Variable Frequency Drive for Cooling Efficiency

Jamie AngaraArticles, Blog

Variable Frequency Drive

Introduction

Data centers use massive amounts of energy and 40% of this goes to cooling systems. Other consumers are the IT equipment itself housed within the facility. Increasing density is set to raise this metric eightfold by 2030. With this, electricity cost has been a pain point for data center operators. Couple this with the carbon emission that stands in the way of sustainability. It is no surprise that operators are chasing ways to lower their facility’s Power Usage Effectiveness (PUE) by leveraging cooling efficiency practices. One of these ways is integrating Variable Frequency Drive (VFD) into the cooling systems.

What is Variable Frequency Drive?

Variable Frequency Drive (VFD) controls the speed of the electric motors in the cooling system. It uses only adequate energy to provide the right amount of airflow. It controls the energy consumption of the cooling system components such as fans, pumps, and compressors. Some operators set the system to the maximum in a belief that this will maintain efficiency. However, this practice appears to be counterproductive. The energy is wasted as fans are running at full speed while controlling the airflow by throttling and damping.
 
A VFD works by varying the frequency of the system’s power supply. It eliminates the use of standard on/off motors, replacing it with precise control. With this, the motor speed can run up and down, and the IT load’s energy consumption can be maintained. Its energy efficiency has been manifested in the industry for years. Based on research, this solution can save up to 30% –  35% in cooling.

How Does Variable Frequency Drive Improve Energy Efficiency?

VFD’s are used by various industries across the world, including data centers. The ways that this technology counters the massive energy use forced operators to adopt it. In 2019, almost 30% of the data centers have already invested in VFD’s.
 
Here is how installing a VFD improves energy efficiency:
  1. Control Starting Current Too much current in starting the motor consumes a lot of energy and generates more heat. A VFD has the ability at a zero voltage or frequency. This tracks motor winding flexing and heat generation, extending the motor life.
  2. Reduced Variation in the AC Voltage Motor full load current can cause voltage sag. Voltage sag is a disturbance due to the reduction of the RMS value of the line voltage for a period of time. When this happens, the equipment can receive insufficient voltage causing them to trip offline. Installing VFD can prevent voltage sag.
  3. Lower Starting Power Demand Power demand in starting an ac motor across the line is higher than with a VFD. During peak hours, customers can experience surge prices. However, with VFD demanding lower starting power, the issue can be addressed.
  4. Controlled Speed and Acceleration – VFD can accelerate and allows speed to be adjusted by a controller.
  5. Limits the TorqueThe VFD can adjust and limit the amount of torque that prevents the motor from reaching its threshold. This keeps the equipment from being damaged.

The Pump Affinity Laws

The Pump Affinity Law explains the ability of the Variable Frequency Drive to improve energy efficiency. The affinity laws are used in hydraulics, Hydronics, and/or HVAC to express the relationship between variables involved in pump or fan performance. With this, the variables are directly proportional to each other. Flow changes directly with a change in speed. Same with the head and the square of the speed; and required power and the cube of the speed.
 
This means if the pump speed decreases by 20%,  the flow also decreases to 20%, and so on. Therefore, energy savings increases as the demand for flow and corresponding pump speed decreases.

Benefits of VFD to Data Centers

Variable Frequency Drive continues to transform and change the game in the data center industry. Aside from energy efficiency, it can also bring the following benefits:
  1. Scalability – VFD is designed for high-density data centers. Units can be scaled up or down in capacity to meet demand. This can help the cooling system to counter more heat generated by thousands of servers within the facility. In addition, a standard AC motor allows existing data centers to be retrofitted with a new temperature control system.
  2. Redundancy – Installing EC fan units in a fan array can provide redundancy in the failure of one EC motor. However, there is no hand mode so control from the driving keyboard can be lost without connection to the control system.
  3. Reduced Cost – Cooling system efficiency can significantly reduce cost. Although it’s often overlooked due to its expensive installation, its saving capability is worth it as a long-term investment.
  4. Higher Ambient Temperature – It allows the facility to operate at a higher temperature. According to the study, each degree Celsius increase in the center’s operating temperature can provide a 4% reduction in cooling costs. However, operators need to be dedicated to monitoring. The temperature might reach its threshold and damage sensitive equipment if not controlled.
  5. Proactive Maintenance – VFD has automated control systems that allow operators to be more proactive. They are provided with precise control and a chance to take corrective actions for a potential problem.

The Drawbacks of VFD to Data Centers

Although Variable Frequency Drives can benefit data centers in several ways, it also holds some drawbacks. Overseeing these drawbacks can cause unwanted conditions to the data center. Thus, it is essential to know and see how to counter them before installing VFD.
  1. Impaired Reliability – Energy savings is important but the ability to perform in utmost reliability should be the most priority of data centers. VFD can compromise reliability by damaging the windings of motors with low-grade insulation.
  2. Installation Cost – VFD is expensive for smaller and start-up companies. It has several cost considerations in installation and application. It requires additional components that can add up to the cost.
  3. Sensitive Environmental Condition – VFD are more sensitive to very low or high temperatures than across-the-line starters. Drives need climate control and may need to be oversized to cope with intense heat.
  4. Noise and Vibration – VFDs can also destroy the bearings of the motors they control. It can create a crater that roughens its surface. This can initially cause noise and vibration that will lead to bearing failure.

Why Monitor?

Installing Variable frequency drives is a huge capital for data centers. It requires consistent monitoring to ensure that all of its components are working. It can also help operators to evaluate how effective the VFD is. Therefore, integrating automated monitoring systems along with the VFD is a must. AKCP can make this task easier for operators. It offers a variety of sensors for different industries including data centers.
AKCP Monitoring

Vibration Sensor

With the ever-increasing demand for operational efficiency and reduced downtime, predictive maintenance is a valuable tool. The AKCP sensors are multi-purpose sensors for various applications. The AKCP vibration sensor is a normally closed input switch that will detect when there is vibration. It can be connected to both the sensorProbe or securityProbe+ base units and then linked to notification alerts.  The built-in tamper switch is independent of the circuit of the vibration detector for your convenience.

Power Monitoring Sensors

The AKCP Power Monitor Sensor gives vital information and allows you to remotely monitor power eliminating the need for manual power audits as well as providing immediate alerts to potential problems. The AKCP Power Monitor Sensor is specifically designed to be used with AKCP sensorProbe+ and securityProbe base units. It has been integrated into the sensorProbe+ and securityProbe web interface with its own “Power Management” menu, allowing multiple three-phase and single-phase Power Monitor Sensors to be set up on a single sensorProbe+ or securityProbe depending on which readings are required

Wireless Tank Depth Level Sensors

Monitor tanks of depths up to 20 meters. Often tanks are located in outdoor or difficult to cable areas. The WT-TDPS is battery powered or can be powered from a 5V DC or 12VDC source. Track fuel usage, graph the tank level, receive alerts when tank levels are critical. No more constraints on maximum cable lengths from the base unit. Easy installation and pairing with AKCP Wireless Tunnel™ Gateways.

Reference Links:

https://library.e.abb.com/public/49d24d9b978e119385257bf30062a596/ABB-721-WPO_data-center-cooling-systems.pdf

https://www.missioncriticalmagazine.com/articles/92746-driving-improvements-for-efficient-data-center-cooling

https://est-aegis.info/2019/03/reliable-data-center-cooling/

https://www.pumpsandsystems.com/vfd-cost-effective-option-your-application

https://www.wolfautomation.com/blog/benefits-vfd/

Jamie AngaraVariable Frequency Drive for Cooling Efficiency