Author: Rainer Pfluger, Sascha Hammes, Jan Steiger, Wolfgang Hasper

Living Quality Monitoring can be used to monitor the success and quality assurance of renovation measures. It also provides learning opportunities for future projects and planning.

In addition to energy efficiency requirements, there are also target criteria for thermal comfort and indoor air quality. While energy efficiency can be easily assessed using one parameter, the quantitative assessment of health and comfort can be complex and requires the evaluation of several parameters. Indicators such as thermal comfort and indoor air quality must be considered separately as, despite their interdependence, they differ fundamentally both in their effects and in the measures taken to improve them.

Even if individual indicators can be standardized in their unit, many parameters must be evaluated individually in the respective application context and the existing framework conditions. Decisions on threshold values and comparisons of variants only appear appropriate if all indicators show the same trend. An objective comparison of variants is more difficult if individual indicators show opposing trends. At this point, it would then be necessary to combine the individual indicators into a single parameter, which in turn requires weighting. Weighting only proves to be scientifically justifiable if it has been comprehensively validated on the basis of subject studies, which can prove difficult due to the high level of user diversification. The Fanger model is a validated model for assessing thermal comfort (content of the ISO 7730 standard). Health indicators are standardized using the unit DALY (disability-adjusted life years) for various health-damaging effects. EN 16798-1 defines further requirements for indoor air quality, the thermal and visual indoor environment and acoustics. These are sometimes used as a basis for planning, especially for system dimensioning in buildings and for energy efficiency calculations.

However, the validity of individual validated and statistically based indicators can be limited when examining smaller buildings with a limited number of people. Especially if age, gender or behavior are unevenly distributed. This can falsify the assessments of the building envelope and building services. A case-by-case assessment would therefore be appropriate.

Individual behaviors have a significant impact on IAQ and energy consumption [Lopez 2021, Hong 2017]. Knowledge of user-centric targets in planning and operation can therefore help to improve IAQ and energy efficiency by considering the impact of user behavior. To move from existing concepts at an aggregate level to user-centered performance indicators, Han et al. identify requirements in Resolution of performance indicators by building type, Uniform scaling of performance indicators and Stronger quantification for performance quality assessments [Han 2020]. Living Quality Indicators are suitable for quantification and individual assessment, e.g., CO2 concentration, temperature and relative humidity for the indoor climate.

In Nearly-Zero-Energy-Building (NZEB) or Passive House/EnerPHit standards, a high level of airtightness is required to keep heat losses to a minimum. Efficient mechanical ventilation systems are therefore required in this context to minimize the risks of overheating, high humidity and air pollution. Indoor environmental quality (IEQ) is becoming increasingly important in buildings with high energy standards. However, there is currently no general consensus on the measurement, limitations of the assessment classes and weighting of individual categories for the assessment of IEQ [Heinzerling 2013, Han 2020]. Due to the resulting variability in the assessment procedure, there are currently many degrees of freedom for the building assessment. This also applies to indoor air quality (IAQ) parameters. Although the CO2 concentration, as well as the concentration of particles and volatile organic compounds, are good indicators of IAQ, there is no general standard for the quantitative assessment of air quality. However, the CO2 concentration is often used as a quality indicator for IAQ and the calculation of air pollution [Persily 2017, Belmonte 2019]. Correlations can be demonstrated between the CO2 concentration and certain gaseous compounds and bioaerosols [Lopez 2021]. EN 13779 sets specifications for the time in defined concentration ranges for IAQ assessments, e.g., high IAQ for CO2 concentrations below 750 ppm or particularly low IAQ for concentrations above 1200 ppm.

Living Quality Indicators (LQI) are directly or indirectly influenced by the building envelope and building services. Despite a partial overlap, a distinction is made between health and comfort-related indicators. If people are exposed to inadequate comfort conditions in the building over the long term, this can have health consequences. This article is limited to temperature and humidity data for the statistical analysis of overheating frequencies and summer comfort.

Sensor selection proves to be fundamental for living quality monitoring and therefore for monitoring success and quality assurance. In accordance with ISO/DIS 7730, the analytical determination and interpretation of thermal comfort (PMV and PPD indices and local thermal comfort criteria) is based in particular on radiation temperature, air temperature, relative air velocity and humidity. If the air temperature and radiation temperature do not differ significantly, these can be formulated as the operative temperature using the arithmetic mean. For occupied rooms, the requirements for a high level of comfort (PPD < 6 %) are to be determined in particular by low fluctuations in the operative temperature (max: ±0.8 K), low draught risk (<0.08 m/s), low radiation temperature asymmetry (ceiling/floor < 5 K) and low vertical air temperature difference between head and foot when a person is seated (< 2 K). The influence of temperature is of the greatest importance here. The EnerPHit standard also ensures good airtightness with a maximum n50 ⩽ 1.0 h-1 and is systematically validated with pressure build-up and pressure relief tests in accordance with ISO 9972. This minimizes the unintentional risk of draughts.

