IN what has been seen as a ground-breaking move, Waitrose has announced its intentions to use hydrocarbon refrigerants in all its new stores and refurbs. Neil Everitt looks at the reasons for the decision and how the system will work
Due to their size, high profile and impact on our everyday lives it is not surprising that supermarkets have been seen as easy targets by environmental groups.

Indeed, the supermarket industry is one of the largest consumers of power, and refrigeration accounts for a large proportion of this. In fact, it is claimed that about one quarter of the carbon footprint of supermarkets comes from the HFCs used in their refrigeration systems.

In 2007, and probably in response to this envivironmental pressure, six of the top supermarkets announced their intention to move away from HFCs – but where could they go?

A lot of work has been done with CO2 but there are continuing concerns over its suitability – particularly with regard to it being a high pressure refrigerant and the apparent lack of a sufficient number of technicians conversant with this type of equipment.

Waitrose has poured a reported £55m into improving its refrigeration systems in the last five years but has previously admitted that trials of CO2 have been complex, and a lack of technical know-how has been seen as a major barrier to adoption. Even so, it came as some surprise when Waitrose recently broke ranks with its competitors by announcing its intention to use hydrocarbons on all future new stores and refurbishments. Unbeknown to most people, Waitrose had been carrying out trials with the technology over the last 18 months, both live in the field and within test labortories.

Reduced carbon footprint

The system it has developed in association with Synergy Building Services Consultants, Carter Retail Equipment and chiller manufacturer Geoclima is based on the hydrocarbon refrigerants propane and propene, a choice which it says will enable it to cut its carbon footprint by 20%. It is being installed in Waitrose’s Altrincham store which is due to be opened this month and then rolled out in new and refurbished stores across the country.

Nigel Keen, director of building services and development commented: “This is a very exciting new development for Waitrose and for all retailers. Reduction of HFCs is a major concern for supermarkets, and the beauty of this system is its simplicity.” The new refrigeration system will do away with the industry-standard remote centralised dx refrigeration packs and equipment with pipe work distribution to cold rooms and chilled and frozen cabinets.

Waitrose’s new solution employs hydrocarbon refrigerants as the primary cooling medium with water as the secondary heat transfer medium. The primary plant uses air-cooled liquid chillers utilising propane (R290). The cabinets and cold room evaporators will be charged with propene (R1270). In addition the refrigerated cabinets, chillers, cold rooms and freezers incorporate integrated DX units with refrigerant and water plate heat exchangers.

The heat transfer between primary chillers and DX cabinets is provided via flow and return pipework with water as the heat transfer medium. This is a pumped and pressurised closed loop water circuit with branch connections to each cabinet heat exchanger providing flow at all times. The water circuit incorporates two pump sets to provide duty/standby with auto changeover in the event of pump failure.

Geoclima chiller

A typical system will include two 140kW Italian-made Geoclima air-cooled liquid chillers supplied by Klima-Therm and running on R290. The chillers use a combination of liquid pressure amplification (LPA) technology, with floating head pressure and traditional free-cooling to significantly increase operating efficiency. They also use high efficiency aluminium coils.

Liquid pressure amplification units are used to raise the pressure of liquid refrigerant at the inlet to the expansion valve and enable refrigeration systems to operate at lower head pressures. They are electrically driven, but use less power than a compressor would need to achieve the same pressure increase at the inlet to the expansion valve. This results in reduced absorbed power, reduced compressor usage, improved reliability with fewer failures due to lower operating pressures and temperatures leading to longer life expectancy. The chillers have two refrigeration circuits with two-stage compressors.

Commenting on the system, Tim Mitchell, who is heading up the project for Klima-Therm, said: “The relatively high temperature of water returning from the chill cabinets to the chillers means that the chillers can operate in full free-cooling mode from 12ºC ambient downwards. This means that for more than half the time (around 55%), the chiller operates in free-cooling mode, without having to power up the compressor – delivering huge efficiency benefits and reducing carbon emissions.”

Heat recovery

The refrigeration system has also been incorporated into the hvac systems: return water from the cabinets is used to augment DHW and provide heat to the shop area. This heat is entrained into the cold aisles by cold air retrieval and has allowed Waitrose to remove one air handling unit which was providing 365 day heating to these aisles. Cold spill from the cabinets will also be used to cool areas of the shop previously requiring air conditioning. Traditional air conditioning will now only be used in the staff canteen, training suite and general office. All other offices and communication room will be free-cooled via the cold spill from the sales floor. The plant uses a Next Controls system, which enables operation to be monitored remotely via the internet.

The cabinets

Carter Retail Equipment were given the task of producing a close-coupled, water-cooled, remote case with the “look and feel” of a standard remote. “We were keen to ensure that the sales floor aesthetics were not compromised,” commented Waitrose’s projects engineering manager Jim Burnett.

This meant Carters using an existing approved Waitrose remote display case and integralising it with minimal aesthetic impact. A maximum increase in height of only 160mm was allowed. Capacity control was required for low load situations while Waitrose demanded there be no compromise on case reliability. Carter’s original prototype case was approved by Waitrose in December 2006 and includes twin compressors for effective capacity control and system redundancy.

The twin refrigerant circuits contain around 350g per circuit of propene, which is within the required guide lines of volume for safety. Being a factory-sealed system, the cabinet can boast minimum leakage, and give increased reliability due to system cleanliness and is maintenance-free.

In addition, the cabinets are designed to reject around 25% of the heat of rejection from the compressors back into the store to offset the nett environmental cooling effect of the case.

Safety

With hydrocarbons, safety is of paramount importance. Waitrose has worked closely with Cool Concerns, the midlands-based refrigeration consultancy and training provider, to ensure the system as a whole and all elements of the refrigeration system are independently verified to comply with the safety standard BSEN 378 (2008).

The Geoclima chiller itself limits the hydrocarbon charge per circuit to 5kg. It incoporates a first level HP relief valve release to the low side of the circuit rather than to atmosphere, with a secondary release to atmosphere as a second level safety net. These is also a pressure relief valve on the water system close to the evaporator in case of a propane leak into the water system. All HP switches are sealed.

The compressor enclosure and electrical panel are both specially ventilated with the fans powered by brush-less motors. Otherwise, there are no non-ventilated enclosures on any refrigerant-containing sections of the chiller. Anaconda vibration eliminators are included in the refrigerant lines to prevent work-hardening/vibration related leakage.

Training

Waitrose has arranged for the installation and service contractors to be suitably trained by Cool Concerns on the Waitrose specific cabinets and equipment and internal training for key internal engineering and maintenance personnel has already been carried out. Cool concerns will also provide training for branch management teams in accordance with the standard to ensure that persons working within the branch have an awareness of the use of hydrocarbons.

Efficiency

Energy consumption of the new Altrincham store will be of particular interest: “We have ensured that our installation at Altrincham is fully monitored such that we can measure the benefits,” revealed Jim Burnett. “This will be carried out over at least 12 months,” he added.

“Our trials have shown promising results so far. With the energy benefits of the hydrocarbon refrigerant combined with the removal of 60kW of gas heating we are expecting an energy saving of at least 10%.

The results have given the partnership the confidence to move forward with this solution in 2010 on all new builds and major refurbishment projects.

This is undoubtedly a bold move by Waitrose and time will tell how effective it will be. Many eyes are now on them, not least those of their competitors still pondering the possibilities of CO2 in a world increasingly hostile to HFCs.