– SmoothDrive
SmoothDrive in a nutshell:
- SmoothDrive is superior technology for VRF part-load conditions in both cooling and heating
- Hitachi VRF systems maintain a more consistent room temperature
- Hitachi VRF is more energy-efficient than conventional VRF under part-load conditions
- SmoothDrive reduces compressor on-off cycles under part-load conditions
Real life is part-load operation
Did you know that most HVAC systems generally work at partial capacity?
For more than 70% of the year, a VRF System will run under part-load conditions, with most systems operating at 50% or less of their capacity[1].
At Hitachi Air Conditioning, we consider 'part load' any load capacity under 90%.
3 Main reasons why VRF systems generally run at part load:
In real life, buildings face continuous change, from full-load to low-load. These include:
- The weather changes: nighttime, sunlight and seasons affect the ambient temperature
- Users don’t have the same temperature requirements
- Some zones’ indoor units are turned off
>> Example of applications and sectors often facing part-load conditions: hotels, offices, hospitals, residential buildings, hospitals…
Unfortunately, the standard performance data doesn’t always reflect the performance of systems under part-load conditions.
Traditional VRF systems' performance decreases at part-load
To face part-load operation challenges, traditional VRF systems adjust the refrigerant’s evaporation temperature as the load increases or decreases. We call this the INDIRECT capacity control method.
To maintain the degree of superheat within a safe margin, the indoor unit expansion valve will be opened slightly. However, this causes an unwanted effect on the evaporation temperature, increasing it when it should be lowered. As a result, the compressor stops and a repeated on-off compressor cycle occurs when the load reduces.
That’s why, VRF systems often have lower energy efficiency and more unstable control of the room temperature under part-load conditions, rather than at full-load.
The secret behind Smoothdrive: direct control of the capacity
As Hitachi Air Conditioning is committed to making a real difference for its users, Hitachi VRF systems are engineered to meet both the highest industry standards and real-life usage conditions.
That’s why our Japan-based engineering experts have managed to directly control the capacity even at low loads, while other models in the market use the refrigerant temperature as an intermediate leverage on the thermal output. The key resides in superior control of compressor speed, but not only.
- Step 1:
SmoothDrive analyses all the system units’ operations every few minutes. It detects gaps between setpoints and actual room temperature with a 0.1˚C sensitivity[2]. SmoothDrive also analyses the indoor demand trends, whether it goes higher or lower. - Step 2:
SmoothDrive determines the exact heat output necessary to close the gaps - Step 3:
SmoothDrive adjusts the compressor frequency with up to 0.1Hz(6rpm) precision to deliver the required load. It can run at a very low speed, preventing on/off cycles even when the load decreases. With Hitachi manufacturing the world’s first manufacturer of Scroll Compressors in 1983, today, Johnson Controls-Hitachi Air Conditioning has gained superior expertise in compressor operation.
As a result, the demand is met in a continuous cycle. The system can operate at low load with lesser on-off cycle and more efficiency.
Proven Results
We have tested Hitachi VRF vs. the conventional VRF to confirm the true advantages of SmoothDrive technology.
#1 SmoothDrive saves energy
With SmoothDrive, the system consumes up to 79% less energy* under part-load conditions than traditional indirect capacity control (through the refrigerant’s evaporation temperature)
#2 SmoothDrive provides a more stable temperature
Look at the room temperature curves (refer to Figure 2 below). With SmoothDrive the red curves are much more stable, with lesser fluctuations. It means the temperature is more precise and consistent, and comfort is improved for occupants.
#3 Less compressor on/off
Thanks to superior compressor control, the Hitachi Scroll compressor has a lesser on-off cycle. It can keep running continuously even at very low frequency. In addition to the energy efficiency and comfort factors, this smoother compressor operation reduces the wear and tear of the compressor, favouring the durability of the equipment.
