ASHRAE Journal - October 2014 - 71

ARCHITECTURE: BNIM. MIKE SINCLAIR PHOTOGRAPHY

2014 ASHRAE TECHNOLOGY AWARD CASE STUDIES

ABOVE Operable windows are located within

15 ft (4.6 m) of 53% of the interior space of
the IUB/OCA.

LEFT The Iowa Utilities Board and Office of

Consumer Advocate in Des Moines is a model
facility of integrated sustainable design.

The earliest goal of this project was to meet energy
use intensity (EUI) of 28 kBtu/ft2 (317 MJ/m2) per year,
equivalent to 60% energy savings beyond the energy
code baseline of ASHRAE Standard 90.1-2004. Every
decision-from the envelope to materials to controls-
was made with this goal in mind.
The IUB/OCA project demonstrates a "net-zero-ready"
approach. Loads were reduced to the point that on-site
renewable energy was appropriate, knowing more could
be added later.
An integrated team process was employed to deliver
verified results-including, but not limited, to assessing
building placement, open-office versus enclosed-office
relationships, material selection and configuration,
strategies and systems. As a result, the IUB/OCA is a
super-efficient building with an Energy Star rating of
100. (A typical office building this size would use more
than three times the energy.)
Over the first two years of operation, the IUB/OCA has
performed at an extremely high level, with an EUI of
22.1 kBtu/ft2 (251 MJ/m2) per year without renewable
energy, and 18.8 (213 MJ/m2) with the photovoltaics (PV).
This exceeds the baseline by more than 70% and the
LEED energy model by more than 30%. The building is
outperforming efficiency targets, and the PV is providing more on-site energy than expected. For year two,
when the PV was available the entire year, the EUI was
22 without PV, and 17.5 with PV (Figure 1). Energy modeling (completed by The Weidt Group using DOE 2.IE as
part of the LEED submission) was based on ASHRAE
Standard 90.1-2004 using the Appendix G methodology (addendum a), exceptional calculations, and on-site
renewable energy.
Not wanting to overstate results, the design team
developed the energy model to reflect conservative performance. Plug load strategies, for example, were not

given full credit in the model despite the estimation that
they would pay dividends.
Energy modeling is vital to a high performance building, and more upfront effort is needed to meet aggressive goals at the end. Figure 2a shows the distribution of
the energy use for a minimum code-compliant version
of the building and program. Notice that the heating and
cooling are the largest loads, and together are over onehalf of the energy use. (This is for a packaged VAV system
with DX heating and cooling, and is defined by ASHRAE
Standard 90.1-2004.) Figure 2b shows the distribution of
the energy use as designed and confirmed at the end of
construction. Notice the largest load is now plug load,
larger than heating and cooling combined.
Also, notice that the fan/pump energy increased as a
percentage of the overall use. Electronically commutated motors were specified for the heat pumps since
they are extremely efficient and adjustable. This left
the hydronic pumping system to be optimized. Since
typical energy modeling techniques do not reflect the
pumping use well, a spreadsheet was used to evaluate
different methods of pumping.
Several systems configurations were evaluated,
from central pumping with variable frequency drives
(VFDs) to fully distributed pumping at each piece
of equipment. Since several of the loads needed a
constant flow when on, the optimum system was a
combination of central and distributed pumping. The
heat pumps were installed with automatic isolation
valves so that when off, the flow through the unit is
closed, and the flow of the overall system was reduced
by the VFD on the central pumps. Then a couple of
larger loads, such as the ERV and a water-to-water
heat pump, were provided with smaller distributed
pumps that only activate when the unit is on. This
analysis was confirmed in the measurement and
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