In order to fully map the IAQ in addition to thermal comfort, the measurement of the indicators relative humidity and carbon dioxide concentration is used alongside temperature. However, in order to obtain reliable evaluations based on this very limited set of parameters, the measurement uncertainty must not exceed narrow limits [outPHit D.6.5]. Mobile sensors and local data storage with evaluation in post-processing are suitable for practical use, especially for temporary operation.

A before-and-after comparison is required to monitor success. For this reason, monitoring should be carried out for a few weeks in various locations and apartments in the unrenovated state of the building. Longer periods are necessary in order to take into account the influences of user behavior and individual targets in particular, as the validity of statistical target values may be limited, especially in smaller buildings with a limited number of people.

In the outPHit research project, a wireless system based on the low-power wireless network protocol LoRaWAN (Long Range Wide Area Network) has prevailed. However, there are several suitable approaches that need to be evaluated against the respective framework conditions. The aim should be to make installation easy for users and as non-invasive as possible for residents. Data series of max. 10-minute intervals ensure both a long service life for wireless systems, without battery replacement and thus maintenance interventions, which can have a disruptive effect on comfort, and at the same time this ensures a sufficiently precise resolution for data evaluation. This is because temperature developments are generally associated with a certain degree of inertia.

Performance indicators are generally limited to clearly defined areas and categories via standards and guidelines. With regard to the air quality parameter CO2, the effects are primarily limited to health and comfort during occupancy periods. In order to quantify how much and for how long certain environmental parameters in a building exceed defined limit values, the relative limit value deviation (RTD) is used. A distinction is first made between the heating period and the non-heating period. When planning based on the Passive House Planning Package (PHPP, based on the monthly method EN13790/ISO52016), a detailed energy balance model is created. The calculation results can be used to derive the typical heating and non-heating periods based on the climate data set. The measured parameters, e.g., CO2 concentration, relative humidity and temperature in the room, are plotted as a cumulative distribution function for the evaluation period and only for hours with occupancy. The area between the limit value and this function shows the duration and extent to which the limit value was exceeded. This integral limit value deviation is set in relation to the maximum permissible deviation. It should be noted that a combination of parameters is not possible if different scales exist.

The RTD method is best used for seasonal assessment of LQI, as building use and air change rates vary greatly depending on the time of year. In winter, windows are usually closed, while in summer they are opened more often, which affects indoor air quality and energy efficiency. Airborne mold spores can pose a health risk depending on the type and quantity present, see [outPHit D6.10]. Buildings that are renovated to the EnerPHit standard rely on mechanical ventilation with heat recovery (MVHR) in winter, which ensures the air flow required for hygienic reasons at all times and regardless of the weather. Moisture-related risks, such as mold, are eliminated. Good insulation prevents low surface temperatures and moisture build-up.

The PHPP recommends that the temperature is only exceeded on 10% of days. A slight increase can be partly attributed to low manual ventilation rates.

The following Figure 1 show examples of the RTD as a basis for evaluating the building situation with regard to the temperature and humidity parameters. If there are excessive deviations from the corridor, this indicates a need for action. RTD as part of monitoring is an effective method of monitoring success.

In addition to measuring temperature, humidity and CO2, microbiological sampling is essential for assessing indoor air quality (e.g., via impaction, filtration or isokinetic sampling for ventilation systems), as it provides a detailed understanding of the types and concentrations of microorganisms in indoor air.

These can affect the health of occupants, for example through respiratory infections, allergies, asthma or sick building syndrome, and can also damage the building fabric. Bioaerosols in indoor spaces are caused by occupant activities, contaminated building materials or outside air. The proportion of bacteria and fungi in the air differs significantly between indoor and outdoor areas, as indoor areas often offer better conditions for growth. The growth of fungi and bacteria is linked to specific temperatures and usually a relative humidity of at least 60 %. In the context of microbiological assessments, simplified methods are required for an initial, rough assessment [Seifert 2002]. These refer to the difference in the number of colony-forming units per sample volume (CFU/m³) in the outdoor air compared to the respective indoor air count.

