ASHRAE Journal - May 2013 - 92

EMERGING TECHNOLOGIES
Wireless Sensor Networks

Monitoring & Control
By Mildred Hastbacka; Ratcharit Ponoum; Antonio Bouza, Associate Member ASHRAE

W

ireless sensors and wireless sensor networks (WSN)
are especially well-suited for installation in existing buildings. They can assist in controlling large
energy-consuming loads such as HVAC systems and can provide the information necessary for timely fault detection and
diagnostics (FDD). A challenge with these networks is the need
to continually replace batteries, especially in large installations.
This column explores some fundamentals of wireless sensors
and WSNs, compares them to wired sensors and networks, and
identifies challenges and benefits.
Wireless sensor designs can accommodate a range of HVAC
installation requirements and environments, such as mounted
on walls, equipment, and in high moisture areas. Advances in
wireless sensor technology include sensors that measure parameters such as temperature, humidity, light, gases, airborne
particulates, occupancy, and energy consumption.

A Wireless Primer
The device that gathers sensor data and transfers it to a serverbased database is called a wireless sensor node. A wireless
sensor network is comprised of one or more nodes, with each
node associated with multiple sensors.
Networks of wireless sensors may include actuators, gateways, servers, communication and application software, as well
as various energy-consuming devices such as home appliances
that can wirelessly communicate their status. Energy consumption reductions directly attributable to WSN-enabled building
energy management systems have been reported to average
about 10% and range as high as 30% to 40%.1,2
Significant research has been focused on wireless communication standardization. WSNs have adopted and capitalized
on these well-established communication protocols to increase
interoperability, to expand use of smart sensors and actuators
within the wired and wireless network area, and to facilitate
interfacing with various sensor hardware.2
Challenges with wireless networks include connectivity, range,
sensor positioning (e.g., signal attenuation from building architecture and/or materials), network commissioning, and reliability.
However, relative to wired sensors and systems, wireless
alternatives offer cost and labor savings potential in projects
involving large or complex wiring scenarios, particularly in
retrofit applications.3 Wireless systems are often added to an
existing wired system.
92

ASHRAE Journal

Power
Power is a major concern when designing wireless sensor
node hardware that is to run on batteries for months, if not years.
Power consumption and battery life depend on factors such as
node sleep/wake patterns, software efficiency, number of external
sensors connected, power consumption of the microcontroller
and radio, and efficiency of the onboard power supply hardware.
Small form factor sensors make installation easier and have
helped drive the adoption of WSNs, but battery integration in
these miniaturized systems can be a limiting factor. Small batteries are quickly depleted, requiring frequent battery replacements.
Frequent battery replacement is often impractical due to
the high number of sensor nodes in a typical WSN system.
Still, one advantage of a WSN is that it can function, albeit
at a less optimum level, if a few sensors or sensor nodes are
nonoperational due to battery depletion.
Environmental energy harvesting techniques are a potential
alternative power source for WSNs. Environmental energy harvesting is a physical process by which various types of energy (e.g.,
thermal, kinetic, electromagnetic) are extracted from the immediate
surroundings and converted to electrical energy.4 Although commercially available, energy harvesting devices are not yet widely
used and are still considered to be in the development stage.

Fault Detection and Diagnostics
The omnipresent sensing enabled by wireless technology also
can provide information necessary for timely fault detection and
diagnostics (FDD). Use of FDD algorithms can contribute to
realizing energy efficiencies.6
In contrast to wired sensors, wireless sensing can be either
fixed or portable, either permanent or temporary, allowing ondemand monitoring of individual pieces of equipment for early
failure detection. Using inputs from such wireless sensors can
help increase the life span for equipment and lead to reduced
energy consumption.
A real-world example of wireless sensors contributing to fault
detection and related energy savings comes from an operations
improvement/cost reduction project in a pharmaceutical manufacturing plant. The facilities services group applied wireless,
noninvasive clamp-on sensing devices to key pieces of equipment, including steam traps.7
The monitoring sensors on the steam traps were to provide
early indication of steam leakage or blockage. The wireless
May 2013



