Environmental Engineering Reference
In-Depth Information
Picture 11.2
Green roof at the EPA Region 8 office building. Green roofs save significant amounts of
energy for heating and cooling.
Courtesy Environmental Protection Agency.
HVAC systems can benefit from the installation of heat recovery systems. To maintain
good air quality HVAC systems recirculate only a fraction of the air. The rest is discharged
to the exterior and replaced with fresh air. The air that leaves the building contains energy
that can be recovered with the right equipment. Air-to-air heat exchangers and energy
recovery wheels can recover energy with efficiencies up to 80 percent. An air-to-air heat
exchanger brings the outgoing and incoming air streams into thermal contact through a
thin wall, allowing the heat to transfer from the outgoing to the incoming air. Energy
recovery wheels allow both temperature and moisture to be exchanged by means of a rotat-
ing disk filled with a material capable of absorbing heat and moisture. When outgoing air
from the building passes through the disk, heat and moisture are transferred to the mate-
rial. As the disk rotates, the material gets relocated to the incoming air stream, and heat
and moisture get transferred from the disk to the air current. In the summer, the opposite
effect takes place.
Lighting efficiency can be improved by using efficient lighting fixtures, decreasing light-
ing power density in areas where is not needed, and installing occupancy sensors. In new
constructions, the incorporation of skylights and windows maximizes the exposure to natural
light and minimizes the need for artificial lighting.
INNOVATING TECHNOLOGY
As was discussed in Chapter 6, efficiency cannot be improved unlimitedly. At some point, a
ceiling is hit and further improvements in efficiency become ineffective, and then it is time to
innovate technology.
The problem with innovation is that many times the technology does not exist or it is not
mature enough to be implemented in a plant setting. In other cases, the technology is available,
but because it is not proven or because of its novelty, the expenditure of capital can be steep.
In a third scenario, the concept has been well-known for a long time, but the technology was
not available to make the concept to work. A good example is air cycle refrigeration that
