• Eastern Dakota Housing Alliance (EDHA), Applegren Construction

Figure 62 Selkirk Twin Homes, Grand Forks, ND.

Eight dwellings have been built by EDHA on Selkirk Circle in Grand Forks, North Dakota (Figure 62) with the goal of achieving up to 50% energy savings over the 1993 Model Energy Code.

The two story dwellings 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 34.

Phase I (March 2003) and Phase II (Feb 2004) included two twin homes (duplexes) each. These and a theoretical base case house using local conventional construction and code minimums were 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.

Moisture Issues

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 enter the cavity. One 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.

Ventilation

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%. 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 25CFM. 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.

Cost Analysis

One row in Tables 35 and 36 shows the cumulative effect of all measures added to the base case home. Estimated saving in this row includes the cumulative effect of all measures incorporated together in the DOE2 simulation. The heat recovery ventilator (HRV) is broken out from the other measures to provide a meaningful simple payback and first year cash flow figures for the other cumulative measures. The HRV is considered an essential component for the indoor air quality of these homes, but comparing it to a base case home without ventilation means no relative savings are attained; thus this measure is added in a separate row. 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.

The increased utility savings of Phase II over Phase I arise from two energy saving measures unique for this area: Extruded Polystyrene (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.

Annual Energy Use

A performance comparison of the base case and improved structures is shown in Table 37. The increased heating design load in Phases I and II over the base case is caused by the addition of 75 CFM of ventilation introduced on a 20 minutes ON, 40 minutes OFF cycle, which the base case does not have. The DOE2 model predicts the need for very little cooling, however many new homes in this area are being built with central air conditioning.

Four more dwellings (two duplexes) are slated for completion in the summer of 2004. For more information on this project, see Cold Climate Case Study: High Efficiency North Dakota Twin Homes on www.baihp.org.

• Zero Energy Affordable Housing, ORNL and Loudon County Habitat for Humanity

Figure 63 Local sponsors in front of 2nd ZEH built by Loudon County HFH in partnership with ORNL. FSEC provided monitoring for the 1st and 4th ZEHs.

In partnership with Oak Ridge, BAIHP prepared to instrument a zero energy home (ZEH) built by Loudon County (TN) HFH - their fourth (Figure 63). See description in the Technical Assistance section of this report under Habitat for Humanity, Tennessee, Loudon County.

Data is available on-line at www.infomonitors.com . A paper on the study was submitted to the Buildings IX conference by Jeff Christian (ORNL) and David Beal (BAIHP-FSEC).