**4. Monitoring**

In parallel, the authors have conducted a thorough monitoring campaign to modulate the range of the simulations and at the same time to check the usefulness of their outputs. We have to outline that the objective validation of our simulation program has taken place beforehand in other controlled experiments and test chambers [12–23].

To perform the evaluation, we installed data loggers in Saint Louis to monitor the dry bulb temperature, mean radiant temperature and relative humidity. The sensors were Onset models U12-012, UX 120-006 M and TMC6-HD, with data recorded every ten minutes. Temperature sensors had a measuring range from 0 to +100 ◦C and an accuracy of ±0.5 ◦C. The calibration before taking the measurements guaranteed the proper functionality of the setup.

Accumulative measures of light are not helpful from a spatial point of view, one-time measurements conducted simultaneously at a ground-floor grid work usually better. To that end, we have used a lux-meter PCE-170A with ISO calibration, a measuring range from 0 to 40,000 lux and an accuracy of ±0.3%. Of those, we present a comparison with simulated values for partly cloudy sky, which correspond well by not showing relevant discrepancies (Figures 12 and 13). The correlation coefficient of east-west and north-south main axis are 0.93 and 0.92, respectively.

The slight differences registered between simulated and measured data are presumably due to the event that on the days of performance of the experiments, as the sky was partly cloudy, some sunlight filtered from the southern fenestration increasing the levels on the north niche (bottom side in the graph). Besides, the main façade of the church faces east and through the upper choir perceptible intensities appear around midday but these were deliberately taken out of the simulation. The latter would explain minor augments of level near the entrance area to the east (left side of the figure).

**Figure 12.** Comparison of measured and simulated data for partly cloudy sky at midday on 21 December. 0 m corresponds to the central point of the church: (**a**) east-west axis, from entrance (left) to the altar (right). (**b**) south-north axis, from right to left respectively. Source: Almodovar-Melendo.

**Figure 13.** Extension of Figure 12, measurements effected at the ground floor in winter solstice at 12 h. Source: Cabeza-Laïnez.

We investigated other sky plus sun conditions with occasional registers, these showing the reliability of the simulations. As stated above, the model has been validated in previous campaigns of projects with straight parallelepiped shapes in laboratory-like conditions and for that reasons we are not in the position here to offer a full-range validation for such unusual architecture, as is this church.

In order to discuss the environmental performance of the building, measured daylighting values have been correlated to other environmental parameters such as temperature and relative humidity, relevant for the IEQ of the building [33,34]. Measurement data registered during the summer show that the lighting values are in a range of 200 to 400 lux, by all standards a steady level of lighting apt for the majority of visual tasks. On the other hand, we identified consistent temperatures nearing 25 ◦C in the floor level of the nave, at a time in which external shade temperature can reach 45 ◦C or even more on the north face of the cylindrical drum (Figure 14). This means that such adequate illumination is not attained by means of discomfort or excessive overheating, as is the case of so many contemporary buildings, fully glazed. Shading devices are generally not required in this kind of structure. However, we found photographs of late 1920s in which the tall windows were shaded from the inside with fabrics, a curiosity which may attest to the significant amount of light that impinges on the lower levels of the compound.

Theretofore, the property of the capacitive mass of this masonry and tile (ceramics) building is noticeable. Moreover, the low ratio of window to total surface area (under 10% as previously mentioned) averts excessive solar gains and contributes to obtain an optimal thermal performance. In this regard, we have to remind that daylight is the lighting source with the best light to heat ratio (up to 160 lumen/W).

The indoor relative humidity remained around 50% during the daily cycle though it could increase slightly at night.

Similar monitoring results were obtained by the authors at another baroque paradigm, the church of San Lorenzo in Turin (Italy) by Guarino Guarini (Figure 15). However, this temple is located almost 10 degrees more to the north than Saint Louis and markedly receives less solar radiation.

**Figure 14.** Temperature measured at the Church in summer to check overheating effects: (**a**) external temperature at the dome, (**b**) internal temperature at floor level near the altar. Notice that when external temperature in the north face of the drum reaches a scorching 50 ◦C, at the altar zone we measured a much cooler maximum of 26 ◦C. Source: authors.

**Figure 15.** Clear Sky monitoring in April at the famous church by C. G. Guarini. Turin. Lat. 45◦6 N. Source: Cabeza-Laïnez.

### **5. Discussion of the Results**

Due to the particular orientation of the church that defies the postulate of the longitudinal West-East axis from entrance to altar, which presided over European architecture until late Renaissance; the solar events like solstices and equinoxes are critical to define the performance of the central space under consideration. In fact, the fenestrated cylindrical drum allows the capture of solar radiation impinging from every solar position and suppresses the absolute necessity of offering a southern façade to achieve solar gains for natural heating and lighting, especially in winter, as was the case of Gothic architecture in England, France and Germany. The inner cylinder so to speak funnels direct solar radiation and due to its considerable height, it seldom permits the sunrays from reaching the floor level avoiding visual discomfort to the visitors.

In each case, we have investigated two situations: overcast conditions (isotropic but with hourly and monthly variation (Figure 16) and clear sky with sun (where orientation and hourly/monthly variations are mandatory). The first condition refers to conventional models for cold climates while the second condition is more innovative and typical of warmer regions but many simulation programs are unable to deal with it not to mention with the occurrence of curved surfaces (Figures 17–19). The daylighting levels have been calculated in a plane located 1 m above the floor, a position deemed for a sitting person.

Spectroscopy analyses were necessary to evaluate the reflective coefficients for this simulation. To this aim the authors conducted several on site tests. Such values tend to differ from those suggested by conventional colour charts, because ageing, candle fumes or inadequate refurbishments may have altered the original condition of the veneers.

