Stack Ventilation Performance in a Semi-Detached House After Limiting Energy Consumption for Space Heating

Abstract

Increasing requirements for reducing energy consumption result in window tightness, which decreases the air ventilation rate. This study examines the volume flow rate, stack pressure difference, and pressure losses for a one-person workroom of a semi-detached house under changing window tightness; the determination of the pressure losses and the uncertainty estimation of the examined quantities are described in full detail. The basic indoor air properties of relative humidity and density were determined only by readouts from a gauge and thermodynamic constants. One gauge with a vane probe measured the air velocity and temperature at a grille; a second gauge with an indoor air quality (IAQ) probe measured the mole fraction of carbon dioxide, temperature, absolute pressure, and humidity. The measurements were taken in ten one-week series throughout the year. Stack ventilation performance was good, as the IAQ satisfies the present requirements; however, the uncertainties sometimes exceeded the determined values significantly.

1. Introduction

Rising temperatures and a changing global climate are indicated as the results of increased greenhouse gas emissions; these climate changes seem to be so dramatic and irreversible that the Intergovernmental Panel on Climate Change (IPCC) on 8 August 2019 published a report that shows the need to reduce greenhouse gas emissions [1].

Many countries and international organizations have established official rules for reducing energy consumption, particularly limiting fossil fuel combustion, e.g., [2,3]. These new regulations impose new taxes and other charges that encourage residents to save energy. In space heating, this is performed by improving window airtightness, for the heat demand for warming ventilation air is higher than heat losses through the walls. However windows should not be overly airtight so as to preserve the golden rule, “build tight, ventilate right” [4].

Ventilation is the process of replacing stale indoor air with fresh air. This can be enabled using mechanical equipment or without any external work, generally in the form of electrical energy: the former is called mechanical ventilation, the latter natural ventilation. Ventilation air movement in stack ducts is forced by the difference between the outdoor and indoor air specific weights, which results from their temperature discrepancy; simultaneously, ambient air must be supplied to the room, which is enabled by airing or infiltration. Stack ventilation is the simplest and cheapest way of exhausting air from rooms; on the other hand, it is affected by weather conditions including the temperature and vector of wind velocity. These factors may enhance or weaken the stack effect. Hybrid or mixed ventilation is natural ventilation extended by fans; it compensates the above-mentioned weaknesses [5].

Hybrid ventilation equipped with variable-speed fans enables energy consumption reduction by 8.37% for a cross-flow system of natural ventilation, whereas for fully mechanical cooling, the savings are about 27.92% [6]

A mixed mode that allows users to open windows enables up to 40% energy consumption reduction in comparison to mechanical ventilation [7].

The transformation processes from natural (passive) ventilation to a hybrid form were analyzed for a library building; the former extended with heating may be applied in the springtime or autumn. However, after some changes in the building design and construction, stack ventilation could adequately ventilate spaces with more tenants in a natural way [8].

The most common ventilation type in existing buildings is natural ventilation, mainly stack ventilation, so replacing old windows with tighter ones affects stack ventilation performance.

Greater airtightness decreases the concentrations of carbon dioxide or volatile organic compounds, but it increases the concentrations of particular matter of 2.5 µm and nitrogen dioxide [9]. The lower infiltration levels provide improve indoor thermal comfort [10,11].

Finnish detached houses ventilated by the stack effect are supplied with outdoor air mainly due to infiltration [12]. The leakage air change rate per hour at 50 Pa of pressure difference n₅₀ depends on wind conditions at the building location or the placement of the crevices; it is higher for imbalanced systems where the supply and exhaust air flow rates differ by 15%, and this increases with the number of floors.

Enhancement in stack ventilation by installing an exhaust vent at the end of the stack duct over the roof in a multi-storey building was investigated in [13]. Enhancing is not a linear correspondence, for the maximal air flow occurs in the upper storeys when the vent works at 14.2% of its maximal rate; moreover, further increasing the vent rate decreases the exhaust air volume flow rate.

The stack effect depends on outdoor thermal conditions and is strongly affected by the speed and direction of the wind; the wind effect is random, and its prediction is difficult; it may increase the air flow rate in relation to the stack effect [14]. However, other measurements lead to opposite conclusions [15]; stack ventilation may operate even when the temperature difference is less than 12 °C.

Tube houses are buildings that have differently shaped front and back façades; the former is windward, and the latter is downwind. The stack effect is enhanced by wind-driven cross-ventilation when the openings are properly operated, which enables reductions in energy costs for cooling by ca 50% in the demanding climatic conditions of India [16].

In Barcelona’s climate conditions, cross-ventilation when the air flows in and outflows from a room through natural openings, e.g., the windows, is superior to stack ventilation, for the latter one needs a longer time to open the windows to preserve the required indoor air quality [17].

The roof channels linking an opening in a building façade with a stack duct running through the ceiling cool flats passively, and they even reduce the indoor temperature by 4 °C in the climatic conditions of Dezful (in Iran) [18].

