Energy optimization and reuse through systems integration
Nearly 40% of the total U.S. energy consumption in 2012 was consumed by residential and commercial buildings, according to the U.S. Energy Information Administration. While each building is a consumer of energy, they also contain energy resources that are under-utilized or not even considered as energy resources. Most energy-reduction efforts focus on the optimization of individual systems in isolation, but rarely step back to consider the building as a whole. Even less frequently does a corporation consider the potential consolidation of programs for a long-term energy benefit.
A common scenario involves the consolidation of an office and a lab in a single facility. ASHRAE Standard 90.1 requires energy recovery above a minimum design outside airflow percentage and based on the climate zone. An office and an adjacent lab served by independent systems are subject to this requirement, with the lab likely requiring a minimum 50% effective exhaust energy-recovery system to be in compliance. While the result of ASHRAE 90.1 compliance is increased system efficiency, the overall building performance can be further improved by serving both areas with a common system.
This systems integration approach provides a reduction in first cost, as well as an ongoing energy-use reduction. The first-cost reduction comes from the elimination of the office energy-recovery system. The ongoing energy-use reduction comes from lower volumes of outside air to be conditioned (outside air for the office is reused as a portion of single-pass ventilation of labs). This same systems integration concept can also be applied to other building programs for a significant energy improvement.
Labs and data centers are some of the largest energy consumers for buildings. Labs operate continuously and must condition large quantities of outside air. Data centers also operate continuously and require on-going cooling for computer equipment. While these programs seem quite different on the surface, they can be integrated in a way that complements the energy needs of both.
Data centers reject “waste” heat to their surrounding environment. A lab located in a cooler climate will require a large amount of heating in winter. If the “waste” heat from the data center was reused to the lab, there’s the potential for a sizeable heating reduction. At the same time, this heating reduction for the lab translates to a cooling reduction for the data center. The net effect of this integration is an energy-use reduction for both programs. As water is typically used in the process of data center cooling, there’s also a corresponding water-use reduction.
Traditional data centers utilize air-cooled equipment. Unfortunately, air is a poor conductor of heat and has a high transport energy. In contrast, water is an excellent conductor of heat and has a relatively low transport energy. Recently there’s been a resurgence in water-cooled data center equipment, particularly for high-performance platforms. Water cooling allows for higher rack power densities with the potential to generate a high quantity of “waste” heat. When captured in the form of water, the server heat is no longer wasted, but can be effectively applied for building heating.
The heating available can be used not only for labs, but office heating as well. When integrated on a campus, these systems can serve other facilities; and with proper planning could ultimately allow the data center to become a significant part of the heating plant for the campus. The U.S. Dept. of Energy (DOE)’s National Renewable Energy Laboratory (NREL)’s Energy Systems Integration Facility (ESIF), R&D Magazine’s 2014 Laboratory of the Year, takes advantage of this system integration.
Robert Thompson is a registered professional engineer and chief mechanical engineer for the S&T studio in the Phoenix office. Thompson’s designs focus on the environmental design specifics that influence the energy and sustainable performance of buildings. Otto Van Geet is a Principal Engineer at the DOE’s NREL.