Basics of Daylighting in a Green Environment
The use of natural sunlight, known as daylighting, to illuminate a building can save energy, reduce operating costs, create visual appeal, and enhance occupant health and productivity. The U.S. Green Building Council Leadership in Energy and Environmental Design (LEED™) rating system encourages the use of daylighting to achieve high performance buildings. This course provides an introduction to the use of daylighting in commercial spaces. The course objective is to show why daylighting should be considered, the basic guidelines of using daylighting and some words of caution when using certain daylighting techniques.

5.4 Coordination With Mechnical

"Tips for Daylighting" offers some suggestions for increasing savings when using daylighting by coordinating this effort with the mechanical group.

To Reduce First Costs

  • Calculate peak cooling load and energy use with reduced perimeter electric lighting load and size mechanical system accordingly. Be sure to specify proven and reliable daylight controls that will dim or switch electric lighting during peak cooling conditions.
  • Examine cooling system downsizing opportunities with various glazing and shading options. Work with architect in possible fine-tuning of window sizing, window location, shading strategy and glazing selection for a smaller and more efficient system.
  • Insulating glazing may eliminate the need for a terminal reheat system at the perimeter in moderate climates. Winter morning warm-up may be accomplished by the central heating system with appropriate controls. In addition to the energy savings, first costs may be lower with improved glazing versus the added mechanical equipment.

To Reduce Operating Costs

  • Calculate the annual energy saved with improved fenestration elements. Even if there are no mechanical first cost savings, reduced operating costs decreases the payback period. Calculations will show some of the benefit of exterior over interior shading, lower solar heat gain coefficient glazings, and daylighting controls. Be sure to account for cost savings from lower demand charges if appropriate.
  • Select an effective energy management system to optimize building operation and tie together all HVAC, lighting and automated shading controls.
  • Set a larger temperature dead band for circulation spaces. Let these and other non-critical spaces drift more than task areas.

To Maintain Thermal Comfort

  • Window and shading design are strongly linked to perimeter zone comfort, regardless of air temperature. Hot or cold glass behaves like a radiant panel and affects occupant comfort independent of air temperature. The asymmetric nature of this heat gain or loss is an added discomfort. Occupants will respond by adjusting the thermostat, wasting energy without satisfactorily improving comfort. Similarly, unshaded direct sun striking occupants causes discomfort independent of air temperature. Consider comfort as seriously as energy when advising architect on fenestration design.
  • Consider the effect of the window's mean radiant temperature on thermal comfort. Dark tinted glazings or absorptive window films increase the window's surface temperature significantly in summer. Poorly insulated windows (high U-value) decrease the surface temperature in winter. Since the mechanical system controls the room's air temperature, occupants near the windows can be very uncomfortable. As noted above, a low U-value and low solar absorption will keep the glazing surfaces closer to room temperature. Radiant heating and cooling systems can provide some advantages in control of the thermal environment but are not yet commonly used in buildings.

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