Walgreens Achieves Net-Zero

Masonry Wall System Contributes to Energy-Efficient Strategy

Elizabeth Young

As the largest drugstore in the country, Walgreens operates 8500 retail locations. As a retailer, Walgreens promotes health and wellness to its customers and as a corporation, Walgreens understands that its stores create a carbon footprint that affects the health of the environment. Walgreens’ Sustainability team is always monitoring and updating sustainable strategies, processes and practices that can reduce the carbon footprint of its stores. The corporate sustainability plan includes reducing energy use company-wide 20% by 2020, in alignment with the Department of Energy’s Better Buildings Challenge initiative.

System and Strategies

It is already a common practice for Walgreens to use an efficient insulated masonry cavity wall system for structure and enclosure. Energy-efficient lighting retrofits is another sustainable strategy they employ. To date, 150 Walgreens locations are using photo voltaic (PV) arrays to meet a percentage of their energy demands and plans are underway to add PV to 200 more stores. When it came time for a busy Evanston IL location to receive updates, Manager of Sustainability Jamie Meyers and his team asked: “What does it look like when we put all of our energy-efficient and sustainable strategies together in one store?”

The answer is: the first net zero energy Walgreens store, open in November.

The concept of a net zero energy building is that the building employs systems and strategies from which all of its operational energy needs are met onsite by renewable sources. Ideally, it is also a building designed to require greatly reduced operational energy.

Whole Building Performance Evaluation

Because it owns and operates so many locations, Walgreens is well aware of energy costs associated with operating these facilities. A typical 14,000 sf store in the zone 5 climate region uses about 425,000 kWh/yr of electrical energy and more than 5000 therms/year of natural gas. Walgreens partnered with Energy Center of Wisconsin (ECW) for early building modeling scenarios to determine best strategies for achieving net zero energy consumption and zero carbon emissions. It was determined that the new store would only have enough room to accommodate PV to generate 256,000 kWh/yr, so Meyers and team set about finding ways to eliminate all natural gas usage and reduce annual electrical usage by more than 50% to ensure all energy could come from onsite renewable sources. Projections for the new facility say operations will use only 200,000 kWh/yr, leaving potential excess energy able to be sold back to the local utility to be put on the grid.

Walgreens is employing alternative energy strategies including geothermal and wind power as well as solar. Natural ventilation methods via operable clerestory windows and having bright white walls inside reflect sunlight, reducing reliance on high wattage bulbs. Part of its sustainable strategy involves taking care in selecting high performing enclosure systems, like insulated masonry cavity wall. Energy modeling allowed them to determine what R-values were needed for the enclosure to meet optimal energy performance without exceeding a point of diminishing returns.

Ben Heymer, senior energy engineer, ECW, says that Walgreens had an aggressive strategy when it came to designing this prototype store. Achieving net zero was the goal, but not at the expense of providing the services customers expected. The team had to take into account the long, 14-hour operating days and all the same pharmacy and refrigeration capacity of a typical store. The building also had to be architecturally stunning. They began with the assumption that this had to be the best building they could conceive, rather than beginning at code minimum and making additions.

Innovative Envelope

Preliminary models were created using eQUEST, a free building energy analysis software provided by the Department of Energy. Construction practices and materials were based on a climate such as northern Minnesota or Canada (climate zone 7 as recognized by ASHRAE 90.1) rather than Chicago’s (climate zone 5).

When it came to the opaque wall system, Meyers says they were only 1½” of insulation away from meeting the necessary R-value of 20 per the modeling, which was easy to achieve. “We knew we wanted insulated masonry cavity wall because we have been using it and find it to be reliable, easy to maintain and a good fit with Evanston and most communities. It is a proven wall system.”

Instead of adding the extra 1½” in the cavity, it is applied inboard of the CMU, behind the gypsum interior finish wall. This adds another layer of air cavity, increasing the wall system’s R-value.

Heymer says the energy modeling begins from the outside in. “Optimize the envelope first, then lighting and plug loads. Once those are as efficient as possible, the required size of the mechanical systems can be a lot smaller with higher efficiency.” Items like controlling ventilation, recovering heat from refrigeration units and using a ground source heat pump can operate as a single system, with each piece working in concert for maximized efficiency.

As details of the design emerged, energy modeling was performed using TRNSYS17, a transient system simulation program with a modular structure which gives it increased flexibility. In all, modeling efforts required about four weeks during the design phase.

Reduced Enivornmental Footprint

What is different about this masonry wall system is the attention paid to the materials selected. The brick chosen is about 60% sand and 40% flyash collected from the particle filtration systems of a nearby coal-fired electricity plant. Flyash is a post-industrial recycled material and its use removed the material from the waste stream. Instead of firing the brick, this manufacturer uses a curing process, which reduces both the energy use in manufacturing and the CO2 emissions by approximately 80%. While this doesn’t directly impact energy performance of the store, Meyers says it makes sense to look at materials and their environmental foot prints and use those with small footprints when possible.

Walgreens also benefitted from using the enclo sure as structure, reducing the need for two systems. Partially-reinforced CMU contributes to the energy-efficient and environ mentally-friendly envelope. Grey CMU was produced in nearby Mundelein, less than 30 miles away. Units contain locally extracted sand and aggregate material in addition to 30% recycled content. Local materials and recycled content also contribute to LEED points toward the LEED Platinum certification Walgreens is planning to earn.

The design allows for plenty of natural light within the store, while maintaining what is considered to be an efficient ratio of fenestration to opaque wall. The 2009 IECC commercial standards limit the fenestration to 40% of an above-grade wall. Glazed entry and clerestory windows combine for approximately 25% of the total vertical envelope.

Cradle to Cradle

The new building is built on the site of a store that had been operating for nearly 25 years and was in need of mechanical and electrical system updates. It was also a busy store with inadequate parking facilities, so the decision was made to tear it down and begin again, moving the structure to the back of the lot to make room for additional parking. Care was taken during demolition to sort and recycle 86% of the material, including brick, block and reinforcing steel. Nearly all components of a masonry wall system can be reused and/or recycled. Achieving a construction and demolition recycling rate of 75% is worthy of 2 LEED points under LEED 2009.

Walgreens is already a LEED Volume Program participant, with store certifications in progress and executive offices that received Commercial Interiors Certification this year. With this store, Walgreens takes another step forward as leader in green retailing.

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