Legacy Square is a 91 Unit, affordable, multi-family housing project currently under construction, located in Santa Ana, California.
The Project: Legacy Square is a 91 Unit, affordable, multi-family housing project currently under construction, located in Santa Ana, California. The project is funded, in large part, by the Affordable Housing, Sustainable Communities (AHSC) Program, which receives proceeds from State of California's Cap and Trade program, which mandates high performance and deep energy efficiency. The project is "all-electric", utilizes heat pump hot water heaters (one per unit) and will have a rooftop photovoltaic system that will offset approximately 40% of the building's energy loads. Right-sizing HVAC systems at residential unit level is critically important to reducing the building energy load, reducing the amount of renewable energy needed to hit the project's funding goals. This is very important for a project where the architectural style and roof forms are dictated by local standards.
Refining the Conceptual Energy Model for HVAC Analysis: In a previous IESVE Case Study (see the Iris at San Ysidro), National CORE's (NCORE's) approach to conceptual energy analysis was detailed. The next step in NCORE’S process, once the architectural team has refined the building plans, elevations, and window sizes, is to update any geometry changes, confirm window sizes, add shading elements (overhangs, porches, or other local shades), and subdivide larger massing blocks into individual apartments. Whereas in the conceptual energy analysis, residential units were aggregated floor by floor into zones and glazing aggregated to the zone, during this phase, HVAC loads (envelope, glazing, ventilation, internal gains, etc.) are precisely tabulated so that systems can be sized to within 15% of the calculated load, satisfying the LEED for Homes and Energy Star Homes requirements. Without detailed analysis and scrutiny, many design teams can fall back into "rule of thumb" design, or can tabulate sizing based on inaccurate loads. National CORE believes in investing more in higher efficiency equipment, but buying only what is needed, an approach we believe is cost neutral.
Method: NCORE uses IESVE to help them accurately model the building for each individual apartment unit, allowing them to perform visually quality control of construction assemblies, fenestration, and thermal templates, then create ASHRAE level reports that can be used for scrutiny by the design team, or review by others (in their case by a LEED for Homes Green Rater). The HVAC system sizing modeling workflow within IESVE includes:
Final Thoughts & Conclusions: Energy analytics, especially for affordable, multi-family housing, is a multi-step process, beginning with conceptual energy analysis (see previous case study), continuing into the HVAC system sizing analysis. There are other steps in this process, including an analysis of common area vs. residential energy loads, renewable energy analysis, operational economics, and code compliance. These steps will be covered in future case studies. The path to cost-contained, high performance affordable housing requires precision, and whenever possible, modeling efficiencies. NCORE relies on IESVE to help pin down critical analysis, providing detailed reports, paving the way for them towards zero net energy and carbon neutral projects.
"Continuing our exploration of how IESVE benefits the affordable housing projects we design, build and operate, Legacy Square is an example of how we can achieve a high-performance, climate-conscious and affordable building design within a limited budget. National Community Renaissance continues to lead the affordable housing industry, telling the real-world story, showing what is possible in affordable housing. When it comes to high performance, zero net energy, and carbon neutral projects: If we can do this, everyone can."
Tim Kohut, AIA, Director of Sustainable Design at National Community Renaissance, California