Who knows about geothermal heat?

[BridgeRunner]

For you engineering types (and assorted other freaks with esoteric knowledge),

Does a geothermal system have to have a heat pump? 

This is my thought:  The heating/cooling comes from the water, right?  So why have a whole system of drawing the heat from/to the water in an exchanger unit and then running it through ducts?  Why not just run water-filled pipes through the house?

Obviously, this is only practical in new construction designed around such a system.  Piping would have to be planned carefully to facilitate thermally-driven (or primarily thermally-driven) (I'm sure there's a technical term that I'm missing here) water movement, but could be augmented by a water pump.  The system would be reversible summer/winter.  Seems to me it could even be decorative.  I don't know anything about the thermal properties of acrylic, but heated acrylic fish tanks definitely exude some heat--floor-to-ceiling water-filled acrylic pipes could certainly be a decorative element, albeit a whole lot more expensive than ductwork.

Or am I nuts?

[Nick1911]

You would have to move a LOT of water, in my opinion to make such a system work. And then, it'd only kinda work for AC, and not at all for heating.

And, the thermosiphon might kinda work in the winter, but without a significant temperature difference driving it they don't work very well.

Earth ground water around here is about 55 ish.  Would be okay for summer (although non ideal, need a pretty big DX coil), but is too cold for winter.  The whole idea of the heat pump using the earth as a sink is, if you're pumping heat from 55 degree water, it will use less energy then pumping it from 10 degree winter air.  Less sliding up the entropy curve.  Ditto in the summer, when you're trying to move heat from a 40 degree coil to 100 degree outdoor summer air.

Paging Jim and 280...

[CNYCacher]

For you engineering types (and assorted other freaks with esoteric knowledge),

Does a geothermal system have to have a heat pump? 

This is my thought:  The heating/cooling comes from the water, right?  So why have a whole system of drawing the heat from/to the water in an exchanger unit and then running it through ducts?  Why not just run water-filled pipes through the house?

Obviously, this is only practical in new construction designed around such a system.  Piping would have to be planned carefully to facilitate thermally-driven (or primarily thermally-driven) (I'm sure there's a technical term that I'm missing here) water movement, but could be augmented by a water pump.  The system would be reversible summer/winter.  Seems to me it could even be decorative.  I don't know anything about the thermal properties of acrylic, but heated acrylic fish tanks definitely exude some heat--floor-to-ceiling water-filled acrylic pipes could certainly be a decorative element, albeit a whole lot more expensive than ductwork.

Or am I nuts?

You can't do radiant cooling because condensation forms on the cool element at the location that the air is being chilled.  If you strung pipes all through your house and ran cold water through them constantly, it would get very wet.  If they were in your walls, it would become mold central.

This is why all air conditioning units chill the air in a controlled location where condensation can be collected and drained away, and then pushes the chilled air to the living space through ducts.

With that said.  I have often wondered if you could do geothermal on the cheap by pumping cold groundwater through some kind of radiator (yes, like out of a car) and making the forced air blow through it.

A friend of mine has an artesian (no need to pump) well and I all but begged him to let me try it at his house but he wasn't having it. 

[BridgeRunner]

Of course.  Duh.  

I was actually picturing a house-as-radiator effect, with strategically placed vents to create convection, not quite forced air but enough to blow the cooler air:

South wall with high vent>small space>"radiator" pipes>bulk of room/house space>north wall with low vent

But yeah, way too much condensation, at least for such a relatively damp spot as MI.

[280plus]

Well,,, the biggest concern for radiant cooling is condensation on whatever it is that has the cold water running through it. I know a guy who took water from the stream in his back yard, ran it first thoguh a coil in an air handler which A. dehumidified the air and B. warmed the water up past the dew point. THWN he put the water through tubes in his concrete floor. He claimes it works great. I guess it would in a dry climate BUT 55* stream water in a humid climate is not enough to dehumidify to comfortable levels. You need more like 40*.

Heat is a whole other issue. You'd need a heat pump to extract the heat from the 55* water and put it into your house.

[Brad Johnson]

How effective geothermal can be is determined by groundwater temps and temp delta.  If you have a groundwater temp of, say 55 deg F and 100 deg ambient temps (temp delta 45 deg F) it can work quite well.

Unfortunately geothermal systems are also quite costly up front and require regular and fairly strict maintenance regiments.  Even with the advances in tech and reductions in cost over the last 10-15 yrs, I still can't make the numbers work out to anything other than almost dead even over the life of the unit vs a thoughtfully engineered and properly installed conventional high-efficiency system.

Brad

[280plus]

  Even with the advances in tech and reductions in cost over the last 10-15 yrs, I still can't make the numbers work out to anything other than almost dead even over the life of the unit vs a thoughtfully engineered and properly installed conventional high-efficiency system.

Brad

Thank you, that would be my observation as well.