1 megawatt * 1 hour = 3,600,000,000 joules
Water takes 2,257,000 joules / kg to evaporate
Which works out to ~1,600 kg or 422 gallons of water per hour per MW.
However, I don't think they actually want to evaporate all that much water which leaves a lot of residue issues and instead focus on heating a much larger volume of water.
PS: The article is also wrong in that they don't directly cool hot air from their servers with this water. They are cooling air heated by there cooling system and depending on how hot the air from there servers are they may simply vent that if it's warmer than the outside air.
> Basically a 100' square catch basin on the roof of the building would provide all the water they need. Noise.
Which raises the question: Why don't they just do that? I'd imagine it would be less effort to process, and even though you do need to have a buffer against low rainfall periods, water is one of the easiest things to store.
O, I agree it's Noise. However, the reason they don't use a catch basin / just pay for it is Atlanta's high average humidity. There are going to be days where little water is going to evaporate in those cooling towers and most of their energy is going to simply raise the temperature of a large volume of water. So, having access to say 100 times the flow they need is vary helpful.
However, I don't think they actually want to evaporate all that much water which leaves a lot of residue issues and instead focus on heating a much larger volume of water.
PS: The article is also wrong in that they don't directly cool hot air from their servers with this water. They are cooling air heated by there cooling system and depending on how hot the air from there servers are they may simply vent that if it's warmer than the outside air.