Heading towards the nZEB through CHP+HP systems. A comparison between retrofit solutions able to increase the energy performance for the heating and domestic hot water production in residential buildings

Optimize consumptions in the field of civil construction led to define energy classes for residential buildings. To calculate the energy demand in buildings the EPgl was determined (annual consumptions per m2 of primary energy). This paper examines those technical solutions useful to optimize the energy demands for the building heating during space-heating season and domestic hot water production (thanks to energy analysis software as MC11300 and TRNSYS), and at the same time keep into consideration the financial issues that those interventions implied. The total inside heated surface of the building is 1204.00 m2, hence the inside heated volume is about 3250.80 m3. Besides the more traditional interventions (for what concerns the building envelope and its systems), the paper examined the performances of a system realized through the combination of a cogenerator (CHP) and a heat pump (HP), thus substituting the typical boilers of the buildings. CHP+HP solution increases the most the energy class of the building (from a D class with EPgl = 59.62 kW h m−2 year−1, to an A class, with EPgl = 25.64 kW h m−2 year−1), determining an annual energy saving (3114.00 € year−1) that allows to amortize installation costs (54,560.00 €) in a reasonable amount of time (15.4 years). This innovative solution in the domestic sector can be realized through retrofit interventions on existing buildings, hence lead the current house block towards nZEB with a remarkable benefits for the environment.