Microclimatic and Ventilation Conditions in Existing Healthcare Facilities. A Study in the Waiting Room-Testing Centre of a Florentine Historic Hospital

It is well known that energy efficiency is a common task for buildings and related plant systems, but the issue concerning health risk prevention deriving from environmental and pollution factors, microorganism dispersion and environmental and surface contamination, has become a priority, so much so that it requires the involvement of different competent subjects and imposes an integrated interdisciplinary approach [1-7]. On the other hand, among stakeholders, researchers, technicians and public decision makers, awareness of the importance of indoor air quality (IAQ) for guaranteeing people's health and wellbeing is on the increase [8]. Crucial findings have been discussed by recent literature and research concerning experimental and simulated investigation on IAQ, effective ventilation, and occupant behaviour and satisfaction inside historic, existing and newly designed energy-efficient buildings. These studies highlighted the fact that low energy consumption, IAQ, efficiency and efficacy of different air flow patterns and behaviour and self-reported occupant wellbeing can be obtained by integrating solutions for building physics improvement and controlled mechanical ventilation systems [9-12]. Moreover, the current standards and provisions on IAQ, controlled mechanical ventilation, hygiene, health and prevention of contagion risks, imposed by international and national organizations (i.e. WHO, ASHRAE, RHEVA, AICARR and ISS), suggest that heating, ventilation and air conditioning plants (HVAC) must be working 24 hours a day and continuously 7 days a week, without air recirculation and possibly with night attenuation also provided for periods of environmental non-occupation [13-23]. As a consequence, controlled mechanical ventilation systems must be equipped with high air filtration systems without recirculation and with large air flows to be treated. Most of the literature on this subject shows how the IAQ and infection risks are closely related to the air flow field and specific air flow patterns, internal pressure regimes, indoor thermo-hygrometric conditions, air filtration systems, as well as the correct maintenance and cleaning of plants and their components [1, 11]. Therefore, plant adaptation, retrofitting and refurbishment design solutions for existing buildings and in some cases that are also historical and also subject to protection and conservation constraints, are very complex issues. Any intervention solution must find a compromise between energy saving, energy costs necessary to ensure ventilation effectiveness and air quality, health protection of people and cultural heritage objects. Physical distancing and the increase in natural ventilation, both with automatic and manual techniques, are not sufficient to ensure health protection and reduction of contagion and contamination risks.

In this research, a methodological approach based on the combination of physical-real and “virtual”, i.e. measured and simulated information, is developed. The proposed method can therefore be a useful tool for setting up continuous monitoring systems on microclimate and ventilation systems, on user influx/presence and his behaviour, on the real operation (on demand) of the plants and control systems and their adjustment/management. The results obtained show the importance of drawing up useful guidelines for subject (i.e. health workers and people/patients) training and orientation towards a conscious interaction for health protection and wellbeing, but also for better management of environmental quality, which is particularly important for healthcare ambient such as the one studied.

The experimental measurement campaign was carried out during a short time period due to access problems connected to this type of environment and all the limitations subsequently imposed by the COVID-19 pandemia, that we are still experiencing. The period is short but representative of a typical working week (from 12 March to 29 March 2019). A measurement protocol and experimental set-up were defined to obtain sequentiality, continuity and repetitiveness of the measurements, both in the waiting room and corridor. A time step of 5 minutes was fixed for data acquisition and recording. This fact allowed taking into account the influence of the sliding doors opening and closing and people passage.

An initial investigation was carried out with a survey using an infrared FLIR camera. In Figure 2 some significant results of this investigation are shown. The main microclimatic parameters were measured: in the waiting room with a multifunction thermo-anemometer fixed to the reinforcement chain of the cross vault, so as not to hinder the activity carried out within the environment, and in a particular position that is not affected by the influence of the air supply diffusers and/or the sliding doors; in the corridor with two Tinytags positioned on the sign support and on the ceiling light grid. Figure 3 shows the instrument location and measuring points. Technical characteristics of the instruments used are given in Table 1.

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Figure 2. FLIR infrared camera measurements: test areas (left) and the corresponding samples of IR images (right)

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Figure 3. Instruments locations a) thermoanemometer (T1), tinytags (TAG1 and TAG2) in a plan view; b), c), d) respectively, photos: (T1), TAG1 and TAG2

Table 1. Technical characteristics of the used instruments

3.1 Experimental results

In this section experimental results on the waiting room microclimate are analysed and discussed.  Table 2 provides the analysis of the microclimatic parameters obtained during the monitoring campaign: measured data reability and accuracy can be noted. The mean air temperature in the corridors, but especially in the waiting room, as well as the air velocity value, agree with those suggested [13-24]. However, the relative humidity values are generally lower.

Table 2. Microclimatic parameters analysis

Figure 4 a, b shows the trends of the mean air temperature and relative humidity of the waiting room and corridor, in comparison with the corresponding trends of the air temperature and relative humidity in the external environment, during the coldest day of the monitoring campaign. It can be noted, especially during the central hours of the day, how the internal air temperature of the waiting room is affected by the mutual influence between people influx, door opening and closing phases, and higher values of the external air temperature.

