Cooltherm were approached by the Buro Happold Consultancy to work with them to develop a “life Extending” plan for the two main chillers which serve the British Museum in London, the chillers not only provide comfort cooling to the building but they also provide critical humification control to protect the priceless artefacts.
The machines were of the first generation of chiller plant that operated on the then new breed of ozone friendly refrigerants so overhaul rather than replacement could be considered, this approach would be advantageous as site development over the years since the plant was originally installed has left the roof mounted dry air coolers beyond the cost effective reach of mobile cranes.
The chillers on site are bespoke water cooled chillers and served by four roof top dry air coolers and both items are approaching 20 years of age. The chillers being plant room machines cosmetically were in good condition and each chiller had five large Bitzer screw compressors and each compressor had its own dedicated condenser and evaporator, essentially each chiller was five individual chillers served by a common control panel.
The chillers had suffered in recent years with compressor failures and poor operating efficiencies, the Cooltherm service team opted to overhaul all ten compressors (as they are no longer manufactured) replacing all bearings, seals and inspecting all compression surfaces (only one compressor of the ten needed to have a completely new body due to physical damage, which is testament to the quality of the original machines concept).
Because cooling always had to be maintained to the site in a phased manner, we replaced all the chiller electrical switch gear and line control components, temperature probes & transducers, safety devices, expansion valves, and flushed each heat exchanger. Once this work was completed, we recommissioned the chillers into operation.
The dry air coolers were in fair condition, 50% of the coil blocks were in poor condition (mainly due to poor historical acid coil cleaning), and the remaining coil blocks were in serviceable condition. We opted to replace all the dry air cooler fans for new modern alternatives and repainted the frames to extend the plants life further.
Once the work was completed the chillers provided notable energy savings and much closer temperature control than had been achieved in the past. These savings were not due to the implementation of new technology, (albeit the new dry air cooler fans do provide a large improvement over their predecessors) these savings were found by modifying the existing control strategy to provide better part load capacity control and the replacement of all the temperature probes allowed for correct and maintainable calibration. Before the work was completed each compressor was operating significantly longer than was required due to the poor temperature tracking ability of the original probes.
The aim for this project was to extend the operating life of the plant by another three years after which the plant will need to be replaced.