Story at a glance:
- Solar power is often the easiest renewable energy to integrate into new and existing multi-family housing developments.
- Geothermal heat pumps are an efficient way to provide heating and cooling in multi-family housing projects.
- Wind and hydroelectric technologies may be integrated into multi-family housing projects that possess favorable site conditions.
Decarbonizing the built environment is crucial to keeping global temperatures from increasing 1.5℃ above pre-industrial levels, and integrating renewable energies into new and existing buildings is part of the equation.
Technologies like solar panels and geothermal heat pumps have become relatively common features in both single-family residences and many commercial buildings over the last several years, but renewable energy integration in the multi-family housing sector has, by all accounts, lagged behind.
This article is an introductory guide to renewable energy integration in multi-family housing developments.
The Case for Renewable Energy in Multi-Family Housing Projects
The Conservatory Apartments multi-family housing project in Chicago produces fewer operational emissions and boasts reduced operating costs thanks to its use of photovoltaic panels. Photo courtesy of HED
Before we get into how to integrate renewable energies into apartment complexes, let’s take a moment to examine the importance of renewable energy generation in the context of multi-family housing development projects.
Fewer Operational Emissions
Decarbonizing the built environment is crucial to preventing global temperatures from increasing 1.5°C above pre-industrial levels—and the single most effective way of doing so is through the integration of renewable energy technologies that reduce a building’s dependency on fossil fuels. By definition multi-family housing developments that are equipped with renewable energy systems generate fewer operational emissions than apartment complexes that rely solely on electricity derived from the burning of fossil fuels.
Greater Energy Independence
Multi-family housing projects that generate all or a portion of their own energy from onsite renewable energies also have greater energy independence than those reliant solely on electricity bought from an energy provider. This energy independence improves resilience in the face of fluctuating energy prices, fuel shortages, power outages, and imposed rolling brownouts/blackouts.
Reduced Operating Costs & Lower Rent Prices
By producing all or a portion of their own energy, multi-family housing projects outfitted with renewable energy technologies enjoy reduced operating costs, saving building owners money over the long term. Net-positive energy apartment buildings—or buildings that generate more energy than they use—can even establish a secondary revenue stream by selling their surplus electricity to the grid.
Lower utility costs can in turn make apartment units more affordable for tenants by reducing rent prices, improving social equity and housing access.
Renewable Energy Integration in Multi-Family Housing Developments
schleicher.ragaller architects’ multi-family housing and workshop building near Stuttgart, Germany is net-zero energy thanks to its use of renewable energies like solar power. Photo by Zooey Braun Photography
Now that we’ve made the case for renewable energy integration in multi-family housing developments, let’s take a look at the various strategies for equipping apartment complexes with solar, geothermal, wind, and hydroelectric technologies.
Solar Power
Solar is by far the most popular—and often the easiest—renewable energy to integrate into multi-family housing developments. There are two basic types of solar technologies that may prove beneficial for multi-family housing projects: photovoltaic panels and solar thermal systems.
Photovoltaic Panels
Wentworth Commons is a prime example of sustainable, affordable multi-family housing that incorporates photovoltaic panels into its design. Photo courtesy of HED
A photovoltaic or PV panel generates electricity from sunlight via the photovoltaic effect. When light shines on the photovoltaic cell, semiconductors within the panel absorb the light’s energy and transfer it to electrons, creating an electrical current that is then extracted through conductive metal contacts.
As a general rule for projects in the Northern hemisphere, PV panels are most efficient when angled toward the south, although east- and west-facing angles can be utilized if necessary. In urban environments, PV panels are typically installed on rooftops, but there are also windows that utilize photovoltaic technology as well. These systems are often costlier, but allow taller buildings to make strategic use of a larger overall surface area for electricity generation. The actual size of a photovoltaic array will depend on a building’s energy consumption needs and the amount of sunlight available during the day.
The HED-designed Wentworth Commons apartment complex in Chicago’s Roseland neighborhood, for example, features a 33 kWh photovoltaic system supported by exposed trusses at the building’s roof line; the panels provide power for a portion of the building and helped the project earn LEED certification.
Solar Thermal Systems
The Casa Adelante multi-family apartment complex makes use of both PV panels and solar hot water heaters. Photo by Bruce Damonte
Solar thermal systems convert solar energy directly into heat rather than electricity. Most solar thermal systems take the form of solar hot water heaters, a technology that essentially replaces—or is used in conjunction with—traditional electric, natural gas, or propane hot water heaters.
Solar hot water heaters use a solar collector to focus solar energy on tubes containing either potable water (direct systems) or an antifreeze solution (indirect systems); in indirect systems, a heat exchanger is used to transfer the heat from the warmed antifreeze solution to potable water. Once heated, the water is then sent to a storage tank sized in accordance with the amount and timing of peak hot water consumption. When hot water is needed, a pump moves the liquid between the collectors, storage tanks, and end uses.
