A few years ago at a trade show I saw a heat pump that worked with a solar collector on the roof.  Instead of using water, it used a refrigerant.  It was shown by an Asian company.  Does anyone know whether this made it to the market place?

Yazaki has experimented with small to mid-sized lithium bromide absorption chillers using solar input for years. The smallest current commercial product seems to be a 10 ton unit, but they've had 4 & 5 tonners around in previous years IIRC.

They need ~65C+ input water temps and it takes a bit of collector area to run the 10 ton unit (and THEN some!) Probably not suitable for single-family dwellings, eh?

http://www.yazaki-airconditioning.com/en/applications/references/fontedoso.html

The only tiny LiBr chillers suitable for houses I've heard of are these li'l 1.5 ton suckers:

http://schroderzimmerly.com/rotartica.html

http://www.dailytech.com/Solar+Powered+Air+Conditioning+Under+Development/article12430.htm

http://www.sciencedaily.com/releases/2008/07/080714151427.htm

Since it needs a 80-95C water you'd probably only be running them with evacuated tube collectors (Yazaki units are often run off of less expensive flat-plate technology.)

Not sure if it's commercially available in the US yet.

The unit I saw was designed for residences.  I believe it also heated domestic hot water.

Just another angle on an ASHP. The bigger the footprint....more BTU's. It can take BTU's from it's surroundings, is it enough?....Can it go deep into the heating season?......Does it out perform GSHP's?......Will it cool you as well in the summer?......
The questions are always the same with the other ideas.
Good Luck,
Joe

....does it work when it gets snowed on?...

Vapor Absorption has been around since the late 70's. It was developed in the US during the Energy Crisis.
Technically a beautiful idea.
It was unsuccessful at the time because the control schemes were not up to the task and energy prices stabilized.
It was picked up by the Japanese in the 80's.
The machines are complicated and the sensors and pumps require a small computer to control. Actually a PLC.
The idea behind VAP is to substitute another form of energy for the traditional electrical motors to turn screw or piston compressors.
They can be powered by diesel, gas, solar just about anything that will get the required temp.
In the right location they are a wonder. But there are not that many right locations.
I worked on a job were we installed 2- 125ton diesel fired VAPs.
We had installed our own generators for electric to operate all of the ancillary pumps and fan coils( 250KV) but not enough to operate a screw compressor. The big advantage was the price of diesel was subsidized heavily by the government. That was the reason the VAPs could be used successfully.
Electric requirements were minimal, however, maintenance requirements were not.
They work great when they work, but you really need a very well qualified tech for service.
Can they work for heating? Sure, they reverse cycle, if the controls have been installed. But a pretty fruitless effort. The energy you put into the VAP will be less than the energy available to heat the space required. But if it your only method of supplying heat then that is the way it goes.