Johnson Controls York YKEP, Operation And Maintenance

FORM 160.77-O1  

ISSUE DATE: 10/22/2020

JOHNSON CONTROLS

12

SECTION 1 - SYSTEM FUNDAMENTALS

YKEP SYSTEM FLOW EXPLANATION

The YORK YKEP chiller operates much the same as 

the YORK YK Single Stage chiller. The only exception 

is a small economizer loop to compress partially ex-

panded gas to extend capacity and improve efficiency. 

Refer to the illustration in 

Figure 5 on Page 13

 as 

each step in the flow is described.

Step 1. Evaporator

Liquid refrigerant (R134a) flows into the evaporator 

and is distributed for contact to a bundle of tubes that 

carry the chilled liquid for the system. The low pres-

sure liquid refrigerant absorbs heat from the chilled 

liquid causing the refrigerant to boil. The boiled refrig-

erant rises to the top of the tube bundle as vapor and 

passes through a mesh pad that prevents liquid refrig-

erant droplets from being drawn into the compressor.

Step 2. Primary Compressor

The refrigerant vapor that has passed through the mesh 

pad is drawn up to the compressor. Centrifugal com-

pression is used to pressurize the refrigerant and gen-

erate flow. The high pressure refrigerant vapor is then 

discharged from the compressor to the condenser.

Step 3. Condenser

The high pressure refrigerant vapor is distributed 

across a bundle of tubes carrying cooling liquid in the 

condenser. The high temperature and high pressure re-

frigerant vapor rejects heat to the cooling liquid that 

is passing through the tubes. The cooling liquid will 

reject its heat to the environment in a cooling tower. 

When the refrigerant vapor gives up its heat to the 

cooling liquid, it condenses on the outside of the tubes 

and drips down to the subcooler. The liquid refrigerant 

passes through the subcooler where it rejects more heat 

to the cooling liquid as the refrigerant temperature is 

reduced.

Step 4. Expansion and Economizer

The refrigerant liquid from the condenser is partially 

expanded to a pressure intermediate to the evaporator 

and condenser. The partially expanded two phase re-

frigerant is separated to liquid and vapor streams in the 

economizer. The liquid stream is expanded a second 

time to repeat the cycle in the evaporator. The vapor 

stream is drawn out of the economizer by the econo-

mizer compressor. Note that the quality of refrigerant 

delivered to the evaporator as a result of economizing 

extends the refrigerating effect of the flow through the 

evaporator and primary compressor.

Step 5. Economizer Compressor

The economizer compressor draws the refrigerant va-

por from the economizer. The efficiency benefit of the 

cycle is a result of not having to compressor this gas 

over the full head of the chiller system. As in the pri-

mary compressor, centrifugal compression is used to 

pressurize the refrigerant and develop flow. The high 

pressure vapor refrigerant is then discharged from the 

economizer compressor to the condenser.