Disclaimer: This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government, nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agencies thereof.
II. BAIHP Technical Assistance - A
America Homes of Gainesville
All America Homes has been in business for 17 years and builds 10 homes each year in the Gainesville (FL) area. After providing design assistance for the award wining 2002 home (Figure 4) during the 4th budget period, BAIHP provided additional assistance to All America for a second home with solar and energy efficiency concepts during the 5th budget period. The home was built with a photovoltaic (PV) system, and achieved a HERS ‘99 rating of 90.6. This home serves as a model for the hot-humid climate using a combination of on-site power generation and energy efficiency to reach near-zero utility demand, similar to the home built in 2002 (Table 3).
It incorporates energy efficient air conditioning, hydronic solar water heating, excellent air distribution design and construction (pressure tested for validation) and right sizing of the heating and cooling capacity. It also incorporates envelope improvements in the roof, ceiling, walls, windows and infiltration control. A passive fresh sir ventilation system provides filtered outside air to the return side of the mechanical system during operation.
Table 3. All America Homes of Gainesville (FL) Specifications
Florida Home Energy Rating Organization (Florida H.E.R.O.) provided an engineered duct system for 26 models in the Regents Park Townhouse development. This downtown urban infill project will result in 54 units with Building America features including ductwork in the conditioned space, outside air ventilation, and combo hydronic heat and 13 SEER cooling. Each of the 54 units will be individually performance tested. Three completed units were tested, each scoring well over a HERS ‘99 score 89.
Applegren Construction, Eastern
Dakota Housing Alliance (EDHA)
EDHA set a goal of achieving up to 50% energy savings over the 1993 Model Energy Code with superior indoor air quality (AIQ). Phase I (March 2003) and Phase II (Feb 2004) each included two twin homes (duplexes) for a total of eight homes.
The two story dwellings (Figure 5) include an insulated basement with air circulation to the main house, suitable for conversion to living space. Features of the Phase I and Phase II homes are summarized in Table 4 which also shows a theoretical base case house using local conventional construction and code minimums modeled in DOE2 to determine energy savings and cost effectiveness. Estimated combined gas and electric utility savings ranged from 25% on Phase I homes to 35% on Phase II homes over the base case. The homes also met the BA goal of 40% savings compared to the Benchmark house.
Annual Energy Use
A performance comparison of the base case and improved structures is shown in Table 5. The DOE2 model predicts the need for very little cooling, however many new homes in this area, including these, are being built with central air conditioning.
Phase II of construction added a layer of R-10 rigid extruded polystyrene (XPS) to the exterior side of the wall assembly. The low water vapor permeance of rigid XPS foam sheathing (1.1 perms) presents a dilemma in this climate where an interior vapor barrier (usually 6-mil polyethylene) is considered mandatory to minimize moisture diffusion from the conditioned space into the wall cavity. The installation of two vapor barriers leaves the wall vulnerable to moisture accumulation should water unintentionally enters the cavity. One BAIHP recommendation calls for removing the interior vapor barrier and relying on two coats of latex paint on the interior to limit diffusion from the conditioned space into the wall. This option allows the wall to dry to some extent in both directions, but was not chosen by the builder.
A heat recovery ventilator (HRV) mounted in the basement provides controlled mechanical ventilation with an energy penalty estimated at $45/year. The unit contains an 80-watt fan that introduces 75 CFM of outside air while exhausting a similar amount at a heat transfer efficiency of 70%. The HRV can operate either continuously or on an intermittent 20 minutes on, 40 minutes off cycle. Intermittent operation was simulated to meet the old guideline. Attempting to meet the new ASHRAE 62.2 standard (ASHRAE 1999) would require 42 CFM of continuous ventilation. For these simulations however, the old ASHRAE guideline of 0.35ACH was used, calling for a continuous rate of 25 CFM.
Table 4. Applegren Twin Home Specifications
Tables 5 (Phase I) and 6 (Phase 2) show the cumulative effect of All Measures in comparison to the base case home. The heat recovery ventilator (HRV) is also shown separate from the other measures because the HRV is an essential IAQ feature, yet it increases energy use by $45/year. With the exception of the HRV all measures show a positive cash flow on a 6%, 30 year fixed rate mortgage beginning in the first year.
