Comparing Generator Cooling Systems: Air-Cooled vs. Liquid-Cooled

When considering a generator for your home, one crucial aspect to understand is the type of cooling system it uses. Generators come with either air-cooling or liquid-cooling systems, each with distinct advantages and considerations. Air-cooled generators use fans to maintain optimal operating temperatures, making them simpler and often more affordable. However, they tend to be noisier and require more frequent maintenance. On the other hand, liquid-cooled generators utilize a radiator and coolant, similar to a car engine, providing quieter operation and better performance under continuous load. This blog explores the differences between these cooling systems, helping you decide which is best suited for your needs.

Liquid Cooled (left) vs Air-Cooled (right) Generator Images

Why Do Generators Need Cooling?

Most generators have numerous conductors, all of which produce heat as current flows through them. That heat can build up quickly within the system and it must be properly removed to reduce the risk of damage.

If heat is not properly removed from the system, damage to the windings occurs rather quickly. A number of issues can occur including clearance and balance problems. But, it is possible to reduce this heat significantly through various cooling systems. By consistently cooling the generator, it is possible to minimize the risk of any damage to the generator itself. Ultimately, this reduces frustration and prevents the need for repairs.

Air-Cooled Systems

Knowing the value of cooling generators, it is then important to understand how the best air-cooled systems work. For air-cooled systems, there are two main methods of cooling available.

The first is open-ventilated systems. Here, the air in the atmosphere is used with a type of exhaust system. This allows for the air to be released right back into the atmosphere. It pulls in the air and pushes it back out into the surrounding area.

The second type is an enclosed system. An enclosed system, as the name implies, keeps the air in place. It works to then recirculate the air. As it does, the air is cooled which, in turn, keeps the generator cool.

Air cooled systems have some limits including the risk of overheating. However, air cooled systems are mostly restricted to small standby and portable generators that produce up to 22 kilowatts of power per unit.

Liquid-Cooled Systems

Liquid-cooled systems, sometimes referred to as water-cooled systems, are another option. There are numerous types of liquid-cooled systems. Some operate using oil while others use coolants. Hydrogen is another cooling element.

A liquid-cooled system features a water pump that moves the coolant around the engine using a number of hoses. The heat from the generator transfers naturally to the coolant, cooling the unit. This type of system is best for larger generators in particular. They require more heavy duty components to keep the generator cool. This does increase the cost, but these are the most common option for commercial and industrial use.

One key option is the hydrogen-cooled system. These are also used for large generators. The hydrogen used in them has a high thermal conductivity. This allows these systems to pull out heat at a faster rate. As a result, they work well for larger systems that cannot be efficiently cooled using other coolants.

Effectiveness

When choosing the right cooling solution for a generator, the size and use of the generator plays a significant role in the decision process. For systems that are larger, usually all of those over 22 kilowatts of power, air-cooled systems are simply not effective. They cannot pull enough of the heat from the system, allowing them to overheat quickly. Liquid-cooled systems are the most common option for commercial and industrial spaces.

Air-cooled systems are best for portable generators and those used in residential settings. Here, there is less power and less demand, creating less heat. Air-cooled systems work well here and cost less.

Cost Comparison

The cost comparison between air-cooled and liquid-cooled generators can vary significantly based on specific models and brands, but generally, liquid-cooled generators are more expensive. Here’s an approximate cost comparison in percentage differences:

  1. Initial Purchase Price: Liquid-cooled generators can cost approximately 50% to 100% more than air-cooled generators. For example, if an air-cooled generator costs $3,000, a comparable liquid-cooled generator might cost $4,500 to $6,000.
  2. Installation Costs: Installation for liquid-cooled generators tends to be about 30% to 50% higher due to the additional complexity of the cooling system. This includes more extensive setup for the cooling system and potential requirements for additional space and ventilation.
  3. Maintenance Costs: Maintenance costs for liquid-cooled generators can be around 20% to 40% higher due to the complexity of the cooling system, requiring specialized parts and more labor-intensive service procedures.
  4. Operational Costs: Operational costs can also be slightly higher for liquid-cooled generators, around 10% to 20% more, due to the need for coolant and more extensive servicing to maintain optimal performance.
  5. Total Cost of Ownership: Over the lifetime of the generator, the total cost of ownership for a liquid-cooled generator can be approximately 30% to 50% higher than that of an air-cooled generator, factoring in initial purchase, installation, maintenance, and operational expenses.

These percentages are general estimates and can vary based on specific circumstances, such as geographic location, brand, and specific model features.

Maintenance

When choosing cooling systems, maintenance should be a key consideration. The simpler the machine is, the more simplistic the maintenance program will be. Air-cooled systems are easier to maintain because they have a rather simple design. They do not create as much of a mess during the cleaning process and can be done by anyone that is handy enough.

Maintenance for liquid-cooled systems is more complex. Most require a specialized kit available to clean the system. And, maintenance is required more frequently with these systems.

