Don’t believe VRF manufacturers claims of superior energy efficiency
When it comes to moving BTU’s around a building, Hydronic Systems are the most efficient!
VRF manufacturers had been making claims of superior energy efficiency for a number of years without providing any data to back up their claims. In fact, one of the VRF companies likes to say that it’s system is the “most energy efficient system ever developed.”
Some VRF advocates have suggested that because a DX or VRF system does not have a separate pump or fan to push it’s fluid (refrigerant) around a building that it is more efficient than hydronic or air systems in moving BTU’s around a building. This is not the case.
The compressor in a VRF system serves double duty, it compresses and raises the temperature of the fluid and also serves as the pump to push the fluid around the building. As a result the oil to lubricate the pump motor (compressor) is carried with the fluid around the system, unlike hydronic and air systems where the oil to lubricate the pump and fan motors is outside the fluid. The fluid (refrigerant) also undergoes a phase change with a portion of the system becoming a gas in the suction line. In order to carry the entrained oil in the gas the velocity in the suction line must be higher than other portions of the system. These velocities are significantly higher than hydronic or air systems. In fact the velocity in a VRF system can be up to 5 times higher than an air system and 10 times higher than a hydronic system.
Higher velocities in a VRF system translate to significantly higher pumping energy as shown in the graph.
As the graph demonstrates, VRF systems require substantially more pumping energy than hydronic and some air systems.
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