Indoor Environmental Chamber
Effect of air pollutants on cultural heritage buildings has been an emerging issue in the recent years. Conducting field tests to investigate the same has many social, economic and technical constraints. Alternatively, the environmental chambers can easily help us in serving the purpose of testing the construction materials under variable meteorological conditions and identify reasons to take necessary actions. This article focuses mainly on estimation of effects of air pollutants on building materials using ‘Environmental Control Chamber’ and its design...
The Indoor Air Quality (IAQ) not only affects the human health but also the building materials. Earlier main concern of improving air quality was to prevent the human from dangerous health issues, but in recent years the focus has been made on the degradation of building materials due to environmental pollutant like SO2, NO2 and VOCs (Arizzi et al 2012; Haneef et al, 1992). This shift in focus has taken place in order to safeguard the cultural heritage buildings, ancient temples, cathedral (churches) and ancient buildings, where the damage is impossible to recover.
This damaging effect of air pollution on building material have been known from a long time and in the western countries. Moreover, the United Nation Economic Commission (UNEC) has also initiated the assessment of effect of air pollution on material deterioration including monuments and heritage buildings. In order to address this problem, a tubular type environmental chamber has been designed and fabricated. The chamber has a facility to vary the flow parameters as well as the meteorological parameters. Test samples are exposed by placing them on a sample stand, which is arranged in such a way that the uniform flow strikes the samples.
Thus, the behaviour of test samples exposed to different environmental conditions are studied over a period of time (Ausset et al, 1996; Ausset et al, 1999). Further, the exposure of the pollutants is estimated by gravimetric and microscopic techniques.
Types of indoor environmental chambers
Depending up on the objectives of the research, the environmental chambers are classified under various categories. Table 1 shows the various categories and types of the Environmental Chambers.
Figure 1. Environmental Chamber and its Equipments... Fig (a) is the Flue Gas Analyzer, (b) Thermostat (Temperature controller), (c) Rotameter, (d) The SO2, NO2 Aluminium Cylinders, (e) Outlet, (f) Probe of Flue Gas Analyzer, (g) Relative Humidity & Temperature Traceable Instrument, (h) Hot Wire Anemometer.
Figure 1 shows the environmental chamber and its equipments. The environmental chamber is of medium size and having volume of 350 liters approximately. It is made up of Acrylic sheets and it is equipped with good, durable, inert, more accurate measurable equipments. The features of the chamber are:
• Speed regulating mechanism
• Uniform flow designed by perforation plates
• Sample placing assembly
• Concentration monitoring
• Temperature monitoring
• Humidity control and monitoring
• Annular design for achieving streamlined flow
• Reciruclated/one time flow configurations
The test facility consists of an air tight annular chamber, sampling manifolds, gas inlet and outlet probes. Temperature, humidity, and air exchange rate are monitored and controlled by individual devices. Material samples in cuboid shape have been used as test species. The samples are then analysed gravimetrically and by using XRD techniques to check the absorption and reactivity of the pollutants on to the material surface. Environmental parameters were chosen to reflect typical urban hot spot conditions.
The pollutant gas can flow and recirculate inside the annular chamber by the help of fan (which is fixed inside the chamber). The flow velocity inside the chamber can be controlled by the help of a regulator. In order to ensure that the flow is uniform, perforated plates have been designed and installed within the chamber.
These plates help in diffusion and mixing the pollutant gas homogeneously towards downstream to ensure all exposed test samples receive same concentration of pollutant gas.
The perforated plates and their performance has been validated by using a CFD based tool COMSOL (COMSOL, 2013). Figure 2 shows the velocity magnitude within the chamber before and after the perforated plates. It has been found that the turbulence has been decreased significantly at the downstream side.
Figure 2: Velocity magitudes inside the chamber modelled using COMSOL...
Figure 3: Variation in average absolute % change in weight of
test samples with time due to SO2 exposure...
Environmental chambers were extensively used for testing building materials (McGhee, 1992; Martinez et al, 1998; Zappia, 1998; Massey et al 1999).
Experiments have been conducted using Cement Mortar (M), Cement Fly-ash Mortar (F A M) and Lime mortar by exposing them with the pollutant gases SO2 and NO2.
Figure 3 shows the average absolute percentage change in the weight of the test samples when exposed to SO2 and NO2 respectively. It has been observed that the exposure of NO2 is more when compared to the exposure of SO2.
Further it has also been observed that the Lime mortar is more reactive when compared to cement mortar and hence it can be concluded that the lime mortar may deteriorate at a faster rate when compared to the cememt mortar.
Environmental chambers are extremely useful in developing source emission factors, which can be used in developing indoor air quality models. However, the results have to be validated by performing full scale testing in large chambers for more accurate results.
The facility is currently being used at Indian Institute of Technology, Delhi to investigate the effect of VOC’s on the materials.
The testing of the materials like marble and redstone are also been considered. Since the facility can simulate the effect of variations in environmental parameters, it can be extensively used in testing the long term effect of the pollutants on the building materials which has archeological importance.
AUTHOR CREDIT AND PHOTOGRAPH
IIT - Delhi
Ajit Singh Patel
M. Tech. Student
Abhishek Singh Chauhan
M. Tech. Student