**Figure 16.** Cloudy Sky at midday in winter. Source: Almodovar-Melendo and Cabeza-Laïnez.

One of the most unfavourable cases occurs in winter under cloudy sky condition. Even so, the average value is more than 80 lux (Figure 16) which is considered sufficient to perform basic tasks even with modern standards. The light field is rather homogeneous (from 120 to 80 lux) in the central nave and presents a marked axial symmetry appropriate for the liturgy and reinforcement of the design intentions. The minimum levels remain well over 50 lux.

In spring, the situation is much enhanced, as even in the mornings or afternoons the mean illuminance is about 150 lux and values lying in the range from 200 to 300 lux are easily reached (Figure 17). At noon (Figure 18) the average level is over 200 lux and a maximum of circa 1000 lux can be found in several points, the light is more varied but without abrupt contrasts in a soft progression from 200 to 500 lux towards the north niche where the sun impinges during the equinox.

The cloudy sky condition is slightly lower in its intensities but we have not presented that here since it is untypical of Seville in spring and autumn, its probability of occurrence is of 18% according to meteorological data; even so minimum values remain over 50 lux.

In summer, the mean illuminance lies in the range of 150 lux in early morning and late afternoon (Figure 19) and reaches 250 lux at noon.

If, following with the discussion on the simulations, we refer below to the vertical component of the radiation vector; the simulations show an interesting performance of light in the more likely event in Seville of enjoying a clear sky with direct sun (Figure 20). According to a TMY (typical meteorological year) of Seville provided in the software Energy Plus and derived from the Spanish Weather for Energy Calculations (SWEC), the probability of occurrence of non-clear skies in spring, autumn and summer combined is of 11%.

The illumination sectional vector keeps at an angle of around 45 degrees (which means it is not too steep), this clearly allows for distinct perception of artworks and wall decorations unlike Roman pantheon and derived churches like San Bernardo alle Terme (built under the dome of an ancient thermal bath).

**Figure 17.** Spring clear sky with sun. Probability of 74% (76% in autumn). The graph is symmetric at 15.15 h. Source: Almodovar-Melendo and Cabeza-Laïnez.

**Figure 18.** Spring clear sky with sun at midday, at some spots values of 1000 lux are registered. Source: Almodovar-Melendo and Cabeza-Laïnez.

**Figure 19.** Summer Clear Sky with sun. Symmetric with 8.45 h. Source: Almodovar-Melendo and Cabeza-Laïnez.

**Figure 20.** Daylight Section at the spring equinox with sun, midday. Values reach 300 lux at floor level. Source: Cabeza-Laïnez and Almodovar-Melendo.

Such character is less pronounced for the infrequent case of cloudy skies but can still be perceived and it has been checked against monitoring (Figure 21).

To sum up, the results examined from Figures 16–21 show that the daylighting field is balanced; with a range of around 100 lux in plan for cloudy sky in winter. In other sky conditions, values exceeding 300 lux can be amply found and over 200 lux are guaranteed in the central circle of the nave for a 56% of the total daytime. To clarify the results, we have compared in Figure 22 simulated data in Summer, Spring and Winter for clear sky with sun.

The vertical situation of lighting also facilitates orientation and perception of the space and adds variety or spark in the disposition of liturgical spaces for Southern Spain. In a famous poem (by Angel Camacho), dating from 1733 the church of Saint Louis was compared, precisely for its lighting features, to the temples of Jerusalem and Zorobadel in ancient Babylon.

**Figure 21.** Daylight Section at the spring equinox in a cloudy situation. Maximum values of 200 lux on the ground. Source: Cabeza-Laïnez and Almodovar-Melendo.

**Figure 22.** Comparison of simulated data for a clear sky with sun at midday: (**a**) east-west axis, from entrance (left) to the altar (right). (**b**) south-north axis, from right to left respectively. Source: Almodovar-Melendo.

Coming back on the figures to describe this considerable success of religious architecture, the small proportion of window to total surface area (less than 10%) alongside with the low latitude of Seville (37◦22 N) may lead to such admirable results. We should notice that the values in this church are comparatively less than at its earlier baroque counterparts, which were mostly built in temperate north-central Italy and thus using wider fenestration in disregard of the heat.

Such could be the upfront explanation for the subdued illuminance levels attained on the inside of the Saint Louis temple. Especially if we compare them with some jewels of Roman Baroque (Figure 23), like Sant'Ivo by Borromini, the church at the site of ancient University of Rome and mainly Sant'Andrea by Bernini (Figure 24), an oval shaped masterpiece and not casually commissioned by the Jesuits as well.

So far, the analysis performed by the authors permit to trace a sure-handed line in the evolution of centralized temples pertaining to the baroque era. Such line is deeply chiselled in what we may call a proto-scientific artisanship of light within space.

**Figure 23.** Simulations at Sant'Ivo by Borromini in Rome. December at 9:55 am. Clear sky plus sun. Source: Almodovar-Melendo.

**Figure 24.** Simulations at Sant'Andrea by Bernini in Rome. Summer solstice. Source: Cabeza-Laïnez.

As we have clearly seen, sundry environmental and historical design strategies such as lighting, thermal comfort, et cetera, do intertwine in this analysis whilst at the same time they recall human and cultural nuances of architecture. For instance, the introduction of gilding and reflective specular veneers is critical in maintaining an acceptable visual perception with a restrained glazed surface. Such design features contribute to overcoming a situation perhaps created by an excessive seclusion from external climatic conditions.

Moreover, we confirm that the hypothesis by which the galleries of the nave were used as a place of study for the novices is plausible given the bright atmosphere that is achieved at the upper levels and the accuracy in which the educational and liturgical details of the interior of the dome cum drum are perceived from above.
