National Distribution Centre

In 2019, Space Engineering were awarded the refrigeration package for a new National Distribution Centre for one of the UK’s leading supermarkets.  Based in the East Midlands, the multi-temperature facility was going to be one of the biggest for our client.

The facility consists of a large -19°C freezer store, large +2°C chill store and a +2°C cold handling / marshalling area.

With energy efficiency at the forefront of the design, 6no Advansor CO₂ refrigeration packs were selected.  Each LT and HT system incorporated a minimum of one variable speed compressor to achieve optimum load balance at all conditions.  Electrical control and sub-distribution panels are mounted and fully wired on each pack.  Maximum design pressure being 52 / 30 / 60 120 bar.

Our pack design for performance and energy consideration included:

• 5K TD between room temperature and evaporating temperature
• 2K TD allowed between gas cooler outlet temperature and max. ambient temperature = Trans-Critical Operation, 9K TD between condensing temperature and ambient temperature with 5k sub-cooling for subcritical
• Parallel compressor is used for better performance
• Air cooled LT de-superheater is arranged for DT 1, 2 & 3 and heat reclaim plate heat exchanger for freezer underfloor heating connected to DT 4, 5 & 6 LT discharge line as LT de-superheater for better performance
• Pipework is designed to allow a maximum 0.5K pressure drop in all suction lines
• All pipes run high level inside the coldrooms rather than above the coldrooms, to minimize the non-useful superheat in all suction line
• Mechanical subcooling is arranged to accommodate the big liquid rise for max. 28m. after 0.5k pressure drop allowed in liquid line
• Four dual PRV sets are installed on each pack (HT suction, LT suction, liquid receiver and HT discharge). 60 / 80 bar change over PRV on liquid receivers, to aid maintenance and future works
• Minimum 12.6°C condensing temperature restricted by compressor envelope
• Discharge pressure 120 bar
• 3 x 170 Litre receivers for DT1, 2 and 3 and 2 x 170 Litre receivers for DT4, 5 and 6

A pack back-up controller was provided, connected to an extra set of high pressure valve, gas bypass valve and instruments (pressure transmitter, temperature sensors). This is activated in a fault scenario.

The Coolers & Condensers gas coolers were supplied with EC fans, with each fan motor fitted with local electrical isolation. 2K TD between gas cooler outlet temperature and max. ambient temperature for transcritical and max. 10K TD between condensing temperature and ambient temperature for subcritical.

Our gas cooler design consideration for performance and energy included:

• Gas cooler was sized for 2K TD between gas cooler outlet temperature and max. ambient temperature for transcritical and 9K TD between condensing temperature and ambient temperature with 5K subcooling for subcritical
• Gas cooler will be fitted with Ecomesh adiabatic pack for better performance at high ambient temperature
• Blygold coil coating
• Flatbed gas cooler is used for Pack 6 due to limited space

Based on the clients requirements, the Kelvion evaporators have a 5K TD between room and evaporating temperature.  Under careful consideration, electric defrost was selected.  The evaporator defrost time and duration is carefully designed and controlled based on the evaporator locations to reduce the energy usage for defrost and improve the temperature distribution inside the coldrooms.  The evaporators are able to achieve the required air throw without the air straighteners or diffusers.

RDM was selected for the project controls and front end system.  Heat reclaim for the freezer underfloor is connected to packs DT4, 6 & 6 LT discharge.  This removes more heat than air cooled de-superheater due to low water temperature.

The project build was a success, and Space have been working closely with the client supporting their growth, ready for the next NDC opening in 2024.