Looking to optimize the HVAC design of a house in NC near beach on pilings. House is 2580' tight insulation design, inverted floor plan with all closed-cell foam (attic, walls, below 1st floor, etc.) and had planned for 2 zones (one for each floor) with an additional zone on the 2nd floor for the master suite. After a couple of Manual J iterations with an independent engineering firm to get the correct information the results show that 1 ton is needed for 1st floor and 1.2 tons for the 2nd floor. Current plan with HVAC contractor is to now have two Trane 15 SEER XL 1.5 ton units with the new variable speed 2-ton air handlers with an ERV for fresh air for each floor, plus the humidity controlling Tstats, but because of the high outdoor humidity it was suggested to also include a whole-house dehumidifier just on upper floor. After looking at all this I am wondering if this is the optimal design from a cost, energy use and duct-integration considerations.
I am now considering dumping the multi-zone idea and considering other options:
1. Go to single zone for the whole house with a single right-sized 15 SEER XL or even the 20 SEER XL system (2.5 tons?) with single ERV and dehumidifier integrated somehow (I have lived in other houses with a single system for multiple floors, but they never seemed to be comfortable on all floors at the same time);
2. Upgrading to the 2-stage 20 SEER XL and dual zone it for the two floors since it has a two-stage compressor that may allow this (not sure if it's possible to get a good duct layout with this house design...).
3. Use a mini-split system just for the 1st floor (not a big fan of these though after initially looking at costs and reliability, plus they all seem to be non-U.S. made...).
I need to decide on the final concept before following up with the final Manual D, S and T. There seem to be no shortage of ideas out there on these topics, but for this application does any one have better suggestions, and the best way to integrate the ERV and dehumidifier? Thanks!