The traditional design approach for building projects has been sequential. The building architecture is designed first, and MEP installations are specified based on the layout and available spaces. However, collaboration among design professionals provides an excellent chance to improve energy efficiency. Architectural features have a significant impact on how a building uses energy, and they also affect the cost of MEP systems.
Nature can accomplish functions of many electrical and mechanical systems at zero cost. Consider the following examples:
- LED is the lighting option with the lowest energy consumption, but natural lighting is free.
- Demand controlled ventilation achieves a high efficiency, by adjusting airflow according to occupancy. However, natural ventilation consumes no fan power.
- Modern air conditioners are highly efficient, but an airside economizer can achieve free cooling when outdoor air has the right temperature.
- Domestic hot water systems with heat pumps have the highest efficiency, but a solar collector uses a free heat source.
A building can improve its efficiency by using the most efficient equipment and appliances available. However, the best performance can only be achieved by taking advantage of the free lighting, ventilation, heating and cooling offered by nature.
Using Natural Lighting Effectively in Buildings
Sunlight is free, but the careless use of natural lighting has negative consequences. Consider that the sun’s brightness causes glare, and there is also a significant heating effect.
First of all, the sun causes glare when it is in direct line of sight, or when reflected on shiny surfaces. Glare causes discomfort, and long-term exposure is harmful for human vision. In work environments, uncontrolled glare also reduces productivity by causing distraction and discomfort.
The heating effect of the sun is detrimental for energy efficiency, since air conditioning systems must deliver more BTUs of cooling. When a building envelope does not block solar heat gain effectively, the lighting savings are negated by the extra cooling expenses. There are many ways to achieve natural lighting with minimal solar heating:
- Skylights are useful in low-rise buildings, as well as the upper levels of high-rise constructions. Their geometry allows the passage of light, while blocking heat.
- The window layout should also minimize solar heating and glare. External shading and vegetation can be used to block direct sunlight.
- There are also motorized shades that can be automated, to open and close based on the sun’s position. The east side of buildings gets the most sunshine in the morning, while the west side is exposed in the afternoon.
The type of windows also influences the performance of the thermal envelope. Triple-pane windows with low emissivity coating achieve the best performance; the best models can reduce heat transfer through fenestration by over 70 percent.
Natural Ventilation and Free Cooling with Outdoor Air
In many residential and commercial buildings, HVAC systems use more energy than all other equipment combined. As a result, energy efficiency measures that target HVAC can achieve significant savings.
Ideally, a building should have an airtight construction to improve heating and cooling efficiency. However, some climate zones have a high potential for natural ventilation. A common solution is adding an atrium to the building, which causes an upward air current. Individual zones have outdoor air intakes, to replenish the air removed at the atrium.
Places with temperate climate also have the potential for free cooling with outdoor air. Consider that buildings gain heat from both internal and external sources. However, when the weather is mild, the air conditioning system works mostly to remove heat from indoor sources.
- There are times when the outdoor air has a suitable temperature to provide the required cooling, and air conditioning systems can be ramped down.
- An airside economizer increases the outdoor airflow when this condition is detected.
- Economizers increase fan power consumption, due to the higher airflow. However, the air conditioning savings are even higher, and the overall HVAC cost is reduced.
Taking advantage of natural ventilation requires collaboration between architects and HVAC engineers, since the building geometry must be adequate. Even higher efficiency is possible with airside economizers, in climate zones that allow their use.
written by
Michael Tobias, founder and principal of Chicago Engineers, an Inc 5000 Fastest Growing Company in America. He leads a team of 30+ mechanical, electrical, plumbing, and fire protection engineers from the company headquarters in New York City; and has led over 1,000 projects in Chicago, New York, New Jersey, Pennsylvania, Connecticut, Florida, Maryland and California, as well as Singapore and Malaysia.