>Exactly what he said.  We actually run cooling and supplemental heating >in extreme cold.  We need to keep the chiller pulling heat into itself and >pumps moving on high to keep the outdoor components from freezing >up.  During the summer you might run close to or slightly below freezing >on the coolant loops but in these conditions you cannot run that low a >temp because things will freeze up before the coolant returns.  We also >have to keep the room reasonably warm (50F +).  You also need to watch >out for fast temp excursions to keep humidity under control.

A good HVAC team is critical because we have noted that the building management systems often are not flexible enough to automatically deal with super extremes and require some human intervention to tell them to do things like run heat and cooling simultaneously.  Other actions like closing down louvers on evaporators may or may not be automated depending on your systems.  If any part of the system does fail in these conditions you have to move super quick or you could get serious damage fast.  Our biggest monitoring points are flow rate/pressure (which could indicate a freeze up beginning or a pump failing), output and return temp on the loops.

Steven Naslund

Chicago IL