For large Chilled Water Systems is it better to run N Chillers at 100% Load or N+1 Chillers to run at 80-85% (partially) Load?

It is preferable to run as minimum chillers as possible so as to minimise on number of auxiliaries along with the chillers viz primary pumps, condenser pump, secondary pump, cooling tower so as to optimise on KW/TR.........Chillers below50% of load are very inefficient anyway.........

N+1

Hi Muhammad,

It is never recommended to design the redundant system in such a way that the prime units work on 100% efficiency. 

But as you are telling the load is 2000TR, the load will not be the same in every condition and it may decrease during night time and the load on chillers will also reduce.

Now coming to your question which arrangement is better, either running N chillers on full efficiency or N+1 chillers on partial efficienc, there are several things which must be keep in account:

* If your not abide to keep standby unit, it is better to run all chillers(N+1), this will contribute to the load sharing of rest of the chillers. Chillers are internally programmed to load and unload compressors according to the requirement which in case low cooling demand can give rest to the compressors.

* Running N+1 chillers will lead to energizing  of associate primary pumps which will absolutely results to increased power consumption.

You will get a mixed response on this question, and in any case you will gain and loose something, What I think you must go for N+1 arrangement.

Thanks

N chillers them selves are a reason for  distribution from part to peak load with proper controlls ,and VRV So  need of add another 1 for increasing life of the equipment.also we have stand by for the N chillers which will make it N+2. so N with 100 percent is nice idea.

If the tonnage is2 thousand TR and the chillers are TR Each (4 running and1 standby).  it is better to run all5 chillers on partially Load. By this process it will work efficiently.

It is preferable to run as minimum chillers as possible. But the Chiller machine has a thermostatic  control  (out side thermostat & inside thermostat) will  send order to thermal electronic control card to analyzes temperature and  feedback order  to one or more  chiller   machines  in duty work.               (I mean operation of chillers  depending  on inside comfortable Heating  load of the space).

n+1

4 working and one standby with sequence operation for5 chillers and the building never reach to peak load for full year only one time on the year that's mean chillers never run full capacity all time

Running all chillers at part load is advised as

1) It ensures the functioning of all chillers (from Operations point of view)

2) The chillers are not stressed for 100% output.

However in case of shut down of 1 chiller, the N nos. shall bear the total building load on temporary basis.

It is better to run the4 chillers on100% load especially the same 4 chillers shall work on part load after certain time , the building will not be at peak all the time , the5th chiller (stand by ) shall be on lead lag sequence with the working4 chillers through the BMS.

If the Project you are dealing is based on Public Gatherings, then the system will be at peak load for maximum of time and it will be recommended to go for N+1 Chillers. Because the Chiller system controlled by BMS will always trigger it to work at full load and in such circumstances any unfortunate breakdown happens then the system will  Under Perform in cooling which is Highly unacceptable. 

On the Other hand for the other projects, It is better to run  N chillers on 100% capacity load because the building will never stabilize at peak load all the time. The system is always designed considering the Factor of Diversity as per ASHRAE & CIBSE codes. 

The cost for the extra Chiller will be a disadvantage and is liable to cost savings.