• Building America Prototype, Cambridge Homes

Figure 56 The Augusta, Cambridge Homes Building America Prototype.

The partnership between BAIHP and production builder Cambridge Homes began late in 2001. Cambridge Homes had recently signed on with the EPA Energy Star Homes Program as a 100% Energy Star builder and expressed interest in increasing energy efficiency even further, as well as adding some “healthy home” features to their product. Also, Cambridge Homes expressed interest in BAIHP helping them design and build in a way that would prevent moisture related problems and call backs.

BAIHP began by conducting analysis on several typical home designs and presenting results and strategies in a number of meetings with the builder. BAIHP also arranged a special meeting with the American Lung Association of Central Florida to discuss achieving the ALA Health House designation on the showcase model. However, the builder decided not to pursue the health house designation at that time.

To implement Building America strategies outlined by FSEC researchers, Cambridge Homes constructed a “prototype house” (Figure 56) to ensure that the strategies mate well with their current building practices (Table 33). A variety of home plans were reviewed to select an appropriate demonstration home, as well as a standard-practice counterpart. During construction, both homes were outfitted with dataloggers and associated monitoring equipment.

The homes were built in Baldwin Park, a new Orlando subdivision being developed on land that was once home to the Orlando Naval Training Center. The development will be 30% larger than New York’s Central Park, totaling approximately 1100 acres. Four hundred acres have been set aside for parks and open space, while 700 acres will be used for the construction of 3,000 homes, one million square feet of office space, and 200,000 square feet of retail space. Cambridge Homes is one of ten builders constructing homes in the community and plans to build 700 homes in Baldwin Park over the next five years.

The demonstration home gave the builder firsthand experience with unfamiliar design elements, some of which have been incorporated into their standard practices. Such unfamiliar design elements included vapor permeable wall insulation, low-e windows, whole house dehumidifiers, unvented attics, and compact fluorescent lighting. FSEC researchers closely monitored the construction of the prototype and standard practice home, which was built to the Energy Star level. A duct test was performed in the prototype house during mechanical rough in to ensure leakage specs were met. Meetings also were held with the builder's HVAC contractor to discuss installation of the whole-house high efficiency dehumidification, filtration, and ventilation unit in the prototype model.

Upon completion of the home, duct testing was repeated to include inspection of the whole house dehumidification unit, and infrared camera analysis was conducted on the home. Data (Figures 57 and 58) collected from the two homes showed marked improvement in attic temperature (a primary cooling load) and indoor relative humidity control.

BAIHP performed training for Cambridge Homes' sales staff in March 2003. The training took place within the completed “prototype” model. Training focused on the advanced features of the Building America showcase model which Cambridge Homes began offering in April 2003.

Figure 57 Comparison of attic temperatures between Cambridge Homes BA Prototype (Augusta) and Standard Cambridge Homes construction (Covington). Graph shows how sealed attic construction in Augusta results in lower attic temperatures than vented attic construction during cooling season in Orlando, FL.

Figure 58 BA Prototype (Augusta) contains whole house dehumidification system. Plot shows daily cycling of the system resulting in a lower relative humidity in the prototype home than in the standard Cambridge Homes construction.

Late in 2003, Cambridge Homes began construction of a second home similar to the “prototype” model, which was purchased by a customer impressed with its attributes. FSEC staff conducted training for builder and sales staff in December 2003 to review design methodologies and lessons learned from the prototype model. A second meeting was held in January 2004 inspect progress of the home. Upon moving into the home, Cambridge Homes reports that the new homeowner is extremely happy with the home.

To assist Cambridge Homes with reducing callbacks and moisture reduction problems, FSEC researchers have also conducted “total” and to “out” duct tests on six other Cambridge homes to determine why the total duct leakage numbers were high (>10% of fan flow) despite low to “out” duct leakage. “Out” is defined as outside the conditioned space, including buffer spaces like an attic or garage. Consistent leakage was found around the boot to register grill connections. FSEC worked with Cambridge Homes and their HVAC contractor, DEL-AIR, to specify air tight register grills.

