One year ago today: May 14, 2019, these cows like apples.
Five years ago today: May 14, 2015, yes, hair tonic.
Nine years ago today: May 14, 2011, a band bingo week.
Random years ago today: May 14, 2014, divorced from reality.
I went to pay my phone bill today and met with this sign. Mandatory, huh? Says who? This is the tyranny of the minority in America. And a sampling of what life will be like when all small businesses are wiped out and you have no choice but to deal with corporations. I went out to the coffee shop for the second time this month. They had indoor seating, but only two tables. Both with signs saying the “privilege” to sit down could be removed at any time by headquarters. It’s no wonder some people are near the boiling point, but like all peasant rebellions, unless a popular leader emerges, they will squabble themselves back to nothing.
Here’s how I got to that question. I’ve seen both models and did a thought experiment. Assume an infinitely long copper pipe in the sun. As cold water enters one end, it begins to heat until it reaches a maximum some distance down the length. It seems people post these videos without a clue about this concept—that the water is moving. After that point, the water does not heat up any more. My vision says if the water flow increases, that point will move further down the pipe. At any given flow rate, there is a point after which the remaining pipe (remember it is infinite) does nothing but keep the water from cooling.
Enter two constraints. We don’t have an infinite length box for the pipe, and we don’t have infinite money to buy it. If I knew to things, I could cut the pipe and make it zig-zag in a smaller container. I would need the rate of flow and the length of pipe to maximum heat. My calculations will be based on two persons, that is, the maximum number of hot water users at any time will be two. A shower averages 2.1 gallons per minute. I totaled up estimated hot water usages. For here that is showers, clothes washer, kitchen sink, bathroom sink, and ultimately, a dishwasher. Thus, the shower in the shed is the test case. My water bill says monthly I uses 7 “mgal” which probably means 7,000 gallons—or about half what I pay for.
Here’s a mystery picture for some of you. This is one edge of my shed roof, the slope is away from the bottom of the pic toward the top. However, look at that strip of wood along the edge where I’m pointing. What is that for? I had to wait until late afternoon to get up there, whew, she was hot. Let me find you a picture of the double-tarpaper roof that will never leak. I’ve decided to go with the same corrugate roofing material as before, bolstering the purlin (strips) from the inside of the shed where needed. With luck, the roofing material will bend just enough to match the slope of the lean-to.
And price out some better sprayers. I’ve got two of the plastic one-gallon models from Wal*mart, but they are too fragile. In particular, the release valve. To get a decent spray interval, you have to pump the handle 20 times. But pump it 21 and the valve not only releases, it self-destructs. Today I had to complete the insecticide and fungicide spraying by hand. Plants die on me all the time, but not from neglect.
Lipetsk sunflower field.
Remember to use BACK ARROW to return to blog.
Continuing my study, I cannot find good information on how rapidly a copper pipe can heat a given amount of water. A shower averages around 18 gallons. How much water fits in a ten foot length of 1/2” and 3/4” copper pipe. Pssst, Ken, this is where you get to use all the crap you learned in school that you were never gonna use. My guess is V=πr²L, will you okay that, Ken? The cross sectional area times the length, I heard pipes are quoted by inside diameter. This answer is going to come out in cubic inches, but there will be a conversion chart for that. It comes to 23.59 in³ for the 1/2” pipe and 53.09 for the 3/4”
Here we go, one US gallon is 231 cubic inches. This is optimum since I heard horizontal pipes never fill up completely, but vertical pipes are not an option for the shed roof. Here’s a nice picture of the swing planter, all painted up and installed. The bird feeder will hang from the pipe jutting out to the right of the crossbar. The pot inside is just for test and measurement. The planter is designed for pots, not for containing soil. Now back to the pipes.
For a gallon of water to be in the pipes, I would need ten 1/2” pipes or five of the 3/4”. If heating is by conduction, it seems it would take longer to heat water to the center of a 3/4” pipe, so let’s opt for the 1/2”, and in ten parallel runs so any temperature stresses are more evened out. The question remains, how long does it take such an arrangement to heat the water to shower temperature? A 1-gallon heater water would need to refresh itself 17 times during an average 8-minute shower. Video after video, the Internet is full of idiots who leave out too many variables. Air temp, flow rate, even the wind is a factor.
Pay attention to the angle in inclination. Most say use your latitude plus 5 degrees. I have a single pipe in storage which I will weigh with and without water. A true passive system uses a holding tank which has to be above the pipes. That gets heavy. I’m aiming more for a sustained flow of warm water heated only by the pipes. I read that in Australia, they have to install safety valves to prevent fracture if the water boils. I finally found a note saying a 4x8 panel that uses a copper sheet can collect 25,000 BTUs per day. Let’s call that 4,000 per hour during the six hottest hours of the day.
A gallon of water weighs 8.3 pounds. The groundwater temperature in this yard is 72°F. The BTU is the energy needed to raise 1 pound of water 1 degree F in 1 hour. To do the same job in one minute, you would need 60 BTUs. A hot shower is 105°F. The water needs to be heated by 33 degrees. An 8-minute shower uses 133 pounds of water. Call it 16 pounds of water per minute. So, to raise 16 pounds of water by 33°F in one minute, I would need 31,680 BTUs. Instant problem. At 4,000 BTUs per hour, the collector only produces 66.7 BTUs per minute. I would need 8 perfect collectors on a bright sunny day to take a shower. Looking at it another way, a 4x8 panel can heat 16 pounds of water by a puny 4.1°F per minute, and who wants a 76°F shower? Hence the argument for a holding tank.
A holding tank of 16 gallons would weigh the stated 133 pounds, and I’ve stood on that roof before. I tip the scales at 180 (but I’m working on it). The average daily temperature here is 84.8°F with average monthly highs over 90°F in the summer months. The tank would be insulated and in the sun, so can we presume the water would heat itself to 90°F in the tank? Probably more, since I know copper pipe in the sun gets too hot to touch.
No wonder the Internet people avoid the details. They probably don’t even know them. In fact, I don’t have much confidence in the calculations I just did. Have I considered everything? Let’s change the subject. Here is a pretty picture of my double tarpaper roof. Relax, it is the free tarpaper from the church a few months ago. How does this roof compare to other’s I’ve built. Don’t know, I’ve never done anything like this before. The ambient tank idea is better, a tank that raises water to the surrounding air temperature before it hits your hot water heater.
The answer to the riddle of the little sticks along the edges? You can’t see them because they are under the second layer. They are to raise the sides of the roof very slightly so no water drips off the edges. QED.
