Introduction

In developed countries, children spend most of their time at home or at school [1]. The health, well-being and general performance of the population are strongly related to the conditions of the interior environment [2]. There are currently a set of functional requirements that allow for increased occupant comfort due to the high permanence of the population inside the buildings. The quality of life of the occupants of buildings can affect their state of health and even the student’s performance [3].

Indoor Environment Quality (IEQ) plays an important role in all permanently occupied buildings. However, in view of a particularly vulnerable population, special attention should be paid to child day care center (CDCC, is the school for children between 3 months and 3 years old; CDCC includes nursery, that is the compartment for babies over 3 months until the acquisition of walking) and kindergartens (KGT, that is the school for children between 3 and 6 years).

Studies in nurseries and KGT are rare, perhaps due to the difficulty in making observations in spaces where the introduction of equipment and people changes to children’s habits. There are some studies at the international level, but in Portugal there are just few studies on this subject.

More research is needed to better describe the IAQ where the children are spending most of their time. Therefore, this research is intended to contribute to that effort by providing information on CDCC and KGT premises in Portugal. The relevance and novelty of this case study in Portugal is related to the character of the two towns involved, because both are located in the interior of central Portugal and present more stringent external environmental conditions (colder climate in winter), where people tend to reduce ventilation to keep the thermal comfort, which can cause poorer conditions for IEQ. It is also intended to analyses the influence of the discontinuous operation of the air conditioning in these spaces, a very common situation in Portugal.

The aim of this research is to assess the conditions of IEQ in living rooms of nurseries and KGT, namely by measuring the comfort conditions (ambient temperature end relative humidity), concentration of pollutants internally released (CO₂, TVOC and formaldehyde) as well as the respective ventilation rates (ACH), see Figure 1.

Figure 1.

Location of Viseu and Covilhã towns - Portugal.

Literature review

Some studies show that young children are particularly susceptible to indoor air pollution because of their immature immune systems and smaller bodyweight [4].

There is evidence implicating air pollution in adverse effects on children’s health. Effects of air pollution have mainly been investigated concerning lung development and function, respiratory diseases such as asthma, bronchitis, and cough, allergies, rates of infection in smaller children and deficits in neurobehavioral development. Concretely, the developing fetal lung, as well as the infant’s lung, is more susceptible to injury by lung toxicants (including air pollutants) at doses below the no-effect level for adults [5].

Some risk factors identified in children included, namely, plastic materials, formaldehyde, children’s activities and recent painting [6], [7]. In the same way, elevated risks were also reported, among others, for cleaning activities [6], [7].

Adequate ventilation significantly reduces indoor concentrations of pollutants. Low ventilation rates (below 0.5 h^-1 air changes rate - ACH) are associated with increased absenteeism and respiratory symptoms in school and high allergic manifestations among children, namely, in a Nordic climate [8], [9], [10].

Children have different levels of thermal sensation, different metabolic rates, different clothing restrictions and different sensitivities to temperature changes. Levels of response between children also have a lot of variance and classroom activities are more diverse than adult activities over a typical day [11]. Children have a greater sensitivity to changes in their metabolism than adults and prefer lower temperatures than those predicted by the PMV model and the standard EN 15251 [12].

Despite the difficulties in doing studies in nurseries and KGT, some research has been done lately in buildings that house children. For example, St-Jean has shown that an area of 2.75m²/child helps to control body odors in play areas [13]. In the case of Portugal, the spaces and their minimum useful areas per room unit in CDCC, set for 8 children, must be at least 2 m²/child [14].

Ramalho concluded that carbon dioxide (CO₂) as a tracer of some pollution sources cannot be considered as a unique indoor air quality indicator. CO₂ is also often considered as a surrogate of the ventilation rate when the main pollution is caused by the human respiration. Hence, the study confirms that even with good ventilation conditions (i.e. low CO₂ level), the reduction of pollutant sources remains necessary to achieve a satisfactory IAQ [15].

Carreiro-Martins indicate an association between chemical and biologic contaminants at CDCC and wheezing in young children. Those exposures seem to be relevant for every wheezing child, independently of the asthma predisposition [16] and Kolarik suggests the importance of adequate ventilation in CDCC [17].

