Design Strategies in Sustainable Architecture

The built environment is responsible for much of our energy consumption and emissions output. According to this resource from the International Energy Agency, “Operational energy use in buildings represents about 30% of global final energy consumption.” To minimize energy consumption, slash emissions, and cut costs, architects, developers, and property owners often explore the right combination of active and passive design strategies for improved energy efficiency. Active design strategies rely on mechanical and technological systems to actively regulate environmental conditions within a building, while passive design strategies harness natural elements and architectural features to achieve similar objectives. As this resource from the EESI explains, “Passive systems are structures whose design, placement, or materials optimize the use of heat or light directly from the sun.” On the other hand, “Active systems have devices to convert the sun’s energy into a more usable form, such as hot water or electricity.” Most buildings require both active and passive design elements to optimize their energy efficiency. In this post, we explore the fundamental principles, key differences, and real-world applications of these approaches to demonstrate how they contribute to the development of more sustainable, resilient, and energy-conscious buildings. Read on to learn more!

Passive vs Active Design Strategies for Energy Efficiency

Active Energy Efficiency Strategies

Active efficiency strategies for buildings encompass a range of technological solutions designed to actively control and optimize energy consumption. These strategies often involve the integration of advanced systems like HVACs (Heating, Ventilation, and Air Conditioning) with smart thermostats, lighting controls, and energy management systems. 

Through real-time monitoring and precise adjustments, active strategies ensure that a building’s energy use is tailored to its specific needs, maximizing comfort while minimizing waste. By dynamically responding to factors such as occupancy, external weather conditions, and user preferences, active strategies increase energy savings while cutting costs for owners.

While they require ongoing maintenance and energy input, active energy efficiency measures play a crucial role in enhancing the sustainability and performance of modern structures in an energy-conscious world. Below are a few examples of equipment and other elements used in active energy efficiency strategies.

#1 Energy Recovery Ventilation Systems (ERV)

Energy recovery ventilation (ERV) systems are more energy-efficient than traditional ventilation systems because they leverage the principle of heat and moisture recovery. ERV systems exchange the indoor air with fresh outdoor air while simultaneously transferring heat and moisture between the two air streams.

In cold climates, ERVs capture the heat from the outgoing indoor air and transfer it to the incoming outdoor air, pre-warming it before it enters the building. They remove heat and moisture from the incoming air in hot climates – cooling and dehumidifying it before it enters the space. This heat and moisture exchange significantly reduces the need for additional heating or cooling, dehumidification, or humidification – which are all energy-intensive processes.

As such, ERV systems contribute to substantial energy savings by maintaining indoor comfort levels while minimizing the energy required for conditioning the incoming air – making them a more energy-efficient choice for ventilation in both residential and commercial buildings.

#2 Tankless Water Heaters

On-demand or tankless water heaters are generally considered more energy-efficient than storage water heaters. This is because the tankless versions only heat water when needed – eliminating the standby energy losses associated with constantly keeping a tank of water hot. 

When you turn on the hot water tap, a tankless unit activates its heating element or gas burner, heating the water as it flows through the unit. This on-demand heating process is highly efficient and can produce incredible energy savings over time. 

Tankless heaters last longer than tank heaters, reducing the need for replacement and further environmental impact. However, it’s essential to size a tankless unit correctly for your specific hot water demand to ensure optimal efficiency and installation costs can be higher. Still, tankless water heaters are incredibly efficient. As Chauncey Crail and Lexie Pelchen write in this article for Forbes, “A tankless water heater is 24% to 34% more energy-efficient than storage tank water heaters.”

#3 LED Lights

Light-emitting diode (LED) lights are more efficient than traditional incandescent and even fluorescent lights due to several key factors. First, LEDs convert a significantly higher percentage of electrical energy into visible light, while traditional incandescent bulbs release a substantial portion of their energy as heat. 

