Capillary Tube for 1/5 HP Compressor

The capillary tube for a 1/5 HP compressor depends on the refrigerant gas used and the evaporator temperature in the specific application.

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Attention:

At the end of this article, you will find access to the Capillary Tube Course in Refrigeration and Air Conditioning.

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What Capillary Tube Does a 1/5 HP Compressor Use?

Before selecting a capillary tube for a 1/5 HP compressor, it is crucial to understand the following:

1. Total Restriction:
   • The restriction of the capillary tube depends on both its diameter and its length.
   • Changes in diameter have a greater impact on flow than equivalent changes in length.
2. Capillary Tube Length:
   • Longer tubes result in slower flow rates.
   • Excessively long tubes are inefficient and often impractical.
   • Very short lengths cause significant increases in flow, making the tube behave more like an orifice than a capillary tube.
3. General Recommendations:
   • Maintain the tube length between 5′ (1.5 m) and 16′ (4.8 m).
   • This range helps avoid common issues, though exceptions may exist based on specific applications.

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Capillaries in Refrigeration

Typical Temperatures for Selecting a 1/5 HP Capillary Tube

Application	Evaporator Temperature	Condenser Temperature
LBP (Low Back Pressure)	-23.3 °C (-10 °F)	54.4 °C (130 °F)
MBP (Medium Back Pressure)	-6.7 °C (20 °F)	54.4 °C (130 °F)
HBP (High Back Pressure)	7.2 °C (45 °F)	54.4 °C (130 °F)

Source: Tecumseh

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Cooling Capacity of a 1/5 HP Compressor

The cooling capacity of a 1/5 HP compressor varies depending on the refrigerant, operating conditions, and the temperature of the evaporator coil.

Average Capacity with R134a (in BTU/h):

Evaporator Coil Temperature (-°C)	Cooling Capacity (BTU/h)
-35 °C	342.58
-30 °C	488.34
-25 °C	646.75
-20 °C	831.55
-15 °C	1056.50
-10 °C	1335.34

Example:
A 1/5 HP compressor with R134a operating at -10 °C achieves a cooling capacity of approximately 1335.34 BTU/h.

Factors Affecting Cooling Capacity:

• Type and efficiency of the compressor.
• Compressor speed (Hz).
• Ambient temperature.
• Condenser coil cooling method (natural or forced convection).
• Subcooling and superheating of the refrigerant.

Table Reference Conditions:

• Superheating: 5 °C.
• Subcooling: 5 °C.
• Ambient temperature: 35 °C.

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Specifications for Common Refrigerants

R134a

HP	Application	Diameter (in)	Length (m)
1/5	MBP	0.036	2.7

R410A

HP	Temperature	Diameter/Length
1/5	-10 °F	0.031 in / 90″
1/5	25 °F	0.031 in / 60″
1/5	45 °F	0.031 in / 41″

R404A

Temperature	Capacity (BTU/h)	Diameter/Length
-10 °F	750	0.028 in / 5 ft
25 °F	1000	0.031 in / 5 ft

R407C

Application	Diameter (in)	Length (in)
Low	0.031	70
Medium	0.031	46
High	0.031	31

Source: Tecumseh

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