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stmbtwle

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Reply with quote  #31 
I guess it would be a "coiled plastic tube" collector... whatever you like but try to be descriptive.
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Rick H Parker

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Reply with quote  #32 
SolarSpiral collectors are pretty elementary and for a number of reasons they don't perform well but nobody here will rank you into a class.

There are a couple things you could do to increase the performance of your SolarSprial.

1. Paint the backplate flat black, this will convert more sunlight into heat. 

2. Seal the ends of of the glazing, this will help keep hot air from excapeing and cooler air from rushing in.

3. Tilt the collector toward the sun, the less the sun rays and the collector deviates from perpendicular the more energy that gets transfer.  Like shooting pool, if you shoot two balls center to center all the energy from the first ball can be transferred to the second ball then the first ball comes to a dead stop. If two balls hit at an angle the energy will always be split between the two portional to the angle.

There are more then three but lets leave it at that for now.

Rick H Parker

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Rick H Parker
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gbwillson

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Reply with quote  #33 
HVAC is used for Heating, Ventilation, and Air Conditioning.

And for the ZP, I coined the term ZeroPass, which I thought sounded a heck of a lot better than No-Pass, Slot-Flow, Gap-Flow or any of the other stupid names I came up with at the time I built my prototype ZP.

A dual pass collector can also refer to a collector in which the air passes over the same space in what is usually an over-under configuration. The air enters the collector at one end, moves to the opposite end of the collector, before returning and exiting back through the same end as the entry. The thought is that the down and back air can flow get heated twice in the same space. 

Greg in MN
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Reply with quote  #34 
Quote:
Originally Posted by Rick H Parker
SolarSpiral collectors are pretty elementary and for a number of reasons they don't perform well but nobody here will rank you into a class.

There are a couple things you could do to increase the performance of your SolarSprial.

1. Paint the backplate flat black, this will convert more sunlight into heat. 

2. Seal the ends of of the glazing, this will help keep hot air from excapeing and cooler air from rushing in.

3. Tilt the collector toward the sun, the less the sun rays and the collector deviates from perpendicular the more energy that gets transfer.  Like shooting pool, if you shoot two balls center to center all the energy from the first ball can be transferred to the second ball then the first ball comes to a dead stop. If two balls hit at an angle the energy will always be split between the two portional to the angle.

There are more then three but lets leave it at that for now.

Rick H Parker


Thanks Rick for the tips and comments.     A few questions.....   What makes this type not very efficient ?  Or what would make it more efficient ?    Just curious to learn what makes one style better than another, and what the fail points are.

I need to tear this one down and redo a few things,  so i'll paint the panel black.  My thoughts on keeping it silver were to reflect the sun toward the tubing.   But i guess its more of just turning the suns energy into heat.   Would it work better if there were air space around each coil ?

Would i be better off building it differently ?

The glazing is sealed (well for the most part) at the ends,  I feel like i need it vented a little so that condensation can escape in the morning.

If i ever figure out how to mount it to my roof without damage to the shingles and roof,  it will be tilted toward the sun and almost perfect angle.   It really will be the perfect place for it if i can get it up there.
stmbtwle

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Reply with quote  #35 
There are some arguments about painting the metal black.  It will get hotter but I don't know how much of that heat is going to get transferred to the tubing as I think the tube is just sitting there, unlike a finned tube collector.  Of course the hot metal will heat the air in the collector which will help heat the tubing.   Another issue is that the hot metal will radiate a lot of heat out the back of the collector unless you insulate it.  

I don't see any point in spaces between the tubes.  You want the heat in the tubes, not the back, so I would pack them as tightly as I could so the sunlight hits them directly.  

Sealing the ends could cause trouble in the summer, like overheating and melting the pipe.  I'd make the end caps or whatever removable.

Many of us use polyiso insulation board in or for the back of the collector.  It's reflective on one side, has a good insulation rating, is lightweight, easy to work with and probably cheaper than metal.  You can get it at Home Depot, Lowes, or wherever. Worth looking into for your next collector, or to put underneath you existing one.

Anyway we're glad you've joined the "solar community"!  There is no perfect collector, You'll learn from this one and use that information in your next one.  Keep us posted how it works, we're always interested!


 

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SolarInterested

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Reply with quote  #36 
Quote:
Originally Posted by stmbtwle
... Sealing the ends could cause trouble in the summer, like overheating and melting the pipe.  I'd make the end caps or whatever removable.

http://www.builditsolar.com/References/pipeanalysisrs.htm#Pipe

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Rick H Parker

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Reply with quote  #37 

"Thanks Rick for the tips and comments. A few questions.....  What makes this type not very efficient ? Or what would make it more efficient ? Just curious to learn what makes one style better than another, and what the fail points are."

