Traditionally, the building design process has followed a linear approach, where MEP installations are specified with completed architectural drawings. However, there are significant opportunities to improve building energy efficiency if architects and engineers follow a concurrent design approach.
Architectural decisions influence many aspects of mechanical, electrical and plumbing installations. For instance, the number of sprinkler heads to achieve full coverage may vary depending on the architecture, even if the total area does not change. Likewise, window placement influences lighting design and HVAC loads are strongly dependent on the building envelope.
A linear design approach may lead to missed opportunities for energy efficiency, while a concurrent design process allows synergy between architects and engineers.
How Fenestration Influences Lighting Design
LED lighting can achieve savings from 30% to 90%, depending on the type of lighting it is compared with. LED products also save on lamp replacements, thanks to their long service life. However, even the most efficient lighting system cannot compete with free sunlight.
- A building can minimize its lighting costs with smart window placement, and skylights are also viable for upper floors and low-rise construction.
- LED lighting fixtures consume over 60% less electricity than HID lighting, for example, but daylight reduces consumption by 100%.
However, sunlight also has disadvantages that must be considered when designing fenestration. The heating effect on building interiors can be significant, increasing air conditioning expenses during summer. Sunlight can also cause glare issues if the window placement makes the sun directly visible for occupants. Fortunately, there are design strategies that mitigate both issues.
When designing fenestration, a very important factor is understanding the sun’s position in the sky throughout the year.
- For buildings in the northern hemisphere, most sunlight falls on the southern facade throughout the year.
- The eastern and western facades get abundant sunlight in the morning and afternoon, respectively.
- Therefore, windows facing north can provide natural lighting with minimal heating and glare. When facing in other directions, windows must have adequate shading to block direct sunlight.
An optimized window layout yields even better results with triple-pane low-emissivity glass. These windows minimize unwanted heat transfer in both directions: they gain less heat than conventional windows during summer, and lose less heat during winter. Triple-pane windows typically reduce heat transfer by over 60%, and the best products can achieve a reduction of over 80%.
To maximize lighting efficiency, a building can be equipped with a daylight harvesting system, which adjusts lighting fixtures in response to the available daylight:
- When natural lighting is sufficient, indoor lights are turned off completely.
- When additional lighting is required to complement daylight, the indoor lights are set at partial output with automatic dimmers.
- The full lighting output is only provided when natural lighting is unavailable.
The most efficient lighting solution for a building is achieved with a smart fenestration layout, triple-pane low-e glass, LED lighting and daylight harvesting. This also reduces unwanted heat gain during summer and the lighting heat output, saving on air conditioning.
Balancing Airtightness and Natural Ventilation
An airtight building envelope enhances energy efficiency, since it minimizes the heat gain and heat loss caused by air leaks. An airtight envelope complements high-performance windows, achieving a further reduction of HVAC design loads. Of course, the building must have adequate insulation to reduce unwanted heat movement by conduction.
Depending on the local climate, natural ventilation can be an effective strategy to improve energy efficiency. However, natural ventilation is only possible if the building architecture is optimized for the concept. Typically, the building has an atrium to establish a natural upward flow of air, and air intakes are placed strategically to cover the different building areas.
Airtightness is important even with natural ventilation, since the building owner must have the option to use HVAC when the weather demands it. This requires control over the outdoor air supply, which is only possible with an airtight buildings.
HVAC Equipment Selection: Capacity and Efficiency
When architects and engineers collaborate to optimize a building, the HVAC capacity can be reduced drastically. This is highly beneficial for the project owner, since smaller equipment consumes less energy while having a lower price. An oversized installation does not reach optimal performance even if it has the highest efficiency rating in the market, while being more expensive than necessary.
HVAC efficiency does not end with adequate equipment selection. Further efficiency gains are possible with various system upgrades:
- Variable frequency drives (VFD) can control air handlers, cooling towers, hydronic pumps and other motor-driven equipment. Reducing motor speed during part-load conditions is more efficient than intermittent operation, while being less taxing on the service life.
- Energy recovery ventilation (ERV) can exchange heat and humidity between the outdoor air supply and the air exhaust. This can reduce four types of loads: heating, cooling, humidification and dehumidification.
- Demand control ventilation (DCV) consists on adjusting airflow according to occupancy, instead of keeping the full design airflow at all times. This not only reduces fan power, but also the extra heating and cooling associated with a higher airflow.
While these measures can be deployed independently from the architectural design, they can achieve higher savings if the building itself is optimized for minimal HVAC loads. A drastic reduction of both lighting and HVAC expenses is possible when architects and engineers collaborate to boost building efficiency.