## 2 Materials and Methods
### The Cooling and Ventilation System
\begin{table}
\begin{tabular}{p{128.0 pt} p{128.0 pt}} \hline \hline
**EAHX** & \\ \hline Pipes & **(a)** The EAHX consists of two pipes (concrete) with 1 m diameter placed 4 m apart (distance between axes), 70 m long, buried 5.5 m deep (average depth, since pipes are sloped towards the air intake for water drainage). Water-resistant coatings prevent the transfer of water across the pipes towards/from the soil. The pipes’ inner surface coating has fungicidal and bactericidal properties to prevent the growth of mold and bacteria. \\ Air intake & **(b)** Outdoor air is admitted into the buried pipes at a technical space built above ground. A G4 filter [28] installed in this technical space prevents the intake of spores, pollen and coarse dust. \\ Vegetative cover & **(c)** To reduce soil surface temperature (during the summer period), species found in tallgrass priaries (e.g., Loiumperenne, Festuca arundinacea, Poa pratensis, Festuca rubra) were planted covering the ground above the EAHX. \\ Pressure loss & **(d)** Due to the large pipe diameter, pressure loss in the EAHX is related to the air intake filter, which, with its large surface and low face velocity, has negligible pressure loss compared to that in the AHU and in the distribution piping. \\ \hline
**AHU** & \\ \hline Generic description & **(e)** In the direction of the airflow, the EAHX consists of a mixing chamber fitted with registers to allow for EAHX bypass with outdoor air (not used in this study), an M5 filter [28], a heating coil (not used in this study), two fans, a silencer and, prior to the air distribution to the rooms, a final F7 filter [28] for fine dust particles (1\(\sim\)10 μm), preventing the distribution into rooms of bacteria and germs carried on host particles. As for the EAHX air intake, a coarse G4 filter is used at the bypass outdoor air intake. AHU dimensions were intentionally oversized to reduce pressure loss. \\ Fans & **(f)** To supply a nominal flowrate of 8000 m\({}^{3}\)/h of air to the rooms, a redundant set of two electrically commutated plug fans (IE5) with 3.6 kW rated power each are used. \\ Pressure loss & **(g)** Design pressure loss in the AHU is 325 Pa. \\ \hline
**Distribution piping** & \\ \hline Generic description & **(h)** Cooled air is distributed to the rooms using high-density polyethylene (HDPE) corrugated pipes with varying diameters (\(<\)0.40 m) laid along the south facade of the building. Pipes run inside a rectangular pathway, buried 3.0 to 1.5 m deep, made of cement (bottom) and cement blocks (side walls). This pathway is (inside) insulated with XPS (60 mm), limiting heat loss to the soil (through the sides and bottom). \\ Pressure loss & **(i)** Design pressure loss in the distribution piping is 375 Pa. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Cooling and ventilation system specifications. Figure 2: Outline schematic of the cooling and ventilation system. A photograph of the EAHX during construction is presented in Figure 3. This photograph shows a trench, the EAHX air intake at the start of the trench and two parallel pipes leaving this air intake towards the air handling unit (the latter not visible). Sketches of the air intake technical space built above ground and of the airflow pathway in the pipes were superimposed onto the photograph.