DOI: 10.18710/htyhjp
title: Replication Data for: MultiPACK_Projecet_Modeling of a CO2-based integrated refrigeration system for supermarkets

description: This dataset provides the field and numerical data of a study that focuses on the fully integrated CO2 refrigeration system configuration for a supermarket in Porto de Mos, Portugal, which was equipped and fully monitored through the EU funded project MultiPACK. A dynamic system model was developed in Modelica and validated against measurement data from the site recorded for one week. The model is used to provide additional ejector performance data supporting the obtained measurement data and to evaluate system configuration 18 at equivalent boundary conditions.
The integrated CO2 refrigeration units installed in the frame of the MultiPACK project meet refrigeration (freezing and cooling), space heating, space cooling and hot water production loads. The layout of the unit introduced in this dataset is detailed in Figure 1. The system includes the main state-of-the-art technologies for CO2 refrigeration units such as ejector supported parallel compression, with ejectors for expansion work recovery and liquid ejectors for evaporator operation with minimized (or even zero) superheating, space heating and air conditioning through CO2-air rooftop units (RTUs), heat pump mode evaporator, etc
The compressor pack is an ejector-supported booster system with parallel compression. Three semi-hermetic compressors are installed at medium temperature (MT) level, three compressors at low temperature (LT) level, and there are four parallel compressors implemented mostly for air conditioning (AC), as detailed in Table 1. Smooth capacity modulation is achieved by inverter drives for one compressor per compressor level (30 to 60 Hz). The total installed electrical power for all compressors and auxiliary equipment (gas cooler/desuperheater fans, etc.) corresponds to 177 kW, excluding the fans for the RTUs. 
High-pressure CO2 can be applied for heating domestic hot water (DHW) up to 60 °C before the remaining heat may be utilized in the RTUs. Excess heat of the CO2 is then rejected to the ambient air by the gas cooler (GC), which can be partially or completely bypassed if needed. 
Depending on the operation mode of the package, the expansion from the high-pressure level into the liquid receiver tank at an intermediate pressure level in the range of 35 – 45 bar is done by either ejectors (high-pressure ejector or AC ejector) or by a high-pressure control valve (HPV). The ejectors implemented in the system are of fixed geometry and different sizes, arranged in blocks and each ejector enabled or disabled in a coordinated manner depending on the capacity requested (Multi Ejector concept by Danfoss [9]).
The liquid receiver separates the flash gas and liquid phase and accumulates the liquid to manage charge variations in the circuit and to provide a sufficient liquid head. The liquid CO2 is subcooled and distributed to the LT, MT and AC evaporators. The flash gas is either compressed by the AUX compressors or throttled by the flash gas bypass valve (FGBV) to the suction of the MT compressors, depending on the operating conditions.
The LT loads of the supermarket comprise cabinets, freezing rooms and an ice machine. The liquid CO2 mass flow supplied to the LT load is measured by a Coriolis mass flow meter, marked as M4 in Figure 1. The expansion to LT evaporation pressure is realized with electronic expansion valves separately controlled for each load. The low-pressure gas from the LT evaporators is heated due to subcooling of the liquid CO2 before it is compressed by the LT compressors to the MT separator pressure level.
The MT loads consist of open and closed cabinets and cold rooms, which are equipped with separate controlled electronic expansion valves. The supplied liquid CO2 mass flow to the MT loads is measured by Coriolis mass flow meter M3. A separator tank prevents liquid suction by the MT compressors. In case of excess liquid accumulation in the separator tank, a liquid ejector block is activated to return liquid to the receiver. The high-pressure ejector block recovers expansion work to suck part of the gaseous CO2 from the separator tank back to the liquid receiver. This unloads the MT compressors in favour of the AUX (parallel) compressors, which operate with a lower pressure ratio.
The space heating and cooling demand of the supermarket is supplied by means of two rooftop units (RTUs). In the rooftop units, CO2 directly flows into the heating and cooling coils. The arrangement of the rooftop units enables the usage of dehumidification. AC in the rooftop unit can be either provided by an ejector-supported AC operation or by utilizing direct expansion (DX) from downstream the GC:
• For the ejector-supported AC operation mode, an ejector block with low pressure (LP) lift but a high entrainment ratio is utilized. In this case, the entire vapour of the AC evaporators is being sucked by the LP ejector and lifted to the receiver pressure level. Coriolis mass flow meter M1 measures the CO2 mass flow rate for this AC operation mode.
• In the case of a DX AC mode, Coriolis mass flow meter M5 is utilized to determine the CO2 mass flow rate through the RTUs. The direct evaporation in the heat exchanger can be operated with ultra-low superheat. The increased flash gas amount during AC operation is handled by dedicated AC compressors.
The AC compressors can also be utilized for additional heat rejection mode (i.e., heat pump mode). This mode can be activated when the heat that is available during standard cooling mode is insufficient to completely cover the heating demand requested by the RTUs. The heat pump mode utilizes ambient air as a heat source for the separate set of coils in the gas cooler that operate as an evaporator with liquid CO2 supplied by the liquid receiver. A solenoid valve is installed allowing an independent heat pump functionality for some AC compressors, while others still can remove flash gas.