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Chiller and Secondary Pumps Selection Criteria

Chiller and Secondary Pumps Selection Criteria

Dear Engineers,

I work as HVAC Design Engineer in a contracting company.

I wish to gain knowledge regarding chiller selections. Especially arriving the total number of chillers and total number of secondary pumps needed for a system.

I'm working on a commercial building project for office use. It has 12 floors and all are similar except the first floor which has kitchen and pantry.
The cooling loads are: 1st Floor: 180 TR;
2nd to 11th Floor: 130 TR;
12th Floor: 160 TR;
Total: 1640 TR

The consultant has proposed:
Air-cooled Chillers : 200 TR x 5 Nos (4W + 1S) = 800 TR
Water-Cooled Chillers: 350 TR x 3 Nos (2W + 1S) = 700 TR
Proposed 1500 TR;
Diversity: 91.5%
Secondary Pumps: 6 Nos (4W + 2S)

Are there any thumb rules for the above proposal? How do one arrive to these numbers?

Would anyone please help me gain knowledge regarding the selections? Are there any resources that I can refer to?

Thanks in advance for the support!

RE: Chiller and Secondary Pumps Selection Criteria

Those are huge questions, and a somewhat misleading job title winky smile if you are contracting and someone has already designed the system for you why are you interested in finding out? You could ask the consultant's actual HVAC Design Engineer for the design calculations and rationale if he is working for you and depending on the professional services agreement you have in place.

RE: Chiller and Secondary Pumps Selection Criteria

Thanks for the comments @ProcessHVAC. Actually I would like to develop more ideas in that area. I'm trying to find out sources from where I can gain knowledge.

RE: Chiller and Secondary Pumps Selection Criteria

I have not seen water-cooled and air-cooled chiller mixed design and combined for one single building. Why not consultant did designed water-cooled chiller for full building?

RE: Chiller and Secondary Pumps Selection Criteria

Also why not 4 chillers 550 tons each so one is spare? (4) 550 to cooling towers so one is spare. (4) primary pumps and (4) secondary pumps so one of each is spare. Use VFD chillers and VFD secondary pumps.

RE: Chiller and Secondary Pumps Selection Criteria

Diversion factor can be calculated as total block load vs. total load, but final decision comes from educated guess or experience.

RE: Chiller and Secondary Pumps Selection Criteria

Engineering school is a good place to start.

RE: Chiller and Secondary Pumps Selection Criteria

The engineer should present the options to the owner for the owner to the side. The engineer should discuss the pros and cons of each alternative considering operating cost, serviceability, reliability etc. We have had clients opted for air cooled units instead of water cooled because the facility has no local maintenance people, the facility do not operate 24 hours, the cost of water treatment and cooling tower maintenance.

RE: Chiller and Secondary Pumps Selection Criteria

Are all the chillers connected to a common CHW system? If so, you probably don't need to account for a standby WCC and a standby ACC. By doing this, your diversity would exceed 100% (1700/1640)

RE: Chiller and Secondary Pumps Selection Criteria

Thanks everyone for your valuable comments.

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