If the standard equipment breaks down or the desire to upgrade the system to create a storage room, the home master inevitably faces the question of the technical characteristics of the motor. Many people mistakenly believe that the key parameter is only the power consumption in Watts, however, for the correct selection of equipment, volumetric productivity is critically important.
It is the value of the gas supply, expressed in liters per minute or cubic centimeters per minute, that determines whether the unit can effectively remove heat from a given volume. Incorrect calculation This parameter will lead to the fact that the refrigerator will work without interruption. having reached the set temperature, which will quickly disable the equipment.
In this article we will analyze in detail how to convert cubic centimeters into liters, what the real suction power depends on and why you cannot blindly rely on the markings without double-checking the data.
The physical meaning of performance compressor
Performance in the context of refrigeration technology refers to the volume of refrigerant that is capable of pumping the piston unit per unit of time. The standard unit of measurement for household models is cubic centimeters per minute (cm³/min) or cubic centimeters per hour (cm³/hour). To get a clear value in liters per minute, you need to divide the volume in “cubes” by 1000, if we are talking about a minute cycle.
It is worth understanding that theoretical and real performance are different things. The theoretical is determined by the geometry of the cylinder and the piston stroke, while the real is always lower due to the presence of dead volume, valve resistance and gas heating. Feed coefficient usually ranges from 0.6 to 0.75 for household models.
⚠️ Attention: When calculating the system, do not confuse the volume of suction gas with the discharge volume. In the refrigeration cycle, the gas density changes, but to select a compressor, they are always guided by the suction volume under boiling conditions.
The higher this indicator, the faster the compressor can “pump out” heat from the evaporator. However, it is impossible to increase power indefinitely: a too efficient motor on a small evaporator will lead to a drop in suction pressure below the permissible level and freezing of the pipeline.
Why is gas density important?
The density of the refrigerant (freon) changes depending on the temperature. At a lower boiling point, the vapor density drops and the mass output of the compressor decreases, even if the volumetric efficiency remains the same. This means that the same motor will cool worse at -24°C than at -10°C.
Typical values for household models
In the household sector, sealed piston units are mainly used. Their performance varies depending on the class of the refrigerator and the number of chambers. For old-style single-chamber models, such as ZIL or Biryusa, typical indicators are around 30-50 cm³/min, which is only 0.03–0.05 liters per minute.
Modern two-chamber systems require more intensive refrigerant circulation. Here the values already reach 80–120 cm³/min (0.08–0.12 l/min). It is important to note that inverter compressors can have a wide range of performance, since they change the shaft rotation speed depending on the need for cold.
- 🔹 Low-power models (bar refrigerators): 10–25 cm³/min.
- 🔹 Standard two-chamber units: 60–110 cm³/min.
- 🔹 Powerful No Frost systems with large volume: 120–180 cm³/min.
- 🔹 Industrial and dual-motor systems: over 200 cm³/min.
To convert a compressor for an airbrush or inflating tires, these figures are recalculated taking into account the outlet pressure, since when air is compressed to 8 atmospheres, the output flow rate will drop significantly.
Dependence of power on the type of refrigerant
The performance of the compressor directly depends on the type of refrigerant used. Different gases have different densities and heat capacities. A compressor designed for R134awill have different characteristics when working with R600a (isobutane).
Isobutane, which is now used in most modern refrigerators, requires a lower volumetric capacity to remove the same amount of heat compared to R134a freon. Therefore, motors for R600a often look smaller and have a smaller displacement (about 5-8 cm³), but still cope with the task effectively.
| Refrigerant type | Displacement volume (typical) | Performance features |
|---|---|---|
| R12 (Obsolete) | 12–16 cm³ | High volumetric capacity, low pressure |
| R134a | 10–14 cm³ | Average performance, requires system cleanliness |
| R600a (Isobutane) | 5–9 cm³ | Low volumetric productivity, high efficiency |
An attempt to charge a system designed for one gas with another type of refrigerant without replacing the compressor will lead to a violation of the temperature regime. Thermophysical properties substances are radically different, and simply replacing the gas will not produce results.
Calculation of productivity for homemade installations
If you plan to use an old compressor to create a vacuum installation, an airbrush or an air supply system for an aquarium, the calculation of “liters per minute” will be done differently. Here we are interested in output performance at a certain pressure.
For atmospheric pressure (purge), the compressor will produce its maximum volume. The formula is simple: multiply the volume of the cylinder by the number of revolutions per minute. However, as soon as you start pumping up the receiver, performance will begin to drop. Performance curve shows that as pressure increases, the volume of supplied air decreases.