Depending on the research already carried out, it is necessary that adequate conditions of comfort are thought out from the design stage so that during the use phase they are easily achieved [18].

Ramalho [15] establishes the need for further research on the adverse effects intrinsic to CO₂ on human psychomotor performance (decision-making, problem-solving) and sensitive populations such as children. Ramalho [15] also recommends that the awareness of building owners, school directors, teachers and staff of kindergartens and schools, where higher CO₂ levels are observed compared to dwellings and offices, should be improved regarding, e.g. maintenance of ventilation system and ventilation through windows and doors opening to effectively reduce the impact of air stuffiness on health, performance and perceived comfort. The ventilation strategy must also take into account other risk factors such as noise, outdoor air pollution, thermal discomfort, etc., that could hinder an efficient ACH. Kolarik [17] found a significant inverse relationship between the number of sick days among nursery children and ACH.

Air quality and thermal comfort (T_int and RH) are important parameters for an indoor environment suitable for the occupants’ permanence. It is also necessary to check the maximum concentrations of indoor air pollutants.

Table 1 shows the hygrothermal comfort conditions and the protection thresholds for physical-chemical pollutants.

It is also necessary to check the ventilation conditions. Adequate ventilation of the indoor air will restrict the degradation of the building elements, related to humidity, which will reduce the occupants’ well-being. Ventilation must also be carefully designed so as not to cause thermal discomfort and excessive energy consumption are avoided.

The literature review show that the body of knowledge regarding the indoor air quality (IAQ) in CDCC and the impact of the ventilation in the improvement of IAQ is still small. Moreover, the research has been carried out mainly big towns. This research brings new information on the IAQ found in CDCC case studies in small Portuguese towns located at the countryside, where the range of external temperatures is wider and where the outdoor pollution is smaller. In this study the characteristics of the buildings are presented to highlight the impact of the construction characteristics in the IAQ.

Buildings and Compartments Studied - Physical Characterization

This article continues the research already carried out, resulting from two master degree dissertations [19], [20], so that complementary information (eg. used equipment and measurement methodology) can be found in an article recently published [21]. The measurement methods are described in the section 4.

City of Viseu

The city of Viseu is situated at an average altitude of 480 m and has approximately 1700 heating degree days (base 18°C) [22].

Two KGTs were analyzed: KGT 1 (children between 3 and 5 years old): 5 living rooms and 1 dining hall; KGT 2 (children between 1 and 5 years old): 8 living rooms, see Table 2.

Table 3 describes the compartments studied, namely, indoor and outdoor solar protection and the material and system for opening the windows.

City of Covilhã

The city of Covilhã has an average altitude of 750 m and 2000 heating degree days (base 18°C) [22].

Two KGT were analyzed: (1) KGT 3 (children between 3 and 6 years old); (2) KGT 4 (children between 3 and 6 years old; babies between 4 and 12 months old), see Table 4.

Table 5 describes the compartments studied, namely, indoor and outdoor solar protection and the material and system for opening the windows.

Experimental Campaign Presentation and Analysis of Results

Viseu - Experimental Conditions

Measurements of exterior temperature were obtained from the site Wunderground [27]. Whenever possible, it was avoided to place the equipment close to places, namely windows and air conditioning equipment, which could influence the measurements of the interior environmental parameters. Metabolic CO₂ was used, as described in the standards ASTM E741 [28] and ASTM D6245 [29], to determine ACH, using the decay technique, in the post-occupation periods. The Portuguese Technical Note TN-SCE-02, 2009 (This document supports the application of Portuguese regulations in the area of IAQ) [26], allows, for measuring TVOC and formaldehyde, the use of “Photoionization Detectors” (PID). In both cities, equipment was used with the same measuring principle.

Pollutants in the compartments were continuously measured. Measurements were taken during periods of occupation [7:30 a.m. to 7:30 p.m.]. Only one point of analysis of the various parameters was carried out in each compartment, in view of the available equipment [26].

The experimental campaigns took place in January 2016, the first, and between April and May 2016, the second.