This inherent efficiency results in lower energy consumption and reduced electricity costs. Emitting less heat than other bulbs, LEDs can help reduce the cooling load in commercial buildings – especially in climates with high cooling requirements. LEDs are also longer-lasting, which means less frequent replacement and lower maintenance costs. 

Moreover, LEDs are highly directional – emitting light in a specific direction without the need for reflectors or diffusers, reducing light wastage. They are also dimmable and can be easily integrated with smart lighting controls, allowing for further energy savings by adjusting light levels to suit specific needs. 

LEDs have a longer lifespan compared to other lighting options. In a commercial setting, this means less frequent replacement, reduced maintenance costs, and minimal disruption to daily operations. Overall, LED lights are a more energy-efficient lighting option – offering both environmental and economic benefits.

#4 Heat Pumps

Installing heat pumps is another active energy-saving strategy. Heat pumps are more efficient than traditional systems because they leverage the principles of thermodynamics to transfer heat from one place to another rather than generating heat directly. During the heating season (winter), they extract heat from the outside air, ground, or water source and transfer it indoors. During the cooling season (summer), this process is reversed and they remove heat from the indoor space and release it outside. 

The key efficiency advantage lies in the fact that for every unit of electrical energy they consume to operate, heat pumps can move multiple units of heat energy – typically three to four times more. This high coefficient of performance (COP) results in significant energy savings. 

Additionally, many modern heat pumps are equipped with advanced features such as variable-speed compressors and smart controls, allowing for precise temperature control and further energy optimization. Overall, heat pumps are a highly efficient and environmentally friendly option for heating and cooling – especially in regions with moderate climates.

Heat Pump Limitations

These devices are energy-efficient and environmentally friendly, but they do have some limitations. One significant limitation is their reduced efficiency in extremely cold climates. As the outdoor temperature drops, the heat pump’s ability to extract heat from the air or ground diminishes – requiring auxiliary heating sources like electric resistance heaters –  which are less efficient and can increase energy costs.

How Much Do Heat Pumps Cost?

The upfront cost of a heat pump can be higher than that of traditional heating and cooling systems. Of course, this can deter some property owners. Unfortunately, heat pumps may require more frequent maintenance – including filter cleaning and refrigerant checks – to maintain optimal performance. 

Finally, the lifespan of heat pumps can be shorter than some other systems, which means replacement costs over time. Despite these limitations, proper sizing, installation, and maintenance can help mitigate these issues – making heat pumps a viable and efficient option for many residential and commercial applications.

#5 Harnessing Geothermal Energy

Geothermal systems are another active energy efficiency strategy that harnesses the Earth’s natural heat to provide heating, cooling, and hot water in buildings. It involves the use of geothermal heat pumps and water heaters. Geothermal heat pumps actively transfer heat between the ground and a building’s interior. 

During the winter, these systems extract heat from relatively stable and warmer underground temperatures and distribute it inside the building for heating purposes. In the summer, they transfer excess heat from the building back into the cooler ground, effectively providing cooling. 

Geothermal systems require electricity to operate the heat pumps but are highly efficient – typically offering several times the energy output for each unit of electricity input. By actively tapping into the Earth’s heat reservoirs, geothermal energy reduces the reliance on traditional heating and cooling methods powered by fossil fuels – making it an environmentally friendly and energy-efficient solution for maintaining indoor comfort.

#6 Solar Panels

Of all the active and passive energy efficiency strategies on this list, solar panels are the most widely known and implemented. Solar panels are an active energy efficiency system that converts sunlight into electricity. An active energy system, solar panels can generate electricity to meet electricity demand during peak use hours.

These panels consist of numerous solar cells that actively capture sunlight and generate direct current electricity. This electricity can be used to power various appliances and systems within a building – offsetting the need for grid-supplied electricity or other conventional energy sources. 

Through net metering, surplus energy can be fed back into the grid – allowing buildings to earn credits or reduce their energy bills. Solar panels actively contribute to energy efficiency by harnessing a renewable and clean energy source, reducing a building’s carbon footprint, and decreasing dependence on fossil fuels. 

