ASHRAE requirements for cooling towers

The standard rating conditions are the parameters used to determine the minimum efficiency rating (like a heat pump being tested at certain temperatures). If your design situation does not match this it does not matter, the equyipment must meet the minimum efficiency at the rated conditions. The minimum performance requirements would still apply to your situation.

Hi Marcus, In continuation to the query raised above, I have another query on what should be the WBT that we should use in the base case model. My thinking is that the WBT is location dependent parameter and should be the same for both the base case and the proposed case models. For example, the default WBT is of 78 F in eQuest and in general, the design case WBT could be around 82 F for a few locations. In this case, we get a huge difference in terms of the energy consumption by heat rejection units. Your response to this query would be appreciated. Also, can you also throw some light on the number of cooling towers we need to design in the base case model. Should it be 1 only or it shall be equal to the number of chillers my base model is having. Thanks in advance.

The design wet-bulb temperature used for sizing the Baseline cooling tower should be the 1% wet-bulb design condition, which is location-dependent. The Proposed cooling tower should be modeled as-designed.  The Baseline cooling tower controls should be modeled according to G3.1.3.11 (condenser water supply temperature of 70 F when weather permits, floating up to a maximum of 85 F or 10 F approach to wet bulb, whichever is lower.  There's some disagreement as to the number of cooling towers. The LEED Minimum Energy Performance Calculator indicates that one cooling tower should be modeled for the Baseline, which I would recommend for LEED projects. However, the PNNL Standard 90.1-2010 Performance Rating Method Reference Manual (https://www.pnnl.gov/main/publications/external/technical_reports/PNNL-25130.pdf) indicates one cooling tower per chiller.