Energy Production     From the attached chart, (and starting from a 1000 sq ft greenhouse 10 feet high and the SHCS running at 5 times per hour...)   - if your intake is 90 deg F and 90% RH, the air is going in with 2.0 lbs of water per 1000 cu.ft. At 5xhr and 1000x10 cu.ft, that is 20 lbs x 5 = 100 lbs of water an hour enters the heat sink.   - if your exhaust is 65 deg F and 80% RH when it comes out, there is 0.7 lbs of water per 1000 cu.ft coming out.  At 5xhr and same volume, that is 7 lbs x 5 = 35 lbs of water per hour leaving the heat sink.    - therefore you are making vapor and condensing it back at a rate of 105-35=70 lbs an hour... in other words, boiling water at a rate of 70 lbs and hour (close to 10 gallons an hour)   - That is a lot of energy being drawn underground for a 50x20 greenhouse!!