Their deployment as an active energy solution plays a pivotal role in sustainable construction and energy-conscious practices – making them an essential component of the transition to greener and more efficient buildings.

Passive Energy Efficiency Strategies

In contrast to active energy efficiency strategies, passive energy efficiency strategies harness natural phenomena to minimize energy consumption and enhance comfort without relying on active mechanical systems. Basically, a passive design strategy will integrate building science principles with knowledge of the building’s site to create a comfortable, energy-efficient living space. It involves taking advantage of the site and choosing the right materials.

These strategies include optimizing building orientation to maximize natural daylight and minimize heat gain or loss, using high-quality insulation and thermal mass materials to reduce heat transfer through the building envelope, utilizing thermal bridging, ventilating with fresh air, and incorporating passive solar design principles like south-facing windows, exterior shading, and thermal mass to capture and store solar heat. These strategies rely on the local climate and direction of the sun on site to direct heat flow and create natural cooling systems.

Passive strategies often focus on architectural elements, building materials, and site planning to create energy-efficient structures that require minimal energy inputs for heating, cooling, and lighting. By working in harmony with the environment and climate, passive energy efficiency strategies contribute to sustainable and environmentally friendly building designs for both commercial and residential projects.

Below are a few passive energy efficiency strategies used in both commercial and residential buildings. Bear in mind that the term “Passive House” is used to describe a building that relies almost entirely on passive methods to reduce heat gain and improve energy performance.

#1 Solar Orientation

Solar orientation involves positioning a building or structure in a way that optimizes its interaction with the sun’s path throughout the day and seasons to harness the sun’s energy and minimize its adverse effects. Inside a building, one primary goal of proper solar orientation is thermal comfort for residents without significant energy expenditure. By optimizing a building’s relationship with the sun, architects can significantly reduce energy consumption for heating, cooling, and lighting – contributing to greater energy efficiency and sustainability.

With solar orientation, you consider how the angle of the sun changes throughout the year – and even throughout the day. This means that during the summer – when the sun is higher in the sky – the building’s design minimizes direct exposure to reduce cooling loads. In the winter months, the design maximizes exposure for passive heating.

How Solar Orientation Keeps Buildings Warm During the Winter

In colder climates, installing south-facing windows allows the winter sun to warm more of the building. This passive solar gain can provide free heating during the colder months. Properly designed overhangs or shading devices can also prevent excessive heat gain in the summer when the sun is higher in the sky.

How Solar Orientation Keeps Buildings cool during the summer

In warmer climates, the goal is to reduce direct solar heat gain to limit the need for air conditioning and minimize overheating. Orienting the building so that it has fewer windows on the west and east sides and incorporating shading elements like awnings, pergolas, or deciduous trees can help block the harsh afternoon sun.

Solar orientation also plays a crucial role in maximizing natural daylighting within a building. For example, by placing windows strategically on the south side – in the Northern Hemisphere only – and minimizing obstructions on the north side, buildings can reduce their reliance on artificial lighting during the day.

#2 Building Form and Building Type

The building form plays a vital role as a passive energy efficiency strategy by influencing how a structure interacts with its environment – particularly in terms of temperature control, natural lighting, and ventilation. Build mass, thermal inertia, shape, orientation, natural ventilation, and daylighting all minimize energy consumption in well-planned buildings.

The shape and orientation of a building are crucial considerations. A compact building form with minimal external surface area relative to its interior volume minimizes heat transfer through the building envelope. Additionally, orienting the building to take advantage of passive solar heating – with more south-facing windows in the Northern Hemisphere – or to minimize exposure to intense sunlight can help regulate indoor temperatures naturally.

Buildings with significant mass or thermal inertia – such as those constructed with materials like concrete, adobe, or brick – can absorb heat during the day that it later releases at night. This helps stabilize indoor temperatures – reducing the need for mechanical heating and cooling. Thermal mass can be strategically located – such as in interior walls or floors, to optimize its effectiveness.

