REF UNIT 26

Question 1

(26.2) how can a self contained reach in cooler evaporate its condensate?

Answer 1

using heat from the compressor.

Question 2

(26.3) what are the 2 big advantages of using a single compressor for multiple fixtures?

Answer 2

1. the compressor motors are more efficient because they are larger
2. more heat can be captured from the compressor to use for other purposes.

Question 3

(26.3) what type of valve allows for heat reclaimation in a heat reclaim system?

Answer 3

three-way pilot-operated solenoid heat reclaim valve

Question 4

(26.3) T or F: heat reclaim condensers can be in series or in parallel with regular condensers

Answer 4

true

Question 5

(26.4) what type of compressors can be on a rack system?

Answer 5

reciprocating, scroll, screw, or rotary.

Question 6

(26.4) what are the two big disadvantages of a rack system?

Answer 6

1. leaks will affect the entire rack.
2. compressor burnouts will contaminate the oil circulated through all compressors.

Question 7

(26.4) define “load matching”

Answer 7

trying to always match the capacity of the refrigeration system with the evaporators heat load (in a rack)

Question 8

(24.6) how is refrigeration load sensed in a rack system?

Answer 8

using a pressure transducer mounted on suction header and is wired to a control board that uses an algorithm. it changes the pressure signal into electrical for the microprocessor to process.

Question 9

(26.4) define uneven parallel systems

Answer 9

rack systems with compressors with varying capacities.

Question 10

(26.4) what are the 4 major components in the oil distribution of a rack system?

Answer 10

oil separator, oil reservoir, pressure differential valve, oil level regulator.

Question 11

T or F: the oil separator and oil reservoir are usually seperate.

Answer 11

false

Question 12

(26.4) what is the pressure difference the pressure differential valve on an oil level regulator works with?

Answer 12

5 to 20 psi

Question 13

(26.4) how does the oil level regulator sense oil levels?

Answer 13

they use a float.

Question 14

(24.6) can an oil level regulator be adjustable?

Answer 14

yes.

Question 15

(26.4) what is the purpose of having a satellite or booster compressor?

Answer 15

they are often dedicated to the coldest evaporators, which makes it so the other compressors don’t have to operate with low suction pressures, making the system more efficient.

Question 16

(26.4) what are the variable speed drives on satellite compressors called?

Answer 16

inverters. they match the load by altering frequency.

Question 17

(26.4) how do auxiliary metering devices and evaporators achieve subcooling?

Answer 17

some refrigerant from the liquid line is fed through these auxiliary components, which cools the rest of the refrigerant using a shell and tube heat exchanger.

Question 18

(26.4) what are “flow-through receivers”?

Answer 18

store liquid before entering the liquid header. helps in maintaining subcooling.

Question 19

(26.4) what is an SPR?

Answer 19

system pressure- regulating valve. A valve located between the compressor and receiver that allows some liquid refrigerant to bypass the reciever. It senses ambient air.

Question 20

(26.5) what are the 2 most common secondary fluids?

Answer 20

propylene glycol and hydrofluoroethers (HFEs).

Question 21

(26.5) what is the refrigerant name for CO2?

Answer 21

R-744

Question 22

(26.5) what is the triple point of CO2?

Answer 22

where CO2 exists in all 3 states (70°F/75psia). CO2 systems must operate above this point.

Question 23

(26.5) what is the subcritical CO2 cycle?

Answer 23

the CO2 refrigeration cycle that takes place above the triple point and below the critical point.

Question 24

(26.5) what is the transcritical CO2 cycle?

Answer 24

the CO2 refrigeration cycle that takes place above the triple point and goes above the critical point. the “condensing” is referred to as “gas cooling.”

Question 25

(26.5) what is an indirect CO2 system?

Answer 25

system that uses a chiller and a primary refrigerant to absorb heat from the CO2.

Question 26

(26.5) what is a cascade system?

Answer 26

low temperature system where CO2 is the secondary refrigerant and another refrigerant is the primary.

Question 27

(26.5) why are centrifugal pumps sometimes used pumping to the metering device?

Answer 27

the added pressure allow the head pressure to be floated, which allows for a great exchange of heat while maintaining operating pressures.

Question 28

(26.14) what are the heaters on cabinet display doors called?

Answer 28

mullion heaters.