Hi there....I'm about to start building our own ICF home in Northern Virginia. Plan to make it as tight as possible with top windows and a fully sealed attic space, along with the ICF's. Am considering geo but want to make sure it's worthwhile given the $$'s we're putting into the envelope. Question is, does anyone know of an independent consultant who can design the optimal HVAC system for this house? I trust my HVAC contractor but they have little experience with such tight construction and besides, it makes sense to me to split the specification of the system from the guy who is selling it to you?! Also, looking to install radiant floor heating and ERV. Any recommendations would be greatly appreciated. Thanks.

It is not typical at the residential level to split the design and installation tasks. You need a contractor with prior geo, radiant, and ERV experience. He / She should be execute required load calculations and system design.

Good news is that though geo is more expensive up front, your system should come in about half what would be needed for a conventionally detailed stick built house if you go ahead with ICF, high end windows, and sprayfoam.

Major Geothermal in Colorado might design the system for you. Ask for Terry Proffer.

If you don't do the radiant, you can probably do the geo for not much more .

If your HVAC contractor has little experience with your level of construction it is not necessarily a deal breaker if he uses a load calculator he trusts and does a room by room load/design. ERV is handled similarly. However if they are already dropping disclaimers without solutions, time to move on.
RE subdivision of tasks (design vs install) that also causes a subdivision of responsibility.
If something doesn't work is a remote designer going to fix it? The main reason resi customers don't do this is so that one guy is on the hook for performance instead of finger pointing between designer/installer. HVAC contractors generally charge less for design work if you buy the whole job from them.
Good Luck,
Joe

My builder's last job went south for just this reason - Architect did the load calc, and Bozo did the duct work. Result was a nightmare.