Building Form Affects Ventilation and Natural Light Exposure

Building form can facilitate natural balanced ventilation by promoting airflow through the structure. Cross-ventilation – where prevailing winds are channeled through openings on opposite sides of the building – can provide effective cooling in the absence of mechanical systems. The form can include features like courtyards, wind catchers, or operable windows that encourage natural ventilation.

As briefly outlined above, the form of a building also affects its potential for daylighting. A well-designed building form can maximize natural light exposure – limiting the need for artificial lighting. Relying on natural sources of light not only saves energy but also enhances the visual comfort and well-being of occupants.

#3 Insulation

Next, we have insulation. Insulation is a fundamental component of passive energy efficiency strategies as it plays a crucial role in reducing heat transfer between the interior and exterior of a structure. Well-insulated buildings often require smaller heating and cooling equipment, have lower energy bills, and create a more continuously comfortable environment for residents.

Insulation acts as a thermal barrier that restricts the flow of heat between the inside and outside of a building. In cold climates, it prevents valuable indoor heat from escaping to the colder outdoors – helping to maintain a consistent indoor temperature. In hot climates, it impedes the entry of outdoor heat – reducing the need for air conditioning to maintain a cooler indoor environment.

By minimizing heat loss or gain through walls, roofs, and floors, insulation offers substantial energy savings while lowering utility bills and reducing your carbon footprint. Continuous insulation is particularly effective in reducing heating and cooling loads — which are often the largest contributors to a building’s energy consumption.

#4 Triple Pane Windows

Further insulating windows and doors can also help reduce energy consumption by preventing leakage. Triple-glazed windows are formed from three layers of glass separated by insulating spaces filled with gas. 

They offer enhanced thermal insulation, reduced heat gain, minimal heat loss, condensation control, and many other benefits. While triple-pane windows offer excellent energy efficiency benefits, they may come with a higher upfront cost compared to single or double-pane alternatives. However, these windows often provide a compelling return on investment through energy savings, increased comfort, and improved building performance.

Triple-pane windows provide superior thermal insulation compared to traditional single-pane or double-pane windows. The two insulating gaps between the glass layers reduce heat transfer through the window – making it harder for outdoor temperatures to affect the indoor climate. In colder climates, this means less heat loss through the windows during the winter – resulting in reduced heating costs and improved indoor comfort. In a hot climate zone, triple-pane windows help minimize heat gain from outside – effectively blocking a significant portion of the sun’s radiant heat. 

As noted above, triple-paned windows can also help limit the amount of condensation that forms on their interior surface. This can reduce the amount of mold and mildew that grows in your home or office space during high humidity or precipitation events.

#5 Air Sealing

Whether implemented in construction or renovation, air sealing is intended to minimize unintended air leaks that can occur through gaps, cracks, joints, and other openings in a building’s envelope. The building envelope is made up of the structure’s exterior walls, roof, foundation, windows, doors, and other elements that separate interior from exterior. 

Air sealing might involve caulking, weatherstripping, sealing gaps with spray foam or sealants, and using air barriers or vapor barriers. It reduces energy loss, enhances resident comfort, improves indoor air quality, and prevents development of mold and mildew.

#6 Trombe Walls

A Trombe wall is a passive solar heating system that is often integrated into the design of buildings to enhance their energy efficiency. Named after French engineer Félix Trombe, this system consists of a thick, thermally massive wall built on the south-facing side of a building – typically with a large expanse of glazing on the exterior.

Trombe walls work by harnessing and storing solar heat for later use. They can significantly reduce the need for mechanical heating during the day – particularly in cold climates with ample sunlight. This leads to energy savings and a smaller carbon footprint. According to this resource from the National Renewable Energy Laboratory, “the Trombe wall is one of many passive solar features that reduce building energy use by 30% when compared with conventional construction.”

How Do Trombe Walls Work?

