Addressing Disparities in Flow Rates for Efficient HVAC System while considering diversity

[smali1]

I am seeking clarification on the practical implementation of chiller plant diversity. Specifically, when a chiller plant is chosen with a 75% diversified load, indicating that the chiller sizing is based on 25% less capacity. However, upon calculating the combined chilled water flow rate in a riser, it becomes apparent that the flow rate at the header exceeds the capacity that can be managed by the chiller system, taking into account the diversity considerations. I am interested in understanding how to reconcile this disparity in flow rates arising from the actual flow requirements in the riser and the reduced flow capacity of the chiller plant.

 

[trashcanman]

Sounds like a good case for primary-secondary pumping system, You flow the chilled water that the chiller(s) require in the primary loop, then on the secondary loop, you flow the diversified flow rate.
This should work.

 

[HVAC-Novice]

Ideally the flow through chiller(s) and system are equal. Design the system for the same dT the chiller uses.

Diversity also applies to the system flowrates.

If a chiller requires higher flow than system flow under certain circumstances, use a bypass valve (variable primary). In 2024, no one really should use primary/secondary anymore.

 

[smali1]

I am currently working on a project where the calculated load is determined to be 1000 Tons, and we are applying a diversity factor of 75%, resulting in the selection of a chiller with a capacity of 750 Tons.

I am seeking guidance on achieving chilled water balancing, both on the primary and secondary sides of the system. Specifically, I am interested in understanding the procedures and best practices for achieving effective balancing in the case of a Variable Primary Flow (VPF) system with similar capacity and diversity considerations.

Your expertise in this matter would be highly valuable to our project. I appreciate your time and assistance.

Thank you and looking forward to your guidance.

 

[SAK9]

Thanks for asking a good question Smali1!

This is how you do it:

Before you start the balancing process you isolate a certain number of AHUs/FCUs equivalent to 250 tons in your case. You start the pump and balance the operational units at their maximum design flows. Once you accomplish the balancing of operational units, you open the isolated units and close an equal capacity of operational units(meaning flow requirement is kept to 750 tons) and balance the newly opened units to their design flows. Systems with large diversity factors are rather difficult to balance so few iterations may be required. I would suggest your read the NEBB Procedural Standard for Balancing for a deeper understanding.