Solar powered hot water system for use as thermal mass storage


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This is my plan. I would appreciate any feedback from anyone who has experience using heated water for thermal mass or has experience with solar hot water systems...or anyone that just has an opinion.


I am building a solar powered hot water system for use as thermal mass storage for night time heating in cold weather. My plan is to circulate water from the solar collector through 4 – 55 gallon steel drums, gradually increasing the water temperature throughout the day so it can be released back into the greenhouse during the night.

I am building the solar collector using ½" OD x .062 Wall Black LLDPE Tubing and 9 - 4" x 48" Solar Hot Water Heater Absorber Fins with 5/8" channel. The collector will measure 12' long x 1' high with a collection area of 12 square feet using 36 linear feet of tubing. The collector will be housed in an insulated box with the interior painted flat black and it will have a plexiglass cover. This collector will be situated inside my greenhouse approximately 7 feet off the ground and mounted in a horizontal position. The total run in tubing will be approximately 56 linear feet when I take into account the collector, up feed to collector, down feed to drums and piping between drums.

I plan to place the solar panel outside the greenhouse and the pump inside. I am doing the whole project this way to protect the system from freezing on cold winter nights, figuring the 210 gallons of thermal mass and an electric backup heater will keep the pump and tubing from freezing. I know I could use a closed glycol system and heat exchanger, thus allowing me to place the collector and pump outside, but I think this system will work.

Feedback?
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This is what I did about 4 years ago. I was just playing around and built solar heat collector that was 20" x 40"
GH vs Elements 001.JPG

This is the start. I added heavy clear plastic (the kind used on boat top windows). I ran it using only thermosyphoning and the water was circulated from this through about 6' of pipe to a trough holding 13 gallons of water then exhausting back to the collector. It only raised the water about 5f. However, one day I hooked up a pump to the exhaust which blasted the contents out the other end and almost scalded my hand. Got out my thermometer and the heated water was 155f ! I decided that I really didn't want to add a pump, timer for the pump etc so abandoned this idea. Unfortunately not before the heat bent every one of the pipes! I did add a spigot at the exhaust to block it so I could stop thermosyphoning reversing the gain over night. My big fear, also being in a 6a zone, is the chance of freezing damaging the system overnight/cold winter days with no sun.
This was one of my initial tests for thermoshyponing - I used food dye and timed it between the intake and exhaust. Took about 45 minutes. So yes a pump would speed things up but definitely figure out the optimal circulation cycle.
Solar Water Heating 006.JPG


I also made a little solar food dehydrator
Enclosed a little bamboo cart, added screening shelves and a small solar panel and server fans.
Dryer (3).JPG

And this is my sunoven
april 2015 (4).jpg
 
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@MoonShadows I would consider the larger scale of your efforts to be necessarily integrated with the house if realistic. Ground effect hvac heat pumps with buried lines instead of noisey air exchange radiators are coming to mind. Surely the two would be greater combined?
 
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@CanadianLori Nice projects. I thought of using a themosiphon system at first, but I'm not sure that would achieve the heat I need and thus the solar pump. I think you are correct about optimal circulation rate. I have no idea how to calculate all this, so I wrote a lengthy email to Heliatos Solar (http://www.heliatos.com/) asking them for advice on solar panel and pump size based on what I described above. I have found this company very willing to help in the past.

@DirtMechanic Why do you recommend larger scale? Problem with heat pumps is that this area of my property sits on a shale shelf, so the excavation needed to get down deep enough would be extremely labor intensive and probably cost prohibitive.
 
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Maybe have the pump triggered by temp? I don't know if anything exists that would do that though. You can't see in my second picture but I did paint everything black as well as put beverage cans between the pipes after having drilled a hole in their bottoms. Painted those too.

How big an area are you trying to moderate?
 
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@MoonShadows thats too bad because from what I understand those systems are most commonly laid out like septic lines. I would imagine vertical drilling is out as well.