The primary function of a Trombe wall is to absorb and retain the sun’s heat. When sunlight strikes the glazing, the wall behind it absorbs the solar energy and becomes heated. The wall is typically made from high thermal mass materials like concrete. These materials can store heat more effectively than those with a low thermal mass. 

As the wall heats up, it transfers heat to the building’s interior through conduction. This slow and steady release of heat helps stabilize indoor temperature – particularly during the evening and nighttime hours when external temperatures drop.

Some Trombe wall designs incorporate vents or openings near the top and bottom of the wall. These openings can be controlled to regulate the flow of warm air into the interior space. During the day, the lower vent may be opened to allow warm air to rise and circulate while the upper vent may be closed to prevent heat loss. At night, the process can be reversed to retain heat.

#7 Green Roofs

Last on our list of passive approaches is green roofs – which we build into many of our designs at AVLV. Green roofs – also called living roofs or vegetative roofs – are an integral part of passive energy efficiency strategies in building design. These roofs are covered with vegetation – which provides several benefits for energy efficiency. 

First, green roofs offer natural insulation. This limits heat gain in the summer and reduces heat loss in the winter. The insulating effect provided by green roofs helps maintain a stable indoor temperature – reducing the need for mechanical heating and cooling. Second, the vegetation on green roofs absorbs and reflects solar radiation – thereby mitigating the urban heat island effect and reducing heat absorption by buildings. 

Additionally, green roofs contribute to improved stormwater management and air quality – creating a healthier and more comfortable environment within and around buildings. Overall, green roofs are a sustainable and effective passive strategy that enhances energy efficiency, reduces energy consumption, and promotes a greener urban environment.

As the wall heats up, it transfers heat to the building’s interior through conduction. This slow and steady release of heat helps stabilize indoor temperature – particularly during the evening and nighttime hours when external temperatures drop.

Some Trombe wall designs incorporate vents or openings near the top and bottom of the wall. These openings can be controlled to regulate the flow of warm air into the interior space. During the day, the lower vent may be opened to allow warm air to rise and circulate while the upper vent may be closed to prevent heat loss. At night, the process can be reversed to retain heat.

Exploring Passive and Active Approaches to Energy Efficiency in Philadelphia

Back in 2012, Philadelphia issued an ordinance so the government could gather data about energy consumption by large buildings across the city. The Building Energy Benchmarking Ordinance requires owners of certain non-residential buildings in Philadelphia to annually benchmark and report their energy usage data. 

This data includes information about a building’s energy consumption, as well as other building characteristics such as square footage, occupancy, and usage. The ordinance is part of the city’s efforts to reduce energy consumption, lower greenhouse gas emissions, and promote sustainability. According to the city’s 2019 Energy Benchmarking Report, “The average building in Philadelphia is performing slightly better than the national median with an ENERGY STAR score of 55.” In 2021, the average score for Philadelphia buildings was still 55. 

Eleven years after the ordinance was issued, there are many more active energy efficiency solutions commercially available to building owners, developers, and architects in Philadelphia. Interest in and knowledge of passive solutions has also expanded. Below, we celebrate a few projects and programs that promote active and passive energy efficiency strategies for Philadelphia’s built environment.

Onion Flats Stables Development

The Onion Flats Stables development is a series of 27 prefab rowhouse-style homes in Philadelphia’s Kensington neighborhood. This development has garnered attention for Domani Developers’ commitment to environmentally responsible design and community engagement. 

The mixed-use development showcases a harmonious integration of residential and commercial spaces – with an emphasis on passive and active energy efficiency strategies, water conservation, and the use of renewable energy sources. 

As Jennifer Goodman writes in an article for Architect Magazine, these “ultra-energy-efficient structures will generate 100 percent of their power from a 4.23kW PV array…[while consuming] 90 percent less energy than traditionally built homes.” The buildings feature added insulation, green roofs, Intus windows, porous paving, R-34 walls, and R-52 roofs. Residents can monitor their energy consumption, too. 

