410a is a type of refrigerant that is widely used in air conditioning and heat pump systems. It is a blend of two hydrofluorocarbons (HFCs), namely difluoromethane (CH2F2) and pentafluoroethane (CHF2CF3). It has a zero ozone depletion potential (ODP) and a high global warming potential (GWP) of 2088.
One of the most important aspects of working with 410a refrigerant is understanding its pressure-temperature relationship. This means knowing how the pressure of 410a changes with different temperatures, and vice versa. This information is essential for proper charging, troubleshooting, and performance evaluation of 410a systems.
How to Use a 410a PT Chart
A 410a PT chart is a tool that shows the saturation pressure of 410a refrigerant at various temperatures. Saturation pressure is the pressure at which the refrigerant changes phase from liquid to vapor, or from vapor to liquid, depending on the temperature. A 410a PT chart can be used to answer questions such as:
- What is the pressure of 410a at a given temperature?
- What is the temperature of 410a at a given pressure?
- What are the normal operating pressures for 410a systems?
- How to calculate the superheat and subcooling of 410a systems?
To use a 410a PT chart, you need to measure the temperature and pressure of the refrigerant at different points in the system, such as the evaporator, condenser, compressor, and metering device. Then, you can compare these values with the corresponding values on the 410a PT chart to determine the state and condition of the refrigerant.
Here is an example of a 410a PT chart for degrees Fahrenheit (°F):
| Temperature (°F) | Pressure (psig) |
|---|---|
| -60 | 0.9 |
| -55 | 1.8 |
| -50 | 4.3 |
| -45 | 7.0 |
| -40 | 10.1 |
| -35 | 13.5 |
| -30 | 17.2 |
| -25 | 21.4 |
| -20 | 25.9 |
| -18 | 27.8 |
| -16 | 29.7 |
| -14 | 31.8 |
| -12 | 33.9 |
| -10 | 36.1 |
| -8 | 38.4 |
| -6 | 40.7 |
| -4 | 43.1 |
| -2 | 45.6 |
| 0 | 48.2 |
| 1 | 49.5 |
| 2 | 50.9 |
| 3 | 52.2 |
| 4 | 53.6 |
| 5 | 55.0 |
| 6 | 56.4 |
| 7 | 57.9 |
| 8 | 59.3 |
| 9 | 60.8 |
| 10 | 62.3 |
| 11 | 63.9 |
| 12 | 65.4 |
| 13 | 67.0 |
| 14 | 68.6 |
| 15 | 70.2 |
| 16 | 71.9 |
| 17 | 73.5 |
| 18 | 75.2 |
| 19 | 77.0 |
| 20 | 78.7 |
| 21 | 80.5 |
| 22 | 82.3 |
| 23 | 84.1 |
| 24 | 85.9 |
| 25 | 87.8 |
| 26 | 89.7 |
| 27 | 91.6 |
| 28 | 93.5 |
| 29 | 95.5 |
| 30 | 97.5 |
| 31 | 99.5 |
| 32 | 101.6 |
| 33 | 103.6 |
| 34 | 105.7 |
| 35 | 107.9 |
| 36 | 110.0 |
| 37 | 112.2 |
| 38 | 114.4 |
| 39 | 116.7 |
| 40 | 118.9 |
| 41 | 121.2 |
| 42 | 123.6 |
| 43 | 125.9 |
| 44 | 128.3 |
| 45 | 130.7 |
| 46 | 133.2 |
| 47 | 135.6 |
| 48 | 138.2 |
| 49 | 140.7 |
| 50 | 143.3 |
| 55 | 156.6 |
| 60 | 170.7 |
| 65 | 185.7 |
| 70 | 201.5 |
| 75 | 218.2 |
| 80 | 235.9 |
| 90 | 274.3 |
| 95 | 295.0 |
| 100 | 316.9 |
| 105 | 339.9 |
| 110 | 364.1 |
| 115 | 389.6 |
| 120 | 416.4 |
| 125 | 444.5 |
| 130 | 474.0 |
| 135 | 505.0 |
| 140 | 537.6 |
| 145 | 571.7 |
| 150 | 607.6 |
| 155 | 645.2 |
You can see that this 410a PT chart includes high and low side pressures at temperatures ranging from -60 °F to 155 °F. Higher temperature equates to higher pressure. Here are some examples of how you can use this chart:
- Example 1: What is the pressure of 410a at 72 degrees Fahrenheit? We can see that at 72°F, the 410a pressure is 208.4 psig.
- Example 2: What are 410a pressures on an 85 degree day? The operating pressure of 410a on an 85 degree day is 254.6 psig.
- Example 3: What are 410a pressures on a 70 degree day? The operating pressure of 410a on a 70 degree day is 201.5 psig.
- Example 4: What are 410a pressures on a 65 degree day? The operating pressure of 410a on a 65 degree day is 185.7 psig.
How to Calculate Superheat and Subcooling of 410a Systems
Superheat and subcooling are two important parameters that indicate the efficiency and performance of 410a systems. Superheat is the difference between the actual temperature of the refrigerant vapor and the saturation temperature at a given pressure. Subcooling is the difference between the actual temperature of the refrigerant liquid and the saturation temperature at a given pressure.
To calculate the superheat and subcooling of 410a systems, you need to measure the temperature and pressure of the refrigerant at the evaporator outlet and the condenser outlet, respectively. Then, you can use the 410a PT chart to find the corresponding saturation temperatures and subtract them from the actual temperatures.
Here is an example of how to calculate the superheat and subcooling of a 410a system:
- Measure the temperature and pressure of the refrigerant at the evaporator outlet. Let’s say they are 50 °F and 120 psig, respectively.
- Use the 410a PT chart to find the saturation temperature at 120 psig. It is 45 °F.
- Subtract the saturation temperature from the actual temperature to get the superheat. It is 50 – 45 = 5 °F.
- Measure the temperature and pressure of the refrigerant at the condenser outlet. Let’s say they are 100 °F and 350 psig, respectively.
- Use the 410a PT chart to find the saturation temperature at 350 psig. It is 118 °F.
- Subtract the actual temperature from the saturation temperature to get the subcooling. It is 118 – 100 = 18 °F.
The superheat and subcooling values can be used to evaluate the performance of the system and identify any problems or issues. For example, a low superheat indicates that the evaporator is overfed with refrigerant, while a high superheat indicates that the evaporator is underfed with refrigerant or has low airflow. A low subcooling indicates that the condenser is undercharged with refrigerant, while a high subcooling indicates that the condenser is overcharged with refrigerant or has high airflow.
The optimal superheat and subcooling values for 410a systems depend on various factors, such as the type of system, the manufacturer’s specifications, the ambient conditions, and the load conditions. However, a general rule of thumb is that the superheat should be between 8 and 12 °F, and the subcooling should be between 10 and 15 °F.
