AKF - Bulletins - "Green" Mechanical and Electrical Systems

"Green" Mechanical and Electrical Systems

Green design is a philosophy of considering the environmental impact of all components of a building including the materials and the construction means and methods. Building materials have varying environmental impact over their life cycle that can be broken down into three basic phases: manufacturing, useful life and final disposition. Manufacturing imparts imbedded energy into a material either in the process itself, packaging, transportation, or content (virgin versus recycled raw material). The useful life of the material has an impact in either the direct energy usage or savings of the particular product, its impact on the built environment through such things as off-gassing, or its life cycle energy usage (long life, low energy). The final disposition phase relates to the ease with which a given product is absorbed back into the environment or the impact of recycling.

Mechanical and electrical systems are an important part of green buildings. If properly designed and specified, the mechanical and electrical systems will contribute positively to the overall health of the building and help minimize its impact on the environment. Green design is a holistic approach that requires the various disciplines to work collaboratively. The Owner, Architect and Engineer must have a common vision of the project goals in order to achieve a successful design.

Lighting systems have one of the biggest impacts on building performance. They have the double affect of reducing the electrical consumption of the lighting system and the HVAC system. Possible lighting and electrical design strategies are as follows:

Consider low connected load systems such as indirect using T-5 HO lamps.
Target foot candle levels should be toward the low end of the acceptable range. Make sure adequate surface luminance is provided on walls to make lower light levels more comfortable.
Consider occupancy sensors for enclosed spaces
Look at automatic daylight compensating dimming control for perimeter spaces.
Optimize daylight without increasing direct solar load through use of south facing glass with overhangs and light shelves.
Consider the use of photovoltaics.
Use low emission technologies such as fuel cells.

For HVAC systems, some of the largest uses of energy are for fans and outside air. Optimization of both of these portions of the design will have a major impact on overall energy use. The following should be considered:

"Right Size" the HVAC systems. Optimize lighting and power design wattage to minimize impact on tonnage and air flow (fan energy).
Optimize glazing design to limit HVAC load by balancing daylight vs. solar load.
Use variable speed drives and high efficiency motors
Properly size ductwork and air handling units to limit fan horsepower.
Optimize space/supply air temperature differences to reduce required air flow.
Use control system strategies, such as feed back from all zones, to reset air temperatures, etc.
Consider heat recovery to pre-treat ventilation air.
Consider demand-controlled ventilation (minimum ventilation rates that are varied in response to an indicator such as CO2 concentrations in return air). Specify interior finishes that limit off gassing of volatile organic compounds.
Consider systems with low transport requirements such as systems that supply 100% outside air as required to offset the ventilation and latent loads and provide sensible cooling and heating via radiant panels.
Take advantage of natural ventilation during swing seasons.
Use filtration and distribution strategies that control pollutants, such as under-floor displacement type air systems.
Consider gas powered air conditioning equipment.
Evaluate the potential for geothermal or thermal storage systems.
Finally, commission the systems to ensure proper operation.