A state-of-the-art air conditioning system powered by high efficiency natural gas engines is providing low carbon cooling and heating at Scunthorpe General Hospital. The system uses seven Sanyo gas-powered heat pump (GHP) chillers to supply chilled water to air handling units serving a suite of operating theatres.

It replaced two aging Trane chillers, based on hermetic scroll compressors running on R22. The internally located, ducted air-cooled machines, each originally rated at 165 kW, had been installed in 1991 and had become inefficient and expensive to run.

Consultant Pick Everard carried out an evaluation of several possible replacement options, including a traditional electric chiller and compact turbo-based technology. Jeff Fleming, who headed the project for Pick Everard, said: “A key issue at the site was that there was no headroom on the electricity supply. Cooling loads had grown since the original chillers were installed, and replacing with a larger conventional electric chiller would have required a big investment in additional power supply."

“The Sanyo gas-engine driven heat pumps supplied by Oceanair (UK) Ltd not only provided a way round the power problem, they are a highly energy efficient solution. Our studies showed that in terms of life-time costs, energy consumption and carbon emissions, they come out well ahead of comparable electric systems.”

A further benefit of the Sanyo units he says is their low noise, which makes them ideal for use in hospitals. Noise was likely to be a planning issue on the project, and the GHP units exceeded any potential restrictions. “They are exceptionally quiet in operation. You have to actually put your ear to the units to hear they are running at all,” he says.

The seven GHP units, each with an output of 56kW, were chosen from the Sanyo range for their optimum efficiency in order to minimise the hospital’s liability under carbon reduction legislation.

A further benefit of the multiple system is resilience compared with a single large chiller. If one unit is out of action, there is capacity to provide continuity of service. In the case of a conventional chiller installation, breakdown can cause disruption and affect cooling to the building.

The power advantages of the GHP units extend to a much lower start-up current than standard electric chillers. As the process mirrors ignition in a modern vehicle engine, a few dozen Amps are all that are required for start-up rather than several hundred Amps for an electric chiller.

In winter, the heat pump cycle is reversed, providing high efficiency heating to operating theatres. As heating was previously supplied by inefficient steam heater batteries, this is saving significant additional cost, Mr Fleming reports.

Each chiller produces an additional 18kW of waste heat that can be harnessed for use in generating hot water for the hospital’s domestic supply.

Each of the R410A chillers has its own separate refrigerant-to-water heat exchanger within the building, eliminating the presence of water on the roof and overcoming the need for trace heating, anti-freeze and water treatment chemicals.

Mr Fleming says: “Another bonus with the Sanyo system is that we only used one system pump compared to conventional chillers that usually require an additional chiller shunt pump or heat rejection pumps, which have a significant electrical power requirement.”

Servicing is highly economical, with engines requiring servicing every 10,500 hours, which equates to between two and three years.

Jeff Fleming says: “The Sanyo GHP units provided a superb solution that perfectly meets the requirements of the project. The technical support from Oceanair has been excellent throughout. They are the experts when it comes to Sanyo GHP technology, and helped train the hospital engineers in commissioning and optimising the systems. I would have no hesitation in using the Sanyo GHP system again and look forward to working with the Oceanair team.”

Tony Evanson of Oceanair UK Ltd said: “The project is a brilliant example of how a modern GHP system can deliver in all areas – efficiency, power, servicing, low noise and low cost of ownership over the lifetime of the plant. It makes the case for GHP loud and clear. It is a technology that, in the right application, simply can’t be beaten.”

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