REF UNIT 26 Flashcards
(26.2) how can a self contained reach in cooler evaporate its condensate?
using heat from the compressor.
(26.3) what are the 2 big advantages of using a single compressor for multiple fixtures?
- the compressor motors are more efficient because they are larger
- more heat can be captured from the compressor to use for other purposes.
(26.3) what type of valve allows for heat reclaimation in a heat reclaim system?
three-way pilot-operated solenoid heat reclaim valve
(26.3) T or F: heat reclaim condensers can be in series or in parallel with regular condensers
true
(26.4) what type of compressors can be on a rack system?
reciprocating, scroll, screw, or rotary.
(26.4) what are the two big disadvantages of a rack system?
- leaks will affect the entire rack.
- compressor burnouts will contaminate the oil circulated through all compressors.
(26.4) define “load matching”
trying to always match the capacity of the refrigeration system with the evaporators heat load (in a rack)
(24.6) how is refrigeration load sensed in a rack system?
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.
(26.4) define uneven parallel systems
rack systems with compressors with varying capacities.
(26.4) what are the 4 major components in the oil distribution of a rack system?
oil separator, oil reservoir, pressure differential valve, oil level regulator.
T or F: the oil separator and oil reservoir are usually seperate.
false
(26.4) what is the pressure difference the pressure differential valve on an oil level regulator works with?
5 to 20 psi
(26.4) how does the oil level regulator sense oil levels?
they use a float.
(24.6) can an oil level regulator be adjustable?
yes.
(26.4) what is the purpose of having a satellite or booster compressor?
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.
(26.4) what are the variable speed drives on satellite compressors called?
inverters. they match the load by altering frequency.
(26.4) how do auxiliary metering devices and evaporators achieve subcooling?
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.
(26.4) what are “flow-through receivers”?
store liquid before entering the liquid header. helps in maintaining subcooling.
(26.4) what is an SPR?
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.
(26.5) what are the 2 most common secondary fluids?
propylene glycol and hydrofluoroethers (HFEs).
(26.5) what is the refrigerant name for CO2?
R-744
(26.5) what is the triple point of CO2?
where CO2 exists in all 3 states (70°F/75psia). CO2 systems must operate above this point.
(26.5) what is the subcritical CO2 cycle?
the CO2 refrigeration cycle that takes place above the triple point and below the critical point.
(26.5) what is the transcritical CO2 cycle?
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.”
(26.5) what is an indirect CO2 system?
system that uses a chiller and a primary refrigerant to absorb heat from the CO2.
(26.5) what is a cascade system?
low temperature system where CO2 is the secondary refrigerant and another refrigerant is the primary.
(26.5) why are centrifugal pumps sometimes used pumping to the metering device?
the added pressure allow the head pressure to be floated, which allows for a great exchange of heat while maintaining operating pressures.
(26.14) what are the heaters on cabinet display doors called?
mullion heaters.