Table 5. Economic Assessment of Phase I Measures*,**
The higher savings of Phase II over Phase I arise from two energy saving measures unusual for this region: XPS foam sheathing with 2x4 framing and tankless gas water heating. Simple paybacks for these measures were 8.3 and 13.3 years respectively. Electric water heaters are the current norm in the Grand Forks area, but with electricity 26% below the national average and natural gas prices on the rise, simple payback on the tankless model was relatively long. In addition, fluctuating natural gas prices complicate the economic analysis. Initial concerns of how the tankless water heater would perform in this extreme climate were met with positive feedback through the first winter, which was colder than normal including an all-time record low of -44ºF set at the Grand Forks International Airport on January 30, 2004.
Table 6. Economic Assessment of Phase II
Phases III and IV Selkirk Homes
Table 7. Completed Selkirk Homes
In 2005 and 2006, BAIHP provided technical assistance this partner for Phases III, IV, and V (Table 7, Completed Selkirk Homes). Lower HERS ‘99 scores (88.3 – 89.5) on the Phase III units was primarily due to electric resistance water heating (instead of tankless gas) and higher overall duct and envelope leakage. All of the 16 dwellings have outside air brought to the air handler return plenum with 14 of 16 units utilizing heat recovery ventilators (HRVs). Other specifications are outlined in Table 8.
Table 8. Selkirk Split-level Twin Home Specifications – Phase IV
Phase IV floor plans were nearly identical to that used in Phase III featuring a split level design and attached garage instead of the below grade basements and detached garages used in Phases I and II. (Figure 6)
Significant improvements in duct leakage to the outside were seen in Phase IV over Phase III. The improvements resulted from moving the air handler from an enclosed closet in the garage to the basement and using a central return instead of distributed returns which were found to be very leaky with QnOUT measurements of 0.05-0.09 compared to the improved QnOUT measurements in Phase IV of 0.01 to 0.03.
As with previously tested homes, total leakage was still very high and concentrated mostly on the return side where duct pathways were partially constructed by enclosing building cavities. Pressure measurements revealed that with interior doors closed, bedrooms pressures were around +1.0 Pascal, well within the acceptable range. Only the larger bedroom was fitted with a high/low return area pathway.
Each Phase IV unit was tested individually for envelope tightness. Leakage was noticeably higher with an average ACH50 of 4.3, versus the 3.5 seen in the similar Phase III design. No attempt was made to determine leakage through the shared wall of the adjoining unit but this should be similar to the test results on Phase II which found 50CFM of inter-unit leakage.
Table 9. HERS ‘99 Scores and Test Results for Selkirk Phase IV
Improved HERS ‘99 scores in Phase IV can be attributed to reduced duct leakage and switching from electric resistance water heating back to tankless gas units.
Phase V Selkirk Homes
The final phase of Selkirk will consist of six single-level, duplex homes with basement and attached garage, bringing the total build-out to 22 units. Based on past construction practices and equipment efficiencies, this home design should attain a HERS ‘99 score of at least 90 assuming an electric resistance water heater and 92.5 with a tankless gas water heater. Discussions for improving efficiency on these final units even further have centered on the use of a combined space and water heating boiler which may boost the HERS ‘99 score beyond 93. Favorable solar orientation for these homes may allow the use of high solar gain windows to further reduce heating loads.
Other ideas discussed:
Atlantic Design and Construction
Atlantic Design (AD) and Construction’s Mentone Subdivision in Gainesville, FL: 340 homes built out fully in 2006. AD was the winner of the 2001 US Environmental Protection Agency’s (EPA) Energy Star Small Builder of the Year and has achieved their current level of performance through an incremental process of improvements over several years. AD is a small, privately held residential construction company located in Gainesville, FL. Founded in 1985, the firm now directly employs 15 full-time employees and sells about 50 - 60 homes a year. See Figure 7 for a typical home. Like any business, AD is interested in both short-term and long-term profitability.
Figure 7. Atlantic Design and Construction home in the Mentone neighborhood.
While having developed a reputation for building high “quality” homes, the only aspects of their homes which were greater than minimum code requirements was the use of double pane glass and R-30 attic insulation (see Table 10). New materials and systems have been adopted over time. Two factors lead the builder to implement quality control/energy cost changes. First, the builder genuinely had the desire to do the right thing and wanted to provide his clients with a quality home. If the quality of that product could be quantified – all the better. Second, AD had just shifted from a custom homebuilding company to a production company with this subdivision. Though they were already exceeding the minimum Florida Energy code required, they were still flexible enough in these early stages to consider practice changes if those changes could be streamlined/standardized to minimize disruption to the production schedule. Any changes to the production procedures or standard features, however, would need to be backed with proof of their efficacy.
