Firstly, thank you for all the constructive and timely comments. We have done a bit of building work on the farm but i am happiest with a lump hammer and baler twine so air source is a bit of a mystery to me. We had a preliminary discussion with a supplier recommended by our architect who has used them before. The main initial attraction of an ashp was the potential to cool the house but i was immediately told that this was not possible and then the rough cost estimate put doubts in my mind. If a competent plumber could install it then that changes things substantially and having now read (if not understanding the technical bits) the JSH blog it would seem that cooling is possible! I agree with the excess cost of proprietary solar thermal but we built a veranda over the front of the house using a very basic copper tube on insulation with dark glass system and it has worked a treat and looks good too. Having said that it would seem tobe overkill if we can use most of the three pv systems. Anyway, having digested your combined wisdom and on the basis that it will both cool and heat then i think an ashp is the way forward and will speak to our plumber and gauge his reaction to him installing. I will not mention heat boxes yet he might run! I am hoping to get a final heat demand estimate from the architect by the end of June which should steer us to the size of ashp required.
By way of background the old dairy we are converting will be single storey and basically a rectangle with a room tacked on which is currently a propagating house. Total area is approx.200 square metres and from a passive viewpoint is not an ideal shape. We have thought of the enerphit standard but are aiming for passive though the insulation levels are high. A further complication is that we have to work with the existing structure so the plan is to build a house within a building. Occupancy is only going to be the two of us most of the time.