Sustainability Planning Methodology of Passive First – Active Second – Renewables Last
It is well documented in the construction industry that building energy use accounts for 41% of total energy use in the Unites States. This opportunity creates an exciting time for anyone engaged in the built environment. New and innovative materials and equipment labeled “green technology” emerge daily and are marketed to change the way we do business. The search continues for the silver bullet that will fix our energy consumption problem. As we implement the latest technologies, I can’t help but ask; Does this help us reach our goal of true sustainability? Does this impact climate change? Are we, in the AEC community, doing enough to reverse emission trends? The answer to me is obvious – No. The mere existence of ESCO, ESPC, and Sustainability Consultant businesses is sufficient proof that Builders and Designers have room for improvement.
When we look at buildings, we see complex objects operating dynamically. Changes to individual energy conservation measures typically do not result in directly proportional reductions to total building energy consumption. However, changes to groups of energy conservation measures typically have a compounding impact on reduction to total energy consumption. Where do we start? As it turns out, the smoking-gun is the process of how we design, build and use buildings.
Ideally we want a methodology that provides building owners the control necessary to measure and, more importantly, manage a building(s) energy consumption. If we can prove consistency in the methodology, more control means less risk of investment on the part of building owners.
The Natural Order of Sustainability is a sustainability planning methodology of Passive First – Active Second – Renewables Last and the core principal of the Passive House standard. The Natural Order of Sustainability treats buildings as dynamic, living organisms. Natural processes and designs are the standard to which we aspire. Strict adherance to the Natural Order of Sustainability provides an organic pathway to reach zero energy consumption.
Energy Utilization Intensity (EUI) becomes the target performance metric that guides the Natural Order of Sustainability methodology. Using this approach, building owners set performance goals, back it up with sound building science, thus creating the greatest likelihood for delivering short, medium and long term financial returns. In most cases, using the Natural Order of Sustainability has a 2–3 year payback period, but can be customized to meet a client’s financial needs.
Maximizing passive strategies (i.e., insulation, envelope, air barriers, thermal bridges, shading, windows and doors) first will reduce loads for heating and cooling systems, thereby requiring smaller and more-efficient active solutions for mechanical systems.
The Passive House standard is the most rigorous set of design principles based on building science used to attain a quantifiable and ambitious level of energy efficiency within a specific quantifiable comfort level. Passive House sets the performance standard at approximately 14 kBtu/sf/yr on the basis that every functioning building requires some level of energy to operate. Passive House’s philosophy is simple: “maximize your gains and minimize your losses” through climate-specific building science. Passive House has identified the mathematical limits of diminishing returns for envelope performance (see passivehouse.com and phius.org). A passive building is designed and built in accordance with five building-science recommendations:
- Climate-specific insulation levels with continuous insulation throughout its entire envelope.
- Thermal-bridge-free connections for all building-envelope sections.
- High-performance windows (double or triple-paned windows, depending on climate and building type) and doors.
- Airtight building envelope to prevent infiltration of outside air and exfiltration of indoor conditioned air.
- High-efficiency heat and moisture-recovery ventilation.
A comprehensive systems approach to modeling, design, and construction produces extremely resilient buildings. Passive-design strategy uses highly durable material solutions like fenestration, insulation, air barrier membranes, and cladding that have a long use life even in extreme weather conditions. As a result, passive buildings offer tremendous long-term benefits in the form of energy efficiency and indoor air quality. Passive building principles have been successfully applied to all building typologies, from single-family homes to multifamily apartment buildings, offices, hospitals, schools, and skyscrapers.
Some cities, such as Brussels and Dublin, have introduced Passive House criteria—not certification—into their building codes and have achieved transformative results in the energy performance of new construction. As a result, Brussels now demonstrates a large downward trend in GHG emissions, making it a world leader in energy conservation in its building stock.
Implementing passive load-reduction strategies will reduce the size of the active systems and mechanicals required to ventilate, heat, and cool buildings. Design loads in a passive-house building are drastically lower because of the focus on the envelope and insulation, extreme airtightness, and superefficient windows. In simple terms, the building will be easier and cheaper to heat and cool, and the air quality will be better.
Strategies to reduce energy consumption for heating and cooling are most effective when mechanical equipment is decoupled. Logically, planners will optimize passive space-conditioning solutions as a core mixed-mode design strategy. Common passive space-conditioning solutions include an independent balanced mechanical ventilation system with heat and moisture recovery and preconditioning. This strategy will maximize a constant and filtered fresh air supply. Remaining peak loads can then be further mitigated by implementing highly efficient active heating and cooling systems.
Building-enclosure air-tightening means that moist, dirty air isn’t leaking into the building’s interior space from exterior sources. A constant flow of fresh filtered air flushes the living space without pulling in hot, cold, or wet air that the HVAC system must then condition.
Planners are challenged to manage internal loads and plug loads with efficient appliances, HVAC, plumbing and lighting systems that minimize sensible and latent loads and internal gains. If everything is done properly to this point, a new building will be designed to perform at approximately 14 kBtu/sf/yr, and an existing building will be designed to perform at approximately 20 kBtu/sf/yr, making them both perfectly positioned to reach 0 kBtu/sf/yr — Zero-Energy.
Passive-building strategies reduce loads which results in active-building strategies that cost less and consume less energy. As a final step, renewables can be used to zero out remaining energy consumption and carbon emissions. At this point, on-site energy generation, photovoltaic arrays, geothermal well fields, and wind farms are more affordable due to their smaller size and lower first costs. In the future, replacement costs for the renewable solutions are naturally reduced, providing advantageous life-cycle costs for the final renewable solution. Building owners who believe that renewables are the silver bullet to energy efficiency and adopt them before adopting the first two steps of the Natural Order of Sustainability are discovering that the return on investment of a renewables-first energy strategy developed in isolation does not make financial sense when analyzed as first-costs or life-cycle costs.
Many believe that installing rooftop solar panels will resolve many of a building’s energy sins. While they certainly help, the problem is that there is just not enough real estate on the roof of most buildings to handle the total building loads. Quality improvements to the envelope will last for 50 to 100 years. If limited dollars are available for a project, then putting the dollars into improvements that prevent the loss of heating and cooling energy makes more sense than adding more active equipment to mitigate the losses. When you look at the thermal image of a typical existing building on a 20-degree day and the building is blazing yellow or orange, the heat loss in the image may indicate a surface building temperature of 60 degrees. Doesn’t it make more sense to prevent the loss of energy before installing another piece of equipment to generate more energy to make up for that loss? After all, the cheapest form of energy is, naturally, the energy never used.
Natural Order of Sustainability is the Silver Bullet
The silver bullet is the process we use to design, and construct buildings for specific purposes. What we now know is to achieve aspirational results we must begin with the Natural Order of Sustainability. Once the Natural Order of Sustainability is considered, planners will begin to realize the hidden solutions to zero energy. Zero energy is possible without a financial premium or the sacrificing of thermal comfort.
The path to true reduction in energy use in the built environment requires vision and patience and a commitment to energy master-planning.
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