By combining sustainability, innovation, and community involvement, this development serves as a notable example of how responsible urban planning can enhance both environmental and social well-being in the heart of Philadelphia.

The Role of Walls and Roofs with High R-Values

As noted above, well-insulated walls and roofs are part of a passive approach to energy efficiency. For reference, R-34 walls have a thermal resistance of R-34. This means that the wall is well-insulated and can significantly impede the flow of heat between the interior and exterior of a building. High R-values like R-34 are often achieved through the use of thick insulation materials, such as fiberglass, foam board, or spray foam, and are commonly found in well-insulated homes and commercial buildings to reduce heating and cooling energy consumption. 

An R-52 roof indicates that the roofing system has a high thermal resistance of R-52. Roofs with this level of insulation are exceptionally well-suited for retaining indoor comfort and reducing energy costs. They are typically equipped with thick layers of insulation – often including materials like fiberglass or rigid foam board. High R-value roofs are highly effective in preventing undesirable heat transfer from interior to exterior and vice versa. This level of insulation is especially valuable in climates with extreme temperatures to maintain a comfortable and energy-efficient indoor environment.

Passive Rowhouse Manual Project from PHCC

Next, we have the Passive Rowhouse Manual Project from the Green Building United Passive House Community Council. This project is dedicated to retrofitting traditional rowhouses by offering owners a manual by which they can transform these older buildings into passive solar homes that prioritize energy conservation and indoor comfort. Through meticulous renovations and innovative technologies, the Passive Rowhouse Project aims to significantly reduce energy consumption – particularly in heating and cooling – while simultaneously improving the overall livability of Philly’s older building stock. 

By demonstrating the potential for passive design principles in a dense urban setting, this initiative not only sets a high standard for sustainable housing. It also contributes to the preservation of the city’s architectural heritage – demonstrating the compatibility of modern energy efficiency with historical structures.

Ivy Commons and Hemlock Towns Developments by AVLV

At AVLV, our design team often combines passive and active design strategies to make our buildings more energy-efficient and less expensive to operate. For example, we added a solar pergola, shared intensive green roof, and geothermal heating and cooling to our mixed-use Ivy Commons project. This development boasts fourteen residential units, one commercial space, and electric car charging in our shared parking area.

Our Hemlock Towns project — which is a rowhouse development like those described above — offers residents a photovoltaic pergola alongside other sustainable features that reduce the building’s environmental impact. Explore additional AVLV projects here.

Other Initiatives in Philadelphia Include…

  • A new Heat Pump Installation Lab by Philadelphia’s Energy Coordinating Agency
  • The PECO Energy Efficiency Program
  • The Building Energy Performance Program

Final Thoughts About Generating & Saving Energy

With so much energy demand and many emerging technologies, we must reimagine energy efficiency strategies by combining passive and active solutions. From solar thermal panels to heat pumps, developers often worry about the upfront cost of creating an energy-efficient building. While the upfront cost of creating an energy-efficient building can be significant, the cost savings can be enormous too.

Developers and property owners can achieve substantial cost savings by implementing both active and passive energy efficiency strategies in their buildings. Active strategies – such as high-efficiency HVAC systems, lighting controls, and renewable energy installations – directly reduce energy consumption and operational costs. By investing in these technologies and practices, property owners can lower utility bills, decrease maintenance expenses, and extend the lifespan of building equipment. 

Passive strategies – on the other hand – leverage natural elements like sunlight, thermal insulation, and natural ventilation to save energy and minimize the need for mechanical systems. Through careful design, property owners can reduce heating and cooling demands – resulting in long-term energy savings and enhanced occupant comfort. 

Moreover, both active and passive strategies often qualify for government incentives, tax credits, and rebates – further enhancing the economic benefits while fostering sustainability and resilience in the built environment. For more information about the ROI rof energy efficiency strategies, check out this resource recently published in the Journal of Energy Efficiency.




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