat into determined storage size... my thoughts after reading a few of these postings is to use some type of a closed loop Zeropass/ARETHA combination, daisy chaining 2 or 3 of them together to rapidly bring the storage up to temp?? yes/no/maybe? December and January have limited sun exposure due to trees,3 hours at best, so when the sun does hit them I want maximum production.

3) Is there a site or has anyone come up with anything that compares fluid to air heat ex-changer efficiencies?

4) i currently have 9 300watt PV panels that are itching to be put up, I like the simple design of the wattsun dual axis mount, seems simple enough to build--does anyone have a reasonably priced source for slewing drives, and actuators?

Thanks for your input [smile]

__________________
My little boy calls me Thor! [biggrin]
Minnesota!

stmbtwle

Avatar / Picture

Registered:
Posts: 2,858
Reply with quote  #2 
I think a zero pass/ARETHA hybrid would be a good collector, though I haven't built one. I've found a two-stage HEX (heat exchanger) to be very effective, the second stage captures the heat missed by the first. However as the ARETHA recirculates the air, the heat missed by the first pass through a single-stage HEX will come around again, anyway. The difference may be moot.

There's no need to daisy-chain your collectors. Actual heat gain (not temperature) is pretty much independent of flow rate. Over time, the temperature of the storage will rise. This will increase the input to the collector and thus the output. Attempting to get high temperatures in a single pass actually REDUCES efficiency, as more heat is lost through radiation from the collector.  The sooner you can get the heat OUT of the collector and into storage or your home, the more efficient your system will be.  There are lots of discussions on the subject.

While a tracking PV mount WILL increase production, I don't feel its worth the expense, aggravation and maintenance. With PV prices where they are today (and still coming down), it's simpler (and cheaper) to install more PV panels to make up the difference. A fixed array is pretty maintenance free, just hose it down a couple times a year. A tracking mount is expensive to build or purchase, requires periodic maintenance, and is subject to breakdown.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
SolarInterested

Avatar / Picture

Spam Stomper
Registered:
Posts: 1,054
Reply with quote  #3 
Hi Thor. Regarding sizing the BIS site has a good section on this at
http://www.builditsolar.com/Projects/SpaceHeating/DHWplusSpace/OverviewDesign.htm
Look under Sizing the System for Water and Space Heating

__________________
Both temperature rise and airflow are integral to comparing hot air collectors
gbwillson

Avatar / Picture

Registered:
Posts: 2,301
Reply with quote  #4 
Welcome Thor!

Living in a 900SF home in MN I can say that I'm able to heat my house with two solar air heaters totaling 96SF. My heaters pull air out of my unfinished basement and back. This warms the basement 10-12 degrees. Most days when the sun is out my furnace only runs in the morning until the solar heaters kick in and doesn't run again until the next morning. The heaters warm the space between the joists and the wood subfloor which in turn warms the main floor above quite nicely. Of course, if I have a few days without sunshine, the storage capacity of the wood subfloor isn't enough. But since the coldest days are the sunniest, it hasn't been a problem.

Greg in MN[wave]
Thor

Avatar / Picture

Registered:
Posts: 52
Reply with quote  #5 
Thanks guys for the welcome- this is an addicting site for sure...

Willie- Daisy chaining is bad? (Hypothetical numbers here) I was thinking the first collector would boost 15 degrees, the second 8-10 degrees, and third 4-5 degrees, for a total array boost of 30 degrees before returning 60'-70' to storage then back to the array again... in my mind it makes sense anyways.

SolarInterested- thanks for the link!

Greg- I really like that dual screen box you got, if my sunny locations were next to the house I would definitely get one hooked up! but stretching 60'feet of insulated duct is a little to ghetto/redneck for the neighborhood- if ya know what I mean. How fast does you panel heat up? How hot would your box get if it were sealed? how about with a 1" thermopane glazing? 

__________________
My little boy calls me Thor! [biggrin]
Minnesota!
stmbtwle

Avatar / Picture

Registered:
Posts: 2,858
Reply with quote  #6 
A collector captures X energy. 3 of them will capture 3X, period. Daisy chaining them might give you a higher temperature but NOT more energy.

Now for heat loss. The higher the temperature difference, the greater the heat loss. So if the third collector in your chain is three times warmer than ambient, it'll LOSE three times the energy.

Consider damage. The last collector in the chain is that much hotter than the first. It's also more likely to reach a damaging temperature.

Last, you don't need to daisy chain your collectors for high temperatures, just reduce the flow rate. Turn the pump OFF and your collector may reach boiling.

