Case Study 1: Gainesville, Florida

Building America Case Study
Efficient Solutions for New Homes
Attention to Details in High Performance Homes


Gainesville, Florida
Construction: New
Type: Single-Family
Pacific Northwest National Laboratory
Energy Smart Home Plans
Florida H.E.R.O.

Builder: Tommy Williams Homes
Sizes: 2,287 sq. ft. & 1,546 sq. ft.
Price Range: $163 – $169 per sq. ft.*
Date Sold: Feb 2010 & Oct 2010
Climate Zone: Hot-Humid
*Retail Sales Price

Key Energy-Efficiency Measures:

  • 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.


  • 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)

Builder Achieves HERS -2 on First High-Performance Home

HERS Indicies TW1 TW2
HERS Indices w/PV
HERS Indices w/Solar
DHW but excluding





 Avg. KWh/day   Avg. KWh/day
House Total
PV gen


Project Description:


Clearwater Model (TW1)

Jordan Model

Jordan Model (TW2)

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 Energy Smart 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.

The table to the left shows measured home-performance data for a 7.5- month summer period in 2011. The whole-house, cooling, and “other” energy uses for these homes are substantially lower than typical homes in northern Florida. Energy usage in TW1 is about 30% to 45% lower than a typical home and in TW2 it is about 60% lower. The difference in energy usage between TW1 and TW2 is primarily due to occupancy patterns. Zero utility bills over the measurement period are possible because of this high level of efficiency. Below are pictures of two models. The upper has standard hi-performance features (HERS -2), the home in bottom photo has high-performance options (HERS -37).

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.

“I set out to make energy efficiency affordable, and got there on the first try.”

Tommy Williams, President of
Tommy Williams Homes

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