Plot the four state points of a vapor-compression refrigeration cycle on a p-h diagram and compute COP in real time. Supports R134a, R410A, and R290 refrigerants.
Refrigerant & Conditions
Refrigerant
Evaporating temp T_e
°C
Condensing temp T_c
°C
Superheat ΔT_sh
K
Subcooling ΔT_sc
K
Compressor efficiency η
Results
Cooling COP
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Heating COP
—
Carnot COP
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W_comp
—
Q_e (kJ/kg)
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Q_c (kJ/kg)
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p–h Diagram (Mollier)
COP vs Evaporating Temperature (by condensing temperature)
What exactly is a "p-h diagram" and why is it the main plot in this simulator?
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Basically, a p-h diagram is the "map" for refrigeration engineers. Pressure (p) is on the vertical axis, often on a log scale, and specific enthalpy (h) is on the horizontal axis. The beauty is that the area inside the cycle loop on this map represents the energy transfer. In this simulator, you'll see the four key states of the cycle plotted: evaporation, compression, condensation, and expansion. Try changing the refrigerant type above—you'll see the entire curve shape shift because each fluid has unique properties.
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Wait, really? The simulator lets me change the evaporating and condensing temperatures. What happens physically when I slide those controls?
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Great question. In practice, the evaporating temperature (T_e) is how cold the refrigerant gets inside your indoor coil to absorb heat. The condensing temperature (T_c) is how hot it gets in the outdoor coil to reject that heat. When you increase the gap between T_c and T_e using the sliders, you're asking the compressor to "lift" the refrigerant pressure higher. This requires more work, which you'll see directly as a drop in the calculated COP value on the plot.
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So what's the point of the "Superheat" and "Subcooling" parameters? They sound like safety margins.
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Exactly! They're practical tweaks. Superheat (ΔT_sh) ensures no liquid enters the compressor, which would damage it. Subcooling (ΔT_sc) ensures no vapor enters the expansion valve, improving efficiency. In the simulator, adjust the superheat slider. You'll see point 1 (compressor inlet) move right along the constant pressure line, changing the enthalpy h1. This directly affects the COP calculation because it changes how much work the compressor needs to do.
Physical Model & Key Equations
The core performance metric for a refrigerator or air conditioner is the Coefficient of Performance for cooling. It's the ratio of the useful cooling effect (heat absorbed in the evaporator) to the work input required by the compressor.
h1: Specific enthalpy at evaporator outlet / compressor inlet (superheated vapor). h2: Specific enthalpy at compressor outlet (high-pressure, high-temperature vapor). h4: Specific enthalpy at expansion valve inlet / condenser outlet (subcooled liquid).
The difference (h1 - h4) is the cooling capacity per kg of refrigerant. (h2 - h1) is the compressor work per kg.
The Carnot COP represents the maximum theoretically possible efficiency for a heat pump operating between two temperature reservoirs. It sets an absolute upper limit that real cycles, with irreversibilities, can never reach.
T_e, T_c: Evaporating and condensing temperatures in Kelvin. The formula shows efficiency improves as the temperature difference (T_c - T_e) shrinks. In the simulator, the "Second Law Efficiency" compares your real cycle's COP to this ideal Carnot limit.
Frequently Asked Questions
Since each refrigerant has different thermophysical properties (such as vapor pressure and specific enthalpy), the cycle shape on the p-h diagram changes even under the same temperature conditions. The simulator automatically references the property database of the selected refrigerant to redraw the diagram. If the display does not update after switching, please try refreshing your browser.
First, check whether the input values for evaporation temperature and condensation temperature are within a realistic range (e.g., evaporation temperature lower than the ambient temperature, condensation temperature higher than the ambient temperature). Also, verify that the compressor efficiency, superheat, and subcooling settings are not set to extreme values. You can assess validity by comparing with the ideal Carnot COP.
This tool is intended for educational and exploratory purposes and does not support actual equipment design. It does not account for pressure loss, detailed heat exchanger design, or actual compressor characteristics. However, it is effective for initial refrigerant selection studies, understanding cycle behavior, and grasping COP trends. For detailed design, please use dedicated design software.
R290 is a flammable refrigerant (A3 classification), so while the simulator can perform property calculations, actual equipment must comply with safety standards (such as IEC 60335-2-40) regarding leak prevention, ventilation, and elimination of ignition sources. Also, pay attention to refrigerant charge limits and pressure vessel design. This tool cannot verify safety design.
Real-World Applications
Residential HVAC & Heat Pumps: This is the exact cycle in your home's air conditioner and heat pump. Engineers use tools like this simulator to select the right refrigerant (like R410A or the newer, lower-GWP R290) and optimize the T_e and T_c for seasonal efficiency (SEER rating). The compressor efficiency slider directly models real-world mechanical losses.
Commercial Refrigeration: Supermarket freezer cases and walk-in coolers run on this cycle. Precise control of superheat is critical here to prevent compressor failure from liquid floodback, which you can experiment with in the simulator by setting superheat to zero.
Electric Vehicle Thermal Management: Modern EVs use a vapor-compression cycle not just for cabin cooling, but to precisely manage the temperature of the high-voltage battery pack. The cycle must be highly efficient to avoid draining driving range, making COP a key design target.
Industrial Process Cooling: In pharmaceutical manufacturing or chemical processing, precise temperatures are required. Engineers model cycles with significant subcooling (like you can set with the ΔT_sc control) to increase the cooling capacity (h1-h4) without extra compressor work, boosting COP for cost savings.
Common Misconceptions and Points to Note
When starting with simulations, there are several pitfalls that beginners often encounter. First is the misconception that "lowering the evaporation temperature will always make things colder." While it's true that lowering the evaporation temperature increases cooling capacity, it also causes a sharp rise in the compressor's workload. For example, reducing the evaporation temperature from 5°C to 0°C can decrease the COP by about 15%. In real equipment, this can lead to a significant increase in power consumption or compressor overload failure, so you must be cautious.
Next is the assumption that "newer refrigerants are always more efficient." While R410A is more efficient than R134a, its operating pressure is about 1.6 times higher, requiring completely different strength designs for piping and equipment. Even if you set the same temperature conditions in the simulator, the overall system cost and safety can vary greatly. Also, note that points on the p-h diagram represent 'states,' not 'locations.' The evaporator outlet (point 1) is not always on the saturated vapor line corresponding to the evaporation temperature; it shifts to the right by the amount of superheat. If this superheat is too small, it can cause a serious failure called "liquid slugging," where liquid refrigerant returns to the compressor.