ASHRAE Journal - February 2020 - 21

TECHNICAL FEATURE

wheel effectiveness declines as it ages; and ECM supply
fans risk reducing airﬂow to the point of freezing a coil
or negatively affecting building pressures. All these side
effects are well-known to manufacturers when designing variable capacity DOAS equipment.
What is not as common is conﬁrming that DOAS units
perform as intended on every building, independent of
application. To help achieve this, an array of digital and
analog sensors can be used throughout the unit, collecting and transmitting data to a master control facility. For
example, in a supply airstream, temperature and relative
humidity sensors are frequently paired to allow for dew
point calculations throughout each section of the unit.
Figure 1 represents common DOAS sensor positions located
in the outdoor, return, mixed, and supply airstreams.
(Note: DOAS units are generally used for 100% outdoor
air applications. However, some control sequences may
require high recirculation rates during unoccupied times,
which warrant the usage of return sensors.)
Dew-point calculations in a DOAS are essential data
points when cooling and dehumidifying a space. If too
high, moisture from the outdoors is introduced to the
space, accelerating mold and bacteria growth. If too
low, unnecessary energy is wasted in overtreating the
airstream. Therefore, the ability to calculate the outdoor dew point and determine whether it is lower than
the target space dew point allows the system to provide
either "free dehumidiﬁcation" with minimal power
consumption or activate cooling until the desired dew
point is achieved, similar to an enthalpy economizer, but
without the risk of negatively impacting building pressure balance.
Frequently, advanced controls such as this work well
during development and testing but fail when implemented at a macro scale after all variables associated
with climate, construction and installation are considered. In addition, the sensors required to implement
DOAS controls strategies increase the number of potential failure points of these systems. For such complex
systems to achieve the desired results, one solution is to
connect these units to a centralized platform that surpasses traditional BMS data gathering and alarm reporting capabilities by directly incorporating manufacturer
support teams.

Connected Commissioning
The process of connected commissioning involves

FIGURE 1 Typical DOAS temperature and relative humidity sensor locations.
1

Outdoor Air
Temperature and
Humidity Sensor
Mixed Air

Return Air
Temperature and
Humidity Sensor

3
1
4

Mixed Air
Temperature and
Humidity Sensor

Outdoor
Air

Supply Air
Temperature and
Humidity Sensor

Return Air

Supply Air

three main activities: data acquisition (DAQ), data
aggregation and interpretation and the execution
of support strategies. When all three are combined
with active and passive reviews using advanced
analytics, automated faults and remote diagnosis, data trends and patterns begin to develop that
would have been difficult to identify in a lab environment. Sensitive DOAS applications that require
precise control of supply and space conditions cannot rely on a single system commissioning during
start-up. When compared to a single commissioning
approach, connected commissioning can increase
the likelihood that long term performance is maintained throughout the system's lifetime by continuously linking manufacturer technical support teams
to relevant equipment operating data. The manufacturer support teams referenced in this article
applied 2,888 remote adjustments to setpoints, factory settings and schedules throughout the past year
to the 500-plus DOAS units to continuously optimize
their performance.
Data Acquisition. DAQ has been gaining traction
in recent years due to advancements in the Internet
of Things (IoT) ﬁeld. For example, it is common for
household devices such as thermostats, light switches
and wall outlets to be equipped with Wi-Fi capabilities,
allowing these devices to report data and be controlled
through the Internet. This type of integrated remote
monitoring and control technology has been generally
seen as cost prohibitive for more complex equipment,
particularly in light- to medium-scale commercial
buildings, due to the need for expensive building management system (BMS) hardware and specialty controls
contractors for proper implementation. Additionally,
FEBRUARY 2020

ashrae.org

ASHRAE JOURNAL

https://www.ashrae.org/

ASHRAE Journal - February 2020

Table of Contents for the Digital Edition of ASHRAE Journal - February 2020