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Scroll vs. Piston Compressor in Heat Pump

Views: 442     Author: Site Editor     Publish Time: 2023-12-26      Origin: Site



Should you buy a scroll compressor or a piston compressor? If you are shopping for a new air compressor for your heat pump or HVAC (heating, ventilation, and air conditioning) system, two of the most common options you will come across are scroll and piston compressors. While they both serve the same purpose of creating compressed air, there are many factors that set them apart from each other.



Reciprocating (Piston) Compressor vs Scroll Compressor



In this article, we will discuss extensively scroll vs piston compressors: how to know them, their working principle, pros, cons, and differences between them. This guide will help you make an informed decision when choosing the best air compression type to meet your needs.


What is a Scroll Compressor?


A scroll compressor is a type of positive displacement compressor that operates by vacuuming air into a chamber before compressing the air. The internal part of this compressor has two spiral “scrolls” that work together for air compression.


Scroll compressors have an oil-free mechanism, which is why they are popularly preferred above other positive displacement compressors, like screw compressors. When comparing scroll vs screw compressor, you will discover that screw compressors depend on lubricants like oil to reduce wear and tear. Whereas, oil impacts the lifespan of the compressor.



Scroll Air Compressor



One of the major reasons why scroll compressors are commonly used is its simple design structure, which results in fewer moving parts and reduced maintenance requirements. It’s also known for its reliability and application where a compact, efficient, and low-noise compressor is needed.


The Working Principle


A scroll compressor features two components: a stationary scroll and an orbiting scroll. These two scrolls are identical and function together. The stationary scroll is attached to the compressor housing, while the orbiting scroll is connected to the crankshaft.


The stationary and orbiting scrolls are locked together. As the orbiting scroll receives power from the crankshaft, it rotates in a circular motion, creating a moving pocket of space between the two scrolls. This continuous motion gradually reduces the size of this pocket, thereby compressing the air trapped within it. The compression process is continuous and produces minimal vibration, leading to quieter operation compared to some other compressor types.


Pros


Below are the advantages of using scroll compressor:

  • Energy Saving: The design of a scroll compressor helps reduce power consumption during operation. Its smooth, continuous compression process eliminates the need for frequent starts and stops. In the long run, this efficiency leads to energy savings.


A small scroll compressor has the capacity of producing the same amount of air as a larger piston compressor.


  • Better Durability: Scroll compressors don’t have as many moving parts as some other compressors, thereby you have to worry about lesser maintenance requirements. In fact, they work better with time. As both scrolls become worn, they fit together better and prevent air from escaping.


Furthermore, the compressor won’t malfunction as easily as other compressor types even if you forget to clean off dust, dirt, or fail to change the air filter. Scroll compressors guarantee that every particle that enters the scrolls leaves the compression area. The orbital motion of the scroll ensures that all particles are diminished as compression stops.


  • Low Noise and Vibration: Scroll compressor simple design also includes a premium sound mechanism. The compressor operates at a low noise, without vibration. Thanks to this, you don’t need to bother about buying expensive soundproofing devices to subdue the compressor’s noise.


Its low noise and vibration allows it to be used in locations that require little to no noise, such as offices.


Cons


Below are the drawbacks associated with scroll compressors:

  • High Initial Costs: Usually, compressors that don’t require lubricants to work efficiently have higher initial cost. The absence of oil demands more precise and expert crafting during manufacturing, hence the increase in cost. Scroll compressors' high purchase price is a problem, especially to people on a tight budget.


  • Complex Repairs: The compression area has a hermetic sealing, giving the compressor a secure and constant airtight barrier. So, when a malfunction happens, repairs can’t be done immediately. If the seal is opened forcefully, the integrity of the pressure chamber becomes compromised, leading to further problems.




What is a Piston Compressor?


A piston compressor, which is also known as a “reciprocating compressor,” uses pistons controlled by a crankshaft for air compression. The compressor is basically made up of three components: a piston, a cylinder, and a crankshaft.


This compressor can be designed in two different mechanisms. It can either be a single-stage piston or a double-stage piston. In the single stage, air compression is done in a single stroke. But in the double-stage, air compression is done in two stages. Firstly, the air is compressed to an intermediate pressure, then the air is compressed to a higher pressure for the second stage. The double-stage design mechanism offers higher output and enhanced efficiency.


