ASHRAE Journal - February 2011 - 45

Three Wireless Technologies
The three popular wireless technologies are: Wi-Fi, ZigBee and EnOcean. Commercial buildings can benefit by combining multiple wireless technologies at various network levels within the BAS to leverage high data throughput, low cost, and the flexibility that each of these technologies has to offer. Wi-Fi allows the distribution of large amounts of data with its high bandwidth capabilities. Although it is certainly popular, Wi-Fi consumes more power and is more expensive than EnOcean and ZigBee. This wireless technology is best suited for the more expensive BAS devices that are at the highest network level, enabling communications between buildings. Wi-Fi operates at a frequency of 2.4 GHz and has 11 channels from which the IT staff can choose for network isolation within a building. ZigBee is medium-bandwidth wireless technology that consumes less power than Wi-Fi. Because of this, it is well-suited for the field bus communications level. ZigBee operates at the same frequency as Wi-Fi (2.4 GHz); however, it is designed to work within Wi-Fi’s channels. The two wireless technologies are designed to coexist without interference. In addition, ZigBee offers mesh network architecture, which is more reliable for commercial BAS installations. A mesh network is self-healing; a benefit that a wired network does not have. Most popular in Europe, EnOcean specializes in low power consumption to enable the use of batteryless wireless devices. Very small amounts of data can travel on EnOcean’s ultralow bandwidth that operates at a different frequency than Wi-Fi and ZigBee. This technology is typically used for wireless sensors and switches within a BAS.

Material Plasterboard Wall Office Window Cinderblock Wall Glass Wall with Metal Frame Metal Door Metal Door in Brick Wall

Attenuation 3 dB 3 dB 4 dB 6 dB 6 dB 12 dB

Table 1: Attenuation (degradation of signal strength) for various materials. As a rule of thumb, every 6 dB loss decreases the effective range by approximately 50%. The good news is that most commercial buildings are constructed of materials well suited for wireless communications. When laying out a wireless job, it is important to consider the materials used for the interior wall construction. Although there are often metal obstructions, there are rules of thumb to follow that allow wireless communications to operate reliably in most commercial building environments.

Communication Distances and Hop Counts
Wireless system devices have finite communication distances. To help account for this, many wireless devices have built-in signal strength indicators that help during the wireless installation phase without the need for expensive tools. The average distance in which wireless devices remain operational is 50 ft (15 m) in most building environments, yet can range up to 250 ft (76 m) in open-air areas. ZigBee and Wi-Fi wireless devices also have finite hop counts between wireless nodes. For example, a temperature reading across multiple rooms may pass through five VAV boxes along the way. This is considered five hops. If the wireless system provider recommended only four hops, one hop would have to be removed. EnOcean technology is a point-topoint wireless solution and does not support multi-hop networking.

Wireless Signals and Building Materials
Commercial buildings consist of a variety of materials and architecture. These physical environments affect wireless BAS installation. Air, wood and drywall provide excellent mediums for wireless signals. The best opportunity for cost savings using wireless is in large open-air areas with sight lines such as gymnasiums, arenas and hallways. Here, wireless signals have much greater signal strength-to-distance ratio. Wireless signals also travel through brick, concrete and marble walls, but with a significantly reduced range. Most wireless devices have signal range specifications that assume one wall between nodes. For example, most ZigBee devices are powered at 10 mW (a laptop computer uses at least 100 mW) and the signal passes easily through a poured concrete wall. However, if a wireless device signal needs to cross multiple walls, expect a 30% to 50% reduction per concrete wall. Wireless signals do not travel well through metal, which needs to be a primary consideration. I-beams, elevator shafts and metal roofs are examples of metal obstacles that wireless systems often encounter. One unexpected place where metal can be found is in historic buildings where walls have been constructed with wire lattice covered in plaster. In this case, the signals will not transmit well through the walls. Therefore, it is best to leverage line of sight options such as open-air areas and hallways when laying out the wireless system.
February 2011

