Carter Synergy has a number of key clients, one of which is a large food wholesaler and distributor based in Birmingham. A number of high profile and extensive projects have been undertaken in collaboration with the client in the last five years. Most recently one of the client’s critical freezer coldstores was determined to have reached the end of life and a solution had to be developed to replace this room, plant and all the associated electrical, construction and mechanical works to support this.


The initial assessment of the project immediately highlighted that the existing plant was inefficient and posed a high level of financial risk due to the refrigerant in use. Originally designed as an R22 system the four large reciprocating compressor/receiver sets had previously undergone two retrofits, first to R422d and then more recently to R438a (MO99). The client in conjunction with our design department settled on a natural refrigerant solution based on CO2 and a further consideration required the system to include a heat exchanger which would redirect rejected heat from the system into the ambient warehouse area and act as comfort heating for the staff.

A key consideration for the project was the timeframe that the work had to be undertaken in. The existing Coldstore is a critical operating asset of the client and is in use up to 16 hours a day, seven days a week with anywhere up to 400 door openings a day. This high level of use not only impacts on the energy use of the system but also on the level of refrigeration duty required to operate it. With plans in place to relocate the stock, the existing room and concrete floor was removed and the process of renewing it in the same footprint began.

L Shape Freezer

During the build of the room, the phased construction of the new externally located plant area began as well as the extensive changes to the electrical supplies and building structure. On completion of the room build the new services, lighting, evaporators and associated heating services commenced and were completed in the required timeframes. The new transcritical CO2 plant was craned in, installed and commissioned and the month-long temperature pull-down of the room commenced.

Once completed the entire system underwent a two-week test phase to prove to the client that the system was fit for purpose and the handover then took place and the stock moved back into the new structure. The client was delighted and the entire project was achieved within the specified timescale.