Climate Control

HVACR Tech Tip: Everything You Want to Know About Superheat

HVACR Tech Tip: Everything You Want to Know About Superheat - Parker SporlanSuperheat is the temperature of refrigerant gas above its saturated vapor (dewpoint) temperature. Superheat as it relates to thermostatic expansion valves, can be broken down into three Superheat categories:

  1. Static Superheat – The amount of superheat necessary to overcome the superheat spring force biased in a closed position. Any additional superheat (force) would open the valve.

  2. Opening Superheat – The amount of superheat necessary to open the valve to its rated capacity.

  3. Operating Superheat – The superheat at which the valve operates at normal running conditions or normal capacity. The operating superheat is the sum of the static and opening superheat. The figure below illustrates the three superheat categories. The reserve capacity, as shown in the graph, is important since it provides the ability to compensate for occasional substantial increases in evaporator load, intermittent flash gas, reduction in high side pressure due to low ambient conditions, shortage of refrigerant, etc.

 

Parker Application Guide DownloadFor more information, download TEV &AEV Theory and Application - Catalog E-1a.

 


 

Superhead Capacities

 

How to determine superheat

  1. Determine the suction pressure at evaporator outlet with gauge. On close coupled installations, suction pressure may be read at the compressor suction connection.

  2. Use the Pressure-Temperature Chart to determine saturation temperature at observed suction pressure. For example, with a R-22 system: 54.9 psig = 30°F.

  3.  Measure the temperature of suction gas at the expansion valve’s remote bulb location. For example: 40°F.

  4. Subtract saturation temperature of 30°F (step 2) from suction gas temperature of 40°F (step 3). The difference, 10°F, is the superheat of the suction gas.

 

Determining Superheat

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Valve setting

Parker “sets” the thermostatic expansion valve superheat at the static condition described above. Turning the adjusting screw clockwise will increase the static superheat. Conversely, turning the adjusting screw counterclockwise will decrease the superheat. Parker valves can also be adjusted at the operating point, indicated above. When a system is operating, any adjustments made will change the operating superheat. The static superheat range of adjustment is 3°F to 18°F. One full turn clockwise will typically increase superheat 2°F to 4°F. Note: Refer to the valve’s installation bulletin for specific directions on superheat adjustment.

For more information, download TEV &AEV Theory and Application - Catalog E-1a.

For more details on Thermostatic Expansion Valves - Theory of Operation, Application, and Selection - Bulletin 10-9

 

Use of Suction line filter driers for clean-up after burnout of HVAC systems - Glen Steinkoenig Product Manager Contamination Control Products, Parker Hannifin Sporlan Division Article contributed by Glen Steinkoenig, product manager, Thermostatic Expansion Valves, Sporlan Division of Parker Hannifin.

 

 

 

 

Related, helpful climate control content for you:

HVACR Tech Tip: 12 Solutions for Fixing Common TEV Problems

HVACR Tech Tip: Understanding and Preventing Superheat Hunting in TEVs

HVACR Tech Tip: Principles of Thermostatic Expansion Valves

HVACR Tech Tip: Where Should the TEV External Equalizer Be Installed?

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