• Unvented Attic Study, Rey Homes

Rey Homes, a production builder in Orlando, in 2001 pledged to build a community of 200 homes that meet both Energy Star standards (HERS = 86) and the Florida Green Home Designation Standard. Rey’s partnership with FSEC began in October 2001 when researchers analyzed Rey’s standard home designs and construction and made recommendations for complying with these standards.

In the fourth budget period, Rey built 2 homes in their Villa Sol community for side by side comparison of unvented attic construction, a BAIHP recommended strategy. FSEC installed monitoring equipment in both homes, one with an unvented attic and one with a standard vented attic including a set of moisture pins in each house to monitor the moisture content of roof trusses in addition to the usual complement of temperature, humidity, and energy use meters. Instrumentation was complete early in the fifth budget period; however, data collection was not successful due to equipment and site complications.

• Sharpless Construction, Hoak Residence Energy and Moisture Studies

Figure 59 Hoak residence in Longwood, Florida .

This three-story, 4,250 square foot home was completed in February 2001 by Mr. David Hoak and Sharpless Construction in Longwood, Florida near Orlando. (Figure 59) FSEC assisted the owner and builder by recommending a package of features that produced an exceptionally energy efficient design at a reasonable cost. Because the building envelope design and mechanical equipment selection work together as a system, the home can be cooled with a much smaller air conditioner than is needed by most homes of this size in this climate.

Envelope Features:

High Performance Windows

Roughly 25% of the annual cooling load in a typical Central Florida home is introduced through the windows. Recent advances in window technology allow this load to be greatly reduced. The windows in this residence are particularly useful in Florida because they have a very low Solar Heat Gain Coefficient (SHGC) to reduce direct solar gains, and a relatively high Visible Transmittance (VT) for natural daylighting.

Figure 60 Semi-conditioned space for the ductwork.

Unvented Attic

Most Florida homes have vented attics with batt or blown insulation applied just above the ceiling. This exposes the air conditioning ductwork to very high temperatures and magnifies duct leakage problems. Sealing the attic envelope and insulating at the roof deck, as shown in Figure 60, provided a semi-conditioned space for the ductwork. This reduced conductive heat gain and minimized the detrimental impact of duct leakage.

Expanding Foam Insulation

A layer of expanding foam insulation
(Figure 60) was applied to the underside of the roof deck to create an unvented, semi-conditioned attic (R-22). The same insulation was applied to all above-grade walls (R-11). While the insulation R-values were standard, the foam created a nearly airtight seal and greatly reduced outside air infiltration.

Continuous Air Barrier

Figure 61 Heat pump water heater.

Infiltration of Florida’s hot and humid outside air can have a big impact on energy use, building durability, and occupant health. The continuous air barrier, placed toward the outside of the building envelope, reduces this infiltration. Indoor air quality concerns were addressed by installing an energy recovery ventilator to introduce outside air.

The air barrier consists of a tightly taped housewrap installed over the exterior sheathing on all above-grade frame walls, and extruded polyurethane foam boards glued to the interior of the below-grade block walls. Expanding foam insulation provided an extra measure of airtightness at all above-grade exterior surfaces including the roof deck. Special care was taken to seal wall details such as corners, floor interfaces, and the roof junction. Blower door performance tests verified the home’s level of airtightness (ACH50 = 2.0).

Equipment Features:

2-Speed, Zoned Heat Pump

The building envelope design features described above greatly reduced the required air conditioner size. Manual-J HVAC equipment-sizing calculations showed the need for only 2½ tons of heating and cooling capacity. In this case the owner opted for a two-speed compressor, which provides either 2½ or 5 tons of cooling or heating depending on the need.

The Hoak home air conditioning unit typically operated in the 2½-ton mode until the late afternoon when it switched to the 5-ton mode for a few brief periods. In this home, energy use stays low because the low compressor speed operates the majority of the time. But, when quick cool-down or excessive loads require more capacity, the high speed compressor can meet the need.

Measured data indicated that the 5-ton mode operated about one in every four days during the three hottest summer months (June to August), usually for periods of 15 minutes or less. Even these short periods of high-speed compressor operation might have been avoided with proper use of a programmable thermostat. These results verify the Manual J sizing calculations and indicate that if a single speed HVAC system were installed, the optimum size would be 2½ to 3 tons.

