This answer says that the water from a ground source is always 50F. (I think this varies by location, but the concept is valid, anyway.) Why do we even need a heat pump? Why not just run that cold water through the walls? Does that require so much more water flow that the heat pump is a more economic route than a pump that would do the job?
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$\begingroup$ That answer says "The easiest thing you could do with the water is, just pump it through your walls as-is. It would keep your house at around that same temperature" and "In practice people prefer a slightly warmer temperature though, and more control, so they use a little electricity to power what's called a heat pump." $\endgroup$– mmesser314Commented Sep 13, 2022 at 2:53
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$\begingroup$ @mmesser314 Note that I said "cooling". Of course you need the heat pump for heating. $\endgroup$– Loren PechtelCommented Sep 13, 2022 at 2:58
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There is no reason why a source of cold water cannot be beneficially used to chill a house. If lots of water is available, why not? But the heat pump method allows for compact & simple heat exchange (air gets cooled inside the chiller and then blown to where it is needed) instead of having to move water around inside the house. The chiller can be made small because the working fluid in the heat pump system is far cooler than 50F.
Passive air cooling using cold water was practiced in ancient Persia, where long buried aqueducts with airspace above the water served as air/water heat exchangers and wind blowing over the living space was used to draw a suction on it and thereby pull the chilled (and humidified) air into the structure. Scientific American ran an article describing this system about 40 years ago.
answered Sep 13, 2022 at 5:17
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$\begingroup$ So you're saying that using the water directly is inefficient enough that the heat pump is worth it? $\endgroup$ Commented Sep 13, 2022 at 14:28
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$\begingroup$ No, I am saying that it is less convenient. I forgot to mention that a ground water-fed heat pump is a very efficient way of heating a structure during the winter- so if you install one of these to get AC during the hot months, you get winter heat as a bonus! $\endgroup$ Commented Sep 13, 2022 at 16:27