Scunthorpe General Hospital - Gas Engine Heat Pumps
Problem, Requirements & Solution
Scunthrope General Hospital uses seven gas-powered R410A heat pump chillers to supply chilled water to air handling units serving a suite of operating theatres.
It replaced two Trane chillers, almost 20 years old, which used hermetic scroll compressors and ran on R22. The internally located, ducted air-cooled machines, each originally rated at 165kW, had become too inefficient and expensive for the hospital. Consultant Pick Everard evaluated several possible replacements, including a traditional electric chiller and compact turbobased 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 them with a larger conventional electric chiller would have required a big investment in additional power supply. “the gas-engine driven heat pumps (GHPs) not only provided a way round the power problem, they are a highly energy efficient solution. Our studies showed that in terms of lifetime costs, energy consumption and carbon emissions, they came out well ahead of comparable electric systems.”
The annual running costs for the chiller’s was £18,457.00 excluding pumps. A detailed study was carried out to replace the existing inefficient electric chilller’s, with high efficiency new electric chiller’s with the capacity to allow system resilience for the future. It became apparent that the existing power supply for the hospital was also under pressure therefore Pick Everard approached Oceanair for alternative solutions. This project was a challenging one for a number of reasons. Oceanair proposed installing a Gas engine heat pump coupled to Plate heat exchangers to operate the chiller’s. The GHP units replaced two ageing chillers that were serving the operating theatres, the site had expanded and power was short so the consultant with the help of Oceanair selected GHP to service the chiller modules, Tony Evanson conducted a presentation to the main board to explain the benefits of GHP and carbon and energy saving capabilities.
7 x SGP-EW190M2G2W Gas engine Heat pumps
7 x SGP – WE170M1 Plate heat exchangers
A further benefit of the Sanyo units, Tony says, is their quietness, which makes them ideal for use in hospitals. Noise was likely to be a planning issue on the project, and the GHPs overcame any potential restriction. The seven GHP units, with a combined output of 392kW, were chosen from the Sanyo range for their optimum efficiency in order to minimise the hospitals liability under the carbon reduction legislation. A further benefit of the multiple system, supplied by distributor Oceanair UK, is its resilience compared with a conventional single chiller installation. The breakdown of one unit can cause disruption and affect cooling to the building, but multiple chillers mean the service can continue if a chiller fails.
The GHP units also have a much lower start-up current than standard electric chillers. The process mirrors the ignition system in a vehicle engine, which means it requires a few dozen amps to start, the manufacturer says. In contrast, a conventional chiller needs several hundred amps. In winter, the heat pump cycle is reversed, enabling the provision of high-efficiency heating to the operation theatres. Given that the theatres heating was previously supplied by steam heater batteries,
Mr Fleming says the additional cost saving on heating is significant. On top of that, the approximately 18kW of waste heat from each chiller can be harnessed for use heating hot water for the hospitals domestic supply. Each of the chillers has its own separate refrigerant-to-water heat exchanger within the building, eliminating any water on the roof and overcoming the need for trace heating, anti-freeze an water treatment chemicals. There is a further energy benefit, with the Sanyo system only one system pump is used, compared with conventional chillers, which usually require an additional chiller shunt pump or heat rejection pumps, which have a significant electrical power requirement.’
The maintenance requirement is described by Sanyo as ‘highly economical’, with service intervals every 10,500 hours-in effect, this is every two to three years.
Jeff Fleming, Head of project: “the Sanyo GHPs provided a superb solution that perfectly meets the requirements of the project. The technical support from Oceanair has been excellent throughout. “ they are experts when it comes to this technology, and helped train the hospital engineers in commissioning and optimising the systems. I would have no hesitation is using the Sanyo GHP system again.”
Tony Evanson, Managing Director - Oceanair UK: “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.”