Table 10. Atlantic Design and Construction Specifications
At this point, AD was interested in determining what features would need to be added and procedural changes that would need to be made to market their product as Energy Star. To make that determination, Florida Home Energy and Resources Organization (FL H.E.RO.) performed a room-by-room Air Conditioning Contractors Association (ACCA) Manual J load calculation from building plans for a model/Parade home about to begin construction. Results found that right-sizing equipment and developing and implementing strict procedural insulation and mechanical system specifications allowed the mechanical system to be reduced by a full ton. Increasing the air conditioner seasonal energy efficiency ratio (SEER) from 10 to 12 resulted in the home meeting the minimum level required for Energy Star home certification (Home Energy Rating System score of 86 or greater). Savings derived from decreasing the cooling system capacity more than offset the additional $250 - $375 needed for improved duct sealing and insulation and air sealing protocol adjustments. This savings, while sufficient to offset the costs associated with improved sealing methods, was NOT enough to pay for all implemented measures. Increasing the price of the home by $1,250 - $2,500 was sufficient to cover all additional costs AND derive an excellent profit margin. In order to ensure consistent pricing and profit, part of the builder’s job was to bid the criteria for insulation and mechanical specifications among multiple subcontractors. FL H.E.R.O. followed up with the contractors during duct rough-in to educate workers on the specifications and ensure quality installation.
Energy Star®. The builder decided to include “Energy Star” on the homebuyer’s option checklist. If this option was selected, the builder agreed to upgrade the cooling system efficiency to SEER 12, install an electronic programmable thermostat, install sealed and verified ductwork and increase wall insulation to R-13. As one of a list of options, sales of the Energy Star option were not brisk initially. After an analysis of the options program, FL H.E.R.O pointed out to AD that the Energy Star option was the most profitable option on their list, based on the percentage mark-up. As a result, marketing of Energy Star became more aggressive and included sales force training on selling the program. Buyers who didn’t select Energy Star during the closing process were contacted directly by the Project Superintendent. His goal was to explain the value of including energy efficiency, the loss of revenue from not selecting it, and to allow buyers a second chance to include the option. A study commissioned by the EPA and conducted by the University of Florida (UF) verified the energy savings from implemented improvements. By comparing the actual electricity and gas usage from utility billing information, and comparing this to similarly sized and aged code minimum homes, UF determined that the energy efficient homes built by AD resulted in an average annual energy savings of 12.7 Mbtu (savings ranged from 8.4 Mbtu minimum to 17.5 Mbtu maximum). Using this study’s data to proportion approximately 50% of the energy use as electric, and approximately 50% of the energy use as gas, and applying current Gainesville Regional Utilities rates results in an average monthly savings of $23 and a maximum monthly energy cost savings of approximately $30. Finally, AD’s President negotiated a deal with the preferred lender’s mortgage broker that resulted in a 1/8th point discount of the prevailing rates for every home that was designated Energy Star. This allowed the sales representatives an opportunity to demonstrate how much it would COST the buyer NOT to select the Energy Star option! After more than 120 buyers in a row selected this option, it became a standard feature for the builder.
The value of an Energy Star home in the Gainesville, FL market can now also be communicated to buyers in terms of increased resale value. An appraisal obtained on an AD Energy Star home showed a $4,000 increase in appraised value over a similar home in the same area that did not contain the energy efficient features (http://www.natresnet.org/ratings/). Also, the local area Multiple Listing Service (MLS) service has become the first in the nation to include information regarding a home’s status with regard to Energy Star on all listings.
Building America. With Energy Star so ingrained in the AD production process, FL H.E.R.O. worked to ratchet-up the builder’s home parameters by introducing him to Building America (BA) concepts. Having been exposed already to a systems engineering approach, the builder was primed to consider additional ways they could enhance their homes and their marketability. BA opened new avenues for them to increase energy efficiency, durability and enhance indoor air quality. Shifting their minimum standard upward to include a 13-SEER air-conditioning system, 0.90+ annual fuel utilization efficiency (AFUE) heating system and low emissivity (low-E) spectrally selective glass, the builder also embraced positive home pressurization principles through the introduction of filtered outside air to the return side of the plenum. The new upgrades resulted in this production builder’s homes achieving an average Home Energy Rating System (HERS ‘99) score of 89.
