ASHRAE Journal - April 2010 - 51

technology award case studies
conservation strategies, including highefficiency chillers, VAV zone control with tracking exhaust, and air volume setback for unoccupied spaces were incorporated into the design. In addition to these traditional measures, three unique measures were included and are discussed in this article. The estimated incremental (additional) cost of these measures was $570,000, of which approximately $400,000 was paid for by the local power utility.
Air Handler Configuration

Since Harborview policy mandates the use of 100% outdoor air systems, multiple supply air handlers were arranged to discharge onto a common manifold. The air handlers are identical for standardization of spare parts and were sized to optimize equipment space use and achieve a low cost-per-cfm. Although five ideally sized air handlers could meet building supply airflow requirements, a sixth was added to reduce energy consumption, provide redundancy and simplify maintenance. Each air handler is equipped with automatic dampers to isolate it from the common manifold when not in operation. Any one unit can be shut off for maintenance and the variable frequency drives for the other five increase output to avoid impacting service to building. Six separate exhaust air handlers with runaround heat recovery coils are manifolded and operated in a similar fashion, providing full redundancy. All exhaust and supply air handlers are connected to a common heat recovery glycol-water piping system. One of the unfortunate side effects of exhaust air heat recovery is the significant increase in fan energy needed to overcome internal pressure drop associated with multirow heat recovery and preheat coils. This higher internal pressure drop would traditionally result in the need for significantly more electrical energy to operate the fan systems. To mitigate this electrical impact, all air handlers are operated, including the redundant units, maintaining the
April 2010

cfm through each air handler at 83% of capacity. Due to airflow physics, air handler internal pressure drop is reduced as a square of the airflow reduction. After considering the lower airflow and much lower internal pressure drop, one could expect a cube-root reduction of energy. After factoring in a slight reduction of fan, motor and VFD net-efficiency at part load, it was estimated that 83% of the airflow requires 69% of the energy. Even though one extra air handler is operating (20% more air handlers), each is only using 69% of the energy, yielding a 17% net savings.
Multitemperature Distribution Systems

Building at a Glance
Name: Harborview – Norm Maleng Location: Seattle Owner: King County Principal Use: Level 1 Trauma Center Includes: Surgery, recovery, intensive care, airborne infection isolation rooms, specialized clinics and central sterilization/supply Gross Square Footage: 255,000 Substantial Completion/Occupancy: July 2008 Occupancy: 100% National Distinctions/Awards: 2010 ASHRAE Technology Award, Honorable Mention; 2009 Build Washington Award; AGC Award for Public Buildings Over $5 million

As with most hospitals, the Norm Maleng Building uses constant-volume and variable air volume reheat for zone temperature control. Traditionally, air is delivered to internal and perimeter zones at the same temperature. All air is cooled to the temperature required to meet the needs of the zones with the highest air-conditioning load and then reheated as needed to keep all other zones comfortable. Because of the Norm Maleng Building’s high ventilation standard, reheat energy could be significant. To conserve energy, the Norm Maleng Building was constructed with two supply air-distribution systems, one serving only the windowed perimeter zones with minimal internal heat loads (patient rooms, for the most part) and one serving the rest of the process-intensive building having a relatively constant need for cooling. This unique air handler arrangement allows the air for the perimeter zones to

be taken from one end of the manifold, and the air for all other zones taken from the other end. This allows the supply duct riser serving the perimeter zones to provide warmer supply air temperature most of the fall, winter and spring (thanks to Seattle’s famous overcast weather) to minimize reheat. The two air-handling units located close to the perimeter distribution takeoff point provide most of the supply air needed for the perimeter rooms and their discharge temperatures are reset based on

Six Air-Handling Units Perimeter Zones (One-Third Airflow) Interior Zones (Two-Third Airflow)

Figure 1: Supply air-handling unit manifold arrangement. ASHRAE Journal 51

ASHRAE Journal - April 2010

Table of Contents for the Digital Edition of ASHRAE Journal - April 2010