When property management companies are considering building energy efficiency, there is a tendency to focus on mechanical, electrical and plumbing (MEP) installations. While it is true that smart decisions in MEP design can yield long-term energy savings, it is even better if the building itself is also designed for minimal energy consumption. Therefore, civil engineers and architects can also make a significant contribution to lower energy consumption and greenhouse gas emissions in NYC buildings.
The systems that account for the largest share of energy consumption in NYC buildings include space heating, domestic hot water, space cooling, ventilation and lighting. There are two complementary approaches to reduce the energy used by these installations: one option is using high-efficiency equipment and automatic controls to minimize energy usage, but it is also possible to reduce the demand on building systems with smart architectural and structural design choices. The following are some viable options to reduce the energy needs of a building:
- Making ample use of daylight with optimized window and skylight placement.
- Minimizing heat gain from the sun and from outdoor air during the summer.
- Maximizing heat gain from the sun and minimizing indoor heat loss during the winter.
- Designing the building to use natural air convection for ventilation whenever possible.
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Daylighting in NYC Buildings
LED lighting upgrades offer significant energy savings, especially when displacing old and inefficient lighting systems, such as incandescent bulbs or T12 fluorescent tubes. However, keep in mind that LED lighting still consumes electricity - it offers low cost but is not free. The sun is the only source of free lighting.
Keep in mind there are special considerations when building architecture is optimized for daylight. Simply using the largest window area possible to allow plenty of sunlight in is not the best approach. Consider that sunlight brings two negative consequences with careless use: glare and summertime heating.
Glare is a visual impairment that occurs when we look directly at a concentrated light source, or its reflection on a surface. Glare can be classified into two subtypes: disability glare is the type that limits visibility but is tolerable to look at, while discomfort glare is the type that causes an instinctive reaction to look away. For example, the reflection of a lighting fixture on your computer screen causes disability glare, while looking directly at the sun by accident causes discomfort glare. Keep in mind that glare does not serve any practical purpose and must be avoided always, unlike solar heating which can be beneficial during the winter or for domestic hot water.
Solar heating is more complex to manage, since it can be beneficial or detrimental depending on the season. During summer, when building cooling systems are operating at their full capacity, solar heating adds to their load and increases energy expenses. The opposite applies during the winter, when the solar heating effect is subtracted from the load on space heating systems, saving energy.
Architects and civil engineers can arrange building fenestration for effective daylighting, while keeping glare and unwanted solar heating under control.
- North-facing windows tend to be the most effective, since most of the sunlight that reaches the north side of buildings is indirect - there is no glare.
- East-facing windows get direct sunlight during the morning, while west-facing windows receive in the afternoon. Windows with these orientations must be placed so that occupants are not affected by glare.
- South-facing windows get sunlight during the entire year, but note that the sun is lower in the sky during winter. Window shades can be used to block the sun when higher up in the sky during the summer, while allowing sunlight in during the winter. To make this viable, it is important to keep glare prevention in mind.
Skylights are installed on rooftops as implied by their name, and they have a prismatic design that eliminates glare while minimizing heat gain. However, skylights are better suited for single-story buildings with ample floor area, such as warehouses and industrial facilities. Their application in high-rise construction is very limited, since only the upper level can benefit.
Insulation and Airtightness in NYC Buildings
You can have the most efficient HVAC equipment in the market, but energy expenses will stay high if the building envelope is not an effective barrier against heat transfer. Consider that every BTU of heat gained in the summer or lost in the winter represents energy expenses. However, even though reducing heat transfer to zero is not possible, it can be minimized.
Most unwanted heat transfer between a building and its surroundings occurs by two mechanisms: conduction across walls and windows, and air leaks. In the first case heat transfer occurs directly, while in the second case heat is carried by air, but the effect is the same: heating and cooling equipment must work harder to compensate.
High-rise glass buildings have become very common in NYC, but they come with building envelope performance issues. Walls are much better than windows in preventing heat transfer: a high performance triple-pane window conducts much less heat than a single-pane window, but even a simple wall provides far better insulation than both.
Like in the case of daylighting, it is much easier to achieve a high-performance building envelope if you take it into account starting from the architectural design phase. Building envelope upgrades are possible in existing constructions, but rebuilding it completely can have a prohibitive cost.
Natural Ventilation in NYC Buildings
Although ventilation systems consume less energy that space heating and cooling equipment in most cases, their electricity expenses can still be significant. If deployed effectively, natural ventilation can yield massive savings in fan power, especially in high-rise constructions.
In existing buildings, there are normally ample opportunities to deploy daylighting, insulation and airtightness, even if the performance does not match that of a new construction designed with these features. However, natural ventilation tends to be more difficult to deploy: the building’s architecture and structural design must be optimized to make it possible, which would require significant changes in existing buildings.
Natural ventilation in high-rise buildings is based on the fact that air rises and displaces the air above it as it gains temperature. These buildings are normally designed with a very tall atrium, which allows a constant airflow upward, displacing warm air from interior spaces through specially-designed outlets.
Green Construction Certifications for NYC Civil Engineers and Architects
Many organizations provide training and certification for construction industry professionals who want to focus on energy-efficient construction. The following are some of the best-known US programs that include professional certification:
- The LEED program from the US Green Building Council offers a wide range of professional certifications.
- The ENERGY STAR program from the US Environmental Protection Agency offers a directory of Licensed Professionals.
- The Passive House Institute US offers professional certification for consulting, green building and quality assurance / quality control.
Conclusion
MEP engineers can collaborate with civil engineers and architects to ensure that a building achieves the highest possible performance. While MEP design engineers make sure that building systems achieve their purpose at the lowest energy cost possible, architects and civil engineering can deliver a building that minimizes energy consumption by design. Assuming MEP equipment efficiency stays constant, energy expenses will be much lower if the building includes daylighting, insulation, air-tightness and natural ventilation.
