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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Table 4: Reference parameters for the economic analysis. Parameter Unit Value Electricity cost €/MWh 20 Rate of annual increase of O&M costs % 2.0 Real investment rate (r) % 3.0

The globa l costC G(30) for each HVAC solution is thusreported in Fig. 2, divided among investment and runningcosts, including a ll expenses for opera tions and maintenances. The costs of the three HVAC solutions are reported considering the use of two different heat sources: groundwater (GW) or geothermal heat exchangers (GHX). It can be observed from reported results, that the use of groundwater is cheaper than employing geothermal heat exchanger and should be a lways preferable where groundwater is abundant and available as energy source, as in Po Va lley where Mantua is loca ted. The investment cost is higher for the mixedwa ter-air solutiondue to thehigh cost of the radiant floor for such a large space. The a ll-a ir solution is cheaper, while the delocalized HP solution a llows the lower investment cost, as smaller hydraulic distribution is neededand noAHUunits is present. The incidence of runningexpenditures on the final global cost is considerably high for the a ll-air and delocalized HPs solution. On the contrary, the mixed wa ter-air solution has lower running costs. The reason for higher a ll-air O&M costs is due to the large aeraulic distributing system, which leads to larger electricity and maintenance costs. The delocalized HP system present higherO&M costs due to a large number of HP terminals. ThoseHP units do not take advantage of the scale effect that a centralizedHP a llows in terms of performances.Moreover, havingmany HP terminals means requiring formore frequent maintenance, with rela ted human-labour costs.

0 100 200 300 400 500

Global Cost [k€]

Delocalized HP terminals (with GW)

Delocalized HP terminals (with GHX)

Radiant system and primary air (with GHX)

all-ai r system (wi th GW)

all-ai r system (wi th GHX)

Radiant system and primary air (with GW)

Investment Cost

Running Cost (O&M)

Fig. 2. Global cost (spilt in investment and running costs) for each HVAC solution over a 30-years calculation period.

6. Conclusions The presentwork represents the assessment of theenergy and economic impact of different strategies for a historical building in Mantua. The delocalized systems is the most cost-effective in terms of globa l cost on a reference period of 30 years. However, fanoperation and airflowtypically produce noise andarecharacterizedby highermaintenance costs, being indeed convenient for sporadically used spaces. On the contrary, the all-a ir system is characterized by ductingand grilles tha t are invasive fromanaesthetic point of viewfor thehistoric buildings. The radiant systemand primary a ir solution is characterizedby the similar global cost of the previous configurations, but higher investment cost, savings in opera ting costs, thus becoming convenient for frequently used spaces. The radiant floor system, coupled with an air exchange system, is a lso able to guarantee a high level of comfort, low stra tification effect and low noise impact with respect to the other solutions. From the responsiveness point of view, the all-a ir system is preferable if theheating space is characterizedbya high number of people a t the same time, but not continuously during the period of operation. On the contrary, the mixed