__________________
Solar is like the wind. It may be free, but putting it to work isn't!
Willie, Tampa Bay
gbwillson

Avatar / Picture

Registered:
Posts: 2,301
Reply with quote  #7 
Willie is correct. While you may gain higher temps, you will lose efficiency. There will be heat loss between sections and don't forget about the airflow restriction as the air has to transfer from one section to the next. My ZP is designed to warm the air as the air passes between the layers. This is one of the advantages of the ZP. So, in effect you get the increase in air temp continuously from entry to exit inside the screen gap, but you greatly simplify the build with NO separate sections. Now I do have to run my ZP with a lot of air to keep the temps down, but that is not the fault of the design. The idea is to have the lowest temps entering the house that you are comfortable with. Yes, you can certainly bring 120˚ or greater air into the house. But at that temp, you will also be losing a lot of your collected heat through the glazing, Lots of lukewarm air is always more efficient than a small amount of hot air. But at the same time, 90˚ air blowing hard on bare skin will feel cool, but it captures the most BTU's. You have to choose if you want the maximum amount of BTU's versus the feel of warm/hot air. While I'm talking about air, the same pretty much apples to water heat too. Although long outside runs of water could be buried without too much difficulty compared to air. 

My panels heat up quite fast once the sun fully engages them. Since any collector is a block of ice to start, a collector will cycle on and off for a bit until everything warms up. There is little mass inside a good collector, since if you had chunks of iron, rocks, etc, these would have to warm up too which would take a great deal longer. I don't think any sealed collector box would do well if no air were passing through. But while a meltdown on an air collector is usually not fatal, a water collector overheating can not only destroy the collector, but you could have leaks and damage from water too.

I'm not a big fan of using glass, including double pane. It's heavy, can break, and is limited in size and shape to the panes themselves. But if you have free panes, I would certainly consider them if they were permanently mounted. But make sure the lead content is low and that the window are not low-E as these may be fine for a window, but they will limit the amount of sun entering the collector. Since you live in Minnesota(where?), you have Menards near you and one of the best products you can use is twin wall polycarbonate panels below:

http://www.menards.com/main/p-1444424088575-c-5819.htm?tid=-2886618243184983140

These twinwall panels are lightweight, insulate well, are easy to cut, don't break and are cheap. Like the polyiso insulation you will be using they are on sale quite often. I like these far better than the wavy polycarbonate panels.

Greg in MN
Thor

Avatar / Picture

Registered:
Posts: 52
Reply with quote  #8 
Thanks guys.. I think you convinced me that daisy chaining is probably not worth it.

Greg- I'm on the south side of the metro.. menards, home depot, might be a mile away....

attached is a PDF of the collector design I have been pondering for a couple days since reading about the ARETHA design, then I noticed yours, then I thought lets combine the two!  closed loop/ sealed box... how hot do you think it would get in there?  variable speed pump and fan hooked to an arduino/raspberry pi to control GPM and CFM... the GPM flow rate and CFM would control the overall temp of the collector... 

Whatcha think??

 
Attached Files
pdf HYBRID_DUAL_SCREEN.pdf (7.96 KB, 21 views)


__________________
My little boy calls me Thor! [biggrin]
Minnesota!

gbwillson

Avatar / Picture

Registered:
Posts: 2,301
Reply with quote  #9 
A few thoughts...

Interesting design, so where does air enter and exit this design? 2" of polyiso insulation twice the norm, but can't hurt. And a larger ZeroPass design needs a lot of airflow or it can get quite hot. Let's say you are using a 4'x24'ZP. You will need have a lot of moving air through the ZP, especially with the turn around as air will try to slow down a great deal at the turn. I'm not saying it can't be done, far from it. But combining two good designs in one package may be weakening the benefits of both. But I'd love to see you try...

Greg in MN

PS:Ragnar is a traitor!
Thor

Avatar / Picture

Registered:
Posts: 52
Reply with quote  #10 
Well my thought is that is a sealed unit, no air entering or exiting, the same air that is inside when built is constantly being circulated-- like a conveyor belt so to say.... passing through the air to fluid exchanger.  Say the exchanger is constantly being blasted by 200' air... maybe?  The air will be cooled by the exchanger only to get heated up again by passing through the screens... if gets too hot speed fluid flow or fan speed or both.

If it happens to be to efficient at heating the liquid, I'll run lines under the driveway and melt the snow!

__________________
My little boy calls me Thor! [biggrin]
Minnesota!
Previous Topic | Next Topic
Print
Reply

Quick Navigation:

Easily create a Forum Website with Website Toolbox.

 

web statistics