Best Greenhouse base?

This has all got me thinking about a heat source My greenhouse is going to be sited quite near my house, not the ideal spot for all day sun but the best I can do due to limited space. Now I'm always complaining that my Mrs has the house heated far too high! So my cunning plan is to run a pipe from the warmest spot in the house, through the cannibalised PC fan and into the heat sink!!! Trust me, with or without insulation, I'll turn my B&Q aluminium cold greenhouse into the local Botanical gardens!!!! All I need to do is work out is how to get it installed without my wife noticing? Might be tricky.

 

There are only a few shcs systems in the uk that i know of that use the original method developed by John Cruickshank, who sadly passed away in Jan, 2011.
http://www.sopermaculture.org/SOPI/..._Permaculture_Teacher,_Mentor_and_Friend.html

Andy up in Perthshire installed his in a typical 12ft x 8ft polycarb greenhouse. He used the standard tubing layout but had 12v solar panels powering the fans. I know he ran a data logger on the system for a while as he sent me copies of the graphs. Here`s the article he wrote about his experiences and inital results.
http://www.permaculture.co.uk/articles/how-build-solar-greenhouse

Mine has a non standard tubing layout and the fan is mains powered but apart from that its the same basic principle.

 

So why aren't there simple ground-source heap pumps for greenhouses? The heat "lift" would be very modest, the ground source could be in the greenhouse, maximising the solar gain during the day, and the energy required to heat the greenhouse would be highly acceptable - probably going to get a COP off the heat pump of at least 4??

 

I use about 19w of electrical power to put 1000w of energy into the soilmass. The system thrives on high air temps and high RH as the bulk of the heat comes from phase change as the air drops to dewpoint underground.

 

Excellent! Sounds perfect, efficiency-wise. (is 19w to store 1kW a COP of 50? - or is my understanding of the maths wrong? If that's right its a figure I like the look of! Maybe its a COP 0f 25 if you need to spend another 19w to get the 1kW back out again though ...)

 

Thats the electrical fan energy required to heat the soil mass by an equivalent 1000w or 3,413 btu in old money. To raise or lower my soilmass temperature by 1 degree F i have to add or remove 5.3KW of energy, which translates to 100w of electrical power to run the fan.

The plants drive everything with the help of the sun, it doesnt work without plants.
It takes 1 btu to heat a pound of water by 1 degree F, but it takes 970btu to vapourise a pound of water. The plants get the btu`s from the sun and the liquid water via the roots from the soilmass.
The plants transpire the water vapour into the greenhouse (the water has changed phase into a gas) and the fan drives it underground where it reaches dewpoint.. To become liquid water it has to give up the btu`s it gained when it changed phase into a gas. So for every pound of water condensed underground the soilmass gains 970 btu`s of latent heat. The rootzone gets most of the original water back as warm underground rain. The air exiting the tubing is much cooler and drier than it went in, which allows it to absorb a lot more heat and vapour.

Without the shcs or some other method of removing the btu`s and vapour from the air, you`d have no choice but to replace it by venting. The latent heat energy your plants kindly donated in the process of growing would be lost along with the water as that wouldnt make it back to the soilmass.
..and thats pretty much how the shcs works

 

Okay, hope you all got that!
We'll be sending out questionnaires for you to hand around.
( Now, where did I put the Ibuprofen ?)

 

So the SHCS is performing the same "effect" as a heat pump, but without needing the energy for the compression phase? I think its a neat trick

 

Pretty much. The plants perform the expensive compression phase for free (liquid to gas ), which takes a lot of energy but again its provided for free by the sun. The fan just moves the vapour to the "condenser", which is the soilmass/heatsink.
The system just takes advantage of what plants do naturally, which is to transpire water vapour in the process of growing.

David, apologies for the headache mate, i did try to explain it in laymans terms honest.