Quote Originally Posted by Bear_in_HOU View Post
Let me perhaps get more clear about the various options under consideration:

1) Single stage AC + (small) Gas furnace - standard Houston practice, we have this in our current home. Probably two units (one up and one down). If I don't ask for better, this is likely what every contractor my builder polls will spec.
You can do better. Probably lowest first cost option though.

Quote Originally Posted by Bear_in_HOU View Post
2) Single-stage Heat Pump - as above, but without the gas furnace. Electricity runs $0.11/kWhr (more or less) and gas is $0.80/Ccf (more or less). Higher acquisition cost vs. the AC unit, but indeterminate vs. the package.
In tight, well insulated construction this is worth considering. Have you considered Photovoltaic Solar panels to offset utility costs. This option is not as costly in new construction where the roof is going to be new, the electric system is being installed new, structure for the panels can be designed into the home while it is being built, energy studies required to obtain incentives will probably already be needed for the home design anyway or not required due to the expected levels of insulation etc, and incentives may still be available to make the cost reasonable. Solar makes heat pumps a no-brainer, if it is a viable option for your area (I don't know what the feel is for PV solar down there. I have a ground mounted grid tied 8.8 kW system at my house in NJ and I spent less than $200 last year for my grid tied electric with a 3 ton heatpump, heatpump water heater, an outdoor hot tub, electric cooking and clothes dryer and the usual other electric stuff. We used to average $150 per month plus $2000 per year for oil heat.)

Quote Originally Posted by Bear_in_HOU View Post
3) High-efficiency, two-stage iterations of both of the above. Somewhat likely to get "upsold" into a higher tonnage unit(s) to handle peak loads, while the lower speed stage may or may not still be overkill for our average needs. Ductwork and other items also having to be sized to the peak airflow means more added expense.
The upshot of oversizing is that a heatpump may be able to handle heat load without backup in some models, especially in milder climates for heating.

Quote Originally Posted by Bear_in_HOU View Post
4) VRF Heat Pump (Japanese) - Mitsubishi can operate more than one air handler internally (great!), but there are few contractors locally who work with these units (not great), and the ones that seem to work in a ducted application (we need high performance filtration) seem to only have mid-market efficiency ratings. I've read a studies done by FSRC, among others, on these types of units to see what the practical efficiency is. This is still an open question.
I've used these type units on several projects. The question is open because there is difficulty modeling their capabilities. Commercial load programs couldn't model how they take advantage of part load through compressor load matching also, the ratings system did not extend low enough to show their advantage as a heat pump in colder climates through the ability when optimized for heating to do heatpump operation down to 100% rated capacity at 0 degrees in some models without backup heat. The drawbacks are that by code you have to make provision for the smallest room with an interior unit to be able to handle a dumping of the entire refrigerant charge into the room should a catastrophic failure occur, the units do not handle outside air well without a separate dedicated system, and finding an installer with experience who can do all the refrigerant piping work required. They also need to have provision for condensate removal on a local level (at each indoor unit) and the units are in the room, hanging on a wall, up in a ceiling or standing by a wall. The good news is they are very quiet and if installed right are very efficient.

I like the dedicated whole house dehumidifier option for treating incoming OA. If it also connects to RA then it will help reduce the latent load on the AC.

Another option mentioned above in some of the other posts that I have used is the mini chiller system. On the surface these do not appear as efficient as say the VRF minisplits (they look identical by the way), but they can allow for greater diversity for greater possible equipment size reduction. Only water and maybe some glycol (not a very high concentration in your area, I imagine) run through the building so the refrigerant charge is all outdoors so that code restriction of accounting for refrigerant dumping goes away. Installation can be done more easily because it is water piping and not refrigerant, many more contractors can do that kind of installation as certification is less stringent. Well suited to new construction. Same other problems as VRF with condensate disposal. Worth looking into though.