Programming Challenge 1/22 - Passive Solar Pool Heater

[john.uhden]

Alrighty Guys and Gals,

We here in the northern hemisphere have passed our winter solstice so the days are getting longer.  Summer is on its way, which seems to be an annual event.

That means it won't be long until your spouse says it's time to open the pool.  At my house that's usually April 30 or May 1.  While my wife will submerge herself immediately after the first vacuuming, I won't go in above my waist until the water temperature is at least 76°F, which in Monmouth County, New Jersey means about the middle of June.  So if this thing can raise my water temperature just 1° per day, then I might be able to take my first Nestea Plunge before Memorial Day.

I refuse to spend any money on a fuel powered heater, but I've had this idea for a long time of building a passive solar heater.  All you need is some poly pipe, a little plywood, and a Little Giant cover pump (which I already have).

Now materials and dimensions may vary from country to country, but my idea is to lay out a 100 foot coil of 1" poly  pipe on a half sheet of 3/8" to 1/2" plywood with gaps between orbits of about 1/4" to provide for drill holes and zip ties to attach the pipe to the plywood.  The idea is to provide one or more hinged legs on the rear of the assembly to direct the face at the proper horizontal and vertical angle to the sun as the season progresses.

Ergo, your challenge is to write an AutoLisp (including VLisp) function to create the coil design subject to the following rules:

1.  You must check the applicable pipe standards to determine the standard pipe O.D.  I'm talking about piping that would be used for a yard irrigation system.

2.  You may use any unit of measurement which is comfortable to you.

3.  You may not use an initial internal radius of curvature less than 10 inches at the centerline of the pipe lest it might create a kink in the pipe.

4.  You must try to use exactly 100 feet of pipe (or 30 meters or whatever) because couplings are not permitted except at each end for getting piping from the pump and back into the pool.  The outward limit is where the side of the end of the pipe intersects an edge of the plywood.

5.  You must provide only one (1) vertex per quadrant (NE, NW, SW, SE) which will happen to be where the holes will be drilled.  Also that will avoid placing holes near the edge of the plywood.  Your arced segments need not be exact because the radius is changing infinitely, but the result should appear to be exact.  Your poolyline should be drawn at a constant width equal to the pipe O.D.

6.  You may use trial and error to alter the gap size only slightly to have the outer terminus end as described in rule #4.  It would be better not to have any excess pipe that has to be trimmed off.

7.  Include in your drawing the actual dimensions used and the resulting length.  Mtext will be satisfactory because creating a table is just too much code.

Okay everybody, DIVE IN!!  Let's say that we want this submitted before the end of January, which will give you enough time after the Superball and March Madness to actually build your contraption before opening day.

Extra credit goes to any thermodynamically inclined soul who can determine the rate of temperature increase for a 25,000 gallon pool based on average daylight times and conditions. and the flow capacity of the pump.  I have no idea whether it makes any difference if the pool is inground or above ground.  Do not include your analysis in the drawing but just in your response.

Refer any questions to @ronjonp or @hak_vz or @Anonymous because I may not understand them.

[john.uhden]

Corrections:

Rule #3.  I think "crimp" is a better word than 'kink."

Rule #6.  I know you're going to use trial and error to find a place where to start, but I would rather like code that iterates to find the best solution from your perspective.  You should include comments that explain your objectives.

[ronjonp]

@john.uhden Have you read this for sizing a heater?

"Basically, the surface area of your solar collector should equal 50%–100% of the surface area of your pool. In cooler and cloudier areas, you may need to increase the ratio between the collector area and the pool surface area. Adding collector square footage also lengthens the swimming season."

[Sea-Haven]

My former boss had black poly on the roof, if set to pump to spa connected to pool it would raise water temp to way beyond acceptable and cold water from pool had to be added. A thermostat would be a good idea so excessive temp does not happen.

My code submission

Pretty sure will struggle to put 1/2 circle ends in 1" pipe as a reasonable small radius, you may be better with 1/2" use that for garden irrigation can be bent to a loop fairly easy, I would cross each loop so  1 radius on ends so could have simple tie point arrangement.

