Variable Refrigerant Flow (VRF) systems or Variable Refrigerant Volume (VRV) systems are a new kind of air conditioning in the US. They were originally developed in Japan in the early 80’s, but have only recently started to be used here. The systems take advantage of high tech controls to allow more than one hotel room to be connected to a single condenser mounted on the roof. The VRF units are very efficient and quiet, making them the most comfortable hotel room temperature control you could ever imagine.
But there is one catch. Multiple hotel rooms are connected to a single condenser and they share a common piping system for the refrigerant. If a leak occurs in a single unit, all the refrigerant in the system goes into one room. The resulting concentration of refrigerant can be lethal.
This danger has prompted many hotel chains, including Marriott and Hilton, to ban these systems from use in their hotels. There is an exception to this rule if costly refrigerant leak detection alarms are added to the rooms.
In this comic, the refrigerant began filling the room when the VRF unit was struck with the throwing star. The leak detection alarm might have saved the ninjas had it not been cut in half. Unfortunately, there is no NEMA rating that corresponds to “provides protection against ninja sword fights.”
Mark Robison, PE
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In Europe we have a norm EN378, that establish the limit of gas concentration, and has to be verified for every room, so if a leak occurs it is not fatal.
In pratice, for a hotel we get a lot of systems connected to just one centralized control (BMS).
By the way, I really enjoy your cartoons, keep up with the good work.
Regards
Ricardo Perry
Ricardo – Thank you for the comment and kind words about the comic.
Regarding VRV systems, I had dinner last night with Rick Frey, Senior Director of Hilton Engineering Support, and I learned more about this issue. The present Hilton standards call for the volume calculation to include the volume from the floor up to the height of the bed, only. Not the entire room volume. This severely limits the number of fan coils per condenser.
Rick has been doing further research and has concluded that the refrigerant gas mix well enough that the entire volume should be the calculation basis. He indicated that up to 16 guestrooms can be served by a single condenser, typically. I have not confirmed this calculation, but this is good news for the hotel industry.