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Fuelling progress

Carter Synergy designed and supplied an option for a fully integrated CO2 refrigeration solution for the BP estate.

Carter Synergy designed and supplied an option for a fully integrated CO2 refrigeration solution for the BP estate. The key aspects were:

  • To provide all refrigeration capacity
  • To provide a second temperature band for air conditioning
  • To provide all building heat through heat recovery.

The design was presented and approved in late 2013, and the St Ives, Cambridgeshire store was nominated for trial installation. This was completed and running by July 2014.

Following the installation, the system was monitored for direct comparison with a store of the same format in Cockfosters, north London.

Installation and componentry

Refrigeration Pack Central to this scheme is a Green & Cool dual temperature CO2 refrigeration pack, supplied complete with PLC and plate heat exchanger/three-way valve arrangement for heat recovery. The two temperature bands are: -7 deg C (Saturated Suction Temperature) for MT refrigeration and 7 deg C (SST) for air conditioning.

All Green & Cool systems are designed with PRV setpoints at 80 Bar liquid and 60 Bar suction to ensure refrigerant charge is held in the event of a power failure.

The pack is an external unit with an integrated gas cooler, offering a compact footprint for the small format application.

Pack Controller, Remote Access & Interface The pack controller is a purpose-built PLC, with software written by Green & Cool, which provides flexibility in adapting it to different applications, such as heat recovery.

The PLC also allows remote access to the unit, enabling it to be accessed from a computer via the internet, or via an app.

The controller links directly with the store HVAC controller through a 0-10V signal.

For St Ives, this interfaces with a purpose-built RDM solution, but any system able to provide this signal would be compatible. The plant controller also sends an alarm signal to the store monitoring system.

Remote Cabinets The cabinets for this scheme were provided by Carter Retail Equipment, and were the standard M&S Brooklands range adapted for transcritical CO2 operation – namely higher operating and standstill pressures.

Coldstore The coldstore was built by Carter Coldstore Services and comprises standard 80 mm PIR panelling with glazed doors along one wall, facing the sales floor.

Internal shelving is back-filled, allowing stock to be traded from the coldstore.

This layout significantly increases shelving space without compromising refrigerated storage.

HVAC:The distribution of sales floor and office heating and cooling takes place via three ducted fan coil units. These are Marstair units, designed in conjunction with Carter Synergy, and containing two coils for LPHW and DX CO2 respectively.

An LPHW overdoor heater has also been installed due to the high throughput of customers.

All LPHW and CO2 equipment is supplied solely by the refrigeration plant. The HVAC system is controlled by a purpose-built RDM controller, with a program to meet the needs of the specific system developed with Carter Synergy.

The system reacts to changes in the store environment in a more measured manner than typical LPHW systems, to ensure that the free heat output from the plant is maximised.


The site at Cockfosters was selected as a typical refrigeration/HVAC installation for comparison with the integrated scheme at St Ives.

Sub-metering was fitted to all refrigeration and AC plant and associated equipment to allow detailed analysis of the two system performances.

Energy savings

Energy readings have been taken at regular intervals across the period and a more detailed breakdown of the findings is contained in the table below. The headline figures are on the table to the right and the graph below.


For the eight months under study, the store is demonstrating a significant 45 per cent reduction in energy use for refrigeration and HVAC services.

This ensures that the payback on investment will allow significant benefits to BP across the lifecycle of the equipment.

The period monitored to date is an excellent snapshot of a year as it contains months with high ambient temperatures and those with low. The expectation is that these savings will continue. The study will continue for a full 12 months.

The Carter Group intends to continue developing the offer to ensure value and efficiency are maximised.

On the back of the success at St Ives, a second scheme has been allocated for the integrated approach – Carter is looking to alter the proposal slightly, based on the lessons already learned.

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