For example, a compressor from a refrigerator with a capacity of 1/8 hp. (about 12-14 cm³) at idle it can produce about 50 liters of air per minute. But at a pressure of 2 atmospheres, this figure will drop to approximately 20-25 liters, and at 6 atmospheres - to 7-10 liters.
⚠️ Attention: When using the compressor for other purposes (to compress air instead of freon), be sure to monitor the temperature of the head. The air heats up more, and the oil can begin to coke at temperatures above 100-120°C.
For precise selection for a specific task (for example, sandblasting or painting), one household compressor is almost always not enough due to the low performance in liters. A cascade of several motors or the use of specialized equipment is required.
The influence of boiling temperature on output
A critical parameter that is often ignored is the operating temperature. Compressor performance is not constant. It depends on the boiling point (evaporation) and condensation temperature.
There is a classification of compressors by boiling point: LBP (Low Back Pressure) for low temperatures (freezers), HBP (High Back Pressure) for high temperatures (air conditioners, wine coolers) and MBP (Medium Back Pressure) for medium temperatures (regular refrigerators). If you place an LBP motor in a system with a high boiling point, its performance will increase sharply, which will lead to overload of the electric motor and burning of the windings.
- 🔹 LBP: Boiling from -30°C to -10°C. Low productivity, high compression.
- 🔹 MBP: Boiling from -15°C to +5°C. Average indicators.
- 🔹 HBP: Boiling from +5°C to +15°C. High performance, low compression.
Therefore, when answering the question “what productivity”, you always need to clarify: under what conditions was it measured? The technical data sheet always indicates the measurement points, for example, +32°C condensation and -23.3°C evaporation.
☑️ Checking the compressor compliance
Correspondence table of models and volumes
To simplify the search, we provide an indicative table of popular compressor models and their volumetric capacity. The data is average, since modifications may differ.
| Compressor model | Power (hp) | Volume (cm³/hour) | Performance (l/min) |
|---|---|---|---|
| Secop (Danfoss) NL10FT | 1/4 | 460 | ~0.13 |
| Embraco T60H | 1/5 | 350 | ~0.10 |
| Atlant CK-14 | 1/6 | 280 | ~0.08 |
| LG MA95CY | 1/5 | 330 | ~0.09 |
As can be seen from the table, even powerful household models rarely exceed 0.2 liters per minute in terms of net suction volume. This is enough for the circulation of freon in a closed circuit, but not enough for active pneumatics.
Common mistakes when selecting and replacement
The most common mistake is installing a more powerful compressor “by eye”, based on the principle “the more the better.” This rule does not work in refrigeration technology. Excessive capacity will lead to the fact that the compressor will work in short cycles or, conversely, will not be able to build up cut-off pressure while working constantly.
Also often forgotten about oil mode. Compressors are designed for a specific oil (mineral or polyester POE). Mixing oils or working without properly returning oil to the crankcase quickly kills the friction pair, even if the volumetric performance is ideally selected.
Another nuance is the starting torque. A more efficient motor requires a more powerful starting relay and capacitor. Standard refrigerator wiring may not withstand increased starting currents, which will lead to melting of the contacts.
How can you accurately find out the performance without documentation?
If the nameplate is not readable, you can measure the cylinder diameter and piston stroke with a caliper. Volume is calculated using the formula for the area of a circle multiplied by the stroke of the piston. However, this method gives only a theoretical volume, without taking into account the efficiency of the valve group.
Is it possible to increase the compressor performance?
At home - no. You can only increase the pressure (risking breakdown), but not the volume of pumped gas. Increasing the engine speed (for inverter models) is possible, but requires complex electronics and is fraught with destruction of mechanical components.
Why does the compressor hum but not pump?
This is a sign of a broken valve group (plates). The piston moves, the engine hums, but the tightness of the combustion chamber is broken, and the gas is bypassed back. Productivity in this case drops to almost zero.
Does the length of the tubes affect productivity?
Yes, excessively long or narrow connecting tubes create hydraulic resistance. This reduces the actual performance of the system, causing the compressor to work overload. Use tubes of the recommended diameter.
What performance is needed for airbrush?
Airbrush requires a stable pressure of 1.5-2 atm and a flow of about 15-25 liters per minute. An ordinary refrigerator compressor (1/8 - 1/6 hp) with a receiver copes with this task quite well, producing the necessary parameters in intermittent mode.