TechPractices: Keith Swilley House, Koehnemann Construction, Panama City, FL

PATH's Technologies in Practice are large scale housing projects throughout the U.S. where innovative technologies are being installed and used. Information is presented from the viewpoint of builders and remodelers who can use these examples as models for projects of their own.

Summary

This single-family Florida house uses a horizontal loop geothermal heat pump system and an array of energy-saving strategies. Built for less than $50 per square foot (not including land) this home is below median home prices for the region. The high-quality, energy-saving design makes it comfortable to live in and affordable to operate.

Details

Homeowner Keith Swilley wanted his new house to be very energy efficient. Because he might have to move in a few years, every design and technology was scrutinized for maximum energy savings and short-term return on investment. But despite the short payback requirement, he installed a WaterFurnace geothermal heat pump (EER 16.0, COP 3.6), known for being high performing and somewhat costly. Swilley did this because he knew that between the energy savings and the increased resale value of the house, he could recoup the additional expense of the geothermal system. Augmenting the heat pump is a desuperheater that provides "free" hot water as long as the heat pump is in operation. Other efficient solutions include highly insulated walls and ceilings; air-tight construction to reduce infiltration; a sealed HVAC duct system minimizing distribution loss; and energy-efficient lighting and appliances. These products and systems increase front-end costs but greatly improve whole house energy performance.

Located in the western Florida panhandle, Panama City's residential electric rates are $.06/KWH. Because rates are low, even a big percentage reduction in energy use doesn't equate to very large dollar savings monthly. Despite the longer payback and higher initial cost (the Water Furnace system cost about $3,000 more than an air based heat pump) geothermal is used because of its superior heating and cooling performance, and for its capability to dehumidify. This owner sub-meters heat pump and hot water use to monitor actual equipment performance. The average cooling and hot water use in this house is 48% of total household energy use on an annualized basis. That compares to 70% or more for average residential energy use.

Geothermal heat pumps have been recognized by the US Department of Energy as one of the most efficient solutions for residential heating and cooling. Like refrigerators, heat pumps remove heat from where it is not desired (inside a freezer), to a pump it where it can be expelled (the back of the refrigerator.) In the geothermal variety, a fluid-filled polyethelene pipe, buried in the earth, augments the heat exchange process. During operation in the heating season, fluid in the loop transfers heat from the ground, via the heat pump, to the house. In cooling, the heat from the house loops through the ground, is cooled, and returns to the house ready to cool and start the cycle again.

To keep his lighting loads low, the homeowner installed fluorescent pin lamp (PL) lighting fixtures for all general illumination. In the utility rooms and garage he upgraded standard fluorescents to T-8s with electronic ballasts that are said to be 40% more efficient. In the kitchen, an Energy Star refrigerator, a convection oven that cooks food 33% faster and an induction cooktop that uses half the amount of electric energy as a conventional cooktop, help assure energy efficiency.

Installation/Construction

Trenches are dug for the closed loop geothermal heat pump system. The one-acre lot provided enough land with sufficiently moist soil for a horizontal installation with three 100'-long trenches each 5 feet deep. Each 100-foot trench has 600 feet of ¾-inch coiled polyethelene pipe laid in successive loops, called a mat loop, like coils of a slinky. This maximizes ground contact with the least amount of digging. The homeowner saved money by using his house excavator to install these loops as the site was being readied for the foundation. (If lots are small or soil conditions especially rocky, closed loop "wells" can be drilled vertically into the ground.) Extremely durable, polyethelene pipe is used by the natural gas industry for its in-ground gas supply lines.

Once three loops are joined to the 1¼-inch polyethelene feeder pipe and brought to the house, construction can begin. The 40-foot by 50 foot house sits on a slab-on-grade, insulated at the perimeter edge with ¾-inch rigid foam. (Under-slab insulation is not effective because ground temperature in Florida is close to 70 degrees Fahrenheit year round.) This one-story building is framed with 2 x 4 walls that are sealed at the base with Dow sole plate sealer and insulated with R-13 wet blown cellulose which is said to reduce air infiltration when compared to walls of fiberglass batt. The studs are sheathed with ½" plywood, insulated with ¾-inch rigid foam, and covered with conventional stucco. This brings the exterior wall insulation value to R-19. Loose filled cellulose is blown into the ceiling joists making an R-38 ceiling. The roof is framed with engineered trusses, sheathed with ½-inch plywood, and covered with asphalt shingles.

The double-glazed aluminum windows by Mayfair have an infiltration rate of .23 per lineal foot of sash. The Therma-Tru exterior doors are R-8. Doors and windows are sealed in their framed openings with expanded foam sealant to reduce infiltration. A blower-door test of the house revealed an average of 0.25 air changes per hour (ACH), which is less than half the infiltration rate of a typical new house in this region.

The fan coil "furnace" of the heat pump is located in a closet off the garage, while the feeder ground loops are connected through the slab. Metal ducts from the furnace run through the attic space and are oversized to reduce noise. Additional noise reduction is achieved with expensive curved fin diffusers spaced farther apart. Because the ducts run through unconditioned space, trunk lines are insulated with an R-6 wrap and distribution branch lines are R-6 flexible duct. All joints are sealed with mastic to reduce air leakage, and the entire system is tested using a duct blaster before occupancy. A system is considered in compliance if duct losses are less than 3% of floor area. Actual tests revealed only 1.5% duct leakage.

Benefits/Costs

Beside its touted performance and operating superiority, why chose an expensive, geothermal heat pump system, especially if you don't plan to stay in the house as long as the payback period? Other than improved comfort and lower bills, the reason may be marketing. This owner has built and sold three houses. Each included more energy-efficient features than the previous house, and each sold quickly because the buyers appreciated such features. In a cooling-dominated residential market, geothermal heat pumps may be a good way to distinguish otherwise comparable residential properties. This conclusion is shared by builders Carl Franklin Homes of Dallas, who consider geothermal heat pumps an essential sales feature of their affordable housing developments in Texas.

Although this house does not tout affordability, it is priced below the median. Competing with conventional construction while offering long-term operating savings makes this home attractive to conservation minded home buyers.

Code/Regulatory

There were no significant code issues that arose during design or construction. The builder points out that he exceeded all energy codes by 20% to 50%. Although the buried ground loop pipe did not require permits for installation, it did cause a flurry of concern by building inspectors when it was first being installed in the early 1980s.

Feedback

Winning an Energy Value award from NAHB in 1997, and a Grand Aurora award from the Southeast Builders Conference in 1996, puts this house in an elite class. But Keith Swilley is not content to rest on his laurels, and has come up with ways to improve on his award winning work. On his "next house" list are higher performance windows and a floor plan customized to his family's lifestyle. The custom plan would allow him to bring the furnace to the center of the plan, keeping the ducts within the conditioned space and reducing duct runs. He plans to keep building houses with geothermal heat pump systems. But ventilation should also be considered in a house this tight. Relying on window and door leakage may not be sufficient for good indoor air quality.

Contact(s)

Do you have a specific question? Try the contacts listed below:

Gulf Power Company
Panama City, FL
850-872-3202