Heating with a Heat Pump in Wisconsin?

[12AX7]

First,  sorry if this post should have been in my diary.  But being about heating I thought that this was the place to start.

I recently saw a local news blip where someone had installed a geothermal heat pump to heat their house. 
I had heard that heat pumps can be/are very efficient.  But, I've also heard that heat pumps don't work well north of 40deg north.   We're at about 43.48 and it sounds like heat pumps are becoming popular this far north.

I see where some claim efficiencies close to 400%.  To me this begins to sound like "over unity"
I "think" I understand that these efficiencies are related to the differences between the "heat source"  ie ground temps and air temps.
However I haven't seen a "published" chart showing these values.

Checking geothermal systems I see that there are open and closed loop setups.    Vertical and horizontal fields with a wide range of size and depths.
It sounds like the open loop system (if available) are preferred due to costs.

I am guessing that "depth" must effect efficiency since a pump is required.  The deeper the system, the larger the pump must be.
I live next to a small river/stream.  It freezes over the winter, how ever water continues to flow under the ice.  I'm guessing that the river isn't much more than 50 feet from our house.

We have a shallow well,  and I don't know how deep it is.
I haven't had our water tested in a long time (we've always drink bottled water) but the water out of the tap has/is always crystal clear and no problems with rust/iron stains in sinks tub or toilet.

Heat pumps can be used to both heat and cool..  and in our summer months most of our cooling bills are related to the very high humidity (being in a river valley, and so close to the river)
My problem right now is that I don't know enough about these systems to know what questions to ask.

Any ideas where I should start? 
Has or is anyone running a heat pump in "the" north, where winter comes for several months a year?
Anyone running a heat pump with a "open loop" system?
Can one run a heat pump as "just" a dehumidifier?

Any comments??

Thanks!

ax7
Mark

[Simen]

I live in Norway which stretches from 58deg. N to 71deg. N, and temperatures below freezing for months are common. Heat pumps are very popular here; mostly the cheaper air-air pumps, but also sea-air/water and ground-air/water (geo thermal). The popularity are due to the low electricity prices here i guess.

I have an air to air heat pump with a heating CoP (Coefficient of Performance) of 4.2 at 0deg. C. (Putting 1kW of power in, gives 4.2kW of heat out.) C. At -7deg. C, the CoP are around 2.1-2.5 for my unit i think. (I might be a bit off here. )
Edit:
(There is no over unity in play here... definition of CoP: http://en.wikipedia.org/wiki/Heat_pump#Efficiency )

Running heat pump as an dehumidifier are, technically, not a problem, but it varies from model to model if that mode of operation are available. the heat pump at my previous house had a dehumidify mode; this one i have now doesn't, but it does dehumidify to some extent when in cooling mode (air conditioning).
Dehumidify mode are the same as cool mode, but with very little air flow through the unit; that way, it freezes the humidity without cooling too much of the air in the room.

I have little experience with geo thermal heat pumps, but i understand that if one lives in a place where the ground doesn't freeze solid in the winter, it's ok with a shallow loop, but if you have temperatures below freezing for months, going deep are the only option. Here it's normal to drill down to 80+ meters into the rock for geo thermal heat pumps. I do not think depth affect the running cost much; a pump doesn't use much power in a closed loop.

I've just installed an air to water heat pump here, since we've restored part of the house and put water loops in the floors. this heat pump will heat up an 300 liter tank wich will circulate in the floors. The tank also have a 2kW electric heater at the top to raise the 40C water from the heat pump up to 65C+ where the tank has integrated heat exchangers for hot tap water.
We're not completely done yet, so it's not yet operational.

[bob g]

one also should have the type of soil tested before he uses it for a ground loop system,

there are some soil types that "heat or cold soak" and lose efficiency in a hurry, basically if you are using it
for a heat source and it freezes solid, you will lose efficiency as it gets colder down there, so

the soil cannot be of a type that is very dry and high in insulating quality

check with folks in your region that use heat pumps, ground source. if there are tons of them around it is a safe bet
that it will work well for you, if on the other hand you can't find anyone or very few i would want a test done by a soils
engineer and not the guy selling the heat pump.

if you can get a system that works off of a water source, and can work down to near freezing water temps with good efficiency
and you have a moving water source,, that could be used effectively i would think.

as with anything that costs a significant amount of money to purchase and install, educate yourself, and check with at least 3 different suppliers in your area, and see if it makes sense.

bob g

[damian]

The other big factor is ground water depth.  If your heat exchange loop is down into the ground water then you are pretty well clear of soil heat capacity issues.