Energy and Buildings 65 (2013) 292–298 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me pa g e: www.elsevier.com/locate/enbuild Using quantitative infrared thermography to determine indoor air temperature César Porras-Amores a,∗ , Fernando R. Mazarrón b , Ignacio Ca˜ nas a a Department of Construction and Rural Roads, E.T.S.I. Agrónomos, Universidad Politécnica de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain b Rural Engineering Department, E.T.S.I. Agrónomos Universidad Politécnica de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain a r t i c l e i n f o Article history: Received 17 December 2012 Received in revised form 15 May 2013 Accepted 10 June 2013 Keywords: Infrared thermography Air temperature Buildings Construction a b s t r a c t Infrared thermography (IR) has proven to be an effective alternative method for determining room tem- perature within buildings. Nevertheless, IR is limited to surface temperature measurements, as opposed to direct indoor air temperature measurements, and it is not free from errors (emissivity, camera cal- ibration, poor focus, etc.). Therefore, IR tends to be used to obtain qualitative rather than quantitative data. The main contribution of our study is the development of a technique that produces precise quan- titative measurements in building interiors and structures using thermal cameras. A low-cost, portable measuring screen system has been developed for this purpose, and its high precision level has been con- firmed after overcoming problems related to emissivity, focus, and reflected temperature. The technique is versatile and can be applied in a multitude of settings to obtain quantitative measurements of the air temperature distribution in the interior of buildings. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The application of a monitoring system using thermocouples for the experimental study of thermal behaviour within a building is a common technique [1–4] that provides high sensitivity to tempera- ture changes and high measurement precision. In settings featuring aggressive atmospheric conditions with high levels of humidity, there is increased danger of condensation and mould outbreaks [5], making it necessary to use robust sensors, for which most thermo- couples are inadequate. In these cases, it is necessary to use more resistant sensors [6,7] or thermocouples with metallic reinforce- ments [8,9], which results in a loss of sensitivity and a decrease in the sensor’s response time. Infrared thermography (IR) is a potent technique for deter- mining the indoor thermal conditions of buildings and structures and is a suitable substitute for these methods. Many researchers have effectively used this technique for different purposes, demon- strating its positive potential. Balaras [10] has described IR as a valuable tool for inspecting and performing non-destructive testing of building elements. Avdelidis and Moropoulou [11] have pre- sented a revision concerning emissivity measurement techniques in which they indicated the importance of the emissivity values of the surface in the diagnosis of buildings. Furthermore, Martín Oca ˜ na [12] has proposed a thermographic technique that can be used to ∗ Corresponding author. Tel.: +34 913365767; fax: +34 913365625. E-mail addresses: c.porras@upm.es (C. Porras-Amores), f.ruiz@upm.es (F.R. Mazarrón), ignacio.canas@upm.es (I. Ca˜ nas). compare thermal performance among different buildings. Al-Kassir [13] has used this technique to study energetic installations, and Fokaides and Kalogirou [14] have applied IR to the determination of the overall heat transfer coefficient (U-value) in building envelopes. In earthen structures, the emissivity of surfaces is difficult to quantify due to the disparity of different materials present in the terrain. It is important to note that not only the material but also its condition (age, roughness, exposure to the environment) as well as its shape have an important influence on its emissivity [15]. IR is not free from errors, given that, in addition to the problems related to emissivity, there are also other complications related to camera calibration, focus, placement, reflections, etc. For this reason, most studies that use thermographic cameras in the interior of build- ings tend to use them to obtain qualitative rather than quantitative information. IR measures the infrared radiation emitted by an object rather than directly measuring the air temperature. Because of this, it is rarely applied for air temperature measurements. The relevant literature has a variety of objectives. Cehlin [16] proposes an inter- esting method, allowing the temperature of the air and the patterns of air flow to be visualised in air diffusers over a large transversal section. This technique uses a huge porous screen with a high level of emissivity over which thermal images are taken. Another tech- nique worth noting is that of Sezin Eren Özcan [17], which uses the openings in the buildings’ envelope to measure the total air flow. In this system, the heat source is placed perpendicular to the direction of the air flow opening, and the temperature decay is measured very close to the heat source. Nevertheless, such sys- tems have been designed for other purposes and are inadequate for 0378-7788/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.enbuild.2013.06.022