According to Polish rules, the air ventilation rate may not be less than 20 m³/h per person in the design, which complies with regulations [19] and meets the standards [20].

Hybrid kitchen ventilation in a 33-storey building was researched both theoretically and experimentally; the analysis was basis on the Bernoulli and continuity equations. The stack effect in the summer can be neglected; it increased the ventilation air flow by 4–12% in the cold months, which raised the heat demand by 0.5–6% [21].

Stack ventilation should be enhanced by applying a rotary chimney cap in Polish climatic conditions [22]; then, wind will significantly increase the stack ventilation effectiveness [23].

A stack ventilation operation in a multi-storey building was simulated assuming a non-homogeneous density field. For this purpose, the building space was divided into 120 zones. The simulation showed that the airflow through the ventilation opening was in the transitional flow regime, and the discharge coefficient was 0.74 [24]; however, this coefficient should be 0.83, according to [23].

Natural ventilation operation in buildings with a double-skin façade (DSF) is a different area of research [25,26,27,28], as the ventilation air flows through a hollow space generated between an external load-bearing wall and a supplementary outer surface; this surface is generally made from glass and functions as an aesthetical component. The stack ventilation performance and indoor air quality in buildings with a DSF have been extensively researched in terms of energetic or economic profits.

An earlier study led to the conclusion that wind enhances stack ventilation operation [29]. In this paper, stack ventilation performance is studied in other building.

This study aimed at assessing stack ventilation performance in a building where the window airtightness is increased as the external temperature is reduced. The assessment of ventilation performance depends on the following IAQ parameters: carbon dioxide mole fraction, temperature, humidity, and absolute pressure, which are determined in a workroom; to determine the air volume flow rate, stack pressure difference, and pressure losses, the air velocity and temperature at the grille are additionally measured.

2. Materials and Methods

The measurements were conducted in a one-person workroom of a two-storey semi-detached house located in Białystok (Poland) in the IV climatic zone; the house has a simple cubic shape; the workroom is placed on the ground floor; and the measurements were performed for 12 months in the years 2022–2023; eventually, 10 seven-day measurement series were taken.

Figure 1 shows the loci of an IAQ and vane measuring probes; the former is placed on the windowsill, and the latter is placed at the grille 2.05 m above the floor; each is connected with a distinct Testo 435-4 gauge; the measurements are recorded every 5 min. The IAQ probe measures the CO₂ mole fraction χ_CO2, absolute pressure p_abs, internal temperature t_i, relative humidity φ, and external temperature t_e; the vane measuring probe measures the average velocity v_g and temperature t_g at the inlet to the grille.

Table 1. Measurement properties of the applied Testo 435-4 gauge [31].

Probe	Measured Quantity	Symbol	Range	Uncertainty
IAQ	internal dry-bulb temperature	ti	0–50 °C	±0.3 deg
	relative humidity	φ	2–98%	±2%
	absolute pressure	pabs	600–1150 hPa	±10 hPa
	CO2 mole fraction	χCO2	0–5000 ppm	±75 ppm ±0.03 χCO2
			5001–10000	±150 ppm ±0.05 χCO2
thermocouple K	external dry-bulb temperature	te	−60–+400 °C	±0.0075·│te│ [deg]
vane measuring probe	velocity	vg	0.3–20 m/s	±0.1 m/s ±0.015 vg
	temperature	tg	0–50 °C	±0.5 deg

shows the ranges and accuracies of the measurement system; “deg” is the unit of the temperature difference, whose value is exactly the same in both scales, absolute (K) and relative (°C); the International Union of Pure and Applied Chemistry [30] defines “ppm” as the number of micromoles of a substance per one mole of air.

The volume flow rate through the grille is determined assuming the velocity is constant in each five-minute (300 s) period:

$${\dot{V}}_g=300F_g{\displaystyle \sum _{i=1}^{12}{v}_{gi}} \left[{\displaystyle \frac{{\mathrm{m}}^3}{\mathrm{h}}}\right],$$

(1)

where:

• F_g—the surface area of the grille openings [m²].

2.1. Moist Air Properties

The moist air properties depend on the relative humidity φ, which is the ratio between the water vapour mass in the air m_v and the maximum water vapour mass which saturates the air m_s [27,28]:

$$\phi ={\displaystyle \frac{m_v}{m_s}}={\displaystyle \frac{\frac{p_{v}V}{R_{v}T}}{\frac{p_{s}V}{R_{v}T}}}={\displaystyle \frac{p_v}{p_s}} \left[-\right],$$

(2)

where:

• p_v—The partial pressure of water vapour [Pa],
• p_s—The saturation pressure of water vapour at the dry-bulb temperature [Pa],
• R_v—The gas constant of water vapour [J/(kg·K)],
• T—The temperature [K],
• V—The volume [m³].

