Solar thermal array

I’m new here, drawn in by an article on disassembly of a roomba, found other articles and it eventually resulted in this. I have a solar thermal array of 75 evacuated tubes. the tubes are integrated into a boiler loop. I set this up in 2008.
The array/boiler heat an endless pool and a ceramic floor in the addition I built. Unlike normal solar themaI systems, the pool is the reservoir. i designed and installed the system myself as I was unable to find anyone else who would attempt it. The key to the system is (obviously) you can’t have the boiler and the sun heating at the same time. This seems like a no brainer, but tuning which part runs when is where the devil is in the details. Think of things like the sun rises a different time each day (there’s a thermostat product that calculates this!) , and what happens if the power goes out? ( the array can go up a degree a second!)
Speaking in general terms, I am using tekmar controllers and temp sensors which activate icecube relays. lots of ice cube relays. these are a great little device with two sets of points that can turn things off and on based on what comes from the tekmar controllers.
This whole system is monitored each minute by a one-wire network with sensors checking the input and output temperatures of the array. I used to have audio alarms of a person talking out of my pc when something was out of whack, but eventually they were no longer needed. It was annoying that some times the pool would cool off because of a cloudy day, so I got an arduino, learned to program it and have a photo sensor on the roof that can turn the boiler off and on during the day when the light level falls below a certain threshold.
There are 5 zones in the boiler loop; pool, floor, emergency heat dump, hot water tank (not installed yet) and dump to chiller unit.

If anyone finds themselves going down this road, I’d be happy to share. Even though these tubes are on every rooftop in lesser developed countries, here in the US they are a rarity.

That’s an unexpectedly steep angle, is it for flow reasons?

the array is actually adjustable from latitude (47 degrees) to angle for shortest day of the year which I think was about 70 degrees. as it turns out, i use the least heat in the summer when it would be 47 degrees so i don’t usually adjust it. a bonus is the snow never an issue. this is a pumped system, there is no thermo siphon. its a closed loop of glycol. I use heat exchangers to harvest the heat

I’m considering a set of these for hot tub heating in the next year or two. I’ve thought about some home heating with them, but I’m not sure how to integrate them - I’ve got a manufactured home, so not a lot of “mechanical room” for extra water heaters and such.

I expect it’s the same reason you put “year round off grid radio” sort of solar panels at the same angle (80-90 degrees) - snow shedding and winter collection optimization, and in the summer it just doesn’t matter because the day is far longer.

where i live, i had to use glycol because it freezes hard many months of the year. I have a closed loop of glycol. i’m not sure where you live, maybe you could simply use water and a thermosiphon . but i think the basic idea would be to splice a heat exchanger into your hot tub plumbing before the heater so you would be preheating the water. when i built this i think i had to buy a rack that fit at least 10 tubes. that might cook the hot tub along with the person inside. the good thing is you can remove tubes from the rack without any change to the plumbing. they have a copper end that plugs into a manifold and can be easily removed

How do they “idle”? If I just don’t have coolant flow through them, will they hit a steady state temperature and just sit there?

We’re certainly below freezing in the winter, and I was planning to have a glycol coolant loop into some sort of heat exchanger, with a variable speed pump driving things based on temperature needs.

well, a couple of things. what turns my pump off and on is the temperature at the array output. That temp sensor connects to a tekmar controller that is set to turn on and off at certain temperatures. my array doesn’t ever idle because the pool always takes heat faster than the array can create it. just barely though. the array pump is going off and on sometimes every minute or two . i suppose i could adjust the on off temps and get it to run continuously. secondly, if that glycol isn’t taking the heat because its not being pumped through the system, the temperature will get hotter and hotter and the the pressure relief valve (hopefully its installed) will allow it to vent at about 350. ask me how i know that!

another way around this is to have a tiny 12v pump run off a solar panel. I have this wired for my no power situation. when the sun comes up enough to create electricity, its probably creating heat too. its just how much heat it makes vs how much heat the tub takes that you need to figure out. alot of this i learned the hard way and from posts like this on the internet.

I would be interested in a description of your control logic. A long time ago I estimated house space heating (demand of ~1 therm of gas burned a day @ 50% eff), and for 37 degrees N, I found that panels that were perfectly vertical were beneficial to 1- decrease overheat problems during the summer when I had zero use for the excess heat and 2- simplify mounting and 3- easily add shading to further reduce overheating.

I recently installed a heat pump for space heating and cooling, but have always wondered why couldn’t a home’s refrigerator, hot water, clothes dryers, and space heaters be integrated or at least loosely coupled together. For example, drying clothes produces waste heat. In winter, why can’t I use that to heat the house with a simple heat exchanger? (i.e. how to handle condensation and lint)

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