water harvesting

Again, not much to do with food but to another of my favorite topics:
Something I discovered quite by serendipity (I’m surprised I didn’t think of it earlier but have figured out why) this summer was the potential to harvest pretty large quantities of water from air conditioning condensate. a) this summer has been quite a scorcher and b) VA is under a bit of a drought . Can one fact be used to help the other?

While rain water barrels and harvesting rain and gray water recycling have received a lot of attention, water harvesting from air conditioning systems is another possibility. The principle is fairly straightforward - When an a/c removes heat from a room, it do so by contacting warmer air with a compressed refrigerant. The latent heat of evaporation cools the air and thereby condenses the water vapor in the air. This water needs to be removed before the cooler air is returned to the building. What then, can we do with all that water? Presently, most systems either discharge this water as waste or send it to the sewer. The solution is simply, to collect the water. Needless to say, this is not a novel idea (although I’ve seen it rarely discussed) so I just wanted to add my thoughts on the subject. There are several websites dedicated to this concept:
Alliance for water efficiency, Building Green and a little ehow

The AWE (!) has some excellent information on this. In particular - A central AC for an entire home can collect 5 to 20 gallons (18.9 L to 75.7 L) of condensate water per day, equating to more than 300 gallons (1135.3 L) per month in the summer (my calculations for an average house in RVA put that number much higher >1 gallon/hr). I am not sure this will work well for a window unit btw. The climate in RVA with a general humid subtropical pattern is ideally suited for large condensate collection. My system (operating very sparingly at 30% efficiency), for example, has been right at the lower end of the spectrum @ ~5-10 gallons a day !
There are two important considerations here: Since HVAC water typically runs over and through copper coils, there may be some metal content so obviously NO drinking this water! Theoretically however, there shouldn’t be much metal and this water is essentially quite pure (it is actually distilled water). However, since we are generally careful about such things, it may not be a good idea to use the water to irrigate plants used for food consumption (herb gardens, fruits and vegetables etc), but this water is easily put to good use for general irrigation. Since this is right up my alley, I checked the copper content in RVA water. The level is low < 0.01 mg/l. (I checked the copper content in the HVAC water and it is considerably higher, almost by a factor of 100, but still below EPA level. So one must be careful). As a reference, the EPA safety level is 1.2 mg/l
The system I have right now is a batch system, so I manually transfer the collected water to its intended application. Next up - some fairly straightforward tinkering to connect it to a rainwater barrel or some other continuous flow device especially to develop a pressure head and voila!!
Second: For the pragmatist, the city of Richmond for example, charges approx $1.50 for a ccf of water. One ccf ~ 750 gallons. So yes, in all probability, saving this water is not going to save you a lot of money! Perhaps, this is an example of easy, practical sustainability with no “lifestyle sacrifice” involved, especially if you are one that cringes at water wastage. Plus the output in this case is directly proportional to the need - the hotter the day, the more the water !

Epilogue - An example of engineering at its classical and simplistic best – this recent mobile phone trigger for irrigation pumps.
How little things can make a big difference. It is one thing to “talk in bumper stickers” (EG from Ea Pr Lo acknowledged :)) and another thing to actually figure out and implement the mechanics, thermodynamics and design required to make a difference ! And for one who works with “expensive toys”, it is good to get my students to think more along some low cost paradigm nudging lines.