Rule of Thumb for selecting the right chiller cooling capacity ...

Hi all,

I am wondering if there is a rule of thumb to find out the right size of chiller plant according to the total of water fan coil cooling capacity need.

As we know, the chiller plant has to be lower cooling capacity than the real need of the heat load.

I have some rule of thumb such as 2 gpm/ton to 2.5 gpm/ton to find out the flow rate in the water loop and 3 gpm/ton for the seawater condenser.

I am new in the marine industry and I would like to understand how to find it out.

Thank you

Thank you guys for reading my post.

pocketengineer I should have been more accurate you are completely right the gpm/ton is according to the delta T. I read an article from ashrae and they called that a rule of thumb but thank you to tell me what you think. I am not a native english speaker.

So, this a bit annoying for me because there is no rulee and I don't have experience in chiller system. Maybe I have to consider how long time the chiller has to tun and the water volume in the water loop.

In same time to reply to willard3, I do a "good" anaysis of each room to cool down (It's for a yacht), so I know the total load required.

I am not use about yacht airconditioning system because I worked before for heating floor and I get used to size the heat pump at the same size of the loss load.

The problem with chiller for this kind of application if I take the same size is going to be oversized and it will start ans stop so often, maybe low pressure problem and then overheat trouble.

To clarify everything, I have been working for no longtime in a firm in Asia but I am really surprised how they worked, they don't really have the skill to do so but they do!

They even don't ask me about it. I work on something else but I would like to understand because the boss is not able to explain me why he does this way. Sounds crazy but to long to explain.

If you are interested I could tell you some crazy thing he says and does about airconditioning system!! By the way, I am not going to stay too much here but air conditioning on marine industry seems interesting.

Thanks all

You will likely be using water cooled centrifugals in this range as they will be very efficient, and have a good life.

Two 300ton chillers will probably be a better base option, and serve the full building load without needing the lower efficiency pony chiller mentioned above.

What you do from here entirely depends on the class of office building, low load and time spent at reduced load, which relates to climate and patterns of use:

* VFD's are becoming very affordable and almost de rigour(outside of the tropics, where you may not have sufficient wet bulb suppression to make them worthwhile).

* Long periods of low load operation may necessitate a smaller pony chiller, and the size of this will come from your load trends for the whole cooling season, otherwise you might get away with the turndown/Hot Gas Bypass on your base chillers.

* Some applications - occupant requirements or long cooling season for example - may make a third redundant 300ton chiller worthwhile.

I would consider the water quality available too. An office system that size is not likely to get a lot of attention, so having cooling towers is a crap shoot. Air-cooled may be a better life cycle cost choice -- depends on cost of power, LEED, too.

I think this is not so simple a question as the OP believes. This is why engineers charge good money for a design. I would be hesitant to not provide a low load chiller, what happens if a single floor need to be conditioned on say a weekend or after hours. Low load issues seem to be a recurring issue on building without low load chillers.

600t may be the theoretical max load, but in real world operation the plant will run very rarely at full load.

How about some large chilled water storage instead of the low load chiller. If your low load isn't to frequent you could do litres or so of storage to get a reasonable minimum run time on a 50% or 33% chiller. The other thing to consider is redundancy, some clients will want any combination of chillers to meet say 75% of full load or something. Not such an easy question to throw out there.
HVAC68 is hitting the point when he(she) refers to load profile. I have found that spot cooling in a number of critical areas are more common and not so easily answered by a low load chiller. Areas like fire alarm system panels have batteries that tend to overheat if not properly cooled, pharmacies, conference rooms, telecom closets with router switches...you get the picture. All with different needs, different areas, ect. You really need to look at the load profile in the big picture.