The main measurement conditions, parameters and measurement equipment can be consulted in [21]. The accuracy of measurements is ±0.50 ºC for temperature, ±2,5% for relative humidity, ±50 ppm (Telaire 7001) or 2.75% + 75 ppm (Fluke 975 AirMeter) for CO₂ concentration measurement and ±5% of the display reading ± one digit for TVOC.

Covilhã - Experimental Conditions

To assess the ACH, the criteria already presented for the location of the equipment inside the compartments were followed. The weather station at the University of Beira Interior (UBI), located at approximately 680 m altitude, was used to measure the relative humidity and outside temperature. Each reading record was performed continuously for a minimum period of 5 minutes [26]. The measurements of formaldehyde were punctual, in view of the limitations of the device, having recorded, measurements every 5 minutes, the maximum value of 3 measurements. The experimental campaigns took place between February and June 2014, the first, and between April and May 2015, the second. In the 2^nd experimental campaign, measurements were only taken at KGT 4. The measurements refer to the usual period of occupancy: 7.00 a.m. to 7.00 p.m.

The main measurement conditions, parameters and measurement equipment can be consulted in [21] and their accuracy was referred to in the section before.

Analysis criteria

According to Table 1, the following situations were considered excessive and inadequate:

‧ for an average of 8h, CO₂ concentration greater than 1625 ppm;

‧ for an average of 8h, TVOC concentration greater than 0.52 ppm;

‧ for an average of 8h, CH₂O concentration greater than 0.08 ppm;

‧ indoor temperatures outside the acceptable range [20ºC; 25ºC] for more than 20% of the time;

‧ RH_int outside the range [30%; 70%].

City of Viseu

KGT 1 - 1^st experimental campaign

In the living rooms of KGT 1, the average indoor temperatures were below those considered reasonable for the existence of thermal comfort in the studied compartments (values not shown). There is a cyclic variation of the interior temperature in all the compartments analyzed. This variation is due to the occupation of the compartments and the fact that the heating with electric radiators is intermittent (the level of individual intensity of heat release from the radiators is regulated by the users’ thermal perceptions). The analyzed compartments do not present worrying values of average RH, except for living room 4, which presents an average value higher than the recommended maximum limit (values not shown).

The CO₂ and TVOC pollutants measured in KGT 1 are analyzed statistically in Table 6. We can conclude, based on Table 6, that: (1) During the period of habitual occupation, living rooms have a high average of CO₂ values; (2) The values of the standard deviation of the TVOC are high, and it can be concluded that the parameters with more influence (type of activities and ventilation rate) are quite variable during the occupation period; (3) The maximum CO₂ value, obtained in an average of 8 hours, was always higher, in all rooms, than the protection threshold (see Table 1); (4) Living room 4 has a maximum value for the average of TVOC above the protection threshold (see Table 1).

Figure 2 shows, for living rooms 1 and 2 of KGT 2, thermal comfort using the adaptive model proposed by LNEC [30]. In the LNEC model, considering the arithmetic average between T_int (indoor temperature) and T_mp (running mean outdoor temperature; ASHRAE 55, 2020 [31]; EN ISO 7730, 2005 [32]), one can calculate the “Operative temperature” with good approximation.

Figure 2.

Adaptive method of the LNEC - assessment of thermal comfort in KGT 1: 1^st experimental campaign.

The results in the living room 1 and 2, considering the use of central heating with electric radiators (active air conditioning), revealed the existence of a thermally comfortable environment, with the temperature data, most of the time, within the established “comfortable” guideline values.

According to Figure 3, it is possible to observe that for living room 4 the maximum limit of TVOC is exceeded during a long period analyzed. The high concentrations of TVOC may reflect the use of teaching materials, such as the use of paints and glues (materials often used in handicrafts), the exposure of works in the living room and the existence of poor ventilation conditions. The third maximum peak of TVOC occurs around 6 pm, the time that corresponds to the usual cleaning period. Regarding CO₂, its concentration must be associated with human breathing (in the absence of sources with combustion) and also due to the existence of poor ventilation conditions.

Figure 3.

CO₂ and TVOC in living room 4 of KGT 1: 1^st experimental campaign (14 January).

