How do you run ducts for heating and cooling with slab on grade construction?
I will be hiring an architect to design my single floor 2200 sq. ft. home in coastal RI. My hope is to be as passive and net-zero as possible. We intend to have a cold climate air source heat pump that will serve as our sole source of heating and cooling, plus an ERV. I believe we are in Zone 5. We are thinking of a hybrid electric heat pump water heater. We are planning to have a solar roof or a solar array and battery storage system. A slab on grade foundation is foreign to me but I know the cost-effectiveness as well as the environmental benefit. My question is how does one run ducts for the whole house system? If we have a gable roof, can we have the ductwork in the attic space? If we do a flat roof for a more modern design, what are the options to running ductwork? I do not like the look of ductless mini-splits so will certainly have a ducted system.
A slab on grade foundation - or frost protected shallow foundation - is a great alternative to a standard foundation, and they work in all climates, contrary to what a lot of people think. This page is a great start for all things slab related -
How to buid a slab on grade foundation - the Ecohome A to Z guide
You open up a lot of great topics there so I'm going to point you to several other pages on specific topics. First here is out page all about passive heating and cooling. But specifically about your question of how to heat and cool a slab on grade floor, would be a heated floor. here is out page all about different under floor radiant heating systems.
Cooling is a different matter, some people put in air-to-air heat pumps cooling, and radiant cooling is something of a contentious topic but can work, as long as you don't 'over' cool the floor to the point where you are creating condensation.
Heat pumps are a great idea as you mention, you can get an air to water heat pump for use with hydronic /liquid systems, or to use a water coil in an air heated radiant floor.
As for getting ahome battery, that's a great idea for resiliency, but an cheaper alternative to home batteries is a bidirectional charing EV so your car powers your home in an outage.
As to your main question about duct work - outside of heating and cooling you'll still need duct work for ventilation. For a two story house you can run ducts through the first floor cieling, but it is for sure a challenge with single story slab on grade homes. It's not a good idea to run duct work through an attic or slab, but instead you could run a bulk head along a corridor somewhere. I wish we had more options to pitch you but other than the ductless wall insert HRVs and ERVs you're pretty limited.
And a last suggestion, you can find Architects in the Ecohome Green Builders Directory