diy solar

diy solar

Why can't i get high temps?

I agree with collector is to small, needs insulation, needs glass, also make sure your flow is correct through the heat exchanger. Solar input ( hottest fluid ) should be at the hottest water. Mine is DIY tube in tube with flows in opposite directions.
 
At the rate you are pumping you can only can only raise the temp 2 degrees if you have a square meter of collector which you do not have. You need to use a PWM speed controller for the pump, not a potentiometer. Your heat exchanger needs to be insulated too.
Real world results say otherwise though. In the morning, the water in the water heater is around 60-65, after morning showers and stuff, (the geothermal will heat it up to about 110-115 during the night). The temps are freezing outside and as the sun heats things up the system will run off and on till it stays on continuously. This is when I have the aquastat set to about 80 degrees before it will turn the pumps on. So it is actively taking it from 60-65 degrees up to 85-90 degrees. This is more than 2 degrees.

I'll look into a PWM speed controller. I might also just add a 500ohm resistor to make the pumps run more slowly. And I've been trying to find a good material with which to insulate the heat exchanger.
 
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I agree with collector is to small, needs insulation, needs glass, also make sure your flow is correct through the heat exchanger. Solar input ( hottest fluid ) should be at the hottest water. Mine is DIY tube in tube with flows in opposite directions.
Right now I have it hooked up like this (see drawing).This heat exchanger is configured to be hooked up with either concurrent flow direction or counter flow direction. I have it set up for counter flow connection right now.
 

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You may have other heat inputs other than the solar collector that is a 2 degrees rise per pass. With your small collector, you only have about 8000 BTU per day providing no losses.
 
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I DIYed my entire system but purchased a controller. It comes on when collectors are 20 deg F above tank and off when 9 deg F above tank and off when tank reaches max temperature 160 deg F. Your collector should be producing similar you may need a flow valve to adjust to that. Also you should see a 10 deg F drop in fluid temperature across the heat exchanger. So giving up 10 deg in fluid and gaining 10 deg on water. My collector is glass from single pane slinging glass doors so 2 panels approximately 3 feet x 6 feet. Heat plate 26 ga. Sheet Mtl. 3/8 copper tube laying vertical on 2 in. Centers soldered to sheet mtl 3/4 copper headers in a sheet mtl box insulated with 1 inch ico foam. 2 60 watt taco pumps. Heat exchanger is 3/8 copper inside 3/4 copper insulated. Connected to a 60 gallon tank. No electricity connected to it. Summer I get 160 deg daily. Spring and fall 130 to 145. Winter 135 tops, average 125. I have tankless gas backup.
 
Hello to any one who reads this! Lol.

I built my first solar water heater!
It's 1/2" pex under a piece of Polyethylene terephthalate glycol, or PETG plastic.
Inside the pex I have RV fluid/antifreeze so it doesn't burst at night with freezing temps. I have an Aquastat attached to the pex loop so the pumps won't turn on till the loop temp reaches a user defined value. Currently i have it set to about 85 deg F. The RV fluid is pumped through the loop via a solar powered pump to a plate heat exchanger. On the other side of the plate heat exchanger is the domestic hot water. I have two water heaters connected in series and the first one is turned off. The water from the first (powered off) water heater is what is pumped through the plate heat exchanger. I was hoping to use this setup to heat or at least pre-heat the hot water. I suppose i have half of that goal accomplished because it will circulate and get the water temp in the first water heater up to about 87-90 degrees.

My question to all of you: if i build a second loop and connect it to the first would it get higher temps...
A) if connected in series with the first loop
B) if connected in parallel
Or
C) won't matter, thats the best temp I'm going to get?


Side note, cause i know someone might ask. The piping in the photo also goes to our geothermal hvac system. When it is running it heats the domestic hot water. I have check valves on each side so the geo won't pull water backwards through the plate exchanger and vice versa. Typically, right now in the winter, the geothermal heats the water at night and the solar loop heats it during the day because the geothermal doesn't need to run during the day.

I appreciate any feedback good or bad. And thanks for your help!
Second loop built. Should have it hooked up tomorrow.
 