Location. Location. Location. Blueprints called for garage air handler (AH) installations in AD’s standard home. In a hot and humid climate, this architectural design element alone can cause all sorts of problems for the homeowner. In moisture laden climates, ambient conditions in a garage can accelerate rusting in the ferrous heat exchanger and increase evaporator coil sweating, both of which reduce the life expectancy of the heating and cooling system. Any air leakage especially at the blower fan, the point of greatest pressure differential, can introduce the home to moisture, outdoor irritants, automobile exhaust and toxic fumes from the substances most people store in their garage. Insufficient insulation of the AH and leaks on the supply side also lead to moisture condensation on the equipment and its associated ductwork. On the return side of the system, ductwork holes bypass all filters and create a pathway for hot moist air and/or pollen laden outside air to enter the home.
An on-site demonstration with a simple smoke stick, made invisible airflows visible and clinched this builder’s interest. Armed with a clearer understanding of the ramifications of locating the AH in the garage, the builder was convinced of the value of an indoor installation. Initial design modifications forced the mechanical contractor to work in a closeted space that was simply not large enough to allow a good installation. The addition of a duct board plenum adjacent to the furnace from an extended return, made sealing the system almost impossible. Code also required the provision of high and low combustion air to a furnace located within the thermal envelope of a home. Supply of this combustion air put the closet into communication with the attic and resulted in the movement of attic air to the living space via leaks in the duct system.
After multiple approaches were tried, an acceptable method was developed using a .90+ AFUE sealed combustion gas furnace. The sealed system eliminated the need for combustion air from the attic and allowed the equipment room to be completely sealed from the garage and the attic. Supply and return plenums were stubbed-out in the mechanical closet during rough in, and duct, plenum and refrigerant lines were sealed to the sheetrock with an expandable foam at all seams and penetrations. During equipment set, the supply side plenum was first affixed, and then completely sealed with mastic and pressure sensitive tape. A metal tap installed in the return air plenum at ceiling height, was attached to an insulated flex duct, which was connected to a second tap on the furnace side. All duct connects are made with mastic and fiberglass mesh. An insulated exterior door for the mechanical closet with appropriate weather-stripping and threshold sealing completed the installation. Realizing that this approach would increase profits by increasing the home’s conditioned square footage and provide clients with a safer and more energy efficient home, AH location changes were made to all model blueprints.
Indoor air quality. Though indoor air quality was a subject not yet broached, demonstrating the principles of air movement into a tightly constructed home was an educational experience for the superintendent. It quickly became clear to him that controlling how and where outside air was introduced into the home could make a big difference in the indoor air quality (IAQ). In many new homes it is common to have some amount of supply duct leakage resulting in the home being negatively pressurized because the ductwork is commonly located outside the home’s air and thermal boundaries. In a negatively pressurized home, outside air is introduced in an uncontrolled fashion through inadvertent gaps around windows, doors or top and bottom wall plates. Installing a simple, low cost, non-mechanical fresh air system helps restrict the uncontrolled entry of hot, humid, pollen-laden air into a home and its interstitial areas. Filtering the outside air and directing it through the home’s air conditioning system prior to entry ensures mitigation of the outside air’s hot, humid, and pollen-laden characteristics. Including this fresh air system not only made AD’s home more efficient, but more importantly it improved IAQ. This fresh air system now is a standard feature in all of the homes they build.
Broadway, R. and M. Mullens (2004). “Shop Floor Information Systems for Industrialized Housing Production,” Industrial Engineering Research ’04 Conference Proceedings, Houston, May, 2004.
In the summer of 2003, Avis American Homes tested an alpha prototype Status and Control System (STACS) developed by the UCF Constructability Lab researchers (BAIHP Partner). The system is a real-time shop floor labor data collection and reporting system. Production workers use wireless laser scanners to report their current work assignment. STACS reporting is web based and provides both real time manufacturing status and summaries of historical production performance (Figure 8). While labor represents a relatively modest fraction of production cost, typically 10-15%, it has a profound impact on operations, including product quality, cycle time, material waste, and labor productivity.
Avis American employees tested STACS in drywall finishing operations. Test results demonstrated that production workers could operate the system effectively and that the system accurately captured scanned activity.
See also Penn Lyon Homes (Technical Assistance section) and Status and Control System (STACS) (Research Section III).