Case Study

Gainesville, florida

Builder Achieves HERS -2 on First High-Performance Home

These high-performance homes in northern Florida are two that have achieved Home Energy Rating System (HERS) ratings of less than zero since Building America (BA) builders started building them in 2010. The homes (TW1 and TW2) were built in the Gainesville area by Tommy Williams Homes (TW), with technical assistance from the Florida Home Energy and Resources Organization and energy-efficient home design input provided by Wright Jenkins Home Plans.

The homes are being metered by the Florida Solar Energy Center (FSEC) as part of BA efforts to collect data that characterize the performance of the homes and verify that the solar photovoltaic (PV) system used in their design produces more energy than these all-electric homes require, as the HERS rating of <0 implies.

Key Energy-Efficiency Measures:

HVAC:

• SEER 16 AC 9.5 heat pump

• All ductwork in conditioned space.

• Positive pressure whole-house ventilation system (run-time only) all exhaust fans vented to outside.

Envelope:

• R-30 blown ceiling insulation in vented attic

• R-15 spray-in fiberglass insulation in 2×4 frame wall

• Double-pane, low-E vinyls windows (U = 0.35, SHGC = 0.25)

• Tightly sealed house, ACH50 = 2.3 and 2.8

Lighting, Appliances, and Water Heating:

• 100% compact fluorescent lighting CFL

• ENERGY STAR® appliances

• Solar water heater (indirect system)

• PV array size (kWp DC): 6.8 (TW1), 5.4 (TW2)
  

Lessons Learned

• It is indeed possible to achieve a zero utility bill in a high-performance home with a modest number of solar PV arrays.

• Because of the low cost of PV systems and the low loads in these homes, it was not cost-effective to purchase HVAC equipment with a SEER rating greater than 16.

• Significant south roof areas are needed to get to HERS 0. In TW1 and TW2 it was possible to fit all the solar systems on the south roofs, but just barely.

• The interior RH in these low sensible-load homes was well controlled even without a supplemental dehumidification system. The mean monthly interior RH stayed below 60% all the time.

• Occupants in the two homes maintained a very cool 73 to 74 degrees interior temps in the summertime. Still, the cooling energy use in the homes was low, attesting to the excellent performance of the envelope and equipment.

Performance Data

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