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Well, it's hooked up. We didn't really have some good sun today, but for the few minutes that it did run it made me wonder if fluid isn't traveling through both loops equally. I feel like the fluid is going mostly through the first loop and barely through the second. I say this because the temps coming out of the top of the second loop were 110-113ish, but the temps at the top of the first loop were 88-92ish. And when I say the top, I mean the pipe that is coming out the boxes on the return side.

I'll wait for a more sunny day to verify, but I am considering doing some rework and connecting them in series now. Ugh...lol....this project never seems to end.

Side note: I did add some water in addition to the pink glycol solution. It's probably about 1/3 water to 2/3 glycol now.
 

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That is what I would expect from the piping. Is there room on the right of the first. Then tee where piping is balanced. Parallel with give you the most capacity. Series will produce the higher outlet temperature but will not produce as many BTUs. The colder the entering water the more BTUs it will absorb. I don’t recall is this a open system or closed. If it is closed be sure to have a T and P valve and expansion tank. Mine is basically open (2 lb pressure relief) in the summer when it boils it sounds like a kid practicing on a horn.
 
That is what I would expect from the piping. Is there room on the right of the first. Then tee where piping is balanced. Parallel with give you the most capacity. Series will produce the higher outlet temperature but will not produce as many BTUs. The colder the entering water the more BTUs it will absorb. I don’t recall is this a open system or closed. If it is closed be sure to have a T and P valve and expansion tank. Mine is basically open (2 lb pressure relief) in the summer when it boils it sounds like a kid practicing on a horn.
I've learned that i can't get true parallel flow unless i do what's in the attached drawing. So I'm going to connect in series.
 

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I suppose that would be an option. I'll have to figure out which to do. And to answer your other question, it is a closed system. The solar loops go to a heat exchanger inside the house.
 
In the summertime late afternoon the tank is satisfied the panels over heat and boil. I have a 1.5 gallon tank at the high point that serves as a expansion tank and steam trap that is where the pressure relief is.
 
Update for the journal. Last night I anticipated clear skies for today so I tried an experiment. I turned on both water heaters overnight so that once it was warm enough outside on the loops (that are now connected in series) that everything would basically be starting the day at the desired temperature I'm trying to achieve. The thermometer on the water heater was showing 110-115 when the pumps started pushing fluid and I turned the first water heater off. The system managed to hold those temps pretty much the entire time we had useable sunlight. I even turned on the hot water in the kitchen till the temps dropped to 70 at the water heater and it managed to bring the temps back up to about 110. So I think it is showing improvement and promise that it can at least maintain higher temps - once it gets up to those temps...lol....

Tomorrow, I am going to let it go through it's normal cycle. At the beginning of the day the water heater will probably be around 60-70 after showers. I'll see if it can bring the temps up from 60-70 to 110-115 on its own as I now know it is capable of maintaining 110-115. Hopefully weather is good tomorrow.
 
Well, today was a full day of sun. Outside air temp was a high of about 13 f. Temp at the water heater was holding at 95 f.
 
I have researched but never used vacuum tubes but you should look at adding some in series if those are normal outside temperatures.
 
I have researched but never used vacuum tubes but you should look at adding some in series if those are normal outside temperatures.
I'm not sure what you mean. The temps i just talked about are normal temps for where i live. Its really cold outside, i feel like anything above 95 at the water heater is good enough for the middle of winter.
 
I'm not thrilled with it, but I've spent enough time on this project for now. In the summer it won't have a prob generating hot water. And it's too cold outside to want to work on it/change it. For now I'm just accepting this as the best i can get for now.
 
How are you controlling your pump? From what I read it sounds like just with a thermostat so it's on or off.
I built my own controller and use a central heating circulating pump.
To maximise solar gain I control the pump by turning it on and off with varying duration depending on the temperature difference between the tank and the collector.

i.e. if the difference is only 8 degrees then the pump is on 8 seconds, off 2 seconds. When it's 3 degrees it's on 3 seconds, off 8.
Over 10 degrees it's on permanently. This way I get maximum absorption without the complexity of a PWM controlled pump.
 
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