ASHRAE has been placing more emphasis on design engineering and operating data of central plants since the 2000 handbook, Chapter 4 publication. Prior to then, it was difficult to find guidelines that focused on the advantages, disadvantages, system analysis, and selection of both heating and cooling central plants.

Since that time there have been forums, seminars, and symposiums on central plant design, commissioning, and O&M. As I followed along and, at times, participated in these discussions, I have come across a good publication titled Chilled Water Plant Design Guide, published by the Pacific Gas and Electric Company, Pacific Energy Center on what I believe is the full agenda of what ASHRAE is doing.

The TOC Is Great For The 411

When I found a quiet time to sit down and review the book, starting with the table of contents, I found the manuscript covered a very comprehensive, if not complete, range of topics. For me, the table of contents always tells me what is in the book, how the information will flow, and whether there is a method to the process.

Whenever I review a project manual, whether it is a facility survey, energy conservation study, or master plan report (to mention three types of documents), I always use the table of contents as my guide to the document, mainly because I don't want to read the entire text to get what I need out of it. I guess it is the practitioner in me that allows me to drive to the traditional bottom line.

In the book introduction, the reader is provided with a brief, "how to use this guide" discussion that I find very useful because it helps the reader understand where they should focus their attention based on their own experience. Perusing down the table of contents, the information flows from determining the chiller load, to type of equipment, system distribution, controls and instrumentation, optimizing design, procurement, start-up and commissioning, and a wealth of supplemental data.

The format allowed me to quickly jump to the data I need to reference, since the publication is brief and to the point (even if it is around 220 pages). The alternative is to search through four volumes of ASHRAE handbooks for all you want to know about central chilled water plant design guidelines. Now if someone could only publish a similar document for central heating plant design guidelines.

One-Stop Shopping

Regarding the ASHRAE format, don't get me wrong. I find these handbooks to be very useful, and it is easy to find the information I need. There aren't a lot of books out there as organized and/or complete. As most know though, the ASHRAE handbooks are cataloged by fundamentals, equipment, systems, and application so you need to research all four manuals if you are planning on designing a central plant. Finding a design manual that takes you from concept to commissioning sure makes the job easier when you are considering centralized cooling vs. decentralized cooling. This is what the Chilled Water Plant Design Guide achieves: one-stop shopping.

Today, we are recognizing there are a lot more benefits to central systems as opposed to more fragmented concepts. I believe that is why there is a heightened interest in the subject from several ASHRAE technical committees.

A concentration on central system application will allow us to learn more and continuously improve these guidelines to reduce energy and O&M costs. Books that provide "all you need to know" information supplemented by the ASHRAE handbooks are very powerful, educational tools for the reader.

Risk Management And Central Plant Design

Regarding central plants, it has been determined that there is limited historical data on the optimum peak load when assessing distribution, such as in a campus environment with its fluctuations in time-of-day cooling demand. The same can be said for strategically planning the shut down of lightly occupied buildings in the air conditioning season (see the September 2003 "Tomorrow's Engineer" column). Central plant design offers the HVAC engineer (as well as plant management) unique opportunities to find creative ways to conserve energy. This creativity can play an important role when taking calculated risks because central distribution can be more forgiving than decentralized systems.

The latest ASHRAE handbook, 2004, Chapter 4, adds to this central plant-engineering topic by suggesting that hydraulic modeling be used as an engineering tool and should be considered when designing a central plant. Hydraulic modeling software is a computerized method to not only document design conditions, but it can also provide anticipated conditions for master planning, in addition to troubleshooting central plant distribution.

To close out this month's discussion, if you want to know more on central chilled water plant design, e-mail and find out more on "where do you go for design guidelines." ES