From the results presented in Table 7, ACH of living rooms 3 and 4 in KGT 1, we may conclude that the ACH are well below the regulatory value in both living rooms analyzed. The minimum values for fresh air flows (ACH_RECS) were calculated solely according to the occupation (point 2.2.1 of Ordinance 353-A / 2013 [23]), no account was taken of the polluting load due to the materials of the building and use.

For the city of Viseu and in the 1^st experimental campaign, only the results of KGT 1 are presented because KGT 2 does not present such problematic results with regard to comfort conditions or IAQ.

City of Covilhã

1^st experimental campaign

Table 8 shows the results of the pollutant measurements.

Regarding the values presented and taking into account the measurement period (≈ 5 min), we may conclude that: (1) KGT 3 has high concentrations of TVOC in the living room, which may reflect, in particular, poor ventilation and maintenance conditions (e.g., inadequate cleaning products) and the use of teaching materials (e.g. paintings and glues); (2) Two compartments (KGT 3: living room; KGT 4: nursery) have high CO₂ values, which may reflect, in particular, poor ACH or over-occupation for existing ventilation conditions; (3) The nursery of KGT 4 have high levels of formaldehyde. No potential source has been identified, which may be justified by coatings or materials used occasionally.

Figure 4 and Table 9 show the hygrothermal comfort conditions.

Figure 4.

Temperatures at KGT 4: 1^st experimental campaign (21 to 25 April, Monday to Friday).

We can conclude, based on Figure 4 and Table 9, that: (1) The indoor temperature has a cyclical variation; (2) KGT behave differently: KGT 4 does not have pre-emptive values in terms of average temperature or relative humidity; KGT 3 has values well below those reasonable for temperature in the heating season. These temperatures can be explained by the different conditions of thermal insulation of the envelope of the studied buildings; (3) The temperatures are below the regulatory ones in the different compartments analyzed; (4) Two compartments of KGT 4 present relative humidity values that stay above the upper limit a considerable time period (Living room and Nursery).

2^nd experimental campaign

The 2^nd experimental campaign took place in May 2015. The concentration of pollutants and ACH are shown in Table 10.

Figure 5, dining hall, shows the concentrations of TVOC and CO₂. The points with maximum levels of TVOC are identified. The starting points of the decay technique, which served to determine the ACH, are also identified.

Figure 5.

Dining hall - TVOC and CO₂ - in the KGT 4: 2^nd experimental campaign (14 to 19 May).

We may conclude, from Table 10 and Figure 5, that: (1) CO₂ level is too high a significant period of time in the nursery; (2) The nursery presents very low values for ACH. Compared to regulatory values, the dining hall also presents low values; (3) In the dining hall, the peak of TVOC occurs at 10 am on Friday, followed by a decay. The weekend cleaning action followed by a window opening can produce this peak.

Discution

The following main results may be drawn from KGT in Viseu:

‧ the KGT 1 compartments showed poor air conditioning conditions in the heating season, presenting in most cases excessive percentages of time (≥ 20%) with temperature values below the regulation (20ºC);

‧ most KGT 1 compartments do not have worrying values of average RH;

‧ the KGT 1 compartments have a maximum of CO₂ averages (8 hours) above the protection threshold;

‧ living room 4 of KGT 1 has a maximum value, above the protection threshold, for the average of TVOC (8 hours);

‧ the existence of a thermally comfortable environment in the living room 1 and 2 (KGT 1) is observed, by applying the adaptive comfort model proposed by LNEC;

‧ for living room 3 and 4, ACH have values generally well below the regulations.

The following main results may be drawn from KGT in Covilhã:

‧ the KGT 4 nursery has high values of the measured pollutants;

‧ the compartments present excessive percentages of time with temperatures below the regulations;

‧ large part of the compartments, except for two, do not present worrying relative humidity values;

‧ the KGT 4 nursery has very low values for ACH.

