Keeping food fresh with CO2 and brine. Supermarket refrigeration systems commonly use synthetic refrigerants such as R404A and R22.
Historically, these have circulated directly through shops’ freezers and display cases, which has led to refrigerant charges of as much as 1000 kg per store. Average annual leakage rates as high as 30% mean the environmental impact is not acceptable,and the goal now is to design systems that minimize synthetic refrigerant charges as well as leakage rates.
SWEP’s rugged and reliable BPHEs enable such systems to be built economically. Furthermore, SWEP’s wide range of standard and highpressure BPHEs give system builders every opportunity to customize systems for specific customer requirements.
The problem
The refrigerant charges in the cooling systems used in supermarkets throughout the world can be as much as 1000 kg. With leakage rates as high as 30%, the environmental and financial costs cannot be ignored. The challenge is to reduce refrigerant charges and leakage rates while maintaining adequate cooling.
The solution
A robust system is achieved by combining one chiller with a compressor rack. The compressor rack cools the freezers and cold rooms, while a medium-temperature (MT) chiller supplies cold brine. The brine is used in the MT food display cases (fresh food and beverages) and to remove heat from the compressor rack. The system makes it possible to use different refrigerants optimized for each specific temperature zone. Another advantage is that the large temperature difference between the freezer and the surroundings is divided between two refrigerant systems. This enables the total pressure difference to be handled by two smaller compressor units, which have a lower total energy demand than one large compressor unit. These two advantages give better overall system performance, thus decreasing energy input. Furthermore, using brine in the MT display cases also minimizes the refrigerant charge in the store area and substantially reduces the leakage of refrigerants from the system.
System description
The system can be divided into three sections. First, the brine chiller cools the brine to -8°C [1]. Second, the brine system pipes brine to the MT display cases in the store area and to the compressor rack [2]. Third, the compressor rack rejects its heat to the brine while maintaining the temperature of the frozen provisions [3].
The chillers are often located in a machine room, which simplifies maintenance and control, minimizes the refrigerant charge for the brine chiller and avoids leakage into the store area. The brine chiller is often charged with R404A at a low operating pressure, which makes a SWEP standard-pressure BPHE the best option for this chiller. Compressor racks often use CO2 because of its good low-temperature characteristics. The system is typically a direct expansion (DX) system with an
evaporation temperature of -35 to -40°C to maintain -18 to -24°C in the freezer or cold room. The resulting condensing temperature for the CO2 is approximately -15 to -10°C, corresponding to an operating pressure of 22-26 bar. Such CO2 systems are always at risk of standstill, leading to increased temperature and pressure. SWEP’s high-pressure models are ideal for these compressor rack applications because they are tested and approved for these conditions.
In this solution, SWEP BPHEs offer:
- Ruggedness for reliability and minimal maintenance
- Both standard- and high-pressure models for a total system solution
- Safe operation with problematic refrigerants such as CO2
- High efficiency for low running costs
- Compactness that saves valuable retail space