ASHRAE Journal - May 2013

Table of Contents for the Digital Edition of ASHRAE Journal - May 2013

ASHRAE Journal - May 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
VAV Reheat Versus Active Chilled Beams & DOAS
A Stable Whole Building Performance Method for Standard 90.1
Technology Award Case Studies:
PSU Design Build Project
Passive Cooling for School
Standing Columns
Building Sciences
InfoCenter
Refrigeration Applications
IAQ Applications
Engineer's Notebook
Products
Data Centers
Emerging Technologies
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2013 - ASHRAE Journal - May 2013
ASHRAE Journal - May 2013 - Cover2
ASHRAE Journal - May 2013 - 1
ASHRAE Journal - May 2013 - 2
ASHRAE Journal - May 2013 - Contents
ASHRAE Journal - May 2013 - Commentary
ASHRAE Journal - May 2013 - 5
ASHRAE Journal - May 2013 - Industry News
ASHRAE Journal - May 2013 - 7
ASHRAE Journal - May 2013 - 8
ASHRAE Journal - May 2013 - 9
ASHRAE Journal - May 2013 - 10
ASHRAE Journal - May 2013 - 11
ASHRAE Journal - May 2013 - 12
ASHRAE Journal - May 2013 - 13
ASHRAE Journal - May 2013 - Letters
ASHRAE Journal - May 2013 - 15
ASHRAE Journal - May 2013 - Meetings and Shows
ASHRAE Journal - May 2013 - 17
ASHRAE Journal - May 2013 - VAV Reheat Versus Active Chilled Beams & DOAS
ASHRAE Journal - May 2013 - 19
ASHRAE Journal - May 2013 - 20
ASHRAE Journal - May 2013 - 21
ASHRAE Journal - May 2013 - 22
ASHRAE Journal - May 2013 - 23
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ASHRAE Journal - May 2013 - 28
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ASHRAE Journal - May 2013 - 30
ASHRAE Journal - May 2013 - 31
ASHRAE Journal - May 2013 - 32
ASHRAE Journal - May 2013 - A Stable Whole Building Performance Method for Standard 90.1
ASHRAE Journal - May 2013 - 34
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ASHRAE Journal - May 2013 - 36
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ASHRAE Journal - May 2013 - PSU Design Build Project
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ASHRAE Journal - May 2013 - Passive Cooling for School
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ASHRAE Journal - May 2013 - Building Sciences
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ASHRAE Journal - May 2013 - InfoCenter
ASHRAE Journal - May 2013 - 71
ASHRAE Journal - May 2013 - 72
ASHRAE Journal - May 2013 - 73
ASHRAE Journal - May 2013 - 74
ASHRAE Journal - May 2013 - Refrigeration Applications
ASHRAE Journal - May 2013 - 76
ASHRAE Journal - May 2013 - 77
ASHRAE Journal - May 2013 - IAQ Applications
ASHRAE Journal - May 2013 - 79
ASHRAE Journal - May 2013 - 80
ASHRAE Journal - May 2013 - 81
ASHRAE Journal - May 2013 - 82
ASHRAE Journal - May 2013 - 83
ASHRAE Journal - May 2013 - Engineer's Notebook
ASHRAE Journal - May 2013 - 85
ASHRAE Journal - May 2013 - Products
ASHRAE Journal - May 2013 - 87
ASHRAE Journal - May 2013 - Data Centers
ASHRAE Journal - May 2013 - 89
ASHRAE Journal - May 2013 - 90
ASHRAE Journal - May 2013 - 91
ASHRAE Journal - May 2013 - Emerging Technologies
ASHRAE Journal - May 2013 - 93
ASHRAE Journal - May 2013 - 94
ASHRAE Journal - May 2013 - Classified Advertising
ASHRAE Journal - May 2013 - Advertisers Index
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ASHRAE Journal - May 2013 - Cover4
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