Every vacuum pump converts electrical energy into mechanical work. Inevitably, much of that energy becomes heat – resulting from heating in motor windings, friction between moving parts, and gas compression. While heat generation is unavoidable, how it is managed influences not only the efficiency of the vacuum pump, but can also affect the efficiency of other associated systems and equipment located nearby.
Unmanaged heat may reduce vacuum pump reliability and performance. High temperatures can cause lubrication issues, accelerated wear, and breakdowns, as well as reducing the pumping speed and increasing energy consumption.
How to Manage Heat in Vacuum Systems
How heat affects vacuum pump efficiency
Heat can affect vacuum pump efficiency in several ways:- Reduced volumetric efficiency: Hot air is less dense than cold air, meaning that fewer molecules are drawn in per pump cycle, reducing effective pumping speed.
- Thermal expansion: Precisely engineered clearances in rotors, screws, and claws can tighten as metal expands when it heats, increasing friction. In extreme cases, this can cause internal contact or a vacuum pump to seize completely.
- Lubrication degradation: Heat thins oils and accelerates oxidation, reducing the effectiveness of the lubricant. Over time, this can contribute towards the formation of sludge that clogs passages. In oil-lubricated rotary vane vacuum pumps, the thinner oil also affects the vacuum pump’s sealing ability and can reduce pumping efficiency.
- Seal damage: Prolonged exposure to heat hardens elastomers, which are responsible for maintaining leak tightness. In vacuum pumps, seals are used around shafts, flanges, connections and housings to prevent air ingress and oil leakage. As elastomers lose elasticity and develop cracks, the seal’s integrity is compromised, reducing vacuum performance and efficiency.
- Increased motor load: As friction rises and efficiency drops, the motor draws more current, producing even more heat and risking overheating or failure.
Although some of these issues occur immediately and are easy to identify, others occur over time due to prolonged high temperatures and may be more difficult to spot.
The role of ambient temperature
When vacuum pumps operate in warm environments, the difference in air temperature inside and outside the vacuum pump is smaller. This significantly diminishes the vacuum pump’s ability to keep cool by rejecting heat to the surrounding air. Heat rejection slows, and temperatures inside the vacuum pump can become elevated.Enclosed plant rooms are especially problematic, often housing multiple heat-generating machines in close proximity. Without adequate ventilation, temperatures can exceed the maximum permissible ambient temperature that a vacuum pump is designed to operate in (typically 40 °C). Beyond this, the reliability, performance, and efficiency of the vacuum pump could be compromised.
Effect on air-conditioning systems
Most of the energy consumed by a vacuum pump is converted to heat. Whilst locating vacuum pumps in an air-conditioned area can keep them cool, this is an energy-intensive way to do so as it adds a substantial cooling load to the air conditioning system. Air-conditioning systems typically consume 1 kWh of electricity for every 4 kWh of heat that is removed. This means that to remove the heat from a vacuum pump, an air-conditioning system will consume additional energy equivalent to roughly 25% of the vacuum pump’s power consumption.For example, a 10 kW vacuum pump in an air-conditioned space will impose an extra cooling load that causes the air-conditioning system to consume an additional 2.5 kW. This not only raises operating costs but also increases the facility’s carbon footprint and may mean a larger and more expensive air-conditioning system is required. Therefore, relocating vacuum pumps to non-air-conditioned areas is considered best practice.
Managing and reducing heat
The following steps can be taken to manage the heat emitted from vacuum pumps:- Optimize plant room layout: Keep adequate clearance between vacuum pumps and other equipment to allow airflow. Position exhaust outlets and cooling fans to avoid directing heat toward other machinery.
- Assess and improve ventilation: Assess whether plant room ventilation is sufficient considering the heat load from all equipment in the room. Where required, install additional fans or vents to allow hot air out and cooler air in.
- Redirect exhaust heat: Vent vacuum pump exhausts to the outdoors, cutting in-room heat rejection by up to 35%.
- Consider liquid cooling: Liquid-cooled vacuum pumps reject much less heat to the surrounding air, helping to keep vacuum pump and plant room temperatures down.
- Install heat recovery systems: On compatible vacuum pumps, heat recovery kits can capture and reuse up to 85% of waste heat for process water heating, reducing ventilation and air conditioning system loads. Click here to learn more about heat recovery: Heat Recovery System for Vacuum and Overpressure.