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BAIHP Partnership with
Eastern Dakota Housing Alliance
Hillsboro, ND

The Eastern Dakota Housing Alliance plans to build 20 multi-family and single-family dwellings on Selkirk Circle in Grand Forks, North Dakota. Twelve homes have been completed to date and four more are currently under construction.

Four Phase I units completed in March of 2003 had HERS ratings between 88 and 90 with whole-house savings of 25 to 30% against the Building America benchmark. Four Phase II units completed in January 2004 had HERS of about 92.5 and whole-house savings of 40%. The Phase II efficiency boost comes from the addition of a whole-house tankless gas water heater and R10 sheathing on exterior walls. Lower HERS scores (88.3 – 89.5) on the Phase III units was primarily due to electric resistance water heating and higher overall duct and envelope leakage. All units have ventilation air brought to the air handler return plenum with 10 of 12 units utilizing heat recovery ventilators (HRVs).

image
Two completed Phase III units (Dec 2004)

Phase III Testing

A new floor plan was used on the Phase III homes featuring a split level design instead of a full, below grade basement and attached rather than detached garages. Another major difference between these units and previous designs was the location of the air handler in a utility room that opens into the garage. As with previously tested homes, total leakage was very high and concentrated mostly on the return side where duct pathways were partially constructed from building cavity spaces. Duct leakage to out, which was nearly zero in previously tested homes, was substantially higher in the Phase III units. Duct tester results showed that the ratio of duct leakage to out (at 25 Pascals) to conditioned floor area (or Qn) ranged from 0.05 to 0.09. As with previous phases, all Phase III units had high efficiency, sealed combustion gas furnaces.

Selkirk Split-level Twin Home Specifications – Phase III
Conditioned Area 1850 sq. ft. (including basement)
Above-grade Walls Wood Frame (R15+R10 sheath)
Sub-grade Basement Walls R22 Insulated Concrete Forms
Ventilated Attic R-49
IG Vinyl Windows U-0.34, SHGC-0.33
Sealed Combust. Gas Furnace 60kBtu, AFUE-92.6
Strait-cool AC 2-ton, 10 SEER
50 Gal Electric Water Heater EF 0.86
Thermostat Programmable
Lighting 85% Fluorescent
Ventilation 70% HRV

Each Phase III unit was tested individually for envelope tightness. Leakage was higher overall compared to Phases I and II, but this was expected due to the greater exterior surface area created by the attached garage design.

HERS Scores and Envelope Leakage Test Results
Unit
HERS
CFM50
ACH50
ACH
C
n
R
1002
89.5
779
3.12
0.11
22.7
0.90
0.98
1010
88.3
970
3.85
0.32
100.4
0.58
0.97
1018
89.0
999
4.00
0.24
64.2
0.70
0.99
1026
89.1
783
3.14
0.16
38.9
0.77
0.99
Notes: - ACH50 calculation includes area of conditioned basement

Discussion on Next Set of Homes

Four Phase IV homes are currently under construction utilizing the same floor plan and envelope design as Phase III. Plans include the use of high efficiency gas water heaters (probably tankless) and a central return duct system designed to reduce duct leakage (both total and to out). Return air relief for bedrooms will be incorporated into hallway walls with either a high-low grill system or pass-through grills with sound and light baffles. Plans also include relocating air handlers within the conditioned space instead of in a room attached to the garage. This should substantially reduce duct leakage to out.

Recommendations include:

  • Central return located near thermostat in center of home
  • Sealed ductwork from central return to air handler
  • Avoid use of building cavities as air pathways
image
East side of Selkirk Circle, Phases III & IV

Building Science Issues:

  • Combining space heating and hot water with a central gas boiler. Since air conditioning is still a requirement, an air handler with an hydronic heating coil will be required.
  • If only 2 of 4 units are fitted with a combined system it offers the opportunity to compare the efficiency of this system over another unit with separate space and water heating through monitoring.
  • David Duly of Pilkington glass has offered to work with FSEC to determine the benefit of high solar gain glass which could provide substantial savings on space heating. Window orientation and shading are important factors that may work favorably with the remaining south-facing home sites on Selkirk Circle.
BAIHP will be conducting Building America benchmarking analysis of these homes and producing Energy Star ratings of the four Phase III homes as well as the Phase IV units upon completion in spring/summer of 2005.

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