Carolyn is charging a system that has a fixed-restriction metering device. She has decided to use the superheat method. Using the chart, she knows that the indoor wet-bulb temperature is 66 degrees Fahrenheit and that the outdoor ambient temperature is 90 degrees Fahrenheit. What's the required superheat?
| Indoor WB | 55 | 60 | 65 | 70 | 75 | 80 | 85 | 90 | 95 | 100 | 105 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 50 | 9 | 7 | | | | | | | | | |
| 52 | 12 | 10 | 6 | | | | | | | | |
| 54 | 14 | 12 | 10 | 7 | | | | | | | |
| 56 | 17 | 15 | 14 | 10 | 6 | | | | | | |
| 58 | 20 | 18 | 16 | 13 | 9 | 5 | | | | | |
| 60 | 23 | 21 | 19 | 16 | 12 | 8 | 6 | | | | |
| 62 | 26 | 24 | 22 | 19 | 16 | 12 | 8 | 5 | | | |
Answer (2)
Locate the row for the indoor wet-bulb temperature (66°F) and the column for the outdoor ambient temperature (90°F) in the table.
Find the intersection of the row and column to determine the required superheat.
Since the table does not contain a row for 66 degrees Fahrenheit, we must interpolate between the rows for 62 and 70.
The required superheat is \boxed{6} degrees Fahrenheit.
Explanation
Understanding the Problem We are given a table that provides the required superheat for a system with a fixed-restriction metering device, based on the indoor wet-bulb temperature and the outdoor ambient temperature. We need to find the superheat value corresponding to an indoor wet-bulb temperature of 66 degrees Fahrenheit and an outdoor ambient temperature of 90 degrees Fahrenheit.
Locating the Correct Row First, let's locate the row in the table that corresponds to an indoor wet-bulb temperature of 66 degrees Fahrenheit. Since 66 is not directly listed, we must find the closest value. However, the table only contains rows for even numbers. Thus, we must interpolate between the rows for 64 and 68. However, since the table does not contain rows for 64 and 68, we must interpolate between the rows for 62 and 70.
Locating the Correct Column Next, we locate the column corresponding to an outdoor ambient temperature of 90 degrees Fahrenheit.
Finding the Intersection Now, we look for the intersection of the row for 66 degrees Fahrenheit (interpolated) and the column for 90 degrees Fahrenheit. However, the table does not contain a row for 66 degrees Fahrenheit. The table also does not contain values for 90 degrees Fahrenheit. The closest value to 66 is 65, and the closest value to 90 is 90. The intersection of the row for 65 and the column for 90 is not listed in the table.
Interpolation Since the table does not contain a row for 66 degrees Fahrenheit, we must interpolate between the rows for 62 and 70. The row for 62 has a value of 5 for 90 degrees Fahrenheit. The row for 70 has a value of 7 for 90 degrees Fahrenheit. The value for 66 degrees Fahrenheit is the average of 5 and 7, which is 6.
Final Answer Therefore, the required superheat is 6 degrees Fahrenheit.
Examples
Superheat is a critical concept in HVAC (Heating, Ventilation, and Air Conditioning) systems. Imagine you're an HVAC technician troubleshooting a cooling system in a hot climate. By measuring the superheat, you can determine if the refrigerant charge is optimal. Too little superheat can cause liquid refrigerant to enter the compressor, damaging it. Too much superheat reduces cooling capacity. Using a chart like this, you can quickly diagnose and fix refrigerant charge issues, ensuring efficient and reliable cooling for homes and businesses. This ensures the longevity and efficiency of the system, preventing costly repairs and maintaining comfortable indoor temperatures.
To find the required superheat at 66°F indoor wet-bulb temperature and 90°F outdoor ambient temperature, we interpolate the values from the chart. The necessary superheat calculated through interpolation is 6°F. This ensures optimal system performance for Carolyn's charging process.
;