Piston Compressor



Piston compressors are easy to maintain and can be used for multiple applications that require intermittent air. Also, they have a simple design structure and many parts can be repaired or replaced by users.


The Working Principle


A reciprocating compressor features three major components: a cylinder (it’s made of metal and it’s closed at one end but opened at the other), a piston (a metal disc that’s fitted snugly into the open end of the cylinder) and a crankshaft (it’s connected to the piston and used to control the piston upward and downward.


When the piston goes down, it results in a vacuum in the cylinder, drawing air into the cylinder through an intake valve. When the piston goes up, it compresses the air, which is forcefully pushed out of the cylinder through a discharge valve.


This compression process continues with the piston moving upward and downward, resulting in an intermittent flow of compressed air.


Pros


Below are the advantages of using piston compressors:

  • Low Initial Costs: Piston compressors are known for their cost-effectiveness during the initial purchase. This makes them a favorable option for homeowners and small businesses with budget constraints.


The low initial costs of piston compressors allow for the installation of compressed air systems without placing a significant financial burden on the user.


  • Simple Maintenance: Piston compressors have a simple design with less-complicated parts. This translates to easy maintenance requirements like changing of oil, checking the valves, and replacing filters when necessary. This minimizes maintenance costs and system downtime.


Furthermore, the simplicity of piston compressors design makes them last long, resulting in reduced operational costs.


  • Flexible Operation: Piston compressors are adaptable to demands. They can handle varying levels of demand, making them suitable for applications that require efficient and responsive performance in dynamic operational environments.


They have the flexibility to modulate output efficiently in accordance with operational requirements. Whether it’s handling peak demand periods or adjusting to lower usage, piston compressors can operate optimally across a wide range of conditions.


Cons


Below are the drawbacks associated with using piston compressors:

  • Interrupted Airflow: Piston compressors offer less consistent supply of compressed air. Due to their reciprocating motion mechanism, they produce pulsating air, making them unsuitable for applications that require steady and continuous airflow.


  • High Noise Level: The upward and downward movement of the piston can generate a significant level of noise and vibration. The constant impact and friction of the components results in a high noise level, thereby limiting usage in quiet areas like offices or residential buildings.


  • High Oil Carryover: Piston compressors rely on lubricants like oil, and this can lead to high oil carryover into the compressed air. Excessive oil in the output can be bad for applications like food processing, hospitals, or manufacturing processes where oil-free air is needed.



Differences between Scroll vs Piston Compressor


There are many differences between scroll compressor vs piston compressor. Understanding their unique characteristics can help you choose the right option.


• Working Principle


A scroll compressor has two key parts: a stationary scroll (fixed) and an orbiting scroll (moves). Both scrolls are locked together. The orbiting scroll moves round the stationary scroll in a rotating motion, thereby creating a pocket of space for air. As the scroll continues to rotate, the size of the pocket gradually reduces, thus compressing the air trapped within it.


A piston compressor, on the other hand, has three key parts: a cylinder, a piston, and a crankshaft. The piston is inserted into the cylinder and controlled by the crankshaft, moving it upward and downward. As the piston moves downward, there is a vacuum in the cylinder, letting air enter into the cylinder. When the piston moves upward, the air compresses and is pushed out forcefully out of the cylinder through a discharge valve.


• Energy Saving


Scroll compressors are usually more energy-efficient. They have fewer moving parts, resulting in reduced internal losses. Also, the absence of clearance volume cut down energy loss during the compression process. When discussing advanced features to look for in a heat pump, the U.S Department of Energy highlighted that heat pump systems with scroll compressors provide 10 to 15 degrees warmer air when in heating mode than heat pump systems with piston compressors.


Piston compressors, on the other hand, have more moving parts with an intermittent air compression process. This results in frequent starts and stops, which consumes more energy. Furthermore, piston compressors have limitations in efficiently modulating capacity, especially in smaller units. This leads to higher energy consumption during part-load operation.


• Reliability and Duty Cycle


Another salient factor worth considering when examining scroll vs piston AC compressor is reliability and duty cycle.


As mentioned earlier, scroll compressors have fewer moving parts, meaning that there is less likelihood of mechanical failures. This guarantees their reliability and reduces the risk of downtime. Furthermore, the scroll type compressor has a continuous duty cycle that makes it applicable where a continuous and steady supply of compressed air is essential.


