Sony City uses waste heat from sewage treatment plant

Heat pump reduces energy and water consumption dramatically

When talking about a heat pump, most people will think of a system taking heat at low temperature from the ground, the air, or a water reservoir. However, other configurations are possible. Sony City, the new Sony headquarters in Tokyo, receives heating and cooling from a heat pump connected to a nearby sewage water treatment plant.

By recycling the heat from the sewage plant, the system achieves a Coefficient of Performance (COP) of 5.19, which is exceptionally high. It means that the building receives 5.19 units of energy for each unit of primary energy that is consumed.

A CO₂ emission reduction of 70%

This unique system is described in a case story by the World Business Council for Sustainable Development (WBCSD). The system supplies hot water at 43°C in wintertime, while in summer, a centrifugal chiller connected to the system supplies cold water at 7°C. Both hot and cold water systems contain a large buffer reservoir. Compared to a conventional system with a natural gas boiler and an absorption chiller, this heat pump saves 70% of CO₂ emissions (3,500 tons of CO₂/year) and 92% of clean water consumption (107,800 m³/year). To reduce electricity peak demand during the day, the heat pump is coupled to a sodium-sulphur (NAS) electric battery with an output capacity of 2.5 MW. It stores electricity at night and discharges the stored electricity during the day.

Practical and financial barriers

It is a pity that the case story by the WBCSD contains so few technical details about the system, since it seems to be a truly unique concept. What the WBCSD case does describe are the barriers encountered while developing this project. Apparently, 'developing a procedure to use public facilities for private use took up much of the project’s time' and 'the plan had to be submitted to the Tokyo Metropolitan Government for approval, which proved to be a big challenge'. Apart from that, the high construction cost of such a facility will represent another hurdle for other potential users, even if the Internal Rate of Return of the installation is high.

Partnership with a utility company

Sony has developed this project in cooperation with the local utility Tokyo Electric Power Company (TEPCO). The two companies have been working together in a partnership since 1992, which has been a key factor in Sony’s energy savings campaign. Since 2002, TEPCO has developed several heat pump systems for Sony’s technological centres throughout Japan. The coefficient of performance of those heat pumps has been increasing steadily, culminating in this recent project for Sony City.

References

• Article 'High-efficiency Heat Pumps: TEPCO' on the WBCSD Website
• Case study 'High-efficiency Heat Pumps' on the WBCSD Website
• Sustainability Report Tepco 2005