There is a trend occurring in new construction these days, which is being referred to collectively as ‘mixed use.’ Mixed use projects are increasingly common these days. These projects often call for a myriad of different HVAC systems, which must work in conjunction. These might include chillers, cooling towers, chilled water fan coil units, heat pumps, dedicated outdoor-air systems, or a host of other systems. Small square footages may have to be creatively outfitted if there are unusual space constraints or building limitations, particularly if the space will be used for mixed purposes.
One of the systems quite commonly used in these mixed-use projects is the Variable Refrigerant Flow (VRF) system. The VRF technology comes to us from Japan, first introduced by Daikin many years ago. The minisplits have been in increasingly high demand recently, though, for their ability to heat and cool a space. They require very little duct work, which means that they can be fit and operated in tight spaces.
Variable flow means that the compressors will modulate the amount of refrigerant flow to the unit. To laymen, this is like pressing on the gas pedal when you need to go faster in a car. The compressor can speed up to provide more refrigerant to the terminal unit when the load is high (i.e. cold winter day, hot summer day). Or, it can run medium speeds during mild winter days, or cool summer days to reduce the energy consumption. This equates to major savings for the end user. The units are very efficient and often use less power than most home appliances. Also important for the operations of these systems are outdoor air temperature sensors. The on-board computers will often communicate with an outdoor air temperature sensor, and then perform a simple algorithm to determine what compressor speed is needed to provide sufficient cooling and heating to a space.