In the corridor this value is always lower, both because this is a zone characterized by continuous people passage, and due to the greater influence of the sliding doors opening and closing.

An appreciable effect of thermal-buffer and humidity-damping of the corridor on the thermo-hygrometric conditions of the waiting room, compared to the external climatic conditions, is evident if the trend of the relative humidity values is taken into account (Figure 4 a, b).

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(a)

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(b)

Figure 4. Hourly data of the air temperature (a), the air relative humidity (b), measured in the waiting room and corridor in relation to the real data for the coldest day of the experimental campaign

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Figure 5. CFD simulation results for the max people presence condition: a), b) air velocity field at two different section planes; c), d) air temperature distribution at two different section planes

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Figure 6. CFD simulation results for the min people presence condition: a), b) air velocity field at two different section planes; c), d) air temperature distribution at two different section planes

In this section, all the results obtained by transient CFD simulations for the characteristic day and for the two conditions of maximum and minimum people presence are analysed and discussed. Figures 5 and 6 show respectively the air velocity field on different section planes for the condition of maximum and minimum people presence: in the first condition, the effect of short-circuiting and partial air stagnation in the occupied zone can be noted.

This effect is absent for minimum people presence condition. In this last condition, the air velocity field is much more uniform throughout the volume of the environment with relatively higher velocity values near the ceiling, where the Coanda Effect, the shape of the jet and the effect of the launch length from the delivery diffusers, combined with the different temperature distributions, are particularly evident (Figures 5, 6).

These effects can be noted in the distribution maps of the local average air age (LMA) (Figure 7). LMA is one of the most important parameters to evaluate the ventilation efficiency and/or contaminants removal and to quantify the average lifetime of air at a closed space for a steady airflow achieved. The local air age concept expresses the average time for air to travel from a supply inlet area to any location in a forced ventilated room: lower values are more favourable. At the inlet opening it was assumed to be zero (100% fresh). The average value of LMA was computed in the occupied zone at the two conditions of max and min people presence.

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Figure 7. CFD simulation results. a), b) mean air age at two different section planes for the max people presence condition; c), d) mean air age at two different section planes for the min people presence condition

Comparison of these values with the theoretical residence time of air inside the room (i.e. the ratio between the total volume of the room and the mass flow rate of incoming ventilating air), provided the fundamentals for the Air Exchange Efficiency (AEE) index computation. In particular, applying a zonal method and referring to the LMA results obtained for the occupied zone, the AEE by means of the post-processing CFD results in the occupied zone was calculated as follows:

$A E E=\frac{(1 / A C H) \text { real }}{L M A_{\text {calculated }}}$     (1)

For the max and min people presence condition, the AEE obtained was respectively 0,768 and 1,326. This fact means that in the condition of max people presence with EEE <1 (i.e. 0.768) a partial short-circuit of the air with stagnation zones, happens, in particular, in the sitting zone. It can be noted that the air flow pattern in the total volume of the room is strongly conditioned by the subzones with inadequate and insufficient ventilation (Figure 7). Considering the air temperature distribution, it can be noted that for the max people presence condition, the values are on average higher, both in the total environment, and in the sitting zone, compared to those obtained for the min people presence condition (Figure 7). As expected, the zone near the double glazed wall, facing South-West, has lower air temperature values for both conditions. For people wellbeing evaluation, strictly connected to the air quality due to ventilation effectiveness, the Effective Draft Temperature (EDT) was calculated for both the max and min people presence conditions. By means of the CFD results post-processing for the sitting zone, the local average values of the air temperature and air velocity were calculated. Therefore, the following equation for EDT was used:

$E D T=\left(T_{i}-T_{a}\right)-0,8 *\left(v_{\text {mean }}-0,15\right)$     (2)

with T_i mean air temperature in the sub-volume/zone considered, T_a mean air temperature in the environment/total-volume (e.g. the HVAC system set-point value) and v_mean mean air velocity in the considered sub-volume/zone.

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Figure 8. CFD simulation results. a) PMV at the max people presence condition; b) PMV at the min people presence condition

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Figure 9. CFD simulation results. a) operative air temperature at the max people presence condition; b) operative air temperature at the min people presence condition

Usually, the optimal EDT value, which guarantees comfort conditions for people with poor metabolic activity and sessions, is in the range -1.7℃ and 1.1℃ [28, 29]. For the condition of max people presence, EDT was 0.98 and for the min people presence was -0.12. These results confirm those obtained by the VMP and PPD maps (Figure 8). Although the relative humidity is generally low (a condition imposed on the regulation and control system, as indicated by the technical office), the wellbeing conditions for the occupants are still guaranteed, as can be seen from the PMV and PPD distribution (Figure 8) and operative temperature distribution (Figure 9).

The zone around the large glazed surface shows local discomfort, as expected from the analysis of the building's thermo-physical behaviour. From result comparisons, it can be seen how the air motion field, temperature distribution and trend of the mean air age both for precautionary conditions of max people presence, and for the min people presence condition with physical distancing and limited entrances, the HVAC system guarantees air quality, good ventilation and comfortable conditions for occupants.

In particular, ventilation effectiveness and air washing are present in both conditions studied, but with better results for the min people presence condition.