PATH - A Public Private Partnership for Advancing Housing Technology

Tucson, Arizona

Field Evaluation and Demonstration Site: Armory Park del Sol; John Wesley Miller Companies with Tucson Electric Power and Global Solar, Inc.

Project Profile and Results

Interim Report (PDF) April 2004

Armory Park del Sol was created as a sustainable community in the historic Armory Park portion of the inner city of Tucson. Former Mayor George Miller and the City Council endorsed the project, as it met many of their goals to foster a livable inner city.

Using what was a vacant, unused and unattractive lot, Armory Park del Sol, when completed will consist of 99 single-family homes. As of August 1, 2002, thirteen homes had been completed and one was under the final stages of construction. These homes are incorporating many innovative technologies identified by the NAHB Research Center through the PATH program as having the potential to help achieve PATH goals of affordability, durability, and energy efficiency.

The project is incorporating sustainable high-density urban infill development techniques in an effort to preserve open spaces. The community features extensive walkways to encourage pedestrian traffic and reduce the negative effect of vehicle emissions on the environment.

In partnership with the local utility, Tucson Electric Power, homes are being constructed with stringent air infiltration, duct loss, and insulation level requirements. Based on these features as well as the use of active solar technologies, electric utility rates are being discounted over base rates of standard constructed homes, lowering monthly utility bills.

As a significant commitment to environmental sensitivity, all houses are incorporating renewable solar energy technologies to provide electricity and hot water. Armory Park del Sol will play a major role in the Federal Million Solar Roofs Initiative. Homes are also being equipped with the latest water saving technologies. When combined with the use of native vegetation in landscaping, water consumption will be substantially reduced.

Homes are being constructed to strict energy efficiency standards. Energy efficient equipment is being installed, and air balancing performed to provide efficient equipment performance and occupant comfort. Homes are designed using thermal mass walls with exterior insulation, high levels of ceiling insulation, ducts inside conditioned space, and windows that minimize heat loss and gain. Consumption of non-renewable energy is reduced by use of photovoltaic (PV) panels which produce electricity, and solar water heaters. These technologies will reduce costs and reduce the environmental impact of the home.

A monitoring program has been developed to verify these savings and to evaluate performance of the systems. The primary end uses of energy in the home are also being evaluated, including absolute consumption levels; based on square footage, degree-days, and indoor-outdoor temperature differences. System and appliance energy use of particular interest are annual, monthly and hourly:

This data will be used to analyze energy performance, and lend confidence to construction, weather sealing, glazing, equipment, and operation details of the new homes, as compared with other recently constructed homes. Detailed energy data will provide verification of the performance of the construction materials and methods compared with current construction practices. Data may also be used to validate and correct simulation models. In turn, simulation models can be used to provide new construction details to enhance the energy performance of future homes in the demonstration site.

Non-energy related issues, as well as the direct dollar-value of the energy produced from the renewable energy system, often influence the use of such systems in a particular home. The evaluation of the renewable energy systems will cover a number of perspectives related to the systems, including issues of:

Evaluation of the renewable energy systems includes a comparison of energy produced to energy purchased, time-of-day, and in conjunction with the load served. In the case of solar hot water production, for example, energy produced by the hot water system will be evaluated in terms of hot water load to the house, time-of-use of the hot water load, back-up energy used to heat water, and other variables.

With the help of the National Renewable Energy Laboratory (NREL) and support from DOE's Building America Program, the PV and solar hot water systems will be evaluated for overall system efficiency and collector efficiency. Detailed data for the renewable energy systems will provide confidence in the use of the equipment, as well as a clear understanding of the performance of the systems as installed, rather than as simulated. However, the detailed measured results can be used to support models that accurately reflect the performance of systems, as designed and as operated under assumed conditions.

Energy data provided through monitoring of the renewable energy systems will be critical in understanding the time-of-use energy production and cost issues for the case of the PV and solar hot water systems. In areas where the solar energy contribution is significant on a daily basis, system designs may incorporate back-up energy controls that are sensitive to the cost of energy as well as the time of demand. For the PV systems, the value of the output significantly affects the cost-benefit ratio, since PV systems have a high initial investment.

Two houses at Armory Park del Sol were being monitored as of August 1, 2002. Data has been collected for one of these homes, a 961 sq. ft., single level house, since late November, 2001. Whole house energy consumption, as well as the consumption of some easily identifiable loads, such as the heat pump, clothes dryer, refrigerator, and exterior flood lights, is being analyzed, as is the output of the PV system. Indoor space temperatures are also being collected for analysis of the heating and cooling energy consumption.

Data for the second monitored home, an 1100 sq. ft. single level house, has been collected since late June, 2002, when the home was first occupied. Much more detailed information is being collected at this site, including indoor air temperatures at various locations and heights, exterior wall heat flux on the north and south sides of the home, and slab floor heat flux, and temperatures in several locations. Additionally, detailed testing of the solar hot water system is being performed, and its energy consumption is being compared to that of a standard electric tank water heater, also installed in the home. Monitoring of whole house and easily identifiable loads' energy consumption, as well as of the PV system electrical generation is also being performed, similar to the 961 sq. ft. home.

See the project profile for construction photos and status.

Content updated on 9/13/2006

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