## 2 Materials and Methods
### EAHX Performance Assessment  
Figure 4 sketches, for a typical summer day, outdoor air temperature (\(T_{\text{a0}}\)) as it enters the EAHX and EAHX exit air temperature (\(T_{\text{atL}}\)) as it leaves the EAHX. It also represents room setpoint temperature limits--\(T_{\text{US}}^{\text{U}}\) and \(T_{\text{TS}}^{\text{L}}\), with superscripts \"U\" and \"L\" standing for upper limit and lower limit, respectively, between which thermal comfort in a room is judged appropriate. Figure 4 shows that in the morning, with office rooms already being used, outdoor air temperatures (\(T_{\text{a0}}\)) are lower than the room upper setpoint temperature (\(T_{\text{Ts}}^{\text{U}}\)), allowing for free cooling with outdoor air. In the afternoon, since outdoor air temperatures exceed the upper setpoint temperature, the cooling of outdoor air becomes necessary. During nighttime, outdoor air temperatures lie below the lower setpoint temperature (\(T_{\text{TS}}^{\text{U}}\)); still, since the office building is unoccupied, there is no need for heating (actually, as described in item (n) of Table 2, during nighttime, forced ventilation with cold outdoor air can be used in combination with heavyweight building construction elements and with the soil in the buried pathway between AHU and rooms to assist daytime EAHX cooling). \begin{table}
\begin{tabular}{l p{227.6 pt}} \hline \multicolumn{2}{l}{**Diffusion of air and temperature control in the cooled rooms**} \\ \hline Generic ventilation strategy & **(i)** A 100\% fresh air system. Forced (cooled) air is supplied to the rooms at the south facade and at the reception through linear air diffusers placed along the exterior wall at floor level. Air flows to corridors and from there to the outside, exiting the building behind the south facade photovoltaic panels. \\ Pressure loss & **(k)** Linear air diffusers’ specification is such that pressure loss associated with the introduction of supply air in the rooms is negligible compared to that in the AHU and in the distribution piping. \\ Temperature control & **(l)** Temperature control in the cooled rooms is achieved by varying the air-change rate. This control is limited by outdoor air conditions and by heat transfer with the soil. The control law depends (for hot and dry conditions) on room air and room setpoint temperatures, on EAHX exit air temperature, and on outdoor air temperature. To compensate for the system lower room-to-supply-air temperature gradients, large air-change rates are allowed [10; 18]. Special attention is given to the specification of linear air diffusers so that larger airflow velocities in the room do not cause local discomfort with draught. \\ Temperature setpoint & **(m)** Adaptive comfort principles are assumed allowing free-floating room temperatures correlated to outdoor air temperatures. In other words, room setpoint temperature is allowed to vary and may be larger than setpoints typically associated with refrigeration machine cooling (\(>\)27 \({}^{\circ}\)C). \\ Nighttime ventilation & **(n)** Nighttime forced ventilation with cold outdoor air is used in two ways. Firstly, in combination with heavyweight building construction materials (insulated on the outside), making use of the walls’ and floor’s large thermal lag times to decrease room peak cooling requirements and decrease operative room temperatures. Secondly, in combination with the soil covering the insulated rectangular pathway for the distribution piping, allowing the use of the soil thermal mass to increase thermal lag times, contributing to additional daytime cooling of EAHX exit air. \\ \hline \end{tabular}
\end{table} 
Table 2: _Cont._The pattern of the EAHX exit air temperature is similar to the outside air temperature but dampened and slightly forward shifted in time. The extent of the dampening and of the forward shifting determines EAHX cooling performance. Figure 4: Sketch of outdoor air (entering the EAHX) and EAHX exit air temperatures for a typical summer day.