After another meeting with our HVAC subcontractor, I better understand the HVAC design for our new data center.
We will have two integrated systems; each system will have a blower added so we can move the CFM we require.
This design is even simpler than what I previously understood.
I will ask our HVAC subcontractor about using evaporative coolers instead of traditional AC compressors for those rare hot days. Should be even cheaper, hot days are almost always dry days, and we shouldn't need much water for those rare hot days.
We mounted a weather station on the roof to monitor our local conditions. Microclimates around here can vary significantly over a couple of miles, and the official weather station is about five miles away.
During the recent record-breaking heat wave, we were about 10 degrees cooler than the official weather station. Which means that my previous analysis of the days we'll need to cool outside air is very conservative.
We might need to cool outside air only a few hours of a few days each year.