Advice please for SHW experiment

[Joe1250]

Hi all, newbie here looking for advice, thanks in advance!

I’m planning to try to create a DIY cheap solar hot water collector to use in a small greenhouse. I have 2 gas hot water tanks that I’m planning to use as my storage. I want to try to have them set horizontally rather than vertically and the plan is for it to be a very simplistic and cheap drain back system. I’m going to build a cheap collector for the roof and the hope is that the heat stored in the tanks will be enough to keep the spring night time temps in the greenhouse (or a small portion of it) above freezing if outside temps dip. I’m hoping just to be able to rely on convection or perhaps a small fan to draw air through the inner flu of the tanks and transfer the heat rather than an exchanger or pumping the hot water through lines?

First question is, am I totally wasting my time? Is this even feasible?

Second question is, do I need a dedicated drain back tank or can it just drain back into storage?

Third, is there anything I need to know with respect to pipe sizing for supply, collector and return lines?

Fourth, what if anything do I need to manage the air/vacuum in the system? I’m imaging something like a check valve that is closed when the system is running and opens when the system is off to allow air back in so the lines can drain?

Obviously I’m still new to this so ANY advice would be appreciated!

Many thanks,
Joe

 

[Acuario]

I have something similar. I use 2 x 100 Litre ex electric water tanks plus a 50 litre top feed tank mounted upside down so it's open as a drain back tank. I have a hot water panel on the roof of a shed and all the tanks/pump etc. in the shed next to the greenhouse. The 100 litre tanks are in series so effectively 200L storage.

I have 2 heating systems, one is underfloor heating, the other is a home made fancoil (from an old air conditioning system).

I use a 3-way valve to control if the water is circulated through the panel (when the panel is hot) or through the floor/fancoil (when temperature is low).

You will need as a minimum a circulating pump and some sort of controller (mine is home built as it controls lots of features of the greenhouse).

As for pipe sizes, 15mm is fine - as is 12mm for the collector.

 

[Joe1250]

Thanks so much for the response!!! Did you make your controller with arduino? I was thinking of trying to do that for mine. Also what are you using for a pump and how many feet of head do you have?

Thanks,
Joe

 

[Joe1250]

Thanks so much for the response!!! Did you make your controller with arduino? I was thinking of trying to do that for mine. Also what are you using for a pump and how many feet of head do you have?

Thanks,
Joe

Oh, and I guess the more important question is how well does it work? Worth the time and expense to set up?

Thanks again!

 

[Acuario]

I use a central heating circulation pump which is more than adequate.

My 'controller' does a lot more than just the solar hot water, it is a complete control system for the greenhouse. It controls watering, grow lights, cooling fans as well as the hot water solar system and links to a heat-pump for heating when there is no sun for the hot water. The whole system is also run off of a 2.4kW 24V solar system.

It's all built with an ESP8266 (using the Arduino platform) and has a web interface to control everything..

Worth doing, well it was a challenge that is ongoing and I hope it will be worth it - and yes it does work.

You can see photos and so on on the EcoRenovator site.

 

[Joe1250]

Wow!!! That’s amazing and very similar to what I was hoping to accomplish… eventually ?. I’m curious if you have any idea how much temp differential you can maintain? Ie. if the temp drops to 0 degrees C overnight, what temperature are you able to maintain in the greenhouse with just the hot water radiant heat? Also, how big is your greenhouse and how hot does your water get (tank temp) after a spring day of solar?

I live I Canada so not expecting miracles, but was hoping to get an earlier start to the season if I can keep a portion of the greenhouse “warm” on those early spring nights when the over night temps drop to around the freezing point. I have 2 40 gallon HW tanks and was thinking of a DIY solar collector, so not as efficient as evacuated tubes, so not sure what I can reasonably expect for average water temp to draw from over night.

Thanks again for sharing, very impressive!!!

 

[Acuario]

I manage to keep the temperature above 10 degrees minimum. The temperature here is typically around 5C overnight in winter. We do occasionally drop to 2C but it's rare. The water in the tanks can easily reach 50C, sometimes more, on a sunny day. My greenhouse is roughly 4.5 x 2.5 metres.

 

[Aussie]

Check out " thermal syphon systems" . No Power required but heat panels need to be lower then the reciever.
I live in Australia and use this system for hot water at my "shed". Not sure if it will work for what you want.

 

[Joe1250]

Check out " thermal syphon systems" . No Power required but heat panels need to be lower then the reciever.
I live in Australia and use this system for hot water at my "shed". Not sure if it will work for what you want.

Thanks, I’ll look into it!

 

[Joe1250]

I manage to keep the temperature above 10 degrees minimum. The temperature here is typically around 5C overnight in winter. We do occasionally drop to 2C but it's rare. The water in the tanks can easily reach 50C, sometimes more, on a sunny day. My greenhouse is roughly 4.5 x 2.5 metres.

Wow, that’s pretty good! I’m optimistic now! ? would you be willing to share a schematic of your controller and code? Would sure save me a lot of time if I had a template to start working from!

Thanks,
Joe

 

[orangezero]

I've seen people use barrels as well, but if you wanted to increase your water storage for low cost, "IBC totes" can often be purchased for inexpensive and are 250-300gallons. Some of the really cheap ones may have chemicals in it you don't want to deal with. I've seen some online that were $20 and used to ship vegetable oil in bulk on one trip, then sold. Get black plastic ones in a space that gets solar during the day and you've got a little bit of thermal gain right there. Running through pipes on the roof

It will obviously take longer to see a temperature rise as the water goes up in volume, but the physics is the same. Think of the water as a cheap battery that can store energy (heat in this case). X amount of energy to raise one gallon one degree, etc. More water volume just increases the buffer you have.