In general, the results show indoor temperature that is low (see figure 2) and, sometimes, below the comfort condition (see Table 9 and Figure 4). In the interaction with the building, the users tend to keep the windows closed, when trying to reach the thermal comfort. As the ventilation is made just using the natural permeability of the buildings and depending on the natural actions (wind and indoor-outdoor temperature difference), the resulting ventilation rate is too low, when considering the needs of every room due to the human occupation (see Table 7 and Table 10, where the values of ACH_RECS, corresponding to the regulatory ventilation rate that is required according to the human occupation, shall be compared with the measured ventilation rate ACH_av). The study reveals that the indoor pollutants concentration is too high (see Table 6, KGT 3 living room and KGT 4 nursery at Table 8 and Figure 3) and that sometimes the concentration stays significant time periods above the protection threshold, that allows to consider that in such cases the health can be affected.

Recommendations and Conclusions

This study was carried out to assess the IEQ in living rooms of nurseries and KGT in towns in the countryside of Portugal, where is likely to expect lower IEQ due to the more adverse climate.

From the analysis of the results of the two cities and for the heating season the most relevant conclusions are:

‧ the compartments are generally insufficiently heated;

‧ the pollutants measured are above the protection threshold:

‧ ventilation rates (ACH) are reduced.

The previous results imply the need for action concerning heating, maintenance, and ventilation conditions so that the spaces operate within the appropriate conditions of comfort and air quality.

The organizational recommendations are as follows:

‧air conditioning conditions can be improved by raising the awareness of management/directors, educators and assistants to the importance of turning the heating on continuously throughout the entire period of operation of the interior spaces, as well as to the importance of regulation of radiators to appropriate intensity levels;

‧when using teaching materials, namely glues and paints, ventilation must be intensified by opening windows. After carrying out manual work with these materials, they must also be exhibited in more ventilated places. Alternatively, less polluting materials may be used;

‧ the number of residents in the living rooms should be limited/controlled to respect a minimum ratio of 2 m²/child in CDCC;

‧ ventilation conditions can be improved by intensifying the practice of natural ventilation. Windows and doors should be opened after the cleaning period and even when the rooms are empty (at least 1 hour per day and never less than 15 minutes);

‧ for interior maintenance, ammonia cleaners, organic solvents and other chemicals which significantly affect the IEQ should not be used.

The conditions of ventilation and hygrometry can be improved by implementing the following (in order of effectiveness):

‧ mechanical systems, including air intake devices in windows;

‧ exhaust fans with a suitable flow rate for each compartment in the exterior wall;

‧ dehumidifiers where high moisture contents have been recorded.

Despite the valid conclusions, this study has some limitations, such as: being limited to the study of buildings in two towns and only three pollutants. Thus, this study should extend to other locations in the countryside of Portugal and cover other pollutants (eg. PM_2.5).

In Portugal nurseries and KGT in some cases may have poor Indoor Environment Quality (IEQ). The highlights of this research are:

‧ discontinuous heating of spaces (widely used in Portugal) can lead to discomfort, even taking into account the low value of the assumed comfort temperature (20ºC);

‧ when using teaching materials, namely glues and paints, ventilation must be intensified by opening windows;

‧ ventilation conditions must be improved, namely by intensifying the practice of natural ventilation.

Nomenclature

ACH : Air change rate, [h^-1]

CH₂O : Formaldehyde

CDCC : Day Care Center

CO₂ : Carbon dioxide

E, N, NW, S, SE, SW, W : Cardinal points: E - East; N - North; NW - Northwest; S - South; SE - Southeast; SW - South-west; W - West

HVAC : Heating, Ventilation, and Air Conditioning

IAQ : Indoor Air Quality

IEQ : Indoor Environment Quality

KGT : Kindergartens

LNEC : National Laboratory for Civil Engineering

Max : Maximum

MT : Margin of Tolerance

MV : Mechanical Ventilation

n : Number of 8h averages of measurements

NV : Natural Ventilation

Perc : Percentage of time that exceeds a certain value

PMV : Thermal comfort model adopted in the standard ISO 7730:2005

q : Air flow rate, [m³/h]

RH : Relative Humidity, [–]

RR : Restroom

T : Temperature, [°C]

T_mp : Running mean outdoor temperature, [°C]

TVOC : Total Volatile Organic Compounds

Greek symbols

D : Difference

m : Mean (arithmetic mean)

σ : Standard deviation

Subscripts :

av : Average (arithmetic mean)

ext : Referring to the exterior

int : Referring to the interior

Max : Maximum

RECS : Referring to Ordinance 353-A/2013