Daily, monthly and seasonal energy performances and economic assessment on the coupling of an earth to air heat exchanger to an already existing HVAC system: A case study for Italian cities

The main aim of the investigation introduced in this paper is to analyze and identify the energy saving and the economic return deriving from the investment of placing an Earth to Air Heat eXchanger (EAHX) as pretreatment unit of a HVAC system serving buildings of a company operating in the industrial sector in Italy. This hybrid system is aimed to take advantage of the heat capacity of the soil surrounding some buried pipes for passively preheating and/or precooling the air before it is ventilated into the building. The buried pipes can then provide preheated and/or precooled air to improve the energy performance of the HVAC system, and ultimately to ensure indoor thermal comfort conditions. The company has various offices in Italy and so a the hourly, daily, monthly, yearly performances of the EAHX, the energy saving of the hypnotized solution with respect to the base HVAC configuration, as well as the economic impact of the investment in terms of payback time and net present value have been investigated and a comparison among different climatic zones of Italy is reported. To perform the above-mentioned objectives a two-dimensional numerical model of a dominium including the soil, the surface and the buried tubes of the EAHX is introduced. The model, experimentally validated and solved through the Finite Element Method, is forced with dynamic boundary conditions on the intensity of the solar radiation and on temperature and relative humidity of the external air entering the tubes, for many Italian localities. The employment of the EAHX in the HVAC reduces the energy consumptions in the various considered Italian climatic zones from: −30 % to −45 % in heating mode; from −23 % up to −43 % in cooling mode. From an economic point of view, the investment at the end of lifetime (25 years) is always positive and it has a discrete return in all the cases investigated.