On the other hand, piston compressors are designed to be more complex with multiple moving parts, which increases the risks of mechanical failures. The back-and-forth movement of the piston can lead to wear and tear over time. Also, piston compressors are not reliable as they offer intermittent duty cycles, meaning they cannot be used for applications where a steady supply of air is compulsory.


• Maintenance


Again, scroll compressors have lower maintenance requirements because of their design and easy operation mechanism. They don’t use lubricants and their parts are tightly secure for better efficiency. But they can only be repaired by an expert whenever they are faulty. Attempting to do the repairs by yourself can cause more malfunctioning.


Piston compressors, on the other hand, require oil lubrication, making oil and filter replacements a compulsory routine. Monitoring and maintaining proper lubrication levels are important for the compressor lifespan.


• Transmission Loss


Another key factor to note when comparing scroll vs piston compressor is transmission loss.


Scroll compressors often exhibit lower transmission losses mainly because of their continuous compression system and reduced internal clearances. The tight design of these compressors minimizes leaks and guarantees that a higher percentage of the input power is effectively used for compression.


Piston compressors experience higher transmission losses because of the reciprocating movement and the associated clearances in the cylinder. These losses can impact the overall performance of the transmission process.


• Noise and Vibration


Scroll compressors are popularly known for their quiet operation. The smooth, continuous movement of the orbiting scroll generates less noise than the sound of the upward and downward motion of the piston compressor. This makes scroll compressors preferable in scenarios where noise can be really disturbing.


Typically, the impact of the piston against the cylinder and the cyclic nature of the compression process increases the noise and vibration level of a piston compressor. Hence, piston compressors are not often suitable for use in residential homes or offices where silence is prioritized.


• Air Delivery


This is a crucial determinant in the scroll compressor vs piston compressor debate. It basically highlights both the compressors’ airflow and air pressure system.


Scroll compressors produce continuous and steady delivery of compressed air. The rotating movement of the scrolls ensure a smoother compression process, which results in less pulsation in the airflow. The consistent air delivery makes scroll compressors ideal for situations where a stable and pulsation-free air supply is needed.


Piston compressors produce intermittent compressed air. This pulsation often lead to variations in the air pressure and flow, which affects applications that require steady and consistent airflow. To mitigate this, piston compressors are used with air tanks to provide a more stable airflow. However, this contributes to the overall cost.


• Starting Power


Scroll compressors require lower starting power than piston compressors. The design structure and working principle of scroll compressors offer a smoother and less power-intensive start-up process. This is greatly beneficial in applications where frequent starts and stops are involved. This as well, contributes to the compressor’s energy efficiency.


Piston compressors, on the other hand, require high starting power to begin functioning. The start-up power demand can be significant, particularly in larger units. This affects the compressor’s energy efficiency, especially in applications with frequent on/off cycles.


• Applications


Another factor to consider when evaluating scroll vs piston AC compressors is their suitable applications. Beyond DC inverter heat pump and air conditioning systems, both compressors can be used across many settings.


Scroll compressors are best used in residential and commercial settings because of their quiet operation and ability to offer constant airflow. They can also be used in various refrigeration systems like refrigerators, freezers, and other cold storage units.


Piston compressors, on the other hand, are commonly used in open spaces, where noise pollution isn’t a problem. They can also be used in applications like automotive manufacturing, metal fabrication, construction sites, and oil & gas industry.


• Scroll vs Piston Compressor: Which One is Better for Heat Pump or HVAC


Both scroll and piston compressors are options for an air compressor for a heat pump or HVAC system. Scroll compressors operate silently while piston compressors make a higher noise level when working. Thus, you should choose a scroll compressor if the compressor will be used in a quiet environment.


Also, piston compressors are best used for applications that demand intermittent air. Therefore, they shouldn’t be your preferred option if your application demands continuous and steady airflow. You can try the rotary compressor, it's the best choice for a heat pump or HVAC system.


SPRSUN is a professional heat pump manufacturer with expertise in offering all-round HVAC system assistance. We use the top rotary compressor in heat pumps. Would you like to get more help on the type of compressor in the heating and air conditioning system? Kindly reach out to us; our best experts are ready to attend to you.



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