Have you considered increasing the density of the thermal tanks with material denser than water? Some form of rock or metal perhaps, where the fluid would conduct to the denser material?
 
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Before I posted, I wrote an email to Heliatos Solar (http://www.heliatos.com/) in Eversen, WA asking for advice, since this is the company I plan to buy the pump and solar panel from; they had helped me earlier with another question a few months back. I heard back today. Looks like from their response, my plan is viable (y)

Hello,

While I have not built a system like this for a greenhouse it sounds entirely feasible. Putting the panel in the greenhouse will diminish the overall performance somewhat because you will be capturing heat that is already entering the greenhouse, but you will be moving that heat into the thermal mass instead of it simply ending up in the air and on the surface. Anyway we have two pumps, of which you would realistically only need the much less expensive one. So I recommend using the HS-17 pump ( http://shop.heliatos.com/Heliatos-HS-17-Solar-DC-Circulation-Pump-0130021.htm ) which is also waterproof. This would be handy in a greenhouse environment. For the larger tubing and because you have 220 gallons of water I would recommend using a 25W PV panel ( http://shop.heliatos.com/25W-Photovoltaic-Solar-Panel-with-Wire-and-Mounting-Kit-0720019.htm ) with the pump.

Thank You,

Aki Abtahi, Ph.D.
Heliatos Solar
www.heliatos.com
Phone: (661) 7SOLAR7
 
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Have you considered increasing the density of the thermal tanks with material denser than water? Some form of rock or metal perhaps, where the fluid would conduct to the denser material?
Actually, from what I have been reading, water is preferred.

The chart below illustrates why water is a preferred storage medium for retaining the heat in greenhouses. This is especially common in solar greenhouses. The higher the number, the better the material will store heat. Heat storage is also a function of how much of the material you have in the greenhouse.

MATERIAL VALUE (BTU/Sq Ft./degree F)
Brick 24
Concrete 35
Earth 20
Sand 22
Steel 59
Stone 35
Water 63
Wood 10.6
 
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That is a very large area and now I see why you're going for mucho gallons of water. I had thought about using barrels, well, actually I tried with Home Depot 5 gallon pails. Originally I had painted them black, filled with water and counted on the daytime sun to heat things up. It did alter the temps at night slightly. Then I started playing with solar water heating. This is a picture from early days. My greenhouse is only 6 x 8 . The plants at the end are sitting on a trough of water which is hooked up the to solar water heater. I had used greenhouse bubble insulation (it is flat on both sides) but found that it looks sloppy and really didn't make much of a difference.
Tomatoes here and there.JPG
 
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@CanadianLori I tried 5 gallon pails first too, painted the outside a flat black, but the passive gain was minimal. I would need 44 of them to do what these 4 - 55 gallon drums will do. I plan to make a two tier bench on top of the drums to use for plants. I decided against bubble wrap; I couldn't figure out a way to attach it without having a pain removing it in the Spring. Somewhere on this forum (my greenhouse showcase), I have images of how I insulated the North and East walls with reflectix insulation which will be permanent. That has made a significant difference. In fact, from the picture below, on the outside of the greenhouse where the ceiling starts to lean up from the wall, the snow is no longer melting on the outside...a good sign. I may extend that insulation all the way up the ceiling on the north side. I also dropped the ceiling 2 feet with greenhouse film to keep all the warm air from going up into the top. In addition to the solar water heater, I plan to dig as deep as I can around the foundation and put in 4" of pink insulation board vertically to block as much of the cold ground from seeping into the ground in the greenhouse, and building a 3 foot insulated knee wall around the greenhouse. A lot of work ahead of me!

Are you pleased with your solar heating methods that you've developed?

45-Dec_01.jpg
 
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I wasn't prepared to add the amount of mass needed to moderate my area and the water heater was just playing about after I realised the amount of water I would need to heat. I have a small backyard and not enough room erect anything large scale. I may make another small one just for use with the Drumi http://www.yirego.com/drumi I have been waiting for. Then I would have lots of warm water on hand for washing outside.

