Air/water heat pump solar hot house?
 

As a small air to water heat pump is easier/less expensive to install than ground loop how would placing it in a direct(passive) solar heated nonliving space - say mud room(w/thermal mass) improve efficiency? Warmer air is better right? Harvesting heated air for winter heating when available(and stored in interior thermal mass). Mud room(foyer) would be buffer to interior when entering/exiting and taking heat from it would not affect interior. In summer redirected to DHW would be like A/C wouldn't it? Thoughts? Full ground loop system is hard pill to swallow for low energy demand designed home.

Are you saying you're thinking about putting the evaporator portion of a ASHP in a garage, mud room, or greenhouse?

Okay, but understand that an ASHP is going to pump lots of heat out of whatever structure you put the evaporator in. I doubt you can keep a greenhouse or mud room warmer than ambient under conditions like that. In fact, read up on the amount of soil you need thermal contact with per kW of GSHP. I don't think your greenhouse field loop is going to be any cheaper than a buried field loop.

I am looking at ASHP as heat source(to thermal storage). As I understand it out side spilt of ASHP(heat collector) loss efficiency as air temp drops outside in cold climates. Being in solar heated space should lessen/eliminate that depending on space size/ASHP demand when solar heat is available. Not greenhouse, no ground loop, a nonliving conditioned space from which to collect heat from air. In summer collecting heat(to DHW) should "cool space". Space would also serve as airlock for living space. Can mini-splits go from air to water?

Yes they drop in efficiency as the air around them cools. They also cool the air around them when running. So running one in a greenhouse or mudroom at first would be better because it's likely to be warmer. The heatpump will however quickly cool inside that greenhouse quite possibly to even cooler then the outside air making it less efficient. They really do move a lot of air to get the little bit of heat in it.

You would be better off blowing the warm air from the greenhouse/mudroom straight into the house.
Less complicated, cheaper, more efficient.