[john.uhden]

@ronjonp
I am not proposing PV cells.
Back in 1984 a group of families from here at the shore spent a week at Ed
Burke's Tall Timbers camp on Loon Lake in NY.
Ed provided hot water to all 5 cabins via one large coil of 2" poly pipe.
By large I mean like 6' diameter feeding unpowered water heaters just
acting as insulated reservoirs.
I'm not talking about getting the pool up to 150° so I'm guessing that my
little contraption would help. That's all.

[john.uhden]

Nice.
Don't need no thermostat. If the pool gets too warm, just unplug the pump,
which I would do each night for obvious reasons anyway.
I am responding via e-mail, so I haven't looked at your offering yet.
BTW, a former boss told me to use the word "submittal" not "submission."

[john.uhden]

@Sea-Haven 

That's pretty, but I don't need all those colors.  Plain black will be fine with me.  👁

[Sea-Haven]

Need a few of these for pool 

They work surprisingly well.

If you have some poly tube leave in sun and try bending it. It may bend better if actually full of water as the water may stop the kink effect. I just know 1/2" can be bent pretty easy it is supplied as about a 2' wide roll. Would need multiple pipes as pump is probably pushing a reasonable volume.

[Kent1Cooper]

---

@john.uhden wrote:

.... a 100 foot coil of 1" poly  pipe on a half sheet of 3/8" to 1/2" plywood with gaps between orbits of about 1/4" .....

3.  You may not use an initial internal radius of curvature less than 10 inches at the centerline of the pipe....

4.  You must try to use exactly 100 feet of pipe ....

5.  You must provide only one (1) vertex per quadrant .....

---

It looks like 'gaps...about 1/4" ' is going to have to be a little less than 1/4".  With my SPEQ commmand in Spirals.lsp, available >here<, I drew one at 1" Polyline width [though I didn't check actual OD of such piping] with an inner radius of 10", outermost radius of 23.5" so the outside edge gets to no more than 24" from the center, and spacing between turns of 1-1/4" for 1/4" gaps between 1" pipes.  I got this [the outer square is 4' x 4']:

It's a little less than 100' long [1136.7"].  If I force it to be 100' long with LENGTHEN's Total option, I get this:

which violates the sheet size limitation.

So unless I've missed the boat on the concept somehow, the gaps would need to be less than 1/4" to get the 100' in, and it may not even be possible if 1" poly pipe is a nominal size and the actual OD is larger, as with most kinds of piping I know about.

[john.uhden]

@Kent1Cooper,
I doubt that you have ever missed any boat.
So far, I have done my calcs using 1" pipe and 100' fits on a 4x4 sheet. I
don't have the code with me at work, but I think I did have to reduce the
gap to say 7/32". But now the problem is that the OD of nominal 1"
SDR-32.5 pipe is 1.315" so the ultimate solution may fall short of 100
feet. That's part of what this challenge is about. Shortening the pipe is
no big deal. I mean it's got to fit on the sheet, unless I use half of my
ping pong table. But my son likes to think he can beat my eldest
daughter, but he can't, and I like to observe, so I am not scrapping the
ping pong table, especially if she is my doubles partner.
Anyway, I guess it may boil down to what's the minimum gap that would be
suitable to provide a large enough hole for two zip ties to get through.
Oh, there ya go... the hole can be larger than the gap, so it's just a
matter of how thick (not wide) the zip ties are to fit between the pipes.
Okay, I found that a "Cable Tie, 8" Long, UL Rated, 50lb Tensile Strength,
PA66, Black, 1000/pkg" tie is only 0.05" thick, so a 1/8" gap would work.
I shouldn't have to be doing this for any of you. It's supposed to be your
design.

[ronjonp]

@john.uhden Can't you just use PE pipe ? Plenty of options with OD's less than or close to and inch. Plus it's pliable so you can make your coil. Do you even need those gaps ... maybe hold the coil down in 4 places using a rigid bar or something that secures to the center and out to the edge.

[john.uhden]

@ronjonp
The spec I quoted IS for PE pipe, and my irrigation guy sells 100' coils
cheap (at his cost to his good customers). Now they aren't coiled flat.
That would be too easy. But at least they come precurved.
Yes, I could put a couple of pieces of lathe across, but I had decided to
use zip ties, because they would hardly block the sun and in fact would
transfer heat to the pipes. I spent a couple years installing CAT5 cable
so I have this affinity for cable ties. I also figured that a slight gap
might expose more surface area to the sun throughout the day.
Feel free to propose any design you think would work well. I like
challenges that call for some creativity.

