Parameters of indoor air quality (IAQ) in wooden houses

Abstract

Indoor environment quality in wooden family houses was compared to bricked houses or concrete slab apartments. Based on measurements, the influence of selected systems of forced ventilation without heat recovery and with efficient heat recovery were compared in selected houses in consideration of monitored parameters of CO2 and relative humidity in the course of 24 hours. Auxiliary parameters such as temperature and absolute pressure were also measured. The CO2 and relative humidity parameters had demonstrable effects in all the houses. The differences of CO2 values while using recuperation or not in wooden houses reached 21.2%, 44.7%, and 31.6%. The relative humidity value differences reached 6.6%, 2.8%, and 2.9%. More significant differences in values were reached in the course of measuring in a brick building – 73.1% CO2 and 39.4% of relative humidity. In the concrete slab apartment, the value differences reached 46.1% CO2 and 1.8% at relative humidity. The permitted limit of 1,500 ppm of CO2 was exceeded in all the objects without active heat recovery. In the case of efficient heat recovery, the values oscillated around the recommended value of 1,000 ppm of CO2.

Full Article

Parameters of Indoor Air Quality (IAQ) in Wooden Houses

Martin Sviták,^a,* Karel Krontorád,^a Jan Kropáček,^b Luďka Hlásková,^a and Aleš Solař ^a

Indoor environment quality in wooden family houses was compared to bricked houses or concrete slab apartments. Based on measurements, the influence of selected systems of forced ventilation without heat recovery and with efficient heat recovery were compared in selected houses in consideration of monitored parameters of CO₂ and relative humidity in the course of 24 hours. Auxiliary parameters such as temperature and absolute pressure were also measured. The CO₂ and relative humidity parameters had demonstrable effects in all the houses. The differences of CO₂ values while using recuperation or not in wooden houses reached 21.2%, 44.7%, and 31.6%. The relative humidity value differences reached 6.6%, 2.8%, and 2.9%. More significant differences in values were reached in the course of measuring in a brick building – 73.1% CO₂ and 39.4% of relative humidity. In the concrete slab apartment, the value differences reached 46.1% CO₂ and 1.8% at relative humidity. The permitted limit of 1,500 ppm of CO₂ was exceeded in all the objects without active heat recovery. In the case of efficient heat recovery, the values oscillated around the recommended value of 1,000 ppm of CO₂.

Keywords: Indoor air quality; Wooden houses; Ventilation; Heat recovery; CO₂; Temperature; Relative humidity; Absolute pressure

Contact information: a: Department of Wood Processing Technologies, Mendel University in Brno, Zemědělská 3, Brno, 613 00 Czech Republic; b: ThermWet s.r.o., Vlárská 1454/1, Prague 10 – Uhříněves, 104 00 Czech Republic; * Corresponding author: svitas@centrum.cz

INTRODUCTION

The human population spends up to 90% of time indoors. The time of staying indoors differs depending on age, occupation, and other circumstances. In any case, a man spends approximately one third of a day by sleeping or by having rest. The indoor environment quality in residential buildings is set by the building characteristics and its technical equipment as well as by human activities to a significant level.

In consideration of the fact that people spend so much time indoors, it is necessary to adjust the premises accordingly. It is very important to meet specified limit values of main parameters determining the indoor environment. Meeting the values will provide for the environment to be suitable for work or rest – i.e. for long-term stay. Research indicate that as much as 50% of all the diseases depend on quality of indoor environment where people spend their time (Landrigan et al. 2018).