Wireless BAS and Other Networks
Most wireless networks are designed to coexist with other wireless networks in a commercial building environment. One way to accomplish this is for BAS wireless networks to transmit at extremely low power levels (10 mW) thereby limiting interference to devices on the same frequency channels. Wireless systems operate on licensed frequency bands to provide isolation across diverse application types. Only those devices for each specified frequency band can live on that band. For example, police band radios cannot interfere with medical telemetry devices because they operate on two distinct licensed frequency bands. Most ZigBee and Wi-Fi devices operate at 2.4 GHz, which is also known as an Instrumentation Science and Medical (ISM) band. Many types of devices operate in this band, so how can they operate together without interference? Keep in mind that a frequency band defines a range of channels. For
ASHRAE Journal 45



ASHRAE Journal - February 2011

Table of Contents for the Digital Edition of ASHRAE Journal - February 2011

ASHRAE Journal - February 2011
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Thermal Coupling of Cooling and Heating Systems
10 Common Problems in Energy Audits
Hall of Fame Feature: History of the Changing Concepts in Ventilation Requirements
A Guide to Wireless Technologies
Building Sciences
Solar NZEB Project
Emerging Technologies
People
Special Section
InfoCenter
Commissioning
Products
Washington Report
Classified Advertising
Advertisers Index
ASHRAE Journal - February 2011 - ASHRAE Journal - February 2011
ASHRAE Journal - February 2011 - Cover2
ASHRAE Journal - February 2011 - 1
ASHRAE Journal - February 2011 - 2
ASHRAE Journal - February 2011 - Contents
ASHRAE Journal - February 2011 - Commentary
ASHRAE Journal - February 2011 - 5
ASHRAE Journal - February 2011 - Industry News
ASHRAE Journal - February 2011 - 7
ASHRAE Journal - February 2011 - Letters
ASHRAE Journal - February 2011 - 9
ASHRAE Journal - February 2011 - 10
ASHRAE Journal - February 2011 - 11
ASHRAE Journal - February 2011 - 12
ASHRAE Journal - February 2011 - 13
ASHRAE Journal - February 2011 - 14
ASHRAE Journal - February 2011 - 15
ASHRAE Journal - February 2011 - Meetings and Shows
ASHRAE Journal - February 2011 - 17
ASHRAE Journal - February 2011 - Thermal Coupling of Cooling and Heating Systems
ASHRAE Journal - February 2011 - 19
ASHRAE Journal - February 2011 - 20
ASHRAE Journal - February 2011 - 21
ASHRAE Journal - February 2011 - 22
ASHRAE Journal - February 2011 - 23
ASHRAE Journal - February 2011 - 24
ASHRAE Journal - February 2011 - 25
ASHRAE Journal - February 2011 - 10 Common Problems in Energy Audits
ASHRAE Journal - February 2011 - 27
ASHRAE Journal - February 2011 - 28
ASHRAE Journal - February 2011 - 29
ASHRAE Journal - February 2011 - 30
ASHRAE Journal - February 2011 - 31
ASHRAE Journal - February 2011 - 32
ASHRAE Journal - February 2011 - 33
ASHRAE Journal - February 2011 - Hall of Fame Feature: History of the Changing Concepts in Ventilation Requirements
ASHRAE Journal - February 2011 - 35
ASHRAE Journal - February 2011 - 36
ASHRAE Journal - February 2011 - 37
ASHRAE Journal - February 2011 - 38
ASHRAE Journal - February 2011 - 39
ASHRAE Journal - February 2011 - 40
ASHRAE Journal - February 2011 - 41
ASHRAE Journal - February 2011 - 42
ASHRAE Journal - February 2011 - 43
ASHRAE Journal - February 2011 - A Guide to Wireless Technologies
ASHRAE Journal - February 2011 - 45
ASHRAE Journal - February 2011 - 46
ASHRAE Journal - February 2011 - 47
ASHRAE Journal - February 2011 - 48
ASHRAE Journal - February 2011 - 49
ASHRAE Journal - February 2011 - Building Sciences
ASHRAE Journal - February 2011 - 51
ASHRAE Journal - February 2011 - 52
ASHRAE Journal - February 2011 - 53
ASHRAE Journal - February 2011 - 54
ASHRAE Journal - February 2011 - 55
ASHRAE Journal - February 2011 - 56
ASHRAE Journal - February 2011 - 57
ASHRAE Journal - February 2011 - 58
ASHRAE Journal - February 2011 - 59
ASHRAE Journal - February 2011 - 60
ASHRAE Journal - February 2011 - 61
ASHRAE Journal - February 2011 - Solar NZEB Project
ASHRAE Journal - February 2011 - 63
ASHRAE Journal - February 2011 - 64
ASHRAE Journal - February 2011 - 65
ASHRAE Journal - February 2011 - 66
ASHRAE Journal - February 2011 - 67
ASHRAE Journal - February 2011 - 68
ASHRAE Journal - February 2011 - 69
ASHRAE Journal - February 2011 - Emerging Technologies
ASHRAE Journal - February 2011 - 71
ASHRAE Journal - February 2011 - 72
ASHRAE Journal - February 2011 - 73
ASHRAE Journal - February 2011 - 74
ASHRAE Journal - February 2011 - 75
