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It's easy to find examples of projects--of all types--that were not
successful. It is not particularly productive to use such examples,
which are frequently the result of inappropriate application or less than
stellar design as a basis for judging the value of a technology like
thermal energy storage. Over the past decade or more, ASHRAE TC 6.9
has offered a number of programs that present examples of thermal storage
systems that save energy. For obvious reasons, chilled water
storage systems have been among the most successful because they do not
add big chiller COP penalties. One example is discussed in detail
in a paper I co-authored:<br><br>
Bahnfleth, W. and W. Joyce. 1994. Energy use in a district
cooling system with stratified chilled water storage. <i>ASHRAE
Transactions </i>100(1): 1767-1778.<br><br>
The project involved no new chillers, just the addition of TES to an
existing system. Comparison of system performance in the year
before and after addition of storage showed a reduction, adjusted for
weather differences, of about 8% in average kW/ton for cooling.<br><br>
Realization of energy savings potential of thermal storage depends on
good integration and capitalizing on opportunities such as the one noted
in Andy Lau's reply--using the lower temperature source available from an
ice storage system to produce lower temperature air. Large scale
ice storage in district cooling systems has also been used to advantage
to reduce distribution pumping costs by widening the chilled water
temperature difference.<br><br>
The economics of thermal storage do not, as suggested by some of the
replies in this thread, depend exclusively on the electric rate
structure. A number of articles published in the past several years
describe circumstances in which thermal storage still makes sense.
ASHRAE has offered programs on this topic, too, that included
presentations on thermal storage systems that were lower in first cost
than non-storage systems. When the cost of peak capacity from
thermal storage is compared with the cost of capacity in a conventional
cooling plant, it is clear that when starting with new system or
expanding capacity in an existing system, there can be an advantage for
thermal storage. Falling back again on my experience with chilled
water storage systems, I note that the cost of a ton of new plant
(including the building and all auxiliaries) can be well in excess of
$1000 while chilled water storage systems have been built for less than
$300 per peak ton.<br><br>
Thermal storage was oversold in the heyday of demand-side management and
its reputation suffered as a result. I still deserves to be
considered in many projects.<br><br>
Bill Bahnfleth<br><br>
At 10:26 PM 11/26/2004, Andrew S. LAU wrote:<br>
<blockquote type=cite class=cite cite="">On the energy savings potential
of TES. I do recall that with TES, there is an opportunity to save
significantly on fan power if the AHU's are designed to take advantage of
the colder supply air temperatures possible with certain types of TES
systems. There is also first cost savings from smaller fans and
ducts.<br><br>
Andy Lau, 7group<br><br>
<br>
At 02:59 PM 11/26/2004 -0500, mbusman@noresco.com wrote:<br>
<blockquote type=cite class=cite cite="">The last TES I did was for a
military base. I think the base energy manager<br>
must have gone to a seminar and picked up the buzz word, because he
wanted<br>
TES. We tried to talk them out of it and just go with a new
water-cooled<br>
central chilled water plant to replace about 10 rotten air-cooled
chillers.<br>
We explained that TES requires the right combination of factors,
including<br>
high demand charge, high peak hour time of use kWh charge, low off peak
TOU<br>
kWh charge, and quite often a utility company or state rebate for
demand<br>
reduction programs to make the project economically viable. Well
they<br>
wanted their TES and wanted ice storage versus chilled water
storage.<br>
Fortunately, as this was a super ESPC project, the customer was able to
kick<br>
in a few $$ to cover the incremental cost of the ice tanks and
associated<br>
equipment and the rest of the project funded as an energy savings
perforance<br>
contract. Fortunate, because the electric rates were not conducive
to TES.<br>
Perhaps, the customer saw other value or intangible benefits from the
TES.<br><br>
