This exists already and is called a liquid to water heat pump, where a liquid is circulated in long pipes either buried under your lawn (if it's big enough) or

This exists already and is called a liquid to water heat pump, where a liquid is circulated in long pipes either buried under your lawn (if it's big enough) or inserted in holes drilled several hundred feet deep, and then passed through a heat pump to provide hot water that's then distributed through your house. You just need to go ~20 ft down for the thermal mass of the soil to significantly damp out even annual oscillations, so there the soil temperature equals the mean temperature where you live. The main barrier to adaptation is that most people don't have a big enough lawn for the shallow method, and the cost of the deep method is big enough that it takes too long to break-even for most people. What we really need for any such method to succeed is that governments must make it mandatory for new houses, then we can get economies of scale and probably make it viable also for retrofits.