First, those species that can typically reach high concentrations in the outdoor air are compared. Then the sum of all CFU/m³ belonging to genera that indicate increased indoor air humidity is evaluated for increased occurrence. In the third step, individual species within the aforementioned set of genera are examined. Each of the three steps is evaluated. To provide a good overview at a glance, radial diagrams (radar plots) with color coding according to the traffic light scheme are provided for each assessment category. The overall situation can only be categorized as free of findings if all “green” markings are awarded. This is shown as an example in the following illustration.

Indoor air samples and surface temperature measurements can be used to retrospectively check whether a refurbishment measure was successful and whether the building meets the desired performance targets.

Microbiological samples allow the identification and quantification of specific bacterial and fungal species and their concentrations, identifying potential health risks that conventional sensors for temperature, humidity, CO2 and VOC levels do not detect. These samples are an important part of indoor air quality assessment and provide valuable information on the health and safety of indoor environments. They also support the development of effective operational and remediation strategies. Mold, which is often caused by high humidity due to inadequate ventilation, is a significant health risk. The outPHit research project was able to highlight the importance of mechanical ventilation and high energy efficiency standards to prevent mold growth and meet comfort and health requirements (see D6.12 report on microbiological assessment of indoor air quality in case study projects [outPHit D6.12]).

[Belmonte 2019] Belmonte, J.F.; Barbosa, R.; Almeida, M. G. (2019) CO2 concentrations in a multifamily building in Porto, Portugal: occupants’ exposure and differential performance of mechanical ventilation control strategies. Journal of Building Engineering 23, pp. 114-126.

[EN16798-1] Energy performance of buildings - Part 1: Indoor environmental input parameters for the design and assessment of energy performance of buildings in terms of indoor air quality, temperature, light and acoustics - Modules M1-6; Committee 141 - Air-conditioning engineering, 2019.

[Han 2021] Han, L.; Wang, Z.; Hong, T. (2021) Occupant-Centric key performance indicators to inform building design and operations. Journal of Building Performance Simulation 14(6), pp. 814-842.

[Heinzerling 2013] Heinzerling, D.; Schiavon, S.; Webster, T.; Arens, E. (2013) Indoor environmental quality assessment models: A literature review and a proposed weighting and classification scheme. Building and Environment 70, pp. 210-222.

[Hong 2017] Hong, T.; Yan, D.; D’Oca, S.; Chen, C.-F. (2017) Ten Questions Concerning Occupant Behavior in Buildings: The Big Picture. Building and Environment 114, pp. 518-530.

[Lopez 2021] Lopez, M.; Guyot, G.; Golly, B.; Ondarts, M.; Wurtz, F.; Gonze, E. (2021) Relevance of CO2-based IAQ indicators: Feedback from long-term monitoring of three nearly zero-energy houses. Journal of Building Engineering 44, pp. 103350.

[outPHit D6.5] Steiger, J., Grove-Smith, J., Krick, B., Müller, L., Hasper, W.: outPHit D6.5 Description of a certification scheme on “verified building performance”, 2022.

[outPHit D6.10] Maier, M., Kirchmaier, M., Pfluger, R.: outPHit D6.10 Instructions for adequate monitoring equipment for living quality assessment, 2021.

[outPHit D6.11] Pfluger, R., Hammes, S., Steiger, J., Hasper, W.: outPHit D6.11 Report on living quality indicators before and after retrofit, 2023.

[outPHit D.612] Pfluger, R. Hammes, S.: outPHit D6.12 Report on microbiological assessment of indoor air quality in case study projects, 2024.

[Persily 2017] Persily, A. (2017) Indoor Carbon Dioxide as Metric of Ventilation and IAQ: Yes or No or Maybe? Is ventilation the Answer to Indoor Air Quality Control in Buildings? Do we Need Performance-Based Approaches? AIVC Workshop 2017, Brussels, Belgium.

[Seifert 2002] Seifert, B. e.a.: Leitfaden zur Vorbeugung, Untersuchung, Bewertung und Sanierung von Schimmelpilzwachstum in Innenräumen, Umweltbundesamt, Berlin 2002.

[Wingfield 2009] Wingfield, J.; Bell, M.; Miles-Shenton, D.; South, T.; Lowe, R. J. (2009) Evaluating the Impact of an Enhanced Energy Performance Standard on Load-Bearing Masonry Construction – Final Report: Lessons from Stamford Brook – Understanding the Gap between Designed and Real Performance. Leeds Metropolitan University, Leeds, UK.

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