As you can see, my greenhouse is a polycarbonate so I threw out the bubble wrap and replaced it with window film. You know the stuff people use inside their house windows and tighten up with a hair dryer? And it made a huge difference as far as stopping heat loss.

I did add solar powered fans to circulate the air year round and that takes care of any issue with heat rising and staying at the ceiling.

For me, I still see no point in trying to heat outside when it is far less expensive to use LED lighting inside until the temperatures oblige. I have a natural gas heater out there and it cost me just under $200 to run for one month a few winters ago. Not going there again! I do use the heater to get an early start on spring - probably March 29th will be opening day. At that point I only need to bring the temperature up about 10f at night and only 1 to 5f during the day.
 
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Was looking at the pumps. I didn't know pumps with that low a gph were available. Wish I'd known that when I was fooling around. ...o_O

One thing you will need to consider is that there is a lot fewer sunny bright days in the winter. My panels are barely keeping my batteries powered on days like today.

When you get building it, please keep us updated and perhaps add progress photos? I'd love to take this journey with you!
 
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I wasn't prepared to add the amount of mass needed to moderate my area and the water heater was just playing about after I realised the amount of water I would need to heat. I have a small backyard and not enough room erect anything large scale. I may make another small one just for use with the Drumi http://www.yirego.com/drumi I have been waiting for. Then I would have lots of warm water on hand for washing outside.

As you can see, my greenhouse is a polycarbonate so I threw out the bubble wrap and replaced it with window film. You know the stuff people use inside their house windows and tighten up with a hair dryer? And it made a huge difference as far as stopping heat loss.

I did add solar powered fans to circulate the air year round and that takes care of any issue with heat rising and staying at the ceiling.

For me, I still see no point in trying to heat outside when it is far less expensive to use LED lighting inside until the temperatures oblige. I have a natural gas heater out there and it cost me just under $200 to run for one month a few winters ago. Not going there again! I do use the heater to get an early start on spring - probably March 29th will be opening day. At that point I only need to bring the temperature up about 10f at night and only 1 to 5f during the day.
That drumi is a neat little washer.

Yup...I can see that shrinkable film would help. Anytime you can lock in a layer of air, it increases the insulation factor. I never though of using it. Great idea!

I understand what you mean by why heat the greenhouse when I can grow inside with a grow light during the off-season. For me, it's the challenge! Also, while we do have an indoor kitchen garden, it doesn't even supply the volume of salad greens we eat during the winter. I guess I could set up a bigger one in the basement, but once again, it is the challenge. And, projects like these keep me out of trouble! :rolleyes:
 
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Was looking at the pumps. I didn't know pumps with that low a gph were available. Wish I'd known that when I was fooling around. ...o_O

One thing you will need to consider is that there is a lot fewer sunny bright days in the winter. My panels are barely keeping my batteries powered on days like today.

When you get building it, please keep us updated and perhaps add progress photos? I'd love to take this journey with you!
That's gallons per minute, not hour, and the one I am getting probably has too fast a gpm, but with approximately 56 feet of tubing (collector, uplift, down feed, tank connections), the gph will be much less. BTW...I ordered the pump and panel yesterday. I should have them in a week.

Yeah, I know. The sun is less available just when I need it! :ROFLMAO:

But if I want to try and grow year round, I'll take what I can get. A lot of people would just throw a huge heater into their greenhouse and call it a day. I don't want the expense or foot print of an electric or fossil fuel heater. In planning a winter greenhouse, I quickly learned there is no one source for heat gain/retention. My initial expenses are higher, but they should pay for themselves eventually....when I am 101 years old! :whistle:

You can be assured of updates and pics; I always document my projects.
 
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GH Almost spring 2015 (6).JPG
just had a giggle. came across a pic of the first experiment..wayyyy back. Still had bubble wrap. The blue thing under the middle pots is a water bladder. Heated up during the day, release at night. I used to use boot trays from the dollar store but have long since replaced with 1020 trays.
 

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