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A study in energy savings

The National Library of Scotland houses priceless collections which depends on the maintenance of carefully controlled environmental conditions – and the Turbomiser chiller is helping to achieve this.

The National Library of Scotland has installed high-tech oil-free Turbomiser chillers at its main Edinburgh site, saving 11 per cent on building energy use in the process.

The George IV Bridge building houses priceless collections, including more than 15 million printed items. The library is very conscious that preserving its collection for future generations depends on maintaining carefully controlled environmental conditions, and that this needs to be achieved as efficiently as possible.

The library sought the help of the Carbon Trust to develop a Carbon Management Plan, which included harnessing the high efficiency of the Turbomiser chiller to deliver low-cost, low-carbon cooling, in place of two ageing chillers, based on reciprocating compressors, running on R22.

NLS estates manager Jack Plumb says: “I had the opportunity to visit a Turbomiser installation at a local hospital while attending a Conference in Ottawa. I was extremely impressed by its performance. It was not only highly efficient, but extremely reliable,  due to the fact that it does not use oil and effectively has just one moving part.”

The Turbomiser was selected in a tendering process as it offered the most economical and efficient solution to meet the highly variable load conditions.

The chosen solution was to build on the free-cooling approach which had been used at another NLS site, where it had reaped significant energy savings.

The installation comprised two Klima-Therm 300 kW water-cooled Turbomisers linked to a free cooling system, providing chilled water to a number of air handling units serving the building.

The most sensitive areas are the library’s archive collection spaces, which have to be maintained within an environmental envelope agreed with the library’s preservation department.

The public reading rooms present the most significant variable load as a result of changes in ambient conditions and usage levels. At peak times, the rooms can account for the majority of chilled water demand.

BMS know-how

The output from the Turbomisers and free-cooling system feed into a large chilled water low-loss header, which also acts as a buffer vessel.  A Building Management System calculates demand for chilled water, taking account of temperature, flow rate and time of year, as well as the current status of the various chilled water batteries in the AHUs.

The free-cooling circuit harnesses an air-blast cooler and the condenser circuit, routed through a heat exchanger to provide chilled water to the low loss header.

While reading rooms present  the most variable load, the predominant base cooling load  is provided by the archive  collection spaces, as this  represents a round-the-clock cooling requirement.

When conditions allow, the energy-saving BMS program shuts down AHUs serving these spaces, leaving just the public reading rooms as the primary demand.

Maximum demand for chilled water naturally occurs during the summer months; the aim in the winter is to supply the reduced cooling demand through use of the free-cooling system only, significantly reducing energy use, cost and carbon emissions.

The previous chiller plant was not monitored for its individual energy consumption, but as part of the chiller replacement project, sub-metering was installed throughout, showing an overall reduction in building energy use of 11.4 per cent.

Given that this figure covers the warmer summer season only, it is likely that savings will accelerate during the cooler winter period as a result of the use of free cooling and improved efficiency of the Turbomisers at part load.

While the current Turbomiser refrigerant is R134a, Mr Plumb says one of the attractions of the specification is that it could be retrofitted to work with HFO 1234ze, should legislation demand a lower GWP refrigerant in future.

He adds: “From an engineering point of view, the technology is absolutely outstanding – particularly in removing the requirement for oil and moving parts from the electric motor side of the compressor cycle. I would say it is probably the most significant advance in chiller technology since the development of the vapour compression cycle itself.”

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