ASHRAE Journal - February 2011 - 14

letters	
chart makes it clear that to get to the desired room condition of Point 1, the supply air will have to be Point 1A, but Point 1A cannot be achieved with a standard cooling coil because the coil never reaches saturation, so no dehumidification will occur. You would need to use coil bypass, reheat, or some other means to provide the needed dehumidification. So, shutting off the economizer when the outdoor air dew point is above some threshold does not seem to be the right approach. Rather, I would use a space humidity sensor and have it cause the dehumidification to come on. However the dehumidification is achieved, the entering coil condition, whether it is outdoor air or return air, will not affect the ultimate space humidity because the dehumidification coil leaving air condition is always the same: nearly saturated. But energy usage of this coil will be impacted. So your economizer high limit still will want to take the air, either return air or outdoor air, that has the lowest enthalpy, the same as the office building example in my article. In other words, cooling and dehumidifying Point 2 air will take less energy than cooling and dehumidifying Point 1 air, so it should be used. Thus, for integrated economizer control with modulating cooling capability, I still contend that the high limit controller will have no impact on space humidity. (As I stated in the article, if you have cycling like with a small DX system, then the high limit device may have an impact, although I am not really sure what the impact is—it’s complex due to re-evaporation of condensate off the coil.) Steve Taylor, P.E., Fellow ASHRAE, Alameda, Calif.

The Author Responds
We agree with Mr. Byers that point names should be easy for facilities personnel to understand. However, that was not our sole objective when we designed our point naming convention. We chose to use abbreviations in our point naming convention because of the limitations of existing HVAC control products. PC-based operator workstations can usually store and display long point names and point descriptions, but controllers typically impose significant restrictions on the length of point names that they can store. We strongly believe that descriptive point names should be stored in the controllers themselves, not just in the workstations, so we have to strike a balance between readability and length of the point names. It is a requirement of our business process that our point names can be unambiguously understood by our software systems that automatically process HVAC system data. In order to make it easier for our software to understand the point names, we designed a grammar for the point names that is quite restrictive. As well, our point naming convention contains a list of abbreviations that must be used. Our engineers use custom software tools that facilitate the selection of appropriate point names. Jim Butler, Member ASHRAE, Boston

Applying BACnet in the Real World
Congratulations to Mr. Larry Bacher for a fantastic article in the November Journal, reminding all of us not to get too comfortable with an all-BACnet control system. While we recognize some of the biggest advantages provided by BACnet, we cannot ignore the real challenges that still exist in the application of new (and better) technology to a real building, through a complicated (and always imperfect) construction process. I applaud Mr. Bacher for his direct approach, excellent example, and honest examination of the facts. This was one of the most relevant articles (to the control industry) that I have read in many months. Designers and owners should take note of the consequences that can come from gaps in the specification of a BAS. Advanced control system components are not “plug-and-play” like we sometimes wish they were. Many differences, especially at the unit level, still exist between BACnet controllers (as Mr. Bacher helps us to see). We would all do well to study building automation a little more, and to take Mr. Bacher’s recommendations to heart. Patrick Simmons, Associate Member ASHRAE, Bartlett, Tenn.

Point Naming Standards
I enjoyed the “Point Naming Standards” article by Butler and Veelenturf in November’s ASHRAE Journal. Having an organized naming convention for complex systems is essential for efficient operation by the users. However, the authors suggest using abbreviations whenever possible; I contend that abbreviations should be used as little as is reasonable. For instance, Example 1’s point name is BLDGALUMNI/PLANT/CHLR-1/CHWST_SP. Why make facilities personnel have to learn the abbreviation CHWST? Further, why does “BLDG” come before “ALUMNI”? Abbreviating “building” is so common that it might make sense (although this word might not be necessary at all). What if this sample point were named ALUMNI BLDG/ CENTRAL PLANT/CHILLER 1/CHILLED WATER SUPPLY TEMP SETPOINT? There’s no shortage of ones and zeros in the computers where these point names live, so let’s make the names easy to understand without the users having to decode abbreviations. Long ago our firm eliminated valve charts from our projects and required contractors to provide plain English valve tags. For instance, instead of a valve being labeled “52” it might be labeled “West Wing Cold Water Shutoff.” Any personnel encountering this valve know immediately what it does without hunting down an often elusive valve chart. Nathan Byers, Member ASHRAE, Seattle
14	 ASHRAE	Journal	

The Author Responds
Obviously, Patrick has been through the trials and tribulations when it comes to controls. I think the simpler we make controls implementation, through standards like BACnet, the more complex controls become (whether it be for HVAC operation or more competitive choices). I’m glad to see Patrick got something out of the article and hope it will help in his future projects. Larry Bacher, Los Angeles
ashrae.org	 	 February	 2011



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
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ASHRAE Journal - February 2011 - 53
ASHRAE Journal - February 2011 - 54
ASHRAE Journal - February 2011 - 55
ASHRAE Journal - February 2011 - 56
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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
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