[ronjonp]

@john.uhden 

One issue I have with zip ties is they become fragile from UV exposure. Agreed a little bit of gap might give you a bit more heat but I wonder if it's enough more at the expense of tedious assembly. Will the board and all the hardware be black? That would help too.

Sounds like a fun project 🙂

[john.uhden]

@ronjonp
Ooh, I hadn't thought of UV deterioration. My local Ace Hardware sells
twist ties by the coil and they last on my tomato plant cages for a couple
of years.
The tedium is an issue. I wish my two older granddaughters from Maine
could be around. I could put one on each side of the board. But I don't
think they're coming to visit 'til the end of June.
Yes, I will either paint the board black with epoxy paint or cover it with
sheet metal from my ductwork buddy, but the corners might cut you.

[Kent1Cooper]

---

@john.uhden wrote:
.... the OD of nominal 1" SDR-32.5 pipe is 1.315" ....

---

I realized one could get a little more length in with all curves at the min. 10" radius rather than gradually increasing.  And, a routine would have an easier time keeping track of the total length so far if all arc segments are therefore the same length.

But using your tube OD number, and with the gap reduced to about 3/16" [1-1/2" C-C between passes], starting with the 10" tube-center-line radius 3/4 of the way around in the middle and then sliding over for the next lap, I get this:

It's under 83' long [even another pass all the way around, which would exceed the 4' square, wouldn't quite get to 100'], but at least I can kind of imagine a way to get a routine to draw such a thing.

[john.uhden]

@Kent1Cooper
Ahah! A squarish coil, eh? I had actually considered that in a scary
dream the other night.
Design away (all in AutoLisp with generous comments, please).
I just might be building your design (if my heat gun still works; gotta
find it first).
But what the heck do you mean by "would have an easier time keeping track
of the total length?"
So if 83' it is, I could set it back 8.5' from the coping so as not to
waste 17'. I'm gonna need two elbows anyway, and I think they sell one
that has one leg that you clamp and one that is threaded, 'cause I think
I'll connect the pump discharge via a piece of garden hose. Even though it
will slow down the flow rate, the velocity in the coil will be reduced
allowing more time for the sun to heat it up (or so I imagine).

[Kent1Cooper]

---

@john.uhden wrote:
.... what the heck do you mean by "would have an easier time keeping track of the total length?" ....

---

I was thinking that if a routine was to draw something like this, and be limited to 100' of tubing, if there were room to fit it all on the board [not knowing as I was thinking about it that there doesn't appear to be room given current assumptions], you would want it to stop when it got to 100'.  So it should be made to keep track of the total length so far after each Polyline segment it draws along the way.  Having just one amount of length to add for every arc segment would simplify that, compared to calculating the curve length individually after each one because of varying radii.

[Sea-Haven]

You want the feed/return pipe to be at least the size of the 1" tube, a garden hose whilst slowing down the flow would maybe create pressure problems. I would look at even larger feed tube and maybe 2 coils so no pressure problems. After all  if you are talking pump to roof so head needs to be added to pipe friction loss. 

I had an outside spa and it had a small gas heater it took around 3 hours to heat up. So even if flow is fast there will be a temperature differential. Multi coils will slow flow rate.

[ronjonp]

@john.uhden Is THIS the pump that you have?

[john.uhden]

It's too bad you showed your hand (but I like it).  But at least not your code, unless you drew that by hand, in which case you'll have to put it to music.  It's more about the code that makes it happen so that it could be used by Dranko The Dragster from the planet Mirth in units of igzlpigs, or by NASA in light-years to compute the flow rate of a helical worm hole (though I don't think Manning ever considered such roughness coefficients).

Meanwhile, that's why I asked about invisibility.  I additionally specified that the code could perform iterations, so with each iteration of an invisibly drawn polyline you need only get its length property.  But why do I have to say all this?  You could all figure this out for yourselves, as part of answering the challenge.  Or am I being obtuse?  Sorry, Kent, but you might be facing another month in the cooler, and we're gonna dance around your fire of flaming code like wild Injuns.