For using a heat pump, instead of using geothermal, has anyone tried using their cold water source and hot water source (through a thermostat) to use in the heat exchanger? It seems to make sense to me, provided a water reclamation system was also installed. The temperature of the solar heated water would be 120-150 degrees F, providing more heat to the pipes in the heat exchanger than a normal geothermal system. Likewise, the normal cold water for the house is about 50 degrees F and I would think would cool the pipes in the heat exchanger a bit better. It seems like that using these sources would require less volume of water to be used, possibly to the point of using a smaller heat exchanger.

Of course, I think the feasibility would all depend on the output temperature of the water reclamation process. Currently looking at http://www.biomicrobics.com/Products/BioBarrier/about_BioBarrier.html but they have very little information.

And finally, this is theoretical at this point, but maybe put into use in the future.

found out that the idea above is a bust. I had misinterpreted the BioBarrier website and thought that it was cleaning the water good enough to reuse in the home. I now know differently. So the above question is really moot at this juncture. However, I wouldn't mind hearing some of your thoughts, though this is now strictly a theoretical discussion.

Are you saying something along the lines of using a heat pump to extract waste heat from warm gray-water? Could be done and might pay for itself in some situations (like living next door to a commercial building that uses lots of hot water and doesn't reclaim all the heat themselves).

Not quite. What I was thinking was that in the summer, you would send the cold water coming into the house into the heat exchanger of the heat pump. In the winter, you would send the hot water from a solar water heater into the heat exchanger of the heat pump. The cold water from either a well or municipal pipe would "replace" the geothermal system in the summer, while the hot water from the solar water heater on the roof would "replace" the hot water from the geothermal system in the winter.  In either summer or winter, when the heat exchanger was done with this water, it would be sent as gray water to this tank to be "cleaned" and then resent into the house as potable water. This would be the only way to make it economically feasible, otherwise you would be paying for and wasting tons of water. I had goofed in my understanding of the biobarrier product. This doesn't "clean" the water suitable enough to make it potable again.

Domestic water flow is way too low and intermittent to offer a good heat sink for summer air conditioning.

If a way could be found to economically bank solar heat, it could theoretically be transferred back into the home using a heat pump. Unfortunately the size of the storage tank needed is quite large, and therefore not cheap. Compounding matters is the inescapable fact that heating loads peak precisely when solar capability bottoms out.

Grey water on its way out of a house is a pretty good place to recover heat for domestic hot water, and there are contraptions out there that do that.

Be very very very careful with any connection between grey water, no matter how treated and potable water.

I thought I'd ask a question along these lines.  Are you talking about using a water to air heat exchanger and you put the exchanger into the air duct?  I don't quite understand though is why when using the water in the heat exchanger it needs to be considered grey water after it's energy has been depleted?  Isn't the system closed?

Perhaps I should restate the issue, as even when I re-read my own writing I can get a little confused.

The purpose of this idea was to come up with an idea similar to using a geothermal system to both heat and cool your home, without the need to spend a lot of up front expense. As a little background, I've found myself wondering how efficient it is for people to use radiant floor heating in the winter to keep from having to blow the air around the house in the ductwork, only to have to install a different cooling system altogether that does require a blower motor and ductwork (or cutting more holes into the outside walls for split duct systems). I also question the cost effectiveness of paying for and installing 2 separate systems (one heating and one cooling) when one system can do both jobs.

Think of a typical geothermal heating/cooling set up connected to an electric heat pump. The water from a geothermal system stays at a relatively constant temperature year round. So in the summer, it is colder than that ambient air temperature and therefore is able to cool it down. In the winter, while the geothermal water system is at the same temperature, the ambient air temperature is now colder than the water, therefore the water warms up the air that is then transported through the house. It is a simplification, but these general terms help understand the next step. I had proposed, in the summer, instead of using water in a geothermal system, to use water from your cold water tap. It is much colder than water in the geothermal system, allowing for a greater temperature difference between your cooling source (the cold water tap) and the air to be cooled and sent throughout the house in the duct system. The greater the temperature between those two, the better heat transfer you get and the higher the efficiencies, right? Same would hold true in the winter, except now we are trying to heat the air in the house through the normal heat exchange process. The thought here would to use normal hot water. In this case, heated by a solar hot water heater, which would heat the water hotter than the geothermal system would. Again, bigger temperature difference between the air being heated and the source doing the heating, better heat transfer, greater efficiency. For the cooling cycle to work properly, the water supply would have to be an open loop, where you would use fresh new water in each cooling cycle. To maximize other efficiencies by using your solar hot water heater to supply hot water to showers and sinks as well as to the heat pump, this would also have to be an open loop, though, you could have a stand alone hot water heater specifically for use by the heat pump.

The thing making this cost prohibitive is the amount of water used from your water source. If you have a metered water line, you would pay handsomely for all the gallons of water you would need everyday to do this. If you are on a private well, it could go dry very easily, especially during drought years. That's where the idea of the BioBarrier came in. I had originally thought that this product "cleaned" the water that exited your house. That is, when the heat pump was done with the water transfer, the water would then go down the drain into the BioBarrier as grey water, and be cleaned up good enough to be used as potable water once again. This would reclaim many gallons of the water used during the heating and cooling cycles of the heat pump for use as a secondary, un-metered water source. However, I was wrong with that idea and the BioBarrier basically only "cleans" gray water so it can be surfaced pumped (should that be necessary) without spewing harmful waste everywhere.

I hope this explanation is a little easier to read and understand. Perhaps eventually there will be a "home" water treatment tank that will allow us to reuse our own waste water and therefore have to rely very little on new water supplies. This could be a good idea for those in California, Nevada, Arizona, where fresh water is scarce.