As expected, between circulating glycol through the chillers and taking
the<br>
performance hit of recharging the ice tanks with an evaporator
temperature<br>
in the 22 deg.F - 26 deg.F range,kWh consumption during ice charging
period<br>
went up. In the end, though, the difference in kW/ton
between the old<br>
air-cooled recips with corroded condensers and the new electric
screw<br>
chillers measurement and verification (and the few $ of buydown on the
TES<br>
portion) were sufficient and made for a successful project. One
final note<br>
of interest. We ran an analysis with and without the TES and as I
recall,<br>
the TES only contributed a couple of $thousand/year in savings with
about<br>
98% of the electric savings coming from the improved kW/ton of the
electric<br>
cooling.<br><br>
So, don't believe all the buzz words, get the correct rate data and
chiller<br>
part-load data..........and the customer is always right.<br><br>
Mike Busman<br>
Senior Project Engineer<br>
NORESCO, LLC<br><br>
-----Original Message-----<br>
From: Chris Jones
[<a href="mailto:cj@cr-jay.ca" eudora="autourl">mailto:cj@cr-jay.ca</a>]<br>
Sent: Friday, November 26, 2004 10:23 AM<br>
To: BLDG-SIM@gard.com<br>
Subject: [BLDG-SIM] Simulation on Thermal Energy Storage using
DOE2.2<br><br>
<br>
We did an analysis of an existing building with a large heat/cool
storage<br>
system. The Owners were very surprised to find out that the
building was<br>
not energy efficient - it just saved on demand charges. The pumping
of<br>
fluid in and out of the tanks, through heat exchangers occurred 24 hours
a<br>
day significantly increasing the kWh beyond that of a conventional
hydronic<br>
heat/cool building.<br><br>
At 01:26 11/26/2004, you wrote:<br>
>Dear Martin,<br>
>I think the findings may be correct.<br>
>First, for a TES system the leaving chilled water temperature usually
will<br>
>be lower, so the COP will be deduced, but as the outside temperature
is<br>
>lower, it does not deduced alot.<br>
>Second, if the TES system using brine water, i think the efficiency
will<br>
>reduce more.<br>
>As our experience in some project in Hong Kong and Mainland, TES
system<br>
>can only reduce electricity cost due to tariff rate rather than<br>
consumption.<br>
>I hope these comment would help.<br>
><br>
>Regards,<br>
>Ernest Tsang<br>
>Meinhardt (M&E) Ltd<br>
><br>
><br>
>Martin Yip <yipch@emsd.gov.hk> wrote:<br>
>Dear Bldg-sim Subscribers,<?xml:namespace prefix = o ns =<br>
>"urn:schemas-microsoft-com:office:office" /><br>
><br>
>I recently simulated an air cooled chiller plant with cold water
tank<br>
>thermal energy storage using DOE 2.2. I originally expected
some energy<br>
>saving due to improve chiller COP at night charging the storage
when<br>
>compare it with a system without storage. However, the results
showed an<br>
>energy penalty of a few percentages even though hourly data
actually<br>
>showed COP improvement during charging. I have already set the
loss<br>
>coefficient to zero for the TES. I should be most grateful if
anyone can<br>
>comment on this issue and provide some suggestion.<br>
><br>
>Thanks<br>
><br>
>Martin YIP<br>
>Engineer<br>
>EMSD, HKSAR<br>
><br>
><br>
><br>
><br>
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~<br>
Chris Jones<br>
EnerSys Analytics Inc.<br>
14 Oneida Avenue<br>
Toronto, ON M5J-2E3<br>
Tel. 416 203-7465<br>
Fax. 416 946-1005<br><br>
<br>
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Andrew S. Lau, P.E.<br>
7group,
<a href="http://www.sevengroup.com/" eudora="autourl">www.sevengroup.com</a><br>
1007 Bayberry Drive<br>
State College, PA 16801<br>
814-238-4273, FAX 814-863-7229<br>
andylau@psu.edu<br><br>
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<br>
<div>_________________________________________________</div>
<br>
<div>William P. Bahnfleth, PhD, PE, Fellow ASHRAE</div>
<div>Associate Professor</div>
<div>Director, Indoor Environment Center</div>
<div>
</div>
<div>Department of Architectural Engineering </div>
<div>The Pennsylvania State University </div>
<div>104 Engineering Unit A</div>
<div>University Park, PA 16802 USA</div>
<br>
<div>voice: 814.863.2076 / fax: 814.863.4789 </div>
<div>e-mail: wbahnfleth@psu.edu</div>
<div><a href="http://www.arche.psu.edu/faculty/WBahnfleth/" EUDORA=AUTOURL>www.arche.psu.edu/faculty/WBahnfleth/</a></div>
_________________________________________________
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