Everyone,

I have a question regarding the baseline chilled water loop.

ASHRAE 90.1 2007 Section G3.1.3.10 states that for large chilled water systems serving baseline systems 7 and 8 that are greater than 300 tons the loop ?shall be modeled as primary/secondary with variable speed drives on the secondary pumping loop.?

The following section, G3.1.3.11 further goes on to say that ?each chiller shall be modeled with separate?chilled water pumps interlocked to operate with the associated chiller.?

As clarification, does this mean three sets of pumps are required, or just two? Are the ?primary? loop pumps specified as the chiller pumps?

Two reasons why I am confused. Firstly, the Chapter 11 baseline chilled water loop is supposed to be simulated as primary-only variable flow, but still has the similar requirement for interlocked chiller pumps. That would be two sets of pumps. Adding a ?secondary? loop actually adds a third set of pumps.

The second reason why I am confused is that the Simulation Guidebook prepared for Pacific Gas and Electric (same affiliation as CoolTools) has a visual of how to simulate ?primary/secondary? loops on page 52, but they do not include chiller pumps in their image of the eQUEST component tree.

I can?t understand why three sets of pumps would be required. I supposed a follow up question may be if the 22 watts/gpm is inclusive of all three sets of pumps. Hopefully someone can clarify! I appreciate your help.

Michael J. Smith, EIT, LEED? AP