PSI - Issue 29

Alessandro Miglioli et al. / Procedia Structural Integrity 29 (2020) 118–125 Mignoli et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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The annual electricity demand adopting the a ll-a ir system resulted equal to 66 MWh/year and was ca lculated considering an overall efficiency for distribution, regula tion and emission systems equal to 85%, heat pump COP ca lculated on forecasted operating temperatures and ra ted electric power of auxiliaries equal to 6 kW. The total primary energy demand resulted equal to 142 MWh/year, considering a primary energy conversion factor equal to 2.16 as reportedby theItalianelectricityand as authority (2008). 4.2. Radiant systemandprimary air The second configuration consists of a hydronic radiant systemcoupledwith anair-based system for air renovation. The a irflowra te is adjusted to provide only the requireda ir exchange, with thermally neutral characteristics compared to the ambient set-point. The sensible thermal load is provided through a radiant floor heating system. In this sense, lightweight modular elements can beadopted, beingweakly inertial and allowing therefore formore rapid operations than traditional radiant elements. This solution is, therefore, able to sa tisfy the demand for local comfort without significantly a ltering the internal thermo-hygrometric conditions. The low opera tive temperature of the radiant terminals a llows maximising theconversionefficiencyof the water-sourceHPwhich is connected to thehot andcold ba tteries of theAHU. The la tter, unlike the first configuration, has a smaller size, i.e. 6000 m 3 /h total and is equipped with recircula tion to ensure hygrometric control of the room. As in the previous case, both groundwater and geothermal probes canbe adopted forwa ter supply to theHP. This HVAC solution constitutes a mixed type systemwith both hydronic and aeraulic terminals which are able to meet both winter and summer needs. This system indeed guarantees adequate a ir renovation according to the actual occupationandmetabolic activitycarried out, as well as high levels of comfort andpollutant control. The annual electricity demand adopting the mixed radiant andprimarya ir system resulted equal to 45 MWh/year and was calculatedconsideringan overall efficiency for distribution, regula tion andemission systems equal to 87%, hea t pumpCOP calculated on forecastedoperating temperatures and ra tedelectric power of auxiliaries equal to 6 kW. The total primary energy demand resultedequal to 98 MWh/year. 4.3. Delocalized water/air heat pump terminals The proposed configuration consists of the use of deloca lized wa ter/air hea t pump terminals, connected to a hydronic loop which is indirectly fed by groundwater or by a closed wa ter circuit of geothermal probes. Thoseheat pump systems cover sensible and la tent energy demand, while two air exchangeunits each of 3000m 3 /hwith localized hea t recovery (HR) are responsible for the fresha ir supply. In detail, 15 heat pump terminals of approximatively 5 kWof nominal thermal power are expected tobe installed. These units are positioned in the thickness of thefloor. Emission terminals will be wa ter condensedandconnected to a hydronic ring fed bywa ter fromgroundwaterwells or vertica l geothermal probes, beinga lsoable to operate in free cooling, as conventional fan-coil units. Fina lly, flow temperatures of the individual a ir conditioning terminals can regula te according to the boundary conditions. This solution is characterizedby very lowinvasiveness, a llowing for the control of heating/cooling loadandhumidityaccording to the needs, while containingenergy consumption. The annual electricity demandadoptingdelocalized water/air heat pumps result ed equal to 42 MWh/year andwas ca lculated consideringanoverall efficiency for distribution, regulation andemission systems equal to 84%, heat pump COP ca lculatedon forecasted operating temperatures and ra tedelectric power of auxiliaries equal to 3 kW. The total primary energy demand resultedequal to 91 MWh/year. 5. Global-cost analysis A cost-analysis was carried out in order to evaluate the cost-effectiveness of each proposed solution. The global cost (C G ) during a reference lifetime was calculated accounting the initia l investment cost and the annual operation