National Foodservice Distribution Centre

As part of a competitive tender process for a leading UK food service provider, Space Engineering were awarded the refrigeration package on a new RDC in the Midlands.  This was going to be one the biggest of its kind for our customer.

The client is committed to environmentally considerate operation, so selected CO₂ (R-744) systems with heat reclaim as a balanced refrigeration plant solution.  This direct expansion system incorporates heat reclaim for a cold storage underfloor glycol heater mat and site hot water use.

The facility consists of a large -25°C cold store, +4°C chill store and +4°C chilled marshalling area.

Two dual temperature systems were selected with a calculated cooling duty covering 70% per system at each temperature level.  Each booster system has an adiabatic enhanced gas cooler.  As part of each compressor pack, a discharge plant heat exchanger and pump set was included, to serve the glycol underfloor heater mat.

The walk-in housed multi-compressor packaged units includes oil management, vessels and interconnected pipework.  Key requirements included:

• Leak detection with automatic and manual emergency extract ventilation (a manual start push button on the external of the plant housing for emergency extract).
• Motor inverter drives fitted to the lead machines at each stage.
• Parallel compressor  to manage vessel pressure regulation
• Maintenance friendly accessibility for housed components
• High and low temperature suction line accumulators.
• Replaceable liquid line filter drier, and oil filter.
• Electronic oil management system, complete with high pressure oil separator, reservoir, and individual compressor oil injection control solenoids.
• Dual PRV’s with changeover valves, at all pressure stages.

The adiabatic enhanced V-Block gas cooler component of the refrigeration system enables the rejection of thermal energy from the temperature controlled environment and compressors to the external ambient.  Both were installed with maintenance friendly spacing.  The expectation was for the following:

• Electrically communicated (EC) Fans.
• Aluminium-magnesium (AIMg) alloy  for the fin material.
• Adiabatic wetted pad total lost system.
• corrosion resistant casework with a minimum 15 year lifespan.

The design criteria for the gas coolers were:

• Maximum 36°C ambient dry bulb temperature.
• Maximum High-Pressure Valve (HPV) supercritical approach temperature 3 K above ambient dry bulb temperature.
• Maximum HPV subcritical approach temperature 10 K above ambient dry bulb temperature.
• Standard noise criteria 55 dB(A) at 10 m free field.
• The gas cooler capacity calculated at 110% of the associated system Total Heat Rejection (THR).
• Maximum Working Pressure (MWP) of 120 bar.

The dual temperature R-744 compressor packs were installed with an LT discharge de-superheater to ensure LT gas is tempered before entering the HT suction line.  Key design criteria being:

• Duty capacity to be based upon LT compressor selection and required outlet temperature.
• Maximum 36°C ambient dry bulb temperature.
• Fitted fans were EC with appropriate controls and software to maximise energy efficiency.

The Heat reclaim on each compressor pack was fitted with a PHX in the HT discharge.  Each has a variable bypass valve to control the amount of mass flow through the PHX or fully divert the discharge directly to the gas cooler.  The PHX also provides 100% calculated heating required for the underfloor heater mat.

There were a total of 14 evaporators across the three temperature controlled areas – six in the cold store, two in the chill store and six in the chilled marshalling area.  Soft gas defrost were selected for the chill and cold store evaporators, with electric defrost on the marshalling evaporators.

Glycol pump sets with multiple parallel pumps were installed.  Each sized for the full required flow rate, complete with shut off valves, commissioning sets and strainers.  Each system also has:

• Expansion tank and pressurisation unit.
• Pipework connection for charging.
• Dosing pot.
• PRV valve in main pipework.
• Automatic air bleed valves.
• Flow and return pressure gauges and temperature monitors.
• Replaceable floor temperature sensors covering the full flow.

A dehumidification system was installed, with extract ducts above the external dock doors and internal rapid doors, with outlet nozzles directed at the rapid rise doors to the cold store.

An RDM control and monitoring system was installed, with a remote dial out facility and full back up.

Working under a tight programme of works, Space successfully handed over the commissioned system to the client, ready for instant use.