Many energy efficiency measures focus on mechanical and electrical equipment. However, the efficiency of a building can often be improved even before specifying MEP installations. The building envelope and its internal layout influence energy performance, and architectural decisions can impact both lighting requirements and HVAC loads.
Together, HVAC and lighting can account for over 75% of energy expenses. For this reason, any design decision that reduces the need for these building systems is beneficial for energy performance. While it helps to use efficient solutions like LED lighting and variable refrigerant flow systems, even greater efficiency is possible by optimizing the building itself.
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Taking Advantage of Sunlight in Building Designs
Sunlight can be double-edged in architectural design: while it provides natural and free lighting, it can also cause glare and unwanted heating. Adequate use of windows and skylights is very important, since they should ideally allow sunlight in while preventing glare and heating.
For buildings in the northern hemisphere, north-facing windows get indirect sunlight, with minimal glare and heating effects. On the other hand, east-facing windows get plenty of direct sunshine during the morning, while west-facing windows are affected during the afternoon. Finally, south-facing windows have the highest exposure to direct sunshine throughout the year. Window shades and vegetation can be used to minimize glare and heating from building facades that are exposed to direct sunshine.
The type of window also influences performance, and the best effect is achieved when windows have triple-pane glass with low emissivity. A triple-pane low-e window can block around 75% of heat transfer compared with conventional single-pane glass.
Glare is detrimental because it can cause discomfort and distraction, and it can also damage human vision with long-term exposure. On the other hand, the main negative consequence of excessive solar heating is an increased air conditioning load, and cooling is already the highest energy expense during summer for many buildings.
Using Natural Ventilation
While natural ventilation is feasible in small buildings, meeting the requirements of a high-rise construction with natural ventilation by itself is very difficult. For this reason, natural ventilation in tall buildings is normally designed to complement mechanical ventilation, and not intended as a replacement.
The feasibility of natural ventilation is influenced by local wind conditions and microclimates. Wind speeds and the prevailing wind direction are considered when specifying building orientation and air intakes.
With respect to the building interior, a common design strategy is using an atrium to create a natural air current upward. However, this approach can create a significant pressure difference between indoor and outdoor air, making doors difficult to open.
Natural ventilation designs for high-rise constructions typically break down the building into zones, to prevent excessive pressure differences or stack effects.
With adequate outdoor temperatures, natural ventilation can drastically reduce the need for space heating and air conditioning. However, this is strongly dependent on the local climate, and the approach may be unfeasible in regions where HVAC is used all year long.
Optimizing the Building Design to Reduce HVAC Loads
Complete independence from HVAC is rarely possible, but there are many ways to minimize heating and cooling loads. Ideally, a building should minimize summer heat gain and winter heat loss, with an envelope that can conserve indoor temperatures as long as possible. Windows should allow natural lighting while keeping solar heating at bay, and LED lamps can reduce the heat footprint of lighting installations.
Adequate insulation and airtightness are important for a high-performance building envelope, but there is a key design decision at play. Natural ventilation and airtightness are in opposition, and enhancing one aspect limits the other one. In great part, the local climate determines if it makes sense to increase natural ventilation at the expense of airtightness.
Energy efficiency measures are often associated with MEP upgrades, but efficiency can also be enhanced through the building’s architectural design. Ideally, the building should allow natural lighting while minimizing glare effects and unwanted heating. Depending on the local climate, architects can decide if it makes sense to enhance natural ventilation or if the building should be as airtight as possible. High-performance windows and adequate insulation are also vital elements of an efficient building envelope.
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