Tips to design multifamily and mixed-use buildings: Sustainability, energy efficiency

Multifamily dwellings and mixed-use buildings are becoming more prevalent. Some best practices and tips for incorporating sustainable and energy-efficient systems are offered forengineering systems in these residential buildings.

By Consulting-Specifying Engineer July 28, 2017


  • Brian Berg, PE, LEED AP, CEM, Associate Principal, Glumac, Irvine, Calif.
  • David Crutchfield, PE,Principal, RMF Engineering, Charleston, S.C.
  • Kieran Healy, PE, Mechanical Engineer, CCJM, Chicago
  • Lui Tai, PE, Technical Services Director, JENSEN HUGHES, Toronto
  • Robert J. Voth, Executive Vice President, Bala Consulting Engineers, King of Prussia, Pa.

CSE: What unusual systems are owners requesting that help save energy and/or electricity when a space is unoccupied?

Tai: We have received a unique request from a building owner who wants to have occupancy sensors on all exit lights, such that the exit signs will turn off when the room is unoccupied.

Berg: We’ve used key cards in hotel rooms to shut off lights and HVAC. We’ve used occupancy sensors to reset outside-air quantities and temperature setpoints. Demand-control ventilation is pretty common in retail and food and beverage spaces on podium levels to save energy when the customer traffic is light.

CSE: Energy efficiency and sustainability are frequent requests from building owners. What net zero energy and/or high-performance systems have you recently specified on multifamily dwellings and mixed-use buildings (either an existing building or new construction)?

Healy: VRF systems with heat recovery and proper zoning, which take advantage of concurrent heating and cooling needs as a result of the shifting nature of solar-gain loads versus ambient-air loads during shoulder and winter months. The further northern latitude the project is, the more important this strategy becomes with greater energy savings as a result.

Berg: Mixed-use buildings allow for various types of high-efficiency systems. We’ve done some heat recovery on condenser-water systems where boilers have not turned on all winter because there is enough heat extracted from podium retail and food and beverage spaces to be used to heat spaces needing heat. We’ve used radiant heating and cooling both in the floor and ceilings in spaces where it makes sense. We do the normal strategies of VFDs on everything; we oversize cooling towers where space allows to drive condenser-water temperatures down so equipment efficiencies go up. We’ve done some natural ventilation in common areas as well, with the assistance of computational fluid dynamics analysis to optimize effectiveness. In common areas with mechanical ventilation, we’ll use variable-speed outside-air fans with demand-control ventilation. On the plumbing side, we’ll oftentimes use the HVAC condenser-water return for preheating city water upstream of the domestic hot-water heaters. We’ve done the same by using shower drain-water heat recovery for preheating the domestic hot water. Condensate collection from the HVAC units is typically collected, treated, and used as part of a cooling tower make-up system. Onsite water-treatment facilities have been used on occasion to treat greywater for reuse in the building.

CSE: What types of sustainable features or concerns might you encounter on multifamily dwellings and mixed-use buildings that you wouldn’t on other projects?

Healy: Indoor-air quality and compartmentalization between units is extremely important for residential units. Minor inconveniences in commercial units become major areas of conflict in a residential setting. When quality of life and comfort in one’s home is affected, there is generally no talk of compromise or accommodation. We have been an expert witness in a lawsuit in a multifamily condominium development where one tenant sued the condo association that their unit was being adversely affected as compared with all other tenants on the floor. On behalf of the condo association, we were able to demonstrate that the condition the tenant was complaining about was a common condition for all tenants with the same exposure as the litigant, due to prevailing winds and natural stack effect of the building. Ultimately, the suit was dropped. Bottom line, there’s virtually no tolerance for air-quality discomfort in one’s own home, whether due to neighbors or building conditions.

CSE: What types of renewable or alternative energy systems have you recently specified to provide power for such projects? This may include photovoltaics (PV), wind turbines, etc. Describe the challenges and solutions.

Berg: The trend is to have rooftop amenities on these mixed-use projects, so rooftop photovoltaics or solar thermal water heating are typically squeezed out on space. We’re presenting options of PV window shades or other building-integrated renewables to achieve client goals because of the lack of available roof space.

CSE: What are some of the challenges or issues when designing for energy efficiency for such facilities?

Berg: The marketplace is moving toward more glass while energy codes are moving to be more restrictive on glazing and glazing performance. We’re finding that we need to use more frit or spandrel on the window systems while using high-efficiency MEP systems to comply with energy codes.