Nowadays the heat pump is gaining new interest thanks to recent regulations which include this technology among those able to exploit renewable energy sources in addition to the already acknowledged opportunity to achieve significant energy and economic benefits if well applied In particular the use of geothermal energy as heat source/sink looks very promising. Besides the use of ground heat exchangers and water from wells, an adequate availability of surface water can suggest its use for the heat pump especially when it is impossible the application of the other two alternatives. This is the case of the plant here reported. A heat pump installed in the historical centre of Venice and using lagoon water for the HVAC plant of a historical structure refurbished for hotel use. The plant characteristics and the adopted technical solutions are here illustrated as well as the results of an annual monitoring of the building-plant system. The experimental data have also permitted a comparison with the performances of alternative plant solutions simulated in front of the same operative conditions. For this aim the two case studies of a corresponding air source heat pump and a more traditional solution, based on condensing boilers and air cooled chillers, have been considered. The performance analysis shows a net superiority for the surface water heat pump. (C) 2015 Elsevier B.V. All rights reserved.