Dear people, I’m trying to come up with a practical efficient HVAC plan that has the potential to be made more efficient down the road in a project that may seek a net zero certification. Envelope design and existing conditions: In this high efficiency gut reno of our 1890s house in Chester CT ‘green’ features include 2 layers of continuous 2” Rmax with taped staggered seams at all above areas and as much XPS exterior basement insulation clad to protect from insects. Cellulose in stud and rafter bays for a total of R52 at attic and R49 at walls. Currently the envelope is 95% complete and the main services are connected but there is no cellulose nor systems installed, the frame is entirely exposed at the interior. With mostly triple paned windows, load calcs show 12 btu/hr/sf and a total design load with DHW of 24,000 btu/hr. I’m also testing a new automated single hung window design (for night flush cooling) with 80sf of vertical semi tracking solar thermal flat plate collectors as operable automated exterior shutters at an oversize (7’x14’) south facing window. The insulation on the ST panels will insulate the big window on a winter night. With solar thermal infrastructure given, I’m inclined towards mostly radiant with a couple of fan coils for the minimal cooling and dehumidifying load. As I've (clearly) invested too much already, further improvements will come after a c of o as time and money allow, including 16 PV panels, which I’m interested in making hybrid PV - Solar thermal (PV/T) panels as I’m already committed to some solar thermal infrastructure with the shutters. The core conditioned living space is 1970sf though with the studio and basement the total conditionable sf is 2930. There is a wood stove so it's not necessary to plan for over the calculated load for the main living space here in southern ct at 21,500 btu/hr. The property has three abandoned wells one of which is an accessible dug well some 30’ from the house. (Image shows the site and the locations of the wells) The new deeper potable well is 6” in diameter and 150’ deep with a Grundfos 10S05-9 pump at 115’; water line 30’ below surface. If i understand the pump docs properly this pump should offer 13 gpm sufficient for 5gpm (or even 7) to the geo unit. The well produces 40 gal per min. There is a culvert 100’ down the block that goes right to the stream and digging a ditch to bury the dump pipe would have other drainage benefits for us and our neighbor. The city is fine with pump and dump,, so everything suggests an open loop except the water quality: “2.47mg/l iron, bacterial iron present, 179 mg/l chloride, ph 6.12”. HVAC Options: Install a hydronic distribution system (mostly radiant with some fan coils) and a water to water heat cool unit (thinking Nordic W25 or Waterfurnace 500W11) with a sacrificial external heat exchanger and run a pump-and-dump setup through that. Down the road maybe replace the external heat exchanger with a ground loop that connects two to four of our existing wells. Perhaps a cheap narrow 48” trench will connect the wells with a single pipe and U tube down each in series. The trench would be about 290ft, and the well loops would total possibly more than 410 lnft for a total loop circuit length of 700’. Perhaps even less total length would suffice if it is supported by 10,000 KW/year in hot water from the PV/T system which would prime the incoming water in winter and charge the ground loop while cooling the PV in summer. In either of these pump and dump setups, would it be cost effective to replace the pump with a variable speed pump? Would it be better to use the dug well as a buffer, taking the source from the dug well and running the existing deep pump at full capacity for an hour or so at a time to limit cycling of the deep submersible? Could the dug well effectively serve as a heat exchanger if I were to drop a coil in it and flush it with water from the deep well? Install a direct pump and dump 1.5 ton water to water heating only unit to the primary core living areas (1500sf) then also install a Mitsubishi Electric 1800 btu low temp air to air heat pump. This air to air unit would handle the full load efficiently with temperatures down to say 32f, then the water to water would take over down to say 5f, then either the direct vent wood stove and water, or water and air, would handle extreme low temps. Perhaps with such a small load on the geo, (18k btu half of the winter only at 4gpm) we could enjoy the efficiency of the direct pump and dump without worrying about fouling or corroding the unit over 20 years or more. ??? Or should this hybrid option 2 still employ an external heat exchanger? A classic closed loop system feels out of reach because it leaves me without a heating system until I can afford the 7k for the well and 3-4 k for the landscaping. I’m also not convinced it’s the most practical or efficient solution, further If i'm going to invest I would rather it be more innovative. Just do two (one 18k and one 12k) air to air units and keep things simple. Any feedback, thoughts, or useful notes would be appreciated!