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Reciprocating Compressor vs Rotary Compressor in HVAC

Views: 346     Author: Site Editor     Publish Time: 2023-12-27      Origin: Site



Reciprocating and rotary compressors are two of the most common compressors used today. Both have the same functionality of transferring atmospheric air into a chamber, compressing it, and then discharging the compressed air to the room.


Reciprocating Compressor vs Rotary Compressor



While they serve the same function, they have some notable differences, which influence how efficiently they operate and the types of applications they are most suited for. In this article, we will do a detailed comparison of reciprocating compressor vs rotary compressor, highlighting their working principle, structural design, pros, cons, and general performance.


What is a Reciprocating Compressor?

A reciprocating compressor is also referred to as a “piston air compressor.” This is mainly because it uses pistons driven by a crankshaft for its air compression. The use of pistons for air compression can be traced back as far as the mid-1600s, but its structure and working mechanism changed in the late 1800s during the industrial revolution.


Piston compressors are available in 2 forms: single-stage or double-stage. For a single-stage piston, the air is compressed in a single stroke. For the double-stage piston, the air is compressed in two stages. Firstly, the air is compressed to an intermediate pressure, then compressed to a higher pressure. The double-stage system enables higher output and efficiency.


Reciprocating Compressor



Reciprocating compressors are constructed for intermittent air operation, hence more suitable for homeowners, small machine shops, and other small businesses. One exceeding feature of a piston compressor is that it can be operated below its maximum capacity without any adverse effect. What this means is that you can purchase a larger machine and grow into it if you project that your home or shop will need more air in the future.


What is a Rotary Compressor?


The use of rotary compressor can be traced back to the mid-1900s. Its mechanism hasn’t changed much since then, but advancement in manufacturing processes has improved its efficiency and durability.


Moreover, electronic equipment and automation has made these compressors simpler to control and maintain. In today’s world, some rotary screw air compressors feature variable speed drive, allowing users to regulate airflow according to their demand. This helps to save energy and reduce bills.


Panasonic Rotary Compressor


Unlike reciprocating compressors, rotary compressors use two meshing helical screws (commonly referred to as “rotors”) for air compression. As the interlocking spirals turn, air is forced through the chambers and compressed into a smaller space. So, as the rotor continues to turn, air is continuously compressed.


Another popular comparison made is scroll vs rotary compressor. But rotary compressors have fewer moving parts, making them more reliable and lasting longer than reciprocating and scroll compressors. Rotary compressors are, however, more expensive. But in the long run, they are good investments, particularly for industries that require high airflow and continuous operation with applications like heat pumps, conveyor systems, plastic molding, or woodworking.


Reciprocating vs Rotary Compressor: Working Principle


Despite having the same purpose, reciprocating and rotary compressors don’t have the same working principle. Below is a comparison between reciprocating and rotary compressor.


How Does Reciprocating Compressor Work?


Basically, a reciprocating compressor consists of a piston, cylinder, and crankshaft. The piston is a metal disc that’s inserted snugly into the cylinder. The cylinder is made of metal and closed at one end; the other end is open to accommodate the piston. The crankshaft is connected to the piston, driving it up and down inside the cylinder.


The reciprocating compressor uses a piston to compress air inside a cylinder. When the piston goes down, it forms a vacuum in the cylinder, which absorbs air into the cylinder via an intake valve. As the piston goes up, it compresses the air and pushes it out of the cylinder via a discharge valve. This process is continued repeatedly, with the piston moving up and down to create an intermittent flow of compressed air.


How Does a Rotary Compressor Work?


A rotary compressor works by using two rotors (screws) that rotate with close clearances next to each other inside a cylinder. The rotors are often produced with high-strength steel and configured to a helical shape. Groves are cut into them to allow air to move freely through the compressor.


As the rotors rotate, air is absorbed into the cylinder via an inlet valve. As the air moves through the grooves, it is compressed and as the channel's volume decreases, pressure increases. The compressed air is then forced out via an outlet valve. After the compression cycle is completed, the screws must be separated from the air. Oil is usually used to lubricate, cool, and seal the screws.


Structural Design Difference between Reciprocating and Rotary Compressors


An evident feature that can be used to differentiate reciprocating compressor vs rotary compressor is structural design.


Reciprocating compressor is made up of 3 components: a piston, a crankshaft, and a cylinder. The piston is fixed snugly into the cylinder, while the crankshaft moves the piston upward and downward to absorb and compress air.