The objective is to convert the energy of sunlight into thermal energy (Heat).
Trap then move the heat out of the collector before it has a chance to escape
By Conduction, typically through the walls.
By Convection, typically air leaks.
By Radiation, does not convert and reflects back through the glazing.

 

Some collectors are better at converting solar radiation into thermal energy (Heat). Some collectors are better at trapping the heat, some are better at moving the heat. The balance between the three is what determines how efficient the collector is as a whole.

 

We see colors by the light the material reflects. White is ~80% reflective. That is ~80% of the solar radiation that strikes the white area is being reflected back out through the glazing. This is heat loss by Radiation. When I look at your collector and see white I see 80% loss by radiation.

 

Black is on the other end of the Light Reflectance Value (LRV) Black has a LRV of 0 – 20. Meaning 0-20% of the solar radiation is being reflected, 80-100% is being absorbed and converted into heat.

 

When selecting a paint try to get its data sheet, look for the LRV, the lower the LRV the better it will work. Your not going to find a LRV of zero. Zero would be the elusive Blackbody radiation. Blackbody radiation is a goal to strive for but don’t expect to find one. If you cannot get the data sheets, select a flat black in the darkest shade you can find.

 

 

The reason we insulate the walls of a house or a solar collector is to lower the thermal conductance of the wall and slow down the rate in which heat conducts through the wall. You have no insulation in your collector, that tells me the collector has a high rate of heat loss by conductance compared to other collectors. This is heat loss by conductance.

 

 

Your glazeing is corrugated, I look at the ends and I know you not going to get a good seal. The leakage will let hot air out and cooler in in. That is heat loss by convection.

 

You said I feel like i need it vented a little so that condensation can escape in the morning”

Think about that, if condensation can escape it can get back in, so can air that is convection. Your best bet would be to dry out the collector when the humidity is low and seal the collector as best you can.

 

If you look at other peoples projects you see them using metal pipes. They are intently creating a pathway this is highly thermal conductive. In order to encourage the heat to take the path they want it to take. Your plastic tubing is not highly thermal conductive, it does not do this as well. However I don’t knock the use of plastics in solar thermal. Like everything else, performance is not everything, there is economics.

 

In going to stop here for now. You look this over and tell us what improvements you can make in your rebuild or next build that are within your skill set, budget and your tool box.

 

Rick H Parker

 


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Rick H Parker
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Rick H Parker

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Reply with quote  #38 
"Sealing the ends could cause trouble in the summer, like overheating and melting the pipe"

Good catch Wille but it depends. Black Polypropylene tubing is good to 180F. The question is, is it Polypropylene?

Rick H Parker





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Rick H Parker
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Tori

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Reply with quote  #39 
Rick,  thank you for that.  That was exactly what i needed, and i guess should have asked for.  A solid critique.   I especially can appreciate the line about "performance is not everything, there is economics."     I've tried to keep this as low buck as possible, otherwise it'll never pay me back.  Currently at about $100 I think.   Which is okay,  i just didn't want to invest a lot of money to find out there wasn't enough benefit.  Now that i've run it thru last summer, i see it works, albeit more efficiency is needed.    Perhaps i won't need to go larger as initially thought after i paint the collector flat black.  Can you recommend a paint with low LRV ?  

I will check the material of my tubing, but i'm pretty sure it is Polypropylene. 

A typical summer day here is no more than about 75*    Many days are overcast until about 11am, then sun for the rest of the day or maybe the overcast will move back in late afternoon.    I do not have ideal, dependable sunlight day in, day out.   I don't think it overheating will be an issue, especially if the circ pump is on.   Pump has been dead now for a few months, and we've had a few 80* days where i know the collector and tubing inside was DAMN HOT !   It'll never get hotter than that once up an running.

Skill set and abilities are high,  budget,.... well,..... i guess whatever it NEEDS to be,....  biggest downfall is my understanding of options. 

I'll get it painted and see what i can do for sealing it up better.  I know i'll never get it air tight and we'll see if that actually creates a problem with it drying out in the morning.
Rick H Parker

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Reply with quote  #40 
When your starting off, it makes sense to avoid costly materials. That way the mistakes you make as you climb the learning curve, won't hit your back pocket so hard.

Low LRV paint for your use is going to be black.  I assume your going to use a rattle can from one of the big box retailer. What brands do you have in your area. We might be able to look up the LRV online. If you buy from a paint store. Most likely the retailer can look up the LRV of the black paint.

Rick H Parker


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Rick H Parker
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