Making mixed-use buildings sustainable

Engineering mixed-use buildings is a fine art—specifiers must combine multiple engineered systems for several business and residence types into one structure. Many building owners demand sustainable, energy-efficiency buildings.

By Consulting-Specifying Engineer September 16, 2013


Robbie Chung, PE, LEED AP, Senior associate, Environmental Systems Design Inc., Chicago

Raymond Holdener, PE, Senior associate, Dewberry, Fairfax, Va.

Andrew Lasse, PE, LEED AP, Associate principal/senior mechanical engineer, Interface Engineering, Portland, Ore.

Gary Pomerantz, PE, LEED AP, Executive vice president, building systems, WSP, New York City

John Sauer, PE, LEED AP, Senior director, BSA LifeStructures, Indianapolis

LeJay Slocum, Assistant director, Atlanta regional office, Aon Fire Protection Engineering Corp., Suwanee, Ga.

CSE: What cutting-edge energy efficiency systems have you recently worked on in mixed-use buildings? What design aspects or products were included?

Sauer: At Purdue University’s Health and Human Sciences Building, BSA LifeStructures’ design team used a dedicated outdoor air system (DOAS) and heat recovery wheel to achieve energy savings. This lead to a 29% energy reduction compared to ASHRAE 2007-90.1. The design also incorporates LED lighting for the facility’s 850-space parking garage, which contributes a 48% savings (comparison by fixture) in energy over metal halide. In addition the design uses a control scheme that monitors the lighting level in the garage and adjusts the LED lighting output to meet predetermined levels. Less lighting energy is used when more ambient light from outside is available. The design team also installed occupancy sensors to reduce the lighting levels to threshold levels in certain areas of the garage when unoccupied.

Pomerantz: In areas that are always in the cooling mode, we have used the rejected heat from the cooling system for many uses. These uses include domestic hot water production and free reheat.

Holdener: We have used cisterns to capture rainwater to use for irrigation and/or cooling tower makeup water. The cooling towers, when used in projects, require a substantial amount of makeup water. For some reason, cooling tower makeup water is often overlooked. The majority of the cistern water will be used for the cooling tower makeup water. We have examined using other energy-efficient systems, such as photovoltaics (PV), but the cost of these systems was not seen as viable for the projects.

Lasse: We recently installed a split system fan coil system in the residential units of a mixed-use project in Portland, Ore., that had a unique twist. The fan coils include a hot water coil that used the domestic hot water system as its heat source. What was great about this was that we were able to eliminate a set of pumps by using the domestic hot water recirculation pumps to distribute the hot water to units and fan coils, and ran the hot water loop at a lower temperature to capitalize on higher boiler system efficiencies. This solution also saved the up-front cost of routing a separate heating water system throughout the building, as we simply tied into the domestic hot water infrastructure already in place. 

CSE: Have you had experiences with PV, wind turbine, or other renewable energy? If so, please describe.

Holdener: We have examined using these systems on multiple projects including an analysis for the Federal Bureau of Prisons where we looked at photovoltaic, wind turbine, nuclear power, hydrogen fuel cells, as well as other technologies. Depending on where a facility is located will determine which systems are beneficial and how quick the payback may be.

Pomerantz: We have used photovoltaic systems on many buildings. Given the current levels of government subsidies in many locales, there is a beneficial payback. It has been difficult to financially justify these systems without government incentives. Solar thermal to generate hot water usually has a desirable payback without subsidies. It is relatively inexpensive and operates at high efficiencies. Space is required for the panels and for the water storage tanks. The location of the panels must be coordinated with the architecture of the building. The use of solar thermal does not do away with conventional hot water systems in most places in the world, except for those spaces where it is always sunny or it is not critical to have hot water all of the time. 

CSE: For new buildings, are clients requesting LEED certification, and at what level?

Sauer: I have found that many clients are requesting LEED level design, but some might not care as much about actually becoming certified. It seems that clients are expecting new buildings to meet a minimum threshold of sustainability without having to follow through with the entire LEED process.

Chung: In my experience, clients have always desired to achieve some level of LEED certification. At the same time, there’s the same desire to get an early understanding what the cost would be for LEED implementation in order to have an informed decision as to how to move forward. This follows with the internal negotiation of what LEED certification is worth the added expense to the project. The client needs to be well-informed so the proper LEED certification level matches the building usage(s). For example, natural challenges exist for facilities such as a shell and core office or a residential building where savings on the lighting power density are exempt. Another example is water savings from low-flow fixtures such as a low-flow shower, which may be more of a challenge to implement within a residential building where the tenants may be more likely to complain as opposed to an office environment where a low-flow shower isn’t a concern. Overall, a client’s desires will always be for a sustainable facility that typically leads to energy savings, but they need to be educated on the associated cost and impacts of potential points on each certification level.

Holdener: For almost all new buildings, mixed-use and other types, clients are requesting LEED certification due to either their own project requirements or those mandated by the local government. Most of the mixed-use projects with a residential component are targeting Silver, with some going for Gold and others simply Certified. Nonresidential projects are generally targeting LEED Gold or Platinum.

Lasse: LEED certification is always on the table with our clients. What we’ve found is that almost every project we work on is going to meet LEED Silver at a minimum. This is often due to mixed-use projects being located in more dense urban areas, which result in more points for Sustainable Sites credits, and less pressure on the Energy and Atmosphere credits. LEED for Homes Midrise is also becoming more popular, and LEED will require many residential mixed-use projects to pursue this path in the future, instead of LEED NC. Both paths have their advantages, but it appears the rapid rise of LEED for Homes Midrise is not going to slow down, as it fits these project types very well.

Pomerantz: Clients request LEED levels from Certified through Platinum. It varies based on their commitment to sustainability and their business plan objectives. Some clients only do LEED buildings because it is mandated by the authorities.