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Old 02-02-21, 09:22 AM   #14
Apprentice EcoRenovator
Join Date: May 2011
Location: Tortosa, Spain
Posts: 218
Thanks: 2
Thanked 77 Times in 44 Posts

I've finally finished (well, probably as finished as any homebrew project ever gets save the inevitable modifications!) the heating system for the greenhouse.

Typically January/February are the coldest months in the area of Spain where I live but typically this year - not. It's currently 22C and sunny outside and overnight it didn't drop below 16C. But at least now I'm prepared!

I've attached photos of everything and a schematic that shows how it all fits together - the only thing missing is the heatpump which is connected into the tank T1 (yes, it is installed and working). The design for the heat exchanger coil is here. The heatpump controller is one of my IOT controllers.

Originally I planned to make my solar hot water panel using 2 steel panel radiators but then an offer I couldn't miss appeared - brand new unused solar hot water panels for 50 euros! Only I had to collect them and buy 10 on a pallet - but it was an offer too good to pass up. I've used 1 on the greenhouse, I'm going to add 4 or maybe 5 to the house heating and the rest..

Anyway, as well as the water panel I also bought 2 x 410W solar panels and a cheap 3Kw hybrid inverter. As I just swapped out my gel batteries for LiPo4 I moved the old batteries into the garden shed to run the greenhouse.

The system is a drain back system that uses a 3-way valve to change over from feeding water to the solar panel (when it's hot) or the greenhouse (when it's cold). As a backup there is a heatpump to provide heating (maybe I'll try cooling in the summer!) Heat storage is 2 x 100 liter (ex) water heaters and the drainback reservoir is provided by an (ex) 50 liter water heater (which happened to be a top feed so fixed upside down with the element removed is just perfect.

One problem I discovered is that I seemed to be sucking air from the solar panel so I had to add an air purge system in the return pipe (you can see it on the right of the photo).

In the actual greenhouse there is underfloor heating plus a fan-coil made from an old internal split unit with pretty much everything stripped out, I knew this would come in useful one day - see here how I made it

The control of everything is done using an esp8266 and various I/O modules (for light/humidity/temperature).
The controller handles the solar heating/greenhouse heating, the greenhouse cooling fan, the grow-lights and (soon) will also handle the watering.

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