Ten years history of a real gas driven heat pump plant: Energetic, economic and maintenance issues based on a case study

The building named “San Nicola” belongs to the public building stock in the town of Vicenza (IT). It was built in the 15th century and, after a major refurbishment, from 1999 it hosts the Department of Management and Engineering of the University of Padova (Italy). The core of the HVAC system is a gas engine driven heat pump, integrated with condensing boilers.The paper illustrates how, once the initial problems with the control and management strategies were solved, this system led to significant primary energy savings. Upon the offer from the local district heating (DH) provider for connecting the building to the DH network, an assessment was made to compare the existing plant to this solution. The connection to the DH network would have led to an increase in operational costs on one side and in primary energy consumption on the other hand, as described in a previous work by the authors.After about 10 years of operation, while facing the need for some major maintenance both on the mechanical and the control side, the engine half-life is forthcoming. The general service office of the University of Padova, instead of the half-life maintenance, is considering a replacement of the entire generation system with a traditional electric chiller for summer cooling and the uninterrupted use of condensing boilers for winter heating.It is then worthwhile to compare, on the economic side at first and then from the energetic point of view, the present solution and the option for the future. The comparison has been based on the measured consumptions of the past years and the additional cost for extraordinary maintenance not included in the maintenance contract. The analysis proves that the choice of dismantling the actual plant is wrong, even accounting the complete renewal of the actual system with a new one of the same kind. If the loss of productivity - generated by the machine downtime in summertime - is evaluated in terms of an economic loss, the present and the future solutions are quite similar from the economic point of view.

► We illustrate the significant energy savings of a gas engine driven heat pump plant.
► Real operation and maintenance issues are considered in the analysis.
► The plant is compared with a conventional one (boilers + electrical chiller).
► Energetic and economic comparisons are done, considering real consumptions and costs.