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San Antonio

Heating, Cooling And Preserving Historic San Antonio Missions

For the last year, researchers at the University of Texas at San Antonio have been studying the impact of air conditioning and heating at one of the city’s historic missions. The simple act of providing comfort to parishioners and tourists for the last 25 years, plus three centuries of rain and humidity, has devastated some of the frescoes on the walls of Mission Concepción.

A 266-year-old water-damaged fresco in the Mission Concepción's baptistry can barely be seen in this photo. | credit Norma Martinez / Texas Public Radio
Norma Martinez / Texas Public Radio
A 266-year-old water-damaged fresco in the Mission Concepción's baptistry can barely be seen in this photo.

Those researchers are now at the end of their year-long study and are looking to expanding it to San Antonio’s other missions.

TPR's Norma Martinez spoke with Antonio Martinez-Molina, assistant professor at the UTSA College of Architecture, Construction and Planning. He’s been collaborating with the university’s Center for Cultural Sustainability on this initiative.

NM: This particular mission, for people who might not be familiar with it, it's about three centuries old. And, three centuries ago, there was no air conditioning. It was built with the parishioners in mind for that day. Nowadays, we're more accustomed to have heating and cooling provided to us to make us comfortable. But again, those buildings were not fitted for that. So they've been since retrofitted with these HVAC units. When these instruments were installed into the mission to make things more comfortable for the parishioners, was any thought put in to what kind of damage it might actually do to the building, to the walls, to the floors?

AMM: I mean, the AC units, when they were installed, (it was) around 25 years ago. So there was not much knowledge of how they were impacting the structure — not (just) that structure, any building in the world — because their AC units were kind of new. And then now after 25 years, yes, as you were saying, we are seeing the damage that those units are creating in the preservation of our buildings. Again, these buildings were designed totally to be passive. Passive means no active systems at all, no mechanical systems. Just natural ventilation: opening windows, opening doors. People...were more accustomed or more willing to suffer a bit of Texas heat back in the time. And now we've got a little bit spoiled, if I may say, and we need to be comfortable. So 25 years ago, they installed the base unit not knowing, but now we are trying to repair the damage. So the problem is the temperature difference between the inside and outside. If we force the temperature inside at 72, 73, 75 degrees, and outside it's 105, 110, that temperature difference is...the problem. So if we reduce the time for operation of that HVAC unit so the temperature will raised a little bit, then the problem will be minimized. So we can actually raise the temperature a little bit and then the wall will suffer less.

42 sensors positioned in 10 helium balloons model natural and artificial (cooling-induced) dynamics of the entire volume of air in the church before, during, and after cooling. The air conditioning unit is located in the balcony of the Mission Concepción. | Courtesy of UTSA Strategic Communications
Courtesy of UTSA Strategic Communications
42 sensors positioned in 10 helium balloons model natural and artificial (cooling-induced) dynamics of the entire volume of air in the church before, during, and after cooling. The air conditioning unit is located in the balcony of the Mission Concepción.

NM: I know you're going to be presenting your findings on the Mission Concepción here soon, but we understand that you've also been awarded a grant to help expand that work to San Antonio's other missions. So can you tell us a little bit about that?

AMM: Sure. When we got the preliminary results from Mission Concepción, we found out that that could be a very, very common problem in this climate. So we decided to apply for a federal grant to study the other three missions — San José, San Juan, and Espada — so we can identify the problems, if they're happening, stop them before it's too late, basically. So we're going to start working on the other three missions very soon. We are actually finalizing the paperwork. So hopefully those missions don't have any damage. And if they don't, we will try to suggest to the Archdiocese of San Antonio some strategies so those problems are not happening, or if they are happening right now, try to stop them as soon as possible.

NM: Do you expect the same kind of damage that was caused at Mission Concepción to be reflected in these other missions? What I'm asking is, is their architecture the same? Are they made with the same materials, or does each mission present a distinct challenge?

AMM: Yeah, each mission is totally different because the AC units are located in a different place. Some of them, they have a different structure, not very different, but there have similarities and some things that are different. The usage is also different. Some missions, they are open to the public more often than the other ones. And also the set points for the HVAC. But every mission is a different animal. So we need to treat them with a lot of caution. They are a World Heritage Site by UNESCO. So we have only one shot. So we cannot we fail in this research and this interaction that we're going to have with these buildings. They are jewels that we have to preserve for years to come. So we need to be very, very cautious and treat them individually as what they are: pieces of art that we need to preserve for new generations.