ASHRAE Journal - April 2021 - 64

2021

ASHRAE TECHNOLOGY AWARD CASE STUDIES

64

ASHRAE JOURNAL

ashrae.org

APRI L 2021

Total CDD-50 Per Week

Energy Consumption (kWh/Week)

* Low airﬂow velocity through
FIGURE 3 Chilled water energy savings.
cooling coils and ﬁlter banks;
100,000
250
* 24/7 telecom room cooling loads
Baseline Energy
Savings
are served by new cooling-only VAV
80,000
200
Business as Usual
boxes to take advantage of econo60,000
150
mizer " free " cooling (the existing
split DX units were converted to
40,000
100
standby duty);
* Dual maximum VAV box control
20,000
50
Measured Energy
logic with airﬂow minimums set to
Cooling Degree Days Base - 50°F
0
0
code-minimum ventilation to reJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2018
|
2019
duce cooling, fan energy and reheat;
Start
Cutover
* VAV box discharge air temperaCommissioning Complete
Of Installation Complete
ture is limited to 20°F (11°C) above
Post-Retroﬁt Period
Baseline Period Retroﬁt Period
the space temperature to avoid
excessive stratiﬁcation, maintain a
dampers and reheat valves were not operational, and
high zone air distribution effectiveness and to prevent
minimum airﬂow setpoints had been reduced below the
short circuiting;
ventilation minimum. Both indoor air quality (IAQ) and
* Demand-controlled ventilation (DCV) for densely
thermal comfort were improved by replacing the AHUs
occupied spaces;
and upgrading the terminal unit controls from pneu* Demand-based supply air temperature and duct
matic to DDC while using Guideline 36-2018 sequences.
static pressure setpoint reset;
* Dynamic reset of outdoor airﬂow setpoints based on The AHU replacements and full BAS upgrade ensured all
equipment was fully operational while providing operazone level CO2 monitoring;
* Request logic for future demand-based reset of
tor visibility, user adjustments of zone temperature
heating hot water and chilled water supply temperature setpoints and the ability to use CO2-based DCV and dual
maximum VAV control logic.
setpoints (central plant controls were not included as
Guideline 36-2018 sequences improve comfort and IAQ
part of this project);
* Rogue zone detection to help maintain effectiveness by ensuring control sequences comply with standards
and codes such as ASHRAE Standards 55-2017, 62.1-2016
of demand-based resets;
* Automatic fault detection and diagnostics (AFDD) to and 90.1-2016 and by alerting operators to noncompliance issues through AFDD. Minimum airﬂow setpoints
alert facilities' staff to operational issues that contribute
for all terminal units were recalculated to the minimum
to wasted energy;
required by California Title 24, which typically exceed
* Series-sequenced outdoor air and return air
Standard 62.1 ventilation rates by about 30% for typical
dampers (as opposed to the more conventional parallel
sequencing) to reduce mixed air plenum pressure drop1 ofﬁces.2
The owner elected not to adopt the voluntary minimum
and thereby reduce fan energy; and
air change rates in Standard 170-2017 for outpatient build* Isolation areas to allow for individual scheduling of
ings. Densely occupied spaces such as conference rooms
zone groups.
and waiting rooms include DCV sequences where required
Indoor Air Quality and Thermal Comfort
by Title 24 to dynamically determine the required occuA pre-retroﬁt investigation revealed that many of
pant ventilation rates at the zone and AHU levels.
the AHU dampers did not actuate fully open or closed,
The new AHU controls provide active control to the
some of the dampers were frozen in place, ﬁxed miniminimum outdoor airﬂow setpoint to meet Title 24 venmum outdoor damper positions were used and a handtilation requirements, compared to the original control
ful of variable frequency drives were inoperable and
method with a ﬁxed minimum damper position. The
bypassed. At the zone level, many of the thermostats,
airside economizer control maximizes operation by
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ASHRAE Journal - April 2021

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