HVAC design for super tight, efficient house
I design buildings to be efficient, but I have really no idea on HVAC items to match them. I believe putting the money into your shell first, then hvac to fit the needs.
Here is some back ground: new construction, Single story house w/ walkout basement (facing north) in NE Iowa. Upper conditioned space is about 1550, plus a bonus room over the garage that is about 400 sqft. I would be fine if this was a stand alone system as well, as we will probably only use it for storage at first, finishing it out completely later.
Basement has family area, 2 bedrooms, bathroom and 2 storage rooms. True conditioned space is about 1250.
Construction type is staggered 2x4 studs on 2x8 plates with blown cellulose fill, then 1.5" XPS exterior insulation with drainage plane. ALl plates caulked to floor and to each other, XPS caulked to stud face, spray foam around electrical penetrations, etc. Basically as sealed as possible. R-60 cellulose in the attic.
Openings are high performance fiberglass with U around .27. South windows (not that many) have u .35 with SHGC of around .5.
After some very generic load calcs, it looks like a 2 ton 2 stage system is the most we need, even pushing the high side. I am attempting to figure out the cost of operating different systems.
We do not have NG at the location, so it would have to be propane. However I would prefer to do an all electric option. The rates around here would be about .1, however with the all electric plan, they drop during the winter months to .04 after the first 600kw are used. THen for summer usage, they jump to .18 after the first 600 is used. However this applies to 3 or 4 months out of the year, I believe the rest are the .04 months.
here are my thoughts: The demand for heat with this house will be low enough that geo probably will not pay for itself in 15 years or less, which is the guested time we will live there. SO I have been looking into air handlers with electric strips and air to air HP options.
Here are some numbers: Waterfurnace 2 ton 2 stage geo, horizontal loops, HRV, electric strip, all duct work- $$$$- fed credit= $$$
more "standard option"-
Lennox CBX27UH-024 blower coil w/ electric heat strip
XP16-024 2 ton 16.5 SEER HP.
HRV, auto switch over thermostat, all ducting and load calcs- $$
adds would be 2 ton 19 SERR HP- $
CBX32MV-024 blower coil- $
CBX40HV-024 Blower Coil- $
so basically just over a $$ difference. I am trying to get operating cost estimates from them as well.
any thoughts on the situation?