  • Cooling System Components:
    • Air-Cooled: Maintenance primarily involves ensuring that fans and cooling fins are clean and unobstructed. Dust and debris must be regularly cleared to maintain efficient airflow.
    • Liquid-Cooled: Involves maintaining a more complex system with radiators, pumps, coolant hoses, and coolant fluid. Regular checks for leaks, fluid levels, and potential blockages are necessary.
  • Frequency of Maintenance:
    • Air-Cooled: Typically requires more frequent maintenance checks due to the higher operating temperatures and greater exposure to dust and debris.
    • Liquid-Cooled: Generally needs less frequent maintenance but includes more involved procedures, such as coolant replacement and system flushes, which are typically performed at longer intervals.
  • Complexity of Service:
    • Air-Cooled: Simpler maintenance tasks that can often be performed by the homeowner, such as cleaning and checking for proper airflow.
    • Liquid-Cooled: More complex and may require professional service due to the intricacies of the cooling system, including checking and repairing pumps, radiators, and coolant lines.
  • Cost of Maintenance:
    • Air-Cooled: Generally lower cost due to simpler maintenance tasks and fewer components needing attention.
    • Liquid-Cooled: Higher maintenance costs due to the complexity of the cooling system and the need for specialized parts and service procedures.
  • Potential Issues:
    • Air-Cooled: More prone to overheating if not regularly maintained, which can lead to increased wear and potential engine damage.
    • Liquid-Cooled: Can suffer from issues related to coolant leaks, pump failures, or radiator blockages, which require more technical knowledge to diagnose and repair.

Recommended Maintenance Schedule

The maintenance schedule for generators varies based on whether they are air-cooled or liquid-cooled, as well as on the manufacturer’s recommendations and the generator’s usage patterns. Here are general guidelines for maintaining each type:

Air-Cooled Generators

  1. Weekly: Run the generator to ensure it starts and runs properly. This helps keep the engine lubricated and batteries charged.
  2. Monthly: Inspect the generator for any visible signs of wear or damage. Check the oil level and add oil if necessary.
  3. Quarterly: Check and clean the air filter. Inspect the spark plugs and replace them if necessary. Inspect the cooling fins and clean any debris to ensure proper airflow.
  4. Annually: Change the oil and oil filter. Replace the air filter and spark plugs if they have not been replaced in the last year. Inspect the fuel system and replace the fuel filter if necessary. Conduct a thorough inspection of all mechanical and electrical components.

Liquid-Cooled Generators

  1. Weekly: Run the generator to ensure it starts and runs properly. This helps keep the engine lubricated and batteries charged.
  2. Monthly: Inspect the generator for any visible signs of wear or damage. Check the oil level and add oil if necessary.
  3. Quarterly: Check and clean the air filter. Inspect the spark plugs and replace them if necessary. Check coolant levels and add coolant if necessary. Inspect the cooling system, including the radiator and hoses, for leaks or damage.
  4. Annually: Change the oil and oil filter. Replace the air filter and spark plugs if they have not been replaced in the last year. Flush the coolant system and replace the coolant. Inspect and clean the radiator and cooling system components. Conduct a thorough inspection of all mechanical and electrical components.

Additional Considerations

  • Load Testing: Periodic load testing is recommended to ensure the generator can handle its rated capacity. This should be done at least once a year.
  • Professional Service: It’s advisable to have a professional technician service the generator annually, especially for more complex maintenance tasks such as coolant system flushing and electrical inspections.

Noise Levels

The noise levels for air-cooled and liquid-cooled generators can vary significantly, with liquid-cooled generators generally being quieter. Here’s a comparison of the typical noise levels in decibels (dBA) for each type:

Air-Cooled Generators

  • Noise Level: Typically range from 65 to 75 dBA.
  • Reason: The higher noise level is due to the use of fans for cooling, which generates additional noise. The air-cooling mechanism itself is less efficient at dampening sound compared to liquid cooling.

Liquid-Cooled Generators

  • Noise Level: Typically range from 55 to 70 dBA.
  • Reason: Liquid-cooled generators are generally quieter because the liquid cooling system absorbs more sound and vibration. Additionally, these generators are often enclosed, which further reduces noise levels.

Comparative Analysis

  • Air-Cooled Generators: 65-75 dBA
    • Suitable for less noise-sensitive environments.
    • Noisier due to fan operation and less sound-dampening.
  • Liquid-Cooled Generators: 55-70 dBA
    • Better suited for noise-sensitive environments.
    • Quieter due to better sound absorption by the liquid cooling system and often superior enclosure designs.

Examples

  • Generac Air-Cooled Generator: Around 66-70 dBA at 7 meters (23 feet).
  • Cummins Liquid-Cooled Generator: Around 60-65 dBA at the same distance.

The noise level comparison provided earlier generally applies to residential generators in the range of 10 kW to 22 kW. These sizes are common for home backup power systems, and the noise levels can vary within this range depending on the specific design and model.

Examples of Noise Levels for Specific kW Sizes:

  1. Generac Air-Cooled Generators:
    • 10 kW to 22 kW: Typically around 66-70 dBA at 7 meters (23 feet)​​.
  2. Cummins Liquid-Cooled Generators:
    • 15 kW to 20 kW: Typically around 60-65 dBA at 7 meters (23 feet)​​​​.

Conclusion

Choosing the right cooling system depends on the size and use of the generator. Air-cooled systems are suitable for smaller, residential generators, while liquid-cooled systems are necessary for larger, industrial units as well as larger homes. Considerations include cost, maintenance, and noise levels.