I am thinking about cooling a green house using 4" pipe buried 2' below slab. Using a slow fan to circulate air in one end of the pipe and out the other end.  To keep condensation from collecting in the pipe I would use perforated pipe in a sock to allow water to drain out. The soil is very sandy and the I don't think I would get ground water in to the pipe. Am I nuts or should this work? any thoughts from you gurus would be helpful.

John Guinness

Alas, I think I have to vote for "nuts".

I doubt condensate would be a problem in the pipe because ground at 2' depth proximate to pipe would rarely be below dewpoint, especially after greenhouse air is pushed through it for awhile. Dry sandy soil is among, if not THE, worst for conducting heat. In other words, I don't believe such a pipe offers sufficient potential for cooling such that condensate accumulation would pose a problem.

Please post desired greenhouse temperature and humidity for us gurus to have a go at describing an economical approach. I'm guessing that desired greenhouse conditions deviate substantially from what is needed in a typical dwelling, to wit 75 F drybulb and 50% RH.

Florida summers are 95 F 95% RH I didn't think I was going to lower that by much with out a much more complex system. This whole idea was some one elses thinking. Would burying deeper or using more footage of a smaller diameter pipe make me less 'nuts'. Personally I think a roof vent will be more effective and less problematic. I was thinking that perhaps coils of poly pipe with water going to a radiator coil with a solar pump and a solar fan behind the radiator would be more effective then just passing air through the pipe but still less effective then a roof vent.

John Guinness

It is a misconception that FL summers are 95 F and 95% RH. Both conditions do exist on a regular basis but not at the same time. When it is 95 F the RH is generally no more than 60%, but that is still uncomfortably muggy. From midnight through sunrise we have temps in the 70s and RH near 100. The true figure of interest for comfort is dewpoint, and it remains in the mid 70s, 24/7, day and night for the 4+ summer months.

Using an array of pipe underground might result in some sensible cooling during the day but I'm willing to bet it would be overwhelmed by an order of magnitude by the solar heat gain of a greenhouse. Undisturbed Florida ground temps are 70+, and that would rise into the 80s if the ground had warm pipes in it.

Attic fans (driven by PV if you like) simply ventilating the space may be your best bet. The extra humidity associated with greenhouses may well result in dewpoints in the low 80s, and ambient air can help with that.

I'm in with the exhaust fan idea........unless you have a pool or fountain you want to heat near by.....
Joe