One Engineer’s Opinion: Please Don’t Drink the Kool-Aid
By Bruce Longino
Don’t “drink the Kool-Aid” phrase came from a great tragedy that occurred November 18, 1978 Jonestown, Guyana. Jim Jones had a cult following of people. His followers were convinced to drink a Kool-Aid like drink laced with cyanide. That day 909 men, women and children perished in a mass suicide.
After that horrible day, the expression “drink the Kool-Aid” is used to describe the behavior of believing what the crowd believes because the crowd believes it. In this article I use the term for people believing that Variable Refrigerant Flow systems are good for all HVAC applications. That is not true.
VRF systems utilize many fan coils connected to only a few outdoor condensing units or heat pumps. Each fan coil has an electronic expansion valve to modulate heating and cooling capacity. On the same outdoor unit, each indoor fan coil can be heating or cooling. If an outdoor unit has requirements for simultaneous heat and cooling it can operate very efficiently. In this case the heat absorbed to cool one area, can heat another area. The indoor fan coils are cassette, wall mounted, floor mounted or ducted.
VRF systems are great for the correct HVAC application. VRF is great for buildings with limited ceiling plenum space where there is not enough duct space for an all air system. However there must be enough space to accommodate an outside air duct system.
The diagram below shows a VRF system with only three indoor fan coils connected to one outdoor unit. In reality most outdoor units will serve 16 to 20 indoor fan coils. In classrooms typically cassettes are used in the center of the room. In today’s classrooms with LED lights and bi-polar ionization the air conditioning load could be as low as 2 tons. However in classrooms a more efficient system could be high efficiency roof top units. The RTUs can take advantage of economizers.
With this article, I am asking you to not “drink the kool-aid.” Consider other alternative systems to VRF.
W. Bruce Longino, P.E., LEED AP, may be reached by email at firstname.lastname@example.org.