Profroid MiniCO2OLcompact Notice D'instructions page 68

11 ADDITIONAL FUNCTIONALITIES – CO2OLTEC EVO SYSTEM USING EJECTORS
11.1 OVERVIEW:
The ejector concept is a technical solution to improve the energy efficiency of CO2 transcritical systems, when used in regions with average
ambient temperature higher than 15°C.
This solution is adapted for all climates and especially in Southern Europe (example: south of 45 degrees)
This solution is also well adapted when the capacity needs in heat recovery mode are high, and require to run the system at higher discharge
pressure.
11.2 BASE PRINCIPLE:
The addition of a modulating ejector using the kinetic energy of the gas cooler outlet fluid makes it possible to pre-compress the vapors coming
from the consumers and thus to reduce the compressor work.
The outlet mixture made of those vapors and the gas cooler outlet fluid are then connected to the liquid receiver.
The gas/liquid separation occurs in the receiver and the compressors suck the entire amount of the flash gas generated (identical to ECO
compressor principle).
A secondary pump is added on the liquid line but will only be activated when the receiver pressure is not high enough to properly feed the MT
consumers.
In addition, since the compressors only suck the flas gas from the receiver and the ejectors suck the entire fluid coming from the MT consumers,
it is possible to run those consumers in semi-flooded mode (superheat close to "0°K" value). The additional evaporating heat transfer surface will
induce an increase of the evaporating temperature in the consumer estimated between 3 and 5°K depending on the specific characteristics of the
heat exchangers being used. This temperature increase does significantly improve the energy efficiency of the system.
11.3 KEY DIFFERENCES BETWEEN CO
11.3.1 Cycle presentation
Baseline = CO2 refrigeration system designed to operate in a traditional transcritical mode :
dual stage system in a booster configuration
two expansion levels (HP and MP flash gas valves)
a liquid gas liquid separator (figure 1)
Figure 1: Simplified schematics (left) of piping and instrumentation of a CO2 transcritical booster system using medium te
temperature (LT) evaporators. P, H diagram (right) of this refrigeration cycle operating in transcritical mode during the summer (continuous line)
and subcritical mode during the winter (dotted line)
OLTEC EVO AND TRADITIONAL CO
2
SYSTEMS
2
mp r e ature (MT) and low