Case Study: Aiming for Net Zero Energy in Florida

The north side of the Parker-Shepperd house after remodeling. Note from the “before” photo (below) that sloped roof trusses were added to accommodate insulation and PV panels, and that an addition pushed out into the original front porch.

Owners: Danny Parker and Lisa Shepperd

Location: Cocoa Beach, Florida

Climate Zone: Hot-Humid

The Parker house was built in 1958. It originally had 1,300 conditioned square feet, with two bedrooms and two baths, plus a garage, an enclosed south porch, and a swimming pool. When the Parkers bought the house in 1989, it had

  • no ceiling insulation;
  • mostly uninsulated concrete block walls;
  • leaky single-pane aluminum windows;
  • an inefficient A/C;
  • ducts in the attic, causing high conductive losses; and
  • aging gray roof shingles.

Danny is a researcher at Florida Solar Energy Center, seeking ways to dramatically improve the energy efficiency of homes, particularly in Florida’s challenging hot-humid climate.

Phase I (1989):

  • removed carpet to expose concrete floor for earth-contact cooling;
  • insulated the attic to R-19 with blown-in fiberglass; 
  • relied on natural ventilation and ceiling fans for cooling during spring and fall;
  • limited A/C use to June through September, with thermostat set to 79°F;
  • lowered thermostat temperature at night in winter months;
  • lowered the water heater set temperature, insulated the water heater tank, and installed low-flow showerheads; and
  • reduced pool pump operation from eight to four hours a day in summer and three hours a day the rest of the year. 

Phase I results

In the first year after they made these changes, the couple used about 10,000kWh—half the norm for similar Florida households (data weren’t available on the previous owners’ utility use).

Sealing the leaky ducts reduced A/C use by 19%.

Phase II (1990–94):

  • sealed leaky ducts;
  • installed a whole-house fan for cooling;
  • changed most lighting to CFLs;
  • coated the roof with white elastomeric coating (this can cause moisture damage in a humid climate, so they replaced the roofing in the next phase);
  • replaced the electric heater, water heater, clothes dryer, and cookstove with gas appliances;
  • installed a PV-powered pool pump; and
  • installed a PV-pumped solar water heater.

Phase II results

The elastomeric coating increased roof solar reflectance from 21% to 73%, reducing A/C use by 25%. Sealing reduced duct leakage from 18.2% to 5.3%, reducing A/C use by another 19%.

Phase III (1998–2009):

  • expanded the conditioned area to 2,000 square feet  (having added two children to the family);
  • added roof trusses with a 19-inch overhang on the east, west, and north and a 3-foot overhang on the south to minimize summer solar heat gain;
    • reduced daytime electric lighting needs by adding two tubular skylights to the interior bathrooms and a conventional north-facing skylight (with solar- control glass) to the kitchen;
    • added low-sone fans to the kitchen range hood and both bathrooms to exhaust warm, moist air;
    • insulated the additions to R-4 in the walls and R-19 in the roof;
    • swapped out six ceiling fans with high-efficiency models;
    • installed a real-time electricity use feedback device, which helped identify 90 watts of phantom load; 
    • replaced the refrigerator, TV, clothes washer, and dishwasher with the  most efficient ENERGY STAR models;
    • replaced the water heater with a tankless model; and
    • installed a 4.92kW PV system that produces 20kWh per day.

This TED device (The Energy Detective) helped identify 90 watts of phantom load.

The new tankless water heater on the wall receives solar-preheated water from the 80-gallon insulated storage tank in the foreground.

Danny Parker on his white-enameled metal roof, surrounded by the new skylights and PV system.

Phase III results

The reductions in electricity use, together with the new PV system, made the Parker home a net electricity producer.

Phase IV (2010–12): 

Aiming for net zero energy

  • installed R-5 EIFS to increase insulation in walls;
  • replaced windows with high-efficiency solar-control low-e windows;
  • added a 26 SEER mini-split heat pump  for heating and cooling, eliminating the furnace, A/C, and ducts; and
  • added another 1.1kW of  PV modules to cover the daily use of a plug-in hybrid automobile.

The concrete block walls were covered with 1 inch of expanded polystyrene insulation, then fiberglass mesh and stucco.

Before the retrofit, the windows were poorly fitting, single-glazed aluminum awning windows.

The new windows have high-efficiency solar-control low-e glazing; the casements open fully for ventilation.

The efficient mini-split heat pump eliminated the need for a furnace, A/C, and ducts. (This outdoor unit was mounted prior to installation of exterior insulation.)

Phase IV results   

Window replacement reduced cooling energy consumption by 20–25%. Natural-gas consumption dropped from 221 therms in 2010 to 84 therms in 2011.

Says Danny, “We’ve transformed an average Florida house to a zero energy home. This means that a zero energy home is available to anyone who is willing to make the investment and effort.”

For more in-depth information, see D. Parker and J. Sherwin, Achieving Very High Efficiency and Net Zero Energy in an Existing Home in a Hot-Humid Climate: Long-Term Utility and Preliminary Monitoring Data: Final Report, DOE Energy Efficiency and Renewable Energy, Building Technologies program, June 2012: osti.gov/bridge.

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