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matching a compressor, condensor en evaporator capacities.

mechanicaldup (Mechanical) (OP)
7 Jul 05 11:57
what guide should be followed when selecting a certain compressor condensor unit for a certain evaporator?

suppliers gives a table with different evoparor temperaturs ( or suction temp on the compressor). How do you select the evaporator temperature?

what other aspects should be taken into acount when matching the compressor and evaporator?

where can I find guidelins in this regard?
AEBuck (Mechanical)
7 Jul 05 22:38
Guidelines ... Trane used to publish a book called "Reciprocating Refrigeration", which covers the basics of most things you need to know.  I've never checked to see if it's been updated for newer refrigerants.  Carrier has something similar, but not nearly as detailed.

Consider the liquid refrigerant temperature entering the evaporator coil to be similar to an entering chilled water temperature.  It doesn't need to be any colder than what's necessary to achieve the desired leaving air condition.  In general, it is up to 5F less than a chilled water application - which explains why refigerant coils usually have several less rows than water-based counterparts.  Higher entering refrigerant temperatures result in less energy consumption by the compressor and condenser fans.  Select the evaporator coil with 10-15F superheat to avoid sending liquid back to the compressor.

The evaporator and compressor/condenser must be "matched" at your load condition.  Manual selection is painful.  Graph both evaporator capacity and compressor/condenser capacity versus a common temperature somewhere in the circuit - usually entering or leaving the evaporator.  Operation will be at the intersection of this "X" - matched as they say.  Of course this intersection must occur at the capacity you need.

Use a Colmac or Heatcraft coil selection program to try different evaporators and get a feel for the variables.  Then, with results from the coil program plus allowances for other pressure/temperature changes in the system (read suggested manuals or equivalent), select a compressor/condensing unit and graph as suggested.  Let a trusting vendor confirm your results.

Anyone with day-to-day experience, please feel free to elaborate.  Years may pass between times I need to do this, and I always have to brush up, but all material is at work and I'm not.
imok2 (Mechanical)
7 Jul 05 23:24
When selecting the correct condensing unit for a specific evaporator you need to determine at what temperature and humidity you want to keep the product (heat load). Once you have that information you can determine the  which of the following temperature ranges you need. To match a condenser with an evaporator all you have to do is go the the mfg web site and follow directions for example for a Tecumseh condensing unit go to: http://www.tcc-nacg.com/index.html

Evaporator Temperature Ranges
Application Approved Evaporator Temperatures

Air Conditioning +32ºF to +55ºF

Improved Performance Air Conditioning +32ºF to +57ºF

Heat Pump (Approved Models) -15ºF to +55º

High Evaporator Temperature +20ºF to +55ºF

Medium Evaporator Temperature -10ºF to +30ºF

Low Evaporator Temperature
(Normal Torque Motor) -30ºF to +10ºF

Low Evaporator Temperature
(High Torque Motor) -40ºF to +10ºF

Commercial Refrigeration  0ºF to +50ºF

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