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Armory Park Del Sol:  Energy Analysis Heating and Cooling Energy

The homes at Armory Park del Sol are designed to satisfy the requirements of the Tucson Sustainable Energy Code (SES). These voluntary requirements are intended to reduce the heating, cooling and water heating energy of the building by 50% from that which would be used if the building were constructed under the Model Energy Code (MEC) or the International Energy Conservation Code (IECC). Other applicable requirements include:

  • Maximum air leakage of 0.35 ACH,
  • Specifications for glazing shading coefficients,
  • Equipment efficiency of 12 SEER for air-conditioning and 7 HSPF for heat pumps,
  • Mastic seal on all ducts and measured leakage rate not to exceed 33 CFM at 25 pascals, and
  • Requirements for water heating systems and equipment

Using the design of the first model home constructed at Armory Park del Sol, an energy analysis shows compliance with the Tucson SES. The following building features are included:

  • Raised-heel trusses and R-38 insulation,
  • Masonry construction with R-12 insulation attached to the exterior,
  • Window U-values of 0.32,
  • Slab edge insulation to full depth of slab, and
  • Minimum equipment efficiencies of 12 SEER and 7.5 HSPF.

With these construction specifications, the basic MEC energy analysis results are shown in Table 1:

Table 1 - Energy Code Comparison

Energy Code1,2

Minimum UA3 Requirement

UA of the Building Design

Tucson Sustainable Energy Code

251

245

1995 MEC

483

246

2000 IECC

483

246

1 Use of software analysis based on SEScheck Ver 1.0 and MECcheck Ver. 3.0.

2 The minimum required UA is modified by the equipment efficiency for each code analysis.

3 UA is the overall component heat loss (U-value) weighted for the area of the particular component such as a wall or ceiling

The house design meets the energy code requirements for the SES based on the equipment efficiency and substantially exceeds the MEC requirements for Tucson. In addition, all of the homes will utilize solar energy systems for both hot water and electrical production. These systems will further reduce the overall energy consumption of the homes.

A detailed energy analysis was also performed on the designed home to provide a more accurate estimate of energy consumption. This energy consumption estimate can be compared with a baseline home to estimate energy savings over "typical" construction practices and to include the use of renewable energy features. This analysis was performed on hourly data and takes advantage of such issues as building orientation, thermal mass, and internal gains.

The base house is assumed to have the same orientation, number and size of windows, foundation construction and roof style. However, the major construction features are based on "typical" practices for the area. In addition, the base house is deemed compliant with current MEC requirements, based on a MECcheck analysis. Table 2 compares the various construction and other features related to the base house and the "as built" home designs at Armory Park del Sol.

Table 2 - Base and As-Built House Construction Features

Construction Feature

Base House

Armory Park Del Sol

Floor Area (square feet)

800

800

Volume (cubic feet)

7600

7600

Wall

Frame 2x4 with R-13

Solid Grout CMU with R-12 exterior foam insulation

Roof

Attic, Truss

Attic, Raised Heel Truss

Window Type

Double Pane, Aluminum Frame

Double Pane, Low-e, Vinyl, with Argon

Slab

No slab insulation

Insulation extends to full slab depth

Infiltration

0.4 ACH, estimated

0.35 ACH estimated

Ducts

3% leakage, 4% conduction loss to outdoors

All ducts in conditioned space

HVAC Equipment*

7.0 HSPF, 10 SEER

7.5 HSPF, 12 SEER

Setpoints

68/Heating, 75/Cooling

68/Heating, 75/Cooling

Added Mass Materials

None

6" of concrete in the slab

2000 IECC Compliance

UA = 346 (maximum, 357 allowed)

UA = 246 (maximum 483 allowed)

* Actual equipment ratings are used in the detailed simulation program.

The detailed energy simulation program is an hourly simulation of the building performance. The simulation takes into account the orientation of the building, the glazing solar heat gain coefficient, and the thermal mass capability of the wall system and any added mass materials. The hourly weather data for the particular location is used as the input into the model and is based on a thirty-year average. The heating and cooling energy use is described in Table 3.

Table 3 - Detailed Energy Simulation Results

 

Base Wood-Frame House

Armory Park Del Sol

Heating Energy (kWh)

1556

959

Cooling Energy (kWh)

3916

2051

Blower Energy (kWh)

527

314

Energy Use Heating

2.13 kWh/square foot

1.32 kWh/square foot

Energy Use Cooling

5.37 kWh/square foot

2.83 kWh/square foot

The Armory Park Del Sol homes are estimated to use 45% less heating and cooling energy than its base house counterpart. The base house is the same floor area but constructed with different wall and roof insulation materials and details. Differences in infiltration estimates are made based on typical practices. Standard loss estimates are applied to the duct system based on duct location.

 

 

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