Jesse, the cooling effect is by transfer of sensible heat from the air to the cold water and further by evaporation of the water into the air. Of course if the air is cooled enough it may be 100% saturated anyway and hence the air will be cooled close to the water temperature entering the vertical heat exchanger.
The lower tank will have 'warm' water entering, mixing with a much larger volume of cold water and hence the water exiting will be cooler than the feed water. At night the conditions are reversed.
I think the trick will be to balance the water and air flows to get it working in the right way and hence both pumps need to be variable flow.
Hot air actually contains very little energy compared to water / deg C.
So hopefully instead of having say a 20 C swing in temperature over a 24 hour period, it can be controlled to a 10 C swing in temperature (at very low cost).
---------- Post added at 10:03 AM ---------- Previous post was at 09:48 AM ----------
Plan is to just adjust both the water and air rates manually and see what happens over 24 hours, a few dataloggers will come in handy... Probably will adjust air rate to change the rate the heat is released back into the greenhouse at night but until i try and see what happens its hard to say exactly.
Originally Posted by Steve Booth
Agreed, Water/air distribution in the exchanger could be tricky and have a huge impact on how well it works...
Without making a fine spray which would be best, the air will need to pass over wetted medium for maximum cooling effect, the more medium the better obviously, but this may impose too great a resistance on your fan, depending obviously on what it is and how much of it there is.
Taking an arbitrary greenhouse size of say 3m x 2.4m x say 2.3 high and say 10 air changes per hour that gives an airflow of 0.04 m3/s (100mm duct will do), or mass flow of about 0.056 kg/s. Original air temp (within greenhouse, full recirculation on the air side?) say 30C and 38-40% saturation, then passing this through your kit (assuming 100% efficiency) would give an off plant (pardon the pun) condition of 20C saturated absorbing 0.766kg/hr of water. Excess water pumped will obviously return to the reservoir.
Thanks Steve, thats an interesting drop in air temp, I can allmost envisage chucking out the autovents and living with 30-35C daytime maximum and high(er) humidity than what i get now. Even if the evaporative cooling effect is reduced, should still be able to absorb much of the air temp into the water resevoirs.
started building a spreadsheet model of the heat balance over an 'any time of year' 24 hour period ( with lots of simplifying assumptions) But had so far neglected the evaporative cooling effect, have to fix that one when I get time...