Rotary compressor, on the other hand, is made up of two meshing helical screws and a cylinder. It has a simpler structure, as the screws rotate to draw in and compress air. This design uses fewer moving parts, enabling efficiency and requiring less maintenance.


Reciprocating vs Rotary Compressor Pros and Cons


Rotary vs reciprocating compressor in AC can also be differentiated based on their advantages and disadvantages.


Reciprocating Compressor


Pros

  • Lower initial cost (about 20-50% lesser than rotary compressor)

  • Double-stage models are super-efficient

  • Energy-efficient for low CFM and intermittent applications

  • Can be used for higher pressures with multi-stage compression


Cons

  • Not suitable for continuous operation

  • Loud noise and vibration

  • Requires downtime to cool because of heat caused by friction

  • Shorter lifespan

  • Higher maintenance cost

  • Can be used in any environment, including clean and dirty operating environment

  • Best for smaller shops and manual applications like manual power tools, blow-off, etc.




Rotary Compressor


Pros

  • Ideal for continuous operation

  • Offers cleaner air

  • Very reliable

  • Longer lifespan

  • Cooler internal operating temperature (about 140-160 degree Fahrenheit)

  • Quiet operation

  • Don’t need air receiver tank

  • Best for industrial applications like high-volume operation, robotic manufacturing, conveyor systems, etc.


Cons

  • Higher initial cost

  • Requires skilled maintenance

  • Must be used in a clean environment


AC Compressor Rotary vs Reciprocating Performance


There are many differences associated with reciprocating vs rotary compressor in terms of performance. Understanding compressor specifications can help you make an informed decision on which is better.


Below, we will discuss the key factors to compare reciprocating and rotary compressors performance:


• Energy Efficiency


In comparing the energy efficiency of rotary compressor vs reciprocating compressor in AC and air source heat pumps, rotary compressor has a greater advantage. This is solely because it has fewer moving components and produces compressed air throughout its operation cycle.


On the other hand, a reciprocating compressor has more moving components, making it lose large energy to friction. Moreover, its efficiency is reduced because of the structural design of the pistons, cylinder, and crankshaft.


Overall, rotary compressors are more efficient in electricity consumption than reciprocating compressors. They use two meshing helical rotors for air consumption, resulting in a continuous stream of compressed air while consuming less energy.


• Airflow


Another performance difference between AC compressor rotary vs reciprocating compressor is the consistency of compressing and discharging air. Effortlessly, a rotary screw compressor can be chosen over a reciprocating compressor because of its smooth and consistent airflow.


Rotary compressors come with two helical rotors that rotate throughout the operation, compressing the air continuously. This results in a steady flow of compressed air.


Reciprocating compressors, on the other hand, depend on the motion of pistons for air compression, which can result in pulsations and fluctuations in the airflow, particularly when they are operated at higher pressures.


• Air Pressure


Your selection between reciprocating compressor vs rotary compressor can greatly affect air pressure output, an essential element for air conditioners during hot seasons and heat pumps for cold climates.


Typically, reciprocating compressors are manufactured to generate compressed air at extremely high pressures, usually up to 200 psi (13.8 bar) or even more; thus, they are ideal for high-air pressure applications like industrial processes and spray painting. Moreover, the pressure generated by reciprocating compressors changes as the piston goes upward and downward.


Rotary compressors, on the other hand, are designed to consistently generate compressed air at 150 psi (10.3 bar). Thus, why they are ideal for applications like operating pneumatic tools.


• Air Tanks and Air Storage Requirements


Another crucial disposition to differentiate reciprocating vs rotary compressor air conditioners is air storage.


Reciprocating compressors, because of their intermittent air production, often come with air tanks to store air. This is to create a reservoir for the continual discharge of compressed air when it is needed.


On the other hand, some rotary compressors come with air tanks while others don’t. This can be attributed to the fact that rotary screw compressors generate air continuously. Hence there is really no need for air tanks.


• Cleanliness of Delivered Air


Both reciprocating and rotary compressors can efficiently produce clean air with necessary filtration and air treatment.


However, rotary compressors tend to produce cleaner, high-quality air with reduced oil carryover and particulate interference. This is because these compressors have a more enclosed design structure, which ensures that the compressed air doesn’t contain contaminants. In fact, many rotary compressors come with an internal filtration system to remove impurities.


