ASHRAE Journal - April 2020 - 51

2020 ASHRAE TECHNOLOGY AWARD CASE STUDIES

TABLE 2 ENR2 code and modeled vs. actual performance.

ENR2 Model

ENR2 2017

Heating (kBtu/yr)

Baseline
1,028,400

228,831

1,981,440

Cooling (kBtu/yr)

6,281,196

6,651,936

5,051,100

Electric Power
(kBtu/yr)

5,206,600

4,115,786

3,434,037

Total (kBtu/yr)

12,516,200

10,996,554

10,466,577

EUI (kBtu/ft2·yr)

their clothing decisions to the ofﬁce environment.
Occupant surveys were distributed the ﬁrst winter
after occupancy and again in the fall of 2018, with
a high level of participation. Seventy-two percent
were satisﬁed with thermal comfort, and over 91%
were satisﬁed with IAQ.

FIGURE 3 Modeled vs. monitored performance for 2016 and 2017.

Innovation
Although hydronic chilled-beams and UFAD systems may no longer be considered innovative in
the HVAC space at large, the systems in the ENR2
building are among the ﬁrst of their type at the
University of Arizona and across southern Arizona.
Some aspects of this installation differ from typical
systems installed elsewhere.
One dual-tunnel air handler was provided for each
of the north and south building blocks. Shown in
Figure 5, these units temper outside ventilation air
through a 1-row preheat coil and a 10-row cooling
coil. A bypass damper reduces fan static pressure
during heating or when downstream sensible cooling is possible. This damper closes to allow the coil
to dehumidify during Tucson's summer monsoon
season (Table 1). Tempered air is then available to
be drawn through either the chilled-beam or the
displacement airstreams, which are nominally
operated at differing temperatures (55°F [12.8°C]
chilled beam [CB], 68°F [20°C] displacement ventilation [DV]). Return air dampers enable mixing, used
primarily in the DV stream. Under occupied conditions, primary air to activate induction in the chilled
beams is, in almost all cases, limited to the minimum ventilation requirements. While this approach
requires large chilled beams, it substantially lowers
fan horsepower, air-handler size, and duct sizes
serving the perimeter.
Another unusual approach taken in the design of
the chilled-beam system is that it is two-pipe, 55°F

FIGURE 4 Energy consumption of cooling, heating, HVAC, lights, misc. loads.
TABLE 3 ENR2 mechanical system cost and payback vs. baseline system.

ENR2

$41.43/ft2

Premium at
123,985 ft2

$177,299

Baseline

$40/ft2

Annual
Energy Savings

$73,500

ENR2
Premium

$1.43/ft2

2.4 Year
Payback

chilled water, with three to four ofﬁces ganged to
each thermostat. Heating is accomplished through
a hot-water coil in a terminal unit, serving each
exposure per ﬂoor. The entire bank of ofﬁces along
the south exposure, for example, are provided with
a single heated air temperature, based on the average of individual room stats. Although this approach
was a cause of concern during design, it has proven
to be satisfactory in operation. Uniform and lowvelocity air distribution induced by the hydronic
units provided with this air appears to address cold
(or hot) draft complaints.
APRI L 2020

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ASHRAE Journal - April 2020

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