Since every value of the saturation pressure is assigned to one temperature value, it is a function which is tabled. Hence, the saturation pressure p_s is read out at the dry-bulb temperature T. The specific humidity ω is obtained as follows [32,33]:

$$\mathsf{\omega }={\displaystyle \frac{\frac{R_{air}}{R_v}\phi p_s}{p_{abs}-\phi p_s}} \left[{\displaystyle \frac{\mathrm{kg} {\mathrm{H}}_2\mathrm{O}}{\mathrm{kg} \mathrm{dry} \mathrm{air}}}\right],$$

(3)

where:

• p_abs—The absolute pressure [Pa],
• R_air—The gas constant of air [J/(kg·K)].

The moist air density ρ is defined by the following formula [32]:

$$\rho ={\displaystyle \frac{p_{abs}\left(1+\mathsf{\omega }\right)}{T\left(R_{air}+\mathsf{\omega }{R}_v\right)}} \left[{\displaystyle \frac{\mathrm{kg}}{{\mathrm{m}}^3}}\right],$$

(4)

After substituting Equations (2) and (3) into Equation (4), one obtains:

$$\rho ={\displaystyle \frac{1}{T}}\left[{\displaystyle \frac{p_{abs}}{R_{air}}}+p_v\left({\displaystyle \frac{1}{R_v}}-{\displaystyle \frac{1}{R_{air}}}\right)\right]={\displaystyle \frac{1}{T}}\left[{\displaystyle \frac{p_{abs}}{R_{air}}}+\phi p_s\left({\displaystyle \frac{1}{R_v}}-{\displaystyle \frac{1}{R_{air}}}\right)\right] \left[{\displaystyle \frac{\mathrm{kg}}{{\mathrm{m}}^3}}\right].$$

(5)

The moist air density has not been expressed earlier in the form of Equation (5); this equation seems to be highly convenient, as the moist air density may be determined by applying only the readouts from the gauge and the thermodynamic constants; the former are the dry-bulb temperature T, absolute pressure p_abs, and relative humidity φ; and the latter are the gas constants R_air and R_v and water saturation pressure p_s at temperature T.

The mass of dry air is applied in the psychrometric charts to determine the intensive parameters, so the ratio between it and the moist air volume is as follows:

$${\rho }_{da}={\displaystyle \frac{\rho }{1+\mathsf{\omega }}}={\displaystyle \frac{p_{abs}}{T\left(R_{air}+\mathsf{\omega }{R}_v\right)}} \left[{\displaystyle \frac{\mathrm{kg} \mathrm{dry} \mathrm{air}}{{\mathrm{m}}^3}}\right];$$

(6)

Substituting Equations (2) and (3) into Equation (6), one obtains:

$${\rho }_{da}={\displaystyle \frac{p_{abs}-p_v}{T{R}_{air}}}={\displaystyle \frac{p_{abs}-\phi p_s}{T{R}_{air}}} \left[{\displaystyle \frac{\mathrm{kg} \mathrm{dry} \mathrm{air}}{{\mathrm{m}}^3}}\right].$$

(7)

Equation (7) has the same advantages as mentioned above for Equation (5).

2.2. Stack Pressure Difference

The stack pressure difference p_spd is computed using the following equation:

$$p_{spd}=gh\left({\overline{\rho }}_e-{\overline{\rho }}_i\right) \left[\mathrm{Pa}\right],$$

(8)

where ${\overline{\rho }}_e$ and ${\overline{\rho }}_i$ are the hourly mean of the values obtained from Equation (5) at T_e and T_i, respectively.

• g—The acceleration due to gravity [m/s²],
• h—The height measured from the grille centre to the end of the stack ventilation duct [m].

2.3. Pressure Losses

The air stream flowing through the workroom and the ductwork encounters the following resistances: the window, grille, tube at a diameter of 130 mm, outflow from this tube to the vertical brick duct, this duct, and outflow from this duct to the atmosphere; the total pressure losses are the sum of the losses due to the above resistances:

$$\Delta p_l=\Delta p_w+\Delta p_g+\Delta p_t+\Delta p_{t-d}+\Delta p_d+\Delta p_{out} \left[\mathrm{Pa}\right].$$

(9)

Figure 2 shows the stack duct. The determination of each summand is explained hereinafter.

Minor losses through the window Δp_w depend on the crevice size, which is changed by the owner; the crevice is the widest in summer and the narrowest in winter:

$$\Delta p_w={\displaystyle \frac{{\overline{\rho }}_e}{2}}{\left({\displaystyle \frac{{\overline{v}}_g{F}_g}{C_d{F}_c}}\right)}^2 \left[\mathrm{Pa}\right],$$

(10)

where:

• C_d—The discharge coefficient of the window crevice [-] [32],
• F_c—The surface area of the window crevice [m²],
• ${\overline{v}}_g$—The hourly mean of the air velocity flowing through the grille [m/s].

The minor losses caused by the grille are computed as follows:

$$\Delta p_g=K_g{\displaystyle \frac{{\overline{\rho }}