Trane TRG-TRC010-EN Compressor Unloading

TRG-TRC010-EN 25

period three

Compressor Capacity Control

notes

Consider a given-diameter compressor impeller that rotates at a constant

speed. As the load on the chiller decreases, the inlet vanes partially close and

the flow rate of refrigerant through the compressor drops. Radial velocity (Vr),

which is proportional to refrigerant flow, decreases as well.

Even though the speed of rotation and diameter of the impeller are constant,

the tangential velocity (Vt) (which is proportional to the product of impeller

rotational speed and impeller diameter) drops because of the pre-swirling of

the refrigerant caused by the inlet vanes.

The result is a shorter resultant velocity vector (R), which means that less static

pressure is generated.

Compressor Unloading

full load part load

Figure36

trgtrc010_book.book Page 25 Wednesday, September 1, 1999 10:39 AM

Contents

Main BUSINESS REPLY MAIL Page Page Preface A Trane Air Conditioning Clinic Contents Page Introduction Chilled Water System helical-rotary absorption centrifugal Introduction Centrifugal Water Chillers period one period one Centrifugal Water Chiller Compressor Compressor Impeller Centrifugal Compressor Energy Conversion Multistage Compressor notes Condenser Condenser Expansion Device Orifice Plates Economizer Economizer notes Evaporator Evaporator Motor Motor gear-drive direct-drive Hermetic Motor Cooling notes Controls and Starter Controls and Starter Starters unit-mounted remote-mounted p h period two p-h) Pressure-Enthalpy ( liquid vapor Chart Page Page Refrigerants Refrigerant Operating Pressures Page Multistage Compressor Impeller 24 refrigerant. Recall that kinetic energy is converted to static energy, or static pressure. Impeller Dynamics V rotational speed diameter V Compressor Unloading full load part load Surge Compressor Map notes Operating Point 2-Stage Compressor Adjustable-Frequency Drives period four period four Maintenance Considerations ASHRAE Guideline 3 Page Mechanical Components Heat Transfer Surfaces Fluid Analysis notes Oil Analysis period five period five Condensing Temperature Control Condensing Temperature Control Cooling Tower Bypass Constant or Variable Evaporator Water Flow Constant or Variable Flow Limitations Short Evaporator-Water Loops Short Evaporator-Water Loops Heat Recovery Heat Recovery Heat-Recovery Chiller Options Free Cooling Free Cooling Refrigerant Migration Equipment Certification Standards ARI Standard 550/590 ARI Standard 550/590 notes period six ReviewPeriod 1 period six ReviewPeriod 2 impellers inlet vanes ReviewPeriod 3 impellers ReviewPeriod 4 ReviewPeriod 5 Engineers Newsletter Engineered Systems Clinics Quiz Questions for Period 1 1) 2) 3) Quiz Questions for Period 4 Questions for Period 5 Answers Standard for Water Chilling Packages Using the Vapor-Compression Cycle, Page notes 85577_Cover.fm Page 2 Wednesday, September 1, 1999 10:08 AM