ASHRAE Journal - June 2013 - 47

2013 ASHRAE Technology Award Case Studies
Energy Efficiency
To verify system operation and comply
with LEED requirements, measurement
and verification (M&V) was completed.
The M&V process entailed tracking the
energy use of the facility for one year
to ensure savings predicted in the energy
model were being realized. The M&V
showed the building was using less energy than anticipated in the energy model
and consuming 25% less energy than allowed by ASHRAE Standard 90.1-2004,
with a recorded energy use of 207 kBtu/
ft2·yr (2 350 899 kJ/m2·yr). Figures 1
and 2 show the monthly energy consumption of the building compared to
the baseline energy model.
To achieve the savings, the team focused on reducing fan and reheat energy, designing an efficient heating/
cooling plant, specifying high efficiency
lighting and optimizing use of the energy recovery chiller.

Fan Energy
Custom air-handling units, coils, and
filters were sized to maintain a maximum face velocity of 350 fpm (1.8
m/s). This reduces pressure drop and fan
horsepower consumption for the life of
the building, also reducing noise levels
to provide a healthier acoustical environment.
Innovative filters within the air-handling units use advanced pleated technology that allow air to travel through
larger filter surface areas in smaller
housings, while lowering overall pressure loss.
Air-handling unit fan system effect
was reduced by properly designing an
evase at each supply fan discharge.
This gradual transition to the supply
duct system accounted for static pressure reductions and overall fan size reduction.
In addition, much of the facility’s ductwork was sized at no more than 0.1 in.
w.c. (24.9 Pa) friction per 100 ft (30 m)
of duct to facilitate lower pressure drop
within the entire duct system.
The reduced fan horsepower showed
significant savings when compared to
typical hospital designs and also showed
savings when compared to the Standard
June 2013

90.1-2004 baseline system. When comparing the fan horsepower to a conventional design, a savings of more than
200 hp (149 kW) was calculated.

Reheat Energy
Energy recovery chillers were installed to transfer energy from the hospital’s chilled water loop to the heating
water loop, rather than rejecting it outdoors. Domestic hot water and boiler
feed water, in turn, were preheated by
the heating water via a double-wall heat
exchanger.
Providing heat from the energy recovery chiller was less expensive than
boiler heat, even when cooling was
not needed. When both heat and cooling were needed, the economics were
extremely favorable. To take advantage
of this, chilled water fan coil units were
used in lieu of overhead air to cool energy intensive spaces (data centers, imaging equipment rooms, etc.). In addition, chilled water coils were added to
the exhaust airstream to harvest energy
from the exhaust air during the prolonged cold periods in Wisconsin. By
maximizing the year-round chilled water load and sizing the energy recovery
chillers to match, the payback for the
energy recovery chillers was optimized
to three years.
Occupancy control in health care is an
important step to reduce fan and reheat
energy. Reducing air change rates in unoccupied areas such as operating rooms
reduced the fan and reheat energy. Occupancy control also was provided for
office and other support areas to minimize energy use during unoccupied periods.

Heating and Cooling Plant
A variable primary chilled water system with a 14°F (7.7°C) DT minimized
pumping energy was installed. Also, efficient centrifugal chillers were chosen
and the chilled and condenser water
temperatures optimized for energy savings and first cost.
High-efficiency vertical water tube
boilers were provided with stack economizers to preheat the boiler feed water.
The low-water volume within the boil-

Atrium at Aurora Medical Center.

Building at a Glance
Aurora Medical Center
Grafton Wisconsin
Location: Grafton, Wis.
Owner: Aurora Healthcare
Principal Use: Hospital
Includes: 107 patient rooms; 18 operating rooms; compounding (USP 797
compliant) and retail pharmacy; imaging equipment including X-ray, MRI,
CT; four cardiac catheterization labs;
nuclear medicine; laboratory, atrium
Employees/Occupants: 594 full-time
employees, 494 visitors, 80 patients
Gross Square Footage: 526,000
Conditioned Space: 526,000 ft2
Occupancy: 95%
National Distinctions/Awards: LEED
Silver
ASHRAE Journal

ASHRAE Journal - June 2013

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