How does the line of thought go that balances out not using cooling towers (e.g. air cooled chillers)? Is it bad to not use a cooling tower? is it good? does it balance out in the energy points? What's the general idea here?
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Tristan Roberts
RepresentativeVermont House of Representatives
LEEDuser Expert
11477 thumbs up
February 7, 2011 - 11:39 pm
Jean, that's a complex question. I would say it has a lot to do with the building, its size and heating/cooling loads, efficiency of relevant equipment, etc.If you don't have a cooling tower you're not eligible for these two points, but I wouldn't let that influence design and operation decisions.
Scott Bowman
LEED FellowIntegrated Design + Energy Advisors, LLC
LEEDuser Expert
519 thumbs up
February 8, 2011 - 8:51 am
This is a massive generalization, but when chillers are the selected system, smaller chillers will be better air cooled, and larger chillers better water cooled. There are all sorts of other factors like load profile, because air cooled (which are often screw or scroll compressors) have very good part load performance, where centrifugal chillers tend to have better full load performance for base loading.
So,it really all depends on the project, and should be examined carefully during the energy modeling early in the project. There are other options when you have a water cooled system such as heat recovery chillers and water-side economizer too.
Jean Marais
b.i.g. Bechtold DesignBuilder Expert832 thumbs up
February 9, 2011 - 1:52 am
I know what you're saying...I've read loads of articles in ASHRAE journal, basically all saying that the efficiencies of Chilling Equipment should really be modelled and not read out of the back of ASHRAE 90.1, exactly because, as you say, the environmental loads, outdoor humidity, size, part loading and many other factors hugely impact on it's efficiency.
I've also read articles testing air cooled and water cooled solutions on specific and divers problems trying to extrapolate trends...basically saying that "well, it depends".
That's why I first felt like this existing building was unduelly penalized for having air cooled chillers.
I'm not going to try and fuddle in a cooling tower where it doesn't fit, don't worry. I just know that there is usually reason behind these things from the USGBC. It could be as simple as that the majority of chillers in the USA are water cooled and this water (probably potable) is being thrown away. I remember how shocked I was to here how late the USA was at bringing in laws forbidding (controlling) the use of potable ground water for cooling in power plants (mostly also cooling towers). It was like 40% of potable water was used in cooling towers in power plants, even right next to the see. Water is obviously way to cheep.
Thanks for the input.
Scott Bowman
LEED FellowIntegrated Design + Energy Advisors, LLC
LEEDuser Expert
519 thumbs up
February 9, 2011 - 8:24 am
Yes, we just did a large rainwater capture project, and in preparing for a presentation, I learned that one of the major users of fresh water (not always treated, but definately non-salt) was power plants, and many were once-through!
In general, if the chiller is in good shape, it would be rare that switching a water cooled unit for the air cooled unit would pay back economically...there are many more energy efficiency measures that should be tried first.
I do think water is too cheap, and it does not take into account the social and infrastructure cost to a city, such as urban areas with combined storm and sewer systems. But that is a different thread. One thing we seem to include in more projects is rainwater capture for cooling tower makeup, which can help reduce chemical treatment costs. So, sometimes it is good to look at smaller systems even if you cannot support a large system for flushing.