ASHRAE Journal - February 2011 - People
ASHRAE Journal - February 2011 - 77
ASHRAE Journal - February 2011 - InfoCenter
ASHRAE Journal - February 2011 - 79
ASHRAE Journal - February 2011 - 80
ASHRAE Journal - February 2011 - 81
ASHRAE Journal - February 2011 - 82
ASHRAE Journal - February 2011 - 83
ASHRAE Journal - February 2011 - 84
ASHRAE Journal - February 2011 - 85
ASHRAE Journal - February 2011 - Commissioning
ASHRAE Journal - February 2011 - 87
ASHRAE Journal - February 2011 - 88
ASHRAE Journal - February 2011 - 89
ASHRAE Journal - February 2011 - 90
ASHRAE Journal - February 2011 - Products
ASHRAE Journal - February 2011 - Washington Report
ASHRAE Journal - February 2011 - Classified Advertising
ASHRAE Journal - February 2011 - 94
ASHRAE Journal - February 2011 - 95
ASHRAE Journal - February 2011 - Advertisers Index
ASHRAE Journal - February 2011 - Cover3
ASHRAE Journal - February 2011 - Cover4
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_KTUZMA
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_ABEDGD
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201910
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201909
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019septmeber_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2019september
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201908
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201907
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201906
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201905
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201904
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019april
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201903
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2019march
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201902
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201901
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_showguide2019
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018december
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018november
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2018fall
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_2018october
http://www.nxtbook.com/nxtbooks/ashrae/ashraemexico_2018
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201810
http://www.nxtbook.com/nxtbooks/ashrae/ashraeinsights_201806
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201805
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201804
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201803
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201712
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201711
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201710
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2017fall
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201709
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201705
http://www.nxtbook.com/nxtbooks/ashrae/ashrae_meetinginsert_201610
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2016fall
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acrexindia
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_amca_2015summer
http://www.nxtbook.com/nxtbooks/amca/2014summer2
http://www.nxtbook.com/nxtbooks/amca/2014summer
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acma_2014summer
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201311
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201309
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_acmasupp_2013fall
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201305
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201303
http://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2013winter
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201211
http://www.nxtbook.com/nxtbooks/ashrae/achr_expo_mexico2012
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201209
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v3
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201208_v2
http://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012summer
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201205
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201203
http://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2012winter
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201111_v2
http://www.nxtbook.com/nxtbooks/ashrae/ashraejournal_201109_v2
http://www.nxtbook.com/nxtbooks/ashrae/pubcatalog_2011summer
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201105
http://www.nxtbook.com/nxtbooks/ashrae/meetingplanner_201103
http://www.nxtbookMEDIA.com