When using reciprocating compressors, the piston and cylinder are exposed to the surrounding environment, allowing all kinds of contaminants, including dust, dirt, and oil, into the compressed air.

• Stability and Durability


HVAC (heat, ventilation, and air conditioning) systems can be expensive, therefore, it’s imperative that you consider the compressors stability and durability before selection.


Reciprocating compressors, because of their working mechanism, which involves the upward and downward movement of the piston, cause more friction and wear over time. This can negatively impact the stability and durability of the compressor.


On the other hand, a rotary screw compressor has a rotating working mechanism, resulting in a smoother operation with less wear and tear. The unique design and working principle improve its stability and durability.


• Noise and Vibration

rotary compressor in SPRSUN heat pump


Noise and vibration should be on your priority list of factors to be considered on reciprocating compressor vs rotary compressor, especially if the HVAC system will be operated in environments where people live or work. You don’t want to cause disturbance.


Reciprocating compressors have a more complex design structure with more moving parts, which tend to cause louder noise and vibration. Piston compressors are smaller when compared to rotary screw compressors, and the smaller the compressor, the more noise pollution it makes. In addition, smaller compressors have lesser sound insulation features. The noise level of reciprocating compressors ranges from 80-90 d(B)A.


On the other hand, rotary compressors are bigger and have a simpler design structure, with fewer moving components. These compressors work with a more consistent flow of compressed air, which helps to minimize noise and vibration. Also, they come with sound insulation features. The noise level of rotary compressors ranges from 70-80 dB(A).


• Duty Cycle


One of the biggest distinctions between rotary compressor vs reciprocating compressor air conditioners is in the duty cycle. A compressor duty cycle is simply the duration of time needed to generate air vs the duration of time it takes to rest. Duty cycle is sometimes called “load/unload time” or “run/rest time.”


Rotary compressors have a 100% duty cycle i.e., they can generate compressed air efficiently at all times. They are easy to regulate. If less air is needed, the compressor turns off (shut down) for a short period and when pressure drops to a lower level, it comes back on. Therefore, if you need a continuous compressor for optimal duty cycle, rotary compressor is the ideal option.


Reciprocating compressors, on the other hand, are produced for intermittent duty cycle. To function properly, they cycle down and cool off from time to time. These compressors are rated below 100% duty cycle and the lower the rating, the more time the compressor spends to rest. If the compressor is overworked or programmed to spend more time producing air than resting, it will result in overheating and lower lifespan.


• Pressure Bands


Pressure band is the difference between the cut-in pressure (the point where the compressor will start producing air) and the cut-out pressure (the point where the compressor will stop generating air). In a few sentences, it means how much pressure is allowed to fluctuate.


Rotary compressors have smaller pressure bands, hence are more suited for applications with tight pressure tolerance. On the other hand, reciprocating compressors are ideal for bigger pressure bands because they generate air intermittently and are rated below 100% duty cycle.


• Maximum Delivery Pressure


When selecting between reciprocating vs rotary compressor, it is crucial to choose an option with a maximum delivery pressure (PSI i.e., pounds per square) that meets your demands.


Single-stage reciprocating compressors can deliver air up to 120 PSI and double-stage reciprocating compressors can compress air up to 175 PSI. Higher pressures can be reached with 3-4 stage of compression. Generally, piston compressors can deliver very high pressure of air, as far as reaching 6,000 PSI. They are great for special applications.


Single-stage rotary compressors, on the other hand, can deliver pressure up to 150 PSI and double-stage rotary compressors can deliver pressure above 175 PSI. Rotary compressors are not ideal for high-pressure applications. The major advantage of rotary compressors is that they can deliver more CFM (cubic feet per minute) with greater efficiency.


• Operating Environment


The environment where the compressor is used can impact performance and maintenance. Substances in the air, such as dust, particulate from combustion engines, or pollen can combine with the absorbed air, contaminate lubricants, and clog inline filters.


In this scenario, reciprocating compressors are best because they are less sensitive to substances in the air. They can be used outside or in a very dirty environment, even a mechanic shop.


Rotary compressors, on the other hand, are best used in neat environments. If the absorbed air is not clean, the filtration features in the compressor can help remove the contaminants so they won’t join the discharged air.


• Continuous Operation


One of the notable differences between reciprocating compressor and rotary compressor is how they compress air.


A reciprocating compressor system requires the upward and downward movement of a piston fixed snugly in a cylinder. Air is only compressed when the piston moves upwards, which is why it is best used for intermittent applications.


