625kW propane chiller keeps Westminster cool

In 2007, a 625kW air-cooled water chiller using hydrocarbon refrigerant R290 (propane) was supplied for comfort air conditioning by Earthcare at the historic Church House building in Westminster, London, close to the Houses of Parliament. “This project proved that larger hydrocarbon chillers can be used safely in the urban environment. Since commissioning, the chiller has been completely uneventful, providing reliable cooling and achieving the predicted energy efficiency. The subsequent project for the DEFRA VLA at Weybridge proves the commercial viability of our range” said Nicholas Cox, Managing Director of Earthcare, to hydrocarbons21.com.

The chiller installed at Westminster is part of the Earthcare Hydrocarbon Series (EHS) range which was designed within the constraints of the EU’s Best Available Technology (BAT) protocol and comprised the first set of air-cooled chillers operating on hydrocarbon refrigerants to deliver very large cooling outputs of up to 1,265kW. The chiller at Westminster, Britain’s largest ever hydrocarbon refrigerant chiller for a building services application, was specified by Max Fordham consulting engineers, while the installation was carried out by AMEC.

Reducing both direct and indirect emissions

Through the use of hydrocarbon refrigerant R290, a replacement for R22, the chiller’s global warming impact is minimised.

What is more, the chiller’s indirect emissions related to the energy use of the system are minimised through a series of features, which achieve potential energy savings in excess of 50% for chillers that operate year round when compared to minimum first cost chillers without energy saving features. More specifically, the energy efficiency measures of the hydrocarbon chiller include:

• R290 favourable thermodynamic characteristics as a refrigerant
   
• the use of subcooling circuits which improve the coefficient of performance
   
• floating head pressure control that allows the condensing temperature to float as low as 20°C if ambient conditions allow, instead of the normal 40°C

According to the Westminster project life cycle cost analysis, the chiller’s COP amounts to 4.15 compared to a value of 2.82 for an HFC134a chiller. Assuming energy cost of 0.063 £/KWh and given capital cost differences between the two systems, an estimated £56,990 can be saved after running the system for 10 years. According to Earthcare, mass production could allow hydrocarbons chillers to be produced for a premium of less than 10% over HFC chillers, while the company believes that there will be increased demand for this type of solution as, until now, specifiers and users of screw compressor chillers have been restricted to choosing between expensive ammonia chillers or HFC chillers.

Technical challenges

The technical challenge in developing the hydrocarbon chillers has been to achieve compliance with the safety regulations governing the use of flammable refrigerants. The most time-consuming element was optimising the selection of compressors, heat exchangers and valves, initially related to difficulties in obtaining data regarding the components and subsequently to obtaining CE marked components.