Many solar hot water systems also feature a backup water heater—to help supplement during times of peak hot water consumption or during low insolation periods (e.g. during winter or on cloudy days)—and are installed alongside photovoltaic panels. The Casa Adelante affordable family apartment complex in San Francisco, for example, is one such multi-family housing development that makes use of a solar hot water array as well as a rooftop PV array.
Geothermal Heating & Cooling
The Chelsea Gardens multi-family housing project incorporates a geothermal heat pump system for heating and cooling. Rendering courtesy of Montgomery Sisam Architects
While not as popular as solar power, geothermal is another form of renewable energy that can be integrated into multi-family housing developments. The most common geothermal system used for small-scale, building-level applications—as opposed to large-scale electricity generation—is the geothermal ground-source heat pump.
In these systems the heat pump acts as the heart and is responsible for pumping a carrier fluid—typically consisting of water and an antifreeze agent like propylene glycol, denatured alcohol, or methanol—through a series of underground pipes and/or coils, where it either absorbs heat from the ground (during winter) or transfers heat to the ground (in summer). The fluid is then pumped back to the surface to be used for heating or cooling the building’s interior.
There are several types of geothermal heat pump systems—vertical closed-loop, horizontal closed-loop, pond closed-loop, open loop, et cetera—that differ primarily in their site requirements; in the case of multi-family housing projects, a vertical or horizontal closed-loop system will typically prove to be the most practical.
Vertical Closed-Loop
A vertical closed-loop geothermal heat pump system consists of several “wells” or bore holes drilled deep into the earth and spaced at least 16 to 20 feet apart. Each well is fitted with a U-shaped pipe that circulates carrier fluid, absorbing or discharging heat from/into the earth and pumping the warmed/cooled fluid back to the surface. Depending on the type of building, pipes may even be integrated with the foundation piles themselves.
Vertical closed-loop geothermal systems are best suited to apartment complexes in highly urbanized areas where there is limited land available, as the installation process is fairly non-intrusive compared to some other types of geothermal systems. This also makes vertical closed-loop geothermal wells ideal for retrofit applications of existing multi-family housing projects.
Montgomery Sisam Architects’ in-progress Chelsea Gardens multi-family housing project, for example, is served by a vertical geothermal loop and distributed geothermal heat pump system. “The geothermal system eliminates almost all of the building’s natural gas consumption and offers some cost certainty to the operator when it comes to heating and cooling,” Alexandra Boissonneault, an associate with Montgomery Sisam Architects, previously wrote for gb&d.
Horizontal Closed-Loop
Horizontal closed-loop systems consist of a series of U-shaped or slinky pipes/coils buried in long, extensive trenches dug deeper than the frost line, typically around six to eight feet deep. From an operational standpoint horizontal closed-loop systems function identically to their vertical counterparts.
A horizontal closed-loop system is ideal for multi-family housing projects in suburban areas where land is available for the digging of trenches and in regions with wetter ground, as water conducts heat better than soil particulates, which in turn improves system efficiency. The addition of buried soaker hoses can make horizontal geothermal systems viable even in areas with naturally dry soil.
Wind Turbines
Small wind turbines can, in theory, be incorporated into multi-family housing projects, though it is exceedingly rare. Photo by Ryan Somma, courtesy of Flickr
It is possible for onsite wind turbines to aid in powering residential apartment complexes, though they are often installed as part of a hybrid system alongside photovoltaics or other renewable energy technologies rather than used as the sole form of power generation.
A site-compatibility analysis or feasibility study is crucial when considering any form of renewable energy, but it is especially important when it comes to deciding whether small urban wind turbines are a realistic option, as factors like wind speed and direction can be extremely variable in urban settings.
Even if wind measurements are favorable, it may be impractical to install wind turbines on a project in a rapidly-developing urban area, as new buildings are likely to alter wind conditions and can greatly reduce system efficiency. The high visibility of wind turbines can also make them a hard sell, as they may be viewed as an eyesore that negatively impacts the architectural and/or historic character of a community.
Hydroelectric Power
Similarly, integration of hydroelectric power generation is a possibility for certain multi-family housing projects, but is largely out of the question for the majority of apartment buildings around the world due to the very specific site conditions it entails. For onsite hydroelectric to be even remotely viable, a project must be located along a continuously flowing water source—typically a river—whose level and flow rate are largely uniform throughout the year.
If the right conditions exist a hydropower system can prove to be an extremely useful asset for multi-family housing complexes, one that greatly reduces reliance on purchased electricity. Getting regulatory approval for hydroelectric power can be more difficult to obtain than other renewable technologies, as it has a greater potential for ecosystem disruption. Small-scale hydroelectric turbines like those used for powering a single building are generally less disruptive than large hydropower dams and reservoirs, though they still have the capacity to interfere with wildlife and may inhibit recreational usage of waterways.