On the other hand, a rotary compressor system has two helical screws and has the capacity to produce compressed air throughout their turning cycle. This is why they are better used for continuous air applications.

• Initial vs Lifetime Cost


Cost is always a crucial factor when choosing between two equipment, especially reciprocating vs rotary compressor. Considering the total cost, including the initial and lifetime expenses, is essential.


Reciprocating compressors are less expensive, making them a more affordable capital investment for smaller shops or startups that cannot keep up with the requirements of rotary compressors. However, the lifetime cost in terms of maintenance and replacement terms increases the total costs.


Rotary compressors are more expensive, requiring a bigger upfront cost. But the lifetime costs are reduced, especially at higher horsepower and CFM ratings. They consume lesser energy and require lower maintenance.


• Lifespan


Another important factor you should refer to when evaluating reciprocating compressor vs rotary compressor is how long they will last. Reliable manufacturers of heat pumps and air conditioners would find the best and most suitable compressor to ensure quality heating and cooling equipment production since the compressor is an indispensable component of HVAC.


Generally, reciprocating compressors have a lifespan of 50,000 hours or less depending on quality usage and maintenance.


Rotary compressors, on the other hand, last longer. They can last for up to 100,000 hours or up to 20 years with quality usage and adequate maintenance. However, oil-free rotary compressors don’t last that long; they usually run efficiently for 10-15 years (70,000 hours).


• Maintenance Requirements


Regarding maintenance, you need to inquire about the maintenance requirements for both compressors, as well as how much you can do for yourself.


As mentioned severally in this article, a piston compressor has more moving components, hence requiring more maintenance because of wear and tear from friction. Some of these maintenance solutions include a change of oil and filter, as well as regular replacement of valves and piston rings. Maintenance of reciprocating compressors can be expensive, but thanks to their simple design, you can do some of the required work at home.


Rotary compressors don’t wear out as much as reciprocating compressors because they have fewer moving parts. Thus, the maintenance is not as rigid as piston compressors. Major maintenance solutions include changing of the oil, the oil filter, and the air/oil separator. However, they have a more complex design structure, requiring the expertise of a professional for proper maintenance.


• Size and Space Requirements for Installation


Both reciprocating and rotary compressors need ample free space to curb overheating. Hence, it is essential to put this into consideration for smooth installation. In terms of the size:


Reciprocating compressors are built with air tanks, so it is important to compare the total size of the unit to the available space.


Rotary compressors, on the other hand, are smaller. This is because they don’t necessarily require air tanks since they produce air continuously. Also, it has fewer moving parts, resulting in a compact design structure.


• Average CFM per Horsepower


Major differences can also be noticed with the horsepowers of both compressors. The tables below shows their varying HP and CFM.


Reciprocating Compressor

Horsepower

CFM @175 PSI

5HP

18

7.5HP

24

10HP

35

15HP

50

20HP

80

25HP

95


Rotary Compressor

Horsepower

CFM @150 PSI

CFM @125 PSI

5HP

16

18

7.5HP

26

38

10HP

38

40

15HP

54

60

20HP

78

85

25HP

102

108

30HP

125

130

40HP

155

160

50HP

185

200

60HP

210

235


• Application


Another clear distinction between reciprocating vs rotary compressor is in their applications.


Reciprocating compressors are best for small-scale functions that require lower CFM (below 20 horsepower) and intermittent air. Some applications are riveting performed by service and tire trucks, small manufacturing operations, and powering air tools.


Meanwhile, rotary compressors are best for large-scale applications that require higher CFM (20 horsepower or higher) and continuous air. Some applications are heat pump systems or air conditioners, food and beverage processing, sewer rehab, and power pneumatic tools.


Rotary vs Reciprocating Compressor in AC: Which One is Better?

SPRSUN heat pump components with rotary compressor


The best option between reciprocating compressor vs rotary compressor solely depends on your application. Reciprocating compressors are better suited for applications that require intermittent airflow. However, the benefits of rotary compressors are better enjoyed when used for large-scale industrial applications that require continuous airflow.


Above are the detailed differences between rotary compressors and reciprocating compressors. SPRSUN is a China heat pump manufacturer with operations around the world. We use the best Panasonic rotary compressor to equip our heat pump, so you don't need to worry about the quality of the SPRSUN HVAC system.


And if you need guidance about any heating and air conditioning system compressor? Contact us; our experts are readily available to answer your questions.


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