Variable-speed Air Handler

Two benefits of using a variable-speed motor for air distribution are better moisture removal and energy efficiency. During the cooling season, slower airflow across a cold coil allows for more moisture removal. Wintertime comfort also is enhanced with this operation, since the coil has more time to warm before the air is brought to full flow.

Indoor relative humidity tends to increase during the fall and winter months when air conditioning activity declines. Without a dedicated dehumidifier, the air conditioner is the only means of reducing indoor relative humidity. When there is a call for cooling - the low-speed compressor in a variable speed system operates more consistently than a larger system and keeps relative humidity from rising to unhealthy levels.

Heat Pump Water Heater

Solar water heating would have been the first choice for this home, but poor orientation and too many shade trees forced a search for other options. (Figure 59) Natural gas also was unavailable in the area. To avoid the inefficiency of electric resistance water heating, a 6,000 BTU/hour heat pump water heater ( Figure 61 ). Heat pump water heater produced all the hot water needs for a four-person household from April to September .

The water heater was connected to a standard 80-gallon electric water heater. By locating the heat pump inside the home, homeowners gained a summertime benefit of additional cooling and year ‘round dehumidification because the system removes moisture each time it operates.

Energy Recovery Ventilator

The energy recovery ventilator acts as a conduit to flush out stale indoor air and replace it with outdoor air. As the indoor air is expelled, a heat exchanger recovers up to 80% of the energy used to heat or cool the air and transfers it to the incoming air stream. This unit also transfers a portion of the moisture between the airstreams, which is useful during periods of high outdoor humidity.

Airtight Ducts

Attic and duct heat gain contribute to about 22% of the cooling needs of a typical Central Florida home when are ducts located in a vented attic above the insulation. While some home efficiency is lost by direct heat-gain through the duct insulation, a great deal more efficiency can be lost from unintended duct leakage from the ductwork into the vented attic. Duct leakage test results showed only 50 CFM of air was lost at 25 Pa of pressure differential in the Hoak residence. This leakage equates to 1.2% leakage per square foot of conditioned floor area - far below the leakage normally found in new Florida homes.

Energy Monitoring:

Monitors on the Hoak residence include 11 attic temperature and relative humidity sensors, three indoor sensors, a Hobo event logger to record the dehumidifier cycling time, and a tipping bucket rain gauge with Hobo logger to monitor the combined condensate of the air conditioner, dehumidifier, and heat pump water heater. In 2002, Alten Design also assembled a new logger monitoring computer with the capability of reading data from two Campbell 21X loggers. This computer was configured with remote monitoring and control capacity so that Partners can program and maintain the system without traveling to the site.

Findings

Duct Leakage

Duct leakage test results showed the Hoak home air loss was only 50 CFM at 25 Pa or 1.2% leakage per square foot of conditioned floor area – far below the amount of leakage normally found in new Florida homes.

Total duct leakage is less than 10% of air handler flow (200 CFM). Blower door performance tests verified the home’s level of airtightness at two air changes per hour at 50 Pa (ACH50 = 2.0). When including leakage around the supply grills, house leakage increased about 30%. Slightly more than half of the house leakage (1479 CFM at 50 Pa) is located in the sealed attic space (760 CFM at 50 Pa).

Cooling Energy

Initial data comparisons were made against data collected from a Lakeland, Florida residence (PVRes), designed by FSEC and monitored for more than a year. The PVRes home contained the most energy-efficient provisions researchers could devise, including a 5 kW photovoltaic system. Data collected at the Hoak home shows the cooling energy is nearly on par with the PVRes Home on a per square foot basis.

Envelope

Weekly data logs of the Hoak home provided by Alten Design from the 14 Hobo temperature and relative humidity sensors and pressure tests through March 2003, confirm that air pathways between the unvented attic and outdoors still exist. Researchers suspect that these pathways may be the primary source of moisture intrusion into the unvented attic space. Several whole house pressure tests (smoke tests) were performed by Alten Design and FSEC to isolate these external sources of air infiltration. Identified leaks were sealed, though actions have shown some benefit moisture levels are still higher than desired.

In order to isolate areas of leakage, barriers will be placed in the house splitting the areas under test into easier to monitor individual zones.