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Mitsubishi Electric HVAC’s CITY MULTI VRF Systems

Mitsubishi is one of the companies leading the charge of marketing VRF systems to the US currently (which began only in the past 3-4 years). The CITY MULTI VRFZ System is Mitsubishi’s offering for a two-pipe simultaneous cooling and heating system (also referred to occasionally as a VRF heat pump system). The principle behind this type of variable refrigerant system is similar to a water-source heat pump system in that the circulating fluid is used as a heat transfer sync between heat pumps, with excess heat rejected to an outside unit. The only exception is that for the VRF, the circulating fluid is refrigerant as opposed to water. In addition, the system can be provided with ducted or ductless indoor units (similar to a mini-split system which most engineers are familiar with), and operate very quietly, according to the manufacturer.

What is VRF

The zoned nature of this system eliminates recirculation of air between zones, but does require introduction of outside air for ventilation directly into each unit’s zone, and depending on zone usage this quantity of air can very.

Now at first glance, people might think that this isn’t an environmentally friendly solution due to the fact that there are increased levels of refrigerant being used when compared to a typical split system… however the increased levels are minimal compared to the amount of cooling/heating the system provides. This is the basis for the LEED Energy & Atmosphere Credit 4, Enhanced Refrigerant Management. A project I recently worked on that included a VRF heat pump system is anticipated to earn this credit; with a total calculated refrigerant impact per ton of 54.6 (less than 100 is required to earn the credit).

One of the biggest advantages of the CITY MULTI system though, is the energy efficiency. Mitsubishi’s INVERTER compressors ramp up quickly to meet the cooling or heating demand in the zone, then based on feedback from the system controls and sensors the INVERTER varies it’s speed to maintain space setpoint, saving energy when the unit is only required to operate at part-load condition (97% of the time in most locations, according to the manufacturer). Energy modeling software has shown INVERTER-driven VRF split-systems to be approximately 25% more efficient than traditional systems across several major US cities.

information by: Sarah Gudeman

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