The Hartman Company Newsletter
Issue: April, 2002
Topic: All-Variable Speed Chilled Water Distribution Systems
Dear Hartman Company Newsletter subscriber,
As noted in last month's Newsletter, the improvements in efficiency that
all-variable speed technologies offer chiller plants are unprecedented and
exciting to those responsible for plant operation. But there is a much more
immediate problem that plagues a great many large chilled water systems.
This is the problems of low delta T. Low delta T not only robs the plant of
capacity, but it also leads to excessive distribution flow and often an
inability to adequately meet certain loads in the distribution system. Most
of the fixes that have been offered in the past are poorly conceived and
some actually worsen the problem. But there is a relatively simple and
straightforward path to absolutely guarantee low delta T will never plague
your distribution system. The approach involves adding network control and
extending all-variable speed technologies from the chilled water plant to
the distribution system.
If you can attend the ASHRAE Annual Meeting in Honolulu this summer, please
plan on attending Mr. Hartman's presentation on variable flow distribution
in Seminar 27 which is titled "Case Studies of Variable Primary Flow Chilled
Water Systems," at 10:15 AM on Tuesday, June, 25th. Mr. Hartman will describe
a project that employs an all-new "all variable speed" approach to chilled
water distribution control. This approach is simpler, more effective, and
enormously more efficient than any employed in today's systems.
If you are involved with chilled water distribution systems, we urge you to
start right now to bone up on new all-variable speed distribution technologies.
Here is a list of references we have developed to help those who wish to improve
the operation of chilled water distribution systems whether they are now in
operation or just being designed:
1. Primary - secondary chilled water distribution systems have been the standard
for some years, but this technology nurtures the types of problems that plague
many distribution systems. Most often, the fixes that have been applied to these
systems to raise delta T have only added to the problems. Read Mr. Hartman's
article in AutomatedBuilding.com that outlines the problems of primary - secondary
systems and how the use of all-variable speed and network control can provide a
straightforward solution to such problems. You can view this article at:
http://www.automatedbuildings.com/news/apr02/art/htmn/htmn.htm
2. For a brief and to-the-point punch list of things to consider in improving
delta T in your system, take a look at a column Mr. Hartman wrote recently in HPAC
magazine. This column is available at:
http://www.hpac.com/member/archive/0104freaks.htm
3. For a case study of the design and evaluation of a system that combines an
all-variable speed chiller plant and all-variable speed chilled water distribution
system, you may wish to read a paper Mr. Hartman presented to the International
District Energy Association (IDEA) in 1997. This paper describes how the use of
all-variable speed technologies made a central chilled water plant and chilled
water distribution system more attractive than unitary equipment to the developer
of a large downtown commercial and residential complex.
http://www.hartmanco.com/pdf/p05.pdf
4. For a technical discussion of all-variable flow integrated into all-variable
speed chiller plants, you may wish to read Mr. Hartman's presentation at the ASHRAE
Annual Meeting in 1996 in which he outlined the enormous potential benefits of
applying all-variable speed technologies to chilled water distribution systems. At
the time, chiller manufacturers were insistent that flow should not be varied
through chillers. Hartman's paper shows that constant flow is not only not
necessary but that substantial performance benefits can accrue by varying the flow
in an all-variable speed plant and distribution system configuration. The article
is available at:
http://www.hartmanco.com/pdf/p04.pdf
5. If you are still reluctant to leave the chaotic, decoupled world of primary -
secondary chilled water distribution, you owe it to your chilled water system to
read Wayne Kirsner's article in Heating, Piping and Air Conditioning that appeared
shortly after Mr. Hartman's technical presentation to ASHRAE. Mr. Kirsner's
no-holds-barred evaluation of the problems caused by primary - secondary systems
has received (and over the years has withstood) much criticism by traditionalists.
Read it and empower your distribution system to do its job better! It's available
at:
http://www.hartmanco.com/pdf/ao04.pdf
NOTE ON LAST MONTH'S NEWSLETTER: Last month's newsletter was focused on
"all-variable speed" chiller plants. The trend towards variable speed in chiller
plants continues. Several years ago, The Hartman Company issued an RFP for
"all-variable speed air cooled screw chillers." The application was a series of
small communications buildings. Unfortunately, there were no responses at the
time. Now, one major manufacturer (Carrier) has just announced a variable speed
screw chiller offering, and we are given to understand others may follow. Optimized
all-variable speed air cooled screw chillers (chillers in which the compressors and
condenser fans are all-variable speed) promise to cut cooling costs for medium sized
commercial facilities by one-half to two-thirds. And from a maintenance standpoint
they are very simple, reliable and long lived machines.
Applying variable speed to screw compressors is a very important development that
we think will create a substantial new variable speed cooling market. It is not yet
clear whether the first product offerings will include "all-variable speed" air
cooled configurations. If not, the economics will motivate manufacturers quickly
as air cooled variable speed cooling has a distinct competitive advantage over other
cooling options for medium sized commercial applications. Stay tuned!
To search the Hartman Resource Library yourself for additional articles on this
topic, go to:
http://www.hartmanco.com/cgi-bin/dbman/db.cgi?db=resource&uid=default&view_search=1
Linda Zuvich, Editor
THC News
The Hartman Company
THC News
Copyright 2002
All Rights Reserved
Archives of past THC News email newsletters are available at:
http://www.hartmanco.com/thcnews.cgi
To subscribe or unsubscribe to the THC News, please visit:
http://www.hartmanco.com/maillist.htm
The Hartman Company
An HVAC Engineering & Technology Development Firm
http://www.hartmanco.com
|
