Infrared Screening of Residential Buildings for Energy Audit Purposes: Results of a Field Test

Abstract

Abstract:In the European Union (EU), the building sector is responsible for approximately 40% of total energy consumption. The existing building stock is inefficient and can, and indeed must be retrofitted to address this issue. The practical implementation of the European strategies requires knowledge of the energy performance of existing buildings through energy audit techniques. Application of thermography in the fields of energy are very widespread, since, through such a non-invasive investigation, and through correct interpretation of infrared images, it is possible to highlight inefficiencies in buildings and related facilities. The paper shows and discusses the results of an infrared audit campaign on 14 existing buildings located in Milan Province (Italy) made in different construction periods and characterised, therefore, by different building technologies. The U-values obtained in an indirect way through the thermography of the opaque walls of the buildings investigated, were compared with the actual known values in order to verify the reliability of the method and the possible margin of error. The study indicated that the category of buildings in which the application of this method is sufficiently reliable is that of solid-mass structure buildings, the most widespread in Italy, whereas in the case of buildings whose external walls are insulated, the percentage of deviation is very high.

Variations in the U-Value Measurement of a Whole Dwelling Using Infrared Thermography under Controlled Conditions

“…Weather conditions have proven to be highly problematic when implicating short-term IRT [43][44][45], with effects of rain, solar incidence, and wind, leading to a distortion of data and bias in the results. Lucchi [42] goes on to discuss solutions to these problems can be sought by controlling these factors, in order to reduce the impact on the results; suggestions of limiting IRT measurements to dry days with Buildings 2018, 8, 46 6 of 17 low solar incidence, performing IRT during steady conditions, and the acquisition of compensation terms, are all made [44][45][46] Further studies have also sought to perform IRT under controlled conditions, to eliminate the influence of weather, though on a much smaller scale than for whole buildings [47,48].…”

“…Lucchi [42] goes on to discuss solutions to these problems can be sought by controlling these factors, in order to reduce the impact on the results; suggestions of limiting IRT measurements to dry days with low solar incidence, performing IRT during steady conditions, and the acquisition of compensation terms, are all made [44][45][46] Internal and external variables can have a significant effect on U-value measurement outcomes [35]. Researchers have found that external variables, such as wind, precipitation, long wave radiation, and solar gain can have a major impact.…”

Influence of environmental parameters on the thermographic analysis of the building envelope

“…A first group of authors [9,10,11,12,13,14,15] recommends to avoid solar irradiation in general, making no judgement of the impact duration. A second group [6,7,8 ], containing also the European Standards on thermography, gives more precise information on the waiting time after sundown to perform a thermographic survey and mentions that structures with high thermal mass need more attention. A third group [2,3,4,5] of authors distinguishes between guidelines for structures with a different thermal mass.…”

“…Insulation defects Air leakage spots ∆Ti-e >10°C during 4h prior to IR [20] ∆Ti-e >1,7°C during 4h prior to IR [20] ∆Ti-e > 10°C [10] ∆Ti-e > 3°C [10] ∆Ti-e > 10°C [21] ∆Ti-e > 5°C [21] ∆Ti-e > 10°C [11] ∆Ti-e > 3/U (min 5°C) during 24h prior to IR [8,16] ∆Ti-e > 15°C during 24h prior to IR [15,22] ∆Ti-e > 10 -15°C [13,23] ∆Ti-e > 5°C during 24h prior to IR [6,7,12] ∆Ti-e > 10°C during 4h prior to IR [2,24] ∆Ti-e > 10°C (>20°C if possible for U-value determination) [19] Wind velocity (m/s)…”

“…No solar irradiation allowed during 3h prior to investigation [2] No solar irradiation allowed during 8h prior to investigation [2] IR possible several h after exposure [3,4] IR possible 24 h after exposure [3,4] IR possible 48 h after exposure [3,4] IR possible 2-3 h after exposure [5] IR possible 4-6 h after exposure [5] IR possible 8 h after exposure [5] Not allowed 12h prior to IR [6,7,8] Structures with high thermal mass need more attention [6,7] Not allowed [9,10,11,12,13,14,15] Temperature gradient ∆Ts = 0,5 *∆Te,grad [3,4] ∆Ts = 0,35 *∆Te,grad [3,4] ∆Ts = 0,2 *∆Te,grad [3,4] ∆T, grad low and stable during IR [10] ∆Te, grad < 10°C 24h prior to IR, < 5°C during IR [6,7,12] ∆Ti, grad < 2°C during IR [6,7,16] ∆Te, grad < 5°C during IR [6,7,16] …”