Motors for HVAC and Cooling Systems

Which motors should be used in HVAC and cooling systems

In HVAC and cooling systems, motors are everywhere. Fans are rotating, pumps are rotating, and cooling towers are also rotating. Choosing the right motor can make the system more energy-efficient and quieter. Choosing the wrong one will result in high electricity costs and even system shutdown during the hottest summer days.

Where are motors used in HVAC systems

The main power consumers are the supply fans and exhaust fans. The supply fans in the air handling units distribute cold or hot air to various rooms. The exhaust fans remove the dirty air. The power ranges from 0.75 kilowatts to 75 kilowatts. For a building's roof fan, the common power range is 5.5 to 15 kilowatts.

Cooling water pumps and chilled water pumps are responsible for delivering cold or hot water to the end devices. The power is related to the floor height and the length of the pipes. For a ten-story hotel, the chilled water pump motor is approximately 11 to 22 kilowatts.

The cooling tower fans are installed outdoors and are responsible for removing the heat from the cooling water to the air. The power is commonly between 1.5 and 7.5 kilowatts. The trouble is that the cooling tower is outdoors, exposed to wind, sun, and rain, and requires a high level of protection.

What are the special requirements for motors in HVAC systems

They operate 24/7. Many HVAC devices run for over 8,000 hours a year, almost without stopping. When choosing a motor, the bearings should be of high quality, with an insulation grade of at least F, and able to withstand a temperature of 155°C.

Variable frequency is the mainstream. To save electricity, variable frequency drives are commonly used for speed control. However, ordinary motors have poorer heat dissipation at low speeds because the fan also rotates slower. If they often run at speeds below 50%, it is recommended to use a variable frequency motor with an independent cooling fan.

The noise should be low. Office buildings, hospitals, and hotels are sensitive to noise. Standard motors have a noise level of 60 to 80 decibels. For those installed on fan coil units, the requirements are even higher. Adding rubber shock absorbers during installation can also reduce noise.

The protection level should not be low. Motors installed in ducts should have at least IP44 protection. For those installed outdoors or next to the cooling tower, IP55 is the starting point. Some cooling towers have a lot of water mist, and IP56 is required to withstand it.

How to determine the power

The power of the fan motor depends on the air volume and pressure. The calculation formula is power approximately equal to (air volume × pressure) ÷ (3600 × fan efficiency × transmission efficiency). When selecting, engineers calculate the parameters, find the corresponding power from the samples, and leave a 10% to 15% margin.

The power of the pump motor depends on the flow rate and head. The principle is the same. Engineers calculate the hydraulic parameters and find the power from the samples, leaving a 10% to 15% margin.

Take a real example. A mall originally used a 15-kilowatt fan. When it was replaced due to aging, the load was recalculated, and it was found that it only needed 11 kilowatts. A smaller motor was replaced, with the air volume remaining the same, and the annual electricity cost was saved by nearly 10,000 yuan. This shows that the margin was too large originally.

How to select the energy efficiency grade

HVAC equipment runs for a long time, and a small difference in efficiency can result in a significant difference in electricity costs.

IE3 is the basic requirement. Many countries stipulate that motors above 0.75 kilowatts should at least reach IE3. A 15-kilowatt motor runs for 8,000 hours a year, and IE3 can earn back the difference from IE2 in more than one year.

IE4 and IE5 are more energy-efficient but more expensive. Whether to increase to IE4 depends on electricity costs and hours of operation. If it only runs for a few hours a day, IE3 is sufficient. For those running all day, it is recommended to calculate whether IE4 is cost-effective.

Professional matters should be handled by professionals

We have been in the motor industry for over 35 years. We can't even count the number of HVAC systems' motors we have used in a year. Different air volumes, different installation environments, and different operating times have very different requirements for motors. The principles mentioned in the article are only general guidelines. For your specific project, you need to determine the power, the protection level, and whether to equip an independent cooling system based on the actual conditions.

If you have a project in the process of selecting components or your existing motors are frequently malfunctioning and you want to replace them, please feel free to contact us. Please tell us your equipment parameters and the on-site situation. We will help you calculate the specifications accurately. Energy-saving, durable, without malfunctions - this is what a good motor should be like.