Author Topic: Domestic Hot Water solar heater  (Read 4451 times)

0 Members and 1 Guest are viewing this topic.

Larsmartinxt

  • Newbie
  • *
  • Posts: 48
  • Country: no
Domestic Hot Water solar heater
« on: November 09, 2014, 01:38:28 PM »
I have been thinking about making a solar heater for preheating my hot water for a while. After reading tons of great information from other diy'ers I started gathering stuff for my build. My goal was to get this build for as low cost as possible while also having a system with decent performance.
For starters I got 2x 4m^2 double glazed windows and rockwool insulation. Both was given away from someone that was refurbishing their house.

The collector is made with plywood bottom, plank sides, 5cm rockwool for insulation, 100m of coiled pex tubing painted black and a double glazed window pane. 

The tank which currently holds 720L was made with a pallet with walls from stacked pallet frames with epdm tarp and 30cm rockwool insulation. Inside the tank I have coiled up some more pex (about 70m of 15mm) that preheats the water for my electric heater. I'm planning to add an extra 20m of copper for added efficiency.

The collector is placed on a south facing side of my house with 25m of pex run through the attic and down to the crawlspace to the large tank beside my electric hot water tank.

For controlling the pump I'm using a Arduino controller with ethernet. That way I have more possibilities when it comes to logging and displaying the performance of my system. The controller have 4 sensors at the moment: 2 at the input/output from the collector, one in the tank, and another in the collector.

The performance of my collector seems ok but I'll have to wait until spring before getting some real heat out of my system as the winter months in Norway doesn't get much sun.

Anyway the "crude, under development" website running on my arduino is located at fogdeveien.ddns.net

Mary B

  • Hero Member
  • *****
  • Posts: 784
Re: Domestic Hot Water solar heater
« Reply #1 on: November 09, 2014, 02:02:24 PM »
Nice! Solar preheat is on my list of things to work on. Have to finish getting more solar panels up first and the tops on my battery box. More time than money so slow going right now.

madlabs

  • Hero Member
  • *****
  • Posts: 680
  • Country: us
Re: Domestic Hot Water solar heater
« Reply #2 on: November 10, 2014, 04:41:24 PM »
I've made a few solar heaters, mostly for my hot tub projects. One thing I found helped is a air gap and a reflective insulation. I used a 1/2" gap and foil covered foam. My tests showed a small boost in performance.

And some pex doesn't like sunlight, not sure what type you are using. I used copper and found a larger boost in performance with a heat grease to improve contact, coupled with attaching the pipes as well as possible.

If at all possible, keep your eye out for solar glass. Regular glass has iron in it (makes it lok green from the side) which absorbs some energy. I also had good results with greenhouse plastic glazing.

Jo athan

MattM

  • Sr. Member
  • ****
  • Posts: 415
Re: Domestic Hot Water solar heater
« Reply #3 on: November 10, 2014, 06:22:10 PM »
The green tinted glass is good AFAIK.  It let's the light through then shifts the wavelengths so it gets trapped after the first pass.

Larsmartinxt

  • Newbie
  • *
  • Posts: 48
  • Country: no
Re: Domestic Hot Water solar heater
« Reply #4 on: November 11, 2014, 08:17:10 AM »
And some pex doesn't like sunlight, not sure what type you are using.
I did know about the pex and UV issue. The pex is painted black so no pex is in direct exposure to the sun + the window will remove some of the UV-rays.

solartec

  • Newbie
  • *
  • Posts: 2
  • Country: ro
Re: Domestic Hot Water solar heater
« Reply #5 on: November 13, 2014, 04:57:29 AM »
I think I did the cheapest solar water  heater in the world...A dark colour hose lead through transparent plastic bottles,the water get heated enough to have a warm shower...
No need for insulation between bottles,they are just put one into the other with the one bottleneck into a same dimension hole cut in the bottom  of the other...
This could be ``the ultimate survivor shower`` in the forest, like me using a cut beer can like ``de luxe``grill to fry fish...

madlabs

  • Hero Member
  • *****
  • Posts: 680
  • Country: us
Re: Domestic Hot Water solar heater
« Reply #6 on: November 13, 2014, 08:53:13 AM »
Looking at the picture, do you have any kind of metal absorber plate under the PEX? Cheap aluminum flashing will help a lot. I see you have a tight spiral of PEX, I wonder if a gap between coils and a metal absorber would provide better performance?

When I was building mine, I would set up a 5 gallon bucket and set a pump to run at 1gpm. Then it was easy to get a BTU output and test changes. I'll look and see if I can dig up any of my old results. I'd be very curious to see how the all PEX coil compares with the traditional plate absorber design.

Keep us posted!

Jonathan

Larsmartinxt

  • Newbie
  • *
  • Posts: 48
  • Country: no
Re: Domestic Hot Water solar heater
« Reply #7 on: March 11, 2015, 04:22:15 AM »
Small update. Tank temperature is rising for each day now as the sun gets brighter and brighter.
Also changed the data output to json so that i can have show the data on emoncms and make nice graphs. fogdeveien.ddns.net

Mary B

  • Hero Member
  • *****
  • Posts: 784
Re: Domestic Hot Water solar heater
« Reply #8 on: March 11, 2015, 08:02:27 PM »
 Looks like collector was above body temp about 4 hrs from your graph. My solar hot air has a similar curve.