The content of pollutants is the most frequently detected value in buildings; the pollutants are emitted to the environment from various sources, e.g. construction materials, furniture, plastic utensils, combustion processes, etc. (Svoboda et al. 2015; Kauneliene et al. 2016). Pollutants contain some quantities of aldehydes, alcohols, esters and phthalate esters, fragrances and other chemical substances (Gale et al. 2009). Suitable ventilation or air-conditioning are the factors providing sufficient oxygen supply as well as elimination of the pollutants (Weschler 2009), which is frequently neglected because of heat savings (Øie et al. 1998). Besides chemical substances, the indoor environment is also affected by physical parameters of air, such as temperature, pressure or humidity, as well as by humans themselves, expiring carbon dioxide (CO₂) to the air. Just CO₂ is responsible to some level for symptoms belonging to the sick building syndrome (SBS), which in connection with low oxygen contents and unsuitable humidity causes many health problems (Apte et al. 2000; Dimitroulopoulou 2012). High contents of CO₂, as well as the SBS itself are caused by poor ventilation, heating, or air-conditioning of buildings (Fisk et al. 2009). According to earlier research of Seppänen et al. (1999), CO₂directly affects some SBS symptoms, such as headache, fatigue, eye and nasal symptoms, respiratory symptoms (throat and lower respiratory system symptoms as well as difficult breathing). The connection of CO₂ and SBS further deepens in buildings with controlled ventilation. Unfortunately, the CO₂ limits for residential houses are not fixed in national standards in most of the European countries—only in Government instructions or EU directives. Globally, the recommended CO₂ limit of 1,000 ppm has been established and been applied for decades. The value of 1,000 ppm corresponds with CO₂ concentration of 1,800 mg/m³. This value is set based on CO₂ quantity generated by a man indoors as well as CO₂ quantity in air supplied from the outside during ventilation. The necessary aeration rate per person is 7.5 l/s, and the supposed CO₂ production rate by a man is 0.005 l/s, which is in total 1,200 mg/m³. The volume of CO₂ in air supplied from the outside is 600 mg/m³, which in sum with the previous value makes 1800 mg/m³ (ASTM D6245-12 2012; ANSI/ASHRAE 2016). Maximal recommended value in interiors of residential houses is set to 1,500 ppm. The value of 5000 ppm is stated to be the limit value – its exceeding means health risks and persons should not stay long in such premises (ASTM D6245-12 2012; ANSI/ASHRAE 2016). The contents of CO₂ and its influence on human health is a long-time discussed topic, even though there are not any clear results. Some research confirm the decrease of decision-making skills and performance just at the CO₂ concentration level of 1,000 ppm (Satish et al. 2012; Maddalena et al. 2015; Allen et al. 2016), but other research deny this, stating that it is the combination of the CO₂ influence and the interaction with other pollutants (Zhang et al. 2017).

Perfectly sealed new buildings as well as unsuitably performed revitalizations of old buildings negatively affect – from the sufficient ventilation point of view – the home environment (Korsgaard 1983; Pan 2010; Panayiotou et al. 2010; Vili et al. 2013; Langer et al. 2015). New types of windows with multi-level sealing and several glass panes prevent natural air exchange by infiltration that provided air exchange before. This problem can be partially solved by using windows with micro-ventilation, but unfortunately it is at the price of acoustic dampening reduction and heat losses. Users limit such ventilation to a minimal level due to fears of significant heat losses during ventilation through open windows or micro-ventilation. These problems can be currently solved by realization of controlled ventilation systems with heat recovery. Controlled ventilation with recuperation represents a continuous exchange of used air from the interior by fresh, clean air from the exterior. The air drawn inside obtains a prevailing part of heat from the air drawn outside, thus being optimised thermally; moreover, dust, pollen, and allergens are removed due to the used filtration. Sufficient natural or forced ventilation must be ensured for residential rooms, and such rooms must be sufficiently heated, with the possibility of regulation of internal temperature. Regarding ventilation of residential rooms, the minimum amount of exchanged external air of 15 m³.h^-1 per person (residential rooms) or the intensity of ventilation of 0.5 h^-1 must be ensured when people are present. The systems may include installation of sensors measuring the CO₂ or humidity level and automatically react to the current quality of the indoor environment in residential premises. They can automatically solve the situation when the CO₂ or humidity level is above limit, and so it disturbs the indoor environment quality. Research comparing low-energy or passive buildings and standard buildings are performed less frequently. Most of the research studies are performed in Sweden, Finland, Denmark (Langer et al. 2015) or France (Derbez et al. 2014), while multifamily residential buildings in Central and Eastern Europe have been rarely investigated (Földváry et al. 2017).

This research was aimed at the indoor air quality (IAQ) parameters in five buildings, i.e. three wooden houses, one brick house, and one concrete slab apartment. The four parameters were monitored during 24-hour measurement. Carbon dioxide and relative humidity of air were the main factors, whereas the temperature and absolute air pressure were secondary factors.

EXPERIMENTAL

Locations

Measurements were performed in five different locations of the Central Bohemian Region and in the territory of Prague, the capital (Table 1). The conditions of measurement were completely identical, as the measurements were performed in the same time period in summer, without any weather changes such as heavy rainfalls or rain showers.

Table 1. Description of Investigated Buildings at Selected Locations

In concrete terms, there were included the wooden houses in Starý Vestec, Vinoř and Květnice, then a brick house in Prague – Uhříněves, and a concrete slab apartment in Prague – Pankrác. The concrete slab apartment was located in a panel block of flats which had been constructed using the T08B system representing one of the most common construction systems, which consisted of vertical reinforced concrete panels placed next to each other – constructed in Czechoslovakia in the time period of 1962 to 1980. The respective structures were chosen considering the commonly used construction systems in the Czech Republic. Three types of wooden constructions, which are the most used in the Czech Republic, have been chosen. For this reason, the following five types were mentioned as the typical representation of buildings for housing.

Measurement

Measurements of CO₂, relative humidity, temperature, and absolute pressure were performed in selected rooms of the buildings with an identical floor size of 25 m², using the device Testo 435 – 2 (Testo SE & Co. KGaA, Lenzkirch, Germany) with an external IAQ probe. Measurements were performed for the purpose of assessing air quality in the room in the course of 24 h with switched-on or switched-off controlled ventilation system with heat recovery. The results were assessed using the software supplied by the manufacturer of Testo Comfort – Software X35.

In all of the surveyed houses, the device with the probe was placed in the bedroom inhabited by two adults, with comparable air volume. The probe was placed in the height of 700 to 900 mm above the floor and with a minimum distance of 1.5 m from persons. Measurements were performed with the door closed so as not to be affected by air from other residential premises. Measuring was always performed for 24 h and values of CO₂, relative humidity, temperature, and absolute pressure were recorded every 10 min; 144 individual measured points were obtained from each 24-hour measuring cycle. The CO₂ value is the critical parameter for indoor environment quality.

Fig. 1. Testo 435 – 2 measuring instrument with IAQ probe

RESULTS AND DISCUSSION

Wooden house – Starý Vestec

Two measuring cycles were performed in this wooden house made of K-Kontrol panels and the results are stated in Table 2. The first measurements were performed without controlled ventilation and heat recovery (Fig. 2), while the second measurements were performed with controlled ventilation switched-on (Fig. 3).

Table 2. Measured values of parameters in Starý Vestec

Fig. 2. The course of monitored air quality parameters without controlled ventilation and heat recovery in Starý Vestec

The CO₂ curve in Fig. 2 clearly indicates the start of use of the surveyed bedroom and the people going to sleep at about 8.00 p.m. For the entire sleeping time, the CO₂ values oscillated around the acceptable value of 1,000 ppm. A rapid decline in CO₂ and temperature values at 8.00 a.m. indicates bedroom ventilation through a window. The relative humidity increase just before ventilation was caused by use of the bathroom adjacent to the surveyed bedroom, with direct entry to it.

Fig. 3. The course of monitored air quality parameters with controlled ventilation and heat recovery in Starý Vestec

The monitored values measured in the course of controlled ventilation operation are shown in Fig. 3. The main determining parameter of indoor environment quality, CO₂, moved along acceptable limits. The only extreme was the temperature and relative humidity decrease after 12:00 p.m. caused by ventilation through the window.

In both cases, the CO₂ value remained below or at the recommended CO₂ limit value of 1,000 ppm, i.e. well below the limit value of 1,500 ppm. In both cases, relative humidity remained at the lower limit of recommended values.

Wooden House – Vinoř

Even in this wooden house of panels, two measuring cycles were performed, and the results are specified in Table 3. The first 24-h measurements were performed without controlled ventilation (Fig. 4), while the second measurements were performed with controlled ventilation switched-on (Fig. 5).

Table 3. Measured Values of Parameters at Vinoř

Fig. 4. The course of monitored air quality parameters without controlled ventilation and heat recovery in Vinoř

CO₂ values in Fig. 4 indicate that the surveyed bedroom was used approximately from 8.00 p.m. The maximal allowed limit of CO₂, which is 1,500 ppm, was exceeded at 10.00 p.m. and the CO₂ value increased to 2,392 ppm at 5:50 a.m. when the inhabitants woke up. An interesting indicator is the increase of temperature in the bedroom at about 11.00 a.m. due to heat gains from sunshine due to south-east orientation of glass surfaces and sunny weather. Humidity decrease can be observed against the temperature increase.

Figure 5 shows monitored values with switched-on controlled ventilation system. Based on the CO₂ curve it is possible to discover for the people to go to bed at 11.00 p.m. The CO₂values were within acceptable values, except for the time period from 2.00 a.m. to 6.00 a.m., when they woke up. The values exceeded the upper limit of 1,500 ppm by a maximum of 214 ppm.