Raspberry Pi is the platform of choice.

Although closer to a decision on an energy monitoring system for the project house the more I research, the more I discover alternative solutions!  However, the JeeLabs JeeNode still looks favourite for the remote wireless data logging devices. The basic cost is approximately 18.50 euros but to this must be added a few extra components such as a case and battery supply. The next step is deciding on the central management system which appears to be a choice between an Arduino or Raspberry Pi based system. Both have their advantages and disadvantages. The requirement is to log readings, record in a data base and process to calculate such information as degree days from the raw data. Also important is the ability to manage the system remotely, via a browser if possible which implies TCPIP network connectivity.

The Arduino is a very popular platform designed specifically for interfacing with sensors and for controlling external devices. It is programmed through a special program, an integrated development environment (IDE) that runs on a PC. Overall very good for dedicated control applications with a large user community but I think want more flexibility than that. 

The Raspberry Pi, on the other hand, is a more general purpose platform. It runs Linux which is an operating system that is used extensively for commercial IT systems. It is a computer that can be both a development and operating environment in one and so doesn't need an external IDE. Overall, it probably has less support currently for control and management applications and looks more complex to program. That said, support information and products for the Raspberry Pi monitoring system have been found so the convenience of everything in one low cost unit is the deciding factor.

Despite an extensive range of available products one area that does not seem well covered is the packaging of the various electronic devices. The electronics will need housing in suitable cases. One intriguing solution that was found was to convert an Airwick room freshener to house a JeeNode. Details can be found here.