lets do some math, shall we
lets make a few assumptions just for the purpose of illustration and discussion.
for our example lets use the following parameters
ambient temperature 100 degree F
water source temperature 50 degree F
so we have 50 degree's of differential to work with...
lets assume a perfect heat exchanger, that can remove all the available btu's, or in other words make perfect use of the 50 degree differential.
now lets use water weight as 8lbs per gallon
lets assume we have a source of water that free flows 5 gallon per minute, or 300 gallon per hour
the definition of a btu is the amount of heat it takes to raise one pound of water one degree F.
so if we have 300 gallons of water, and it weighs 8lb/gallon, they we have 2400 lbs of water.
using the btu formula, therefore 2400lbs of water (per hour) * 50 degree's differential = 120kbtu's or about 5 tons of cooling, however
we can't get a perfect exchanger, and we aren't likely to want to get down to the base temp of the supply water for space cooling, so lets assume we want to get down to 70 degree F. we would then have a need for about 2400lbs * 30 degree's = 72kbtu's
my bet is the exchanger is likely not going to exceed 50%, so we might end up with 36kbtu's or 3 tons of cooling capability.
so i suppose it is possible to get some good cooling if you have sufficient supply of cold water, enough of a heat exchanger to get as much of the coolth possible from that water (in reality really the ability to dump that amount of heat from the house to the water source), and have everything else worked out.
then there is the deal with humidity and its effect on the systems ability to cool, what to do with condensation water if in a humid area, and a few other issues.
to start with one needs a reasonable size free flowing spring to tap the cold water from, and be able to reintroduce the waste water back to the stream. this is something they frown on with wells, for obvious reasons.
if someone would be so kind as to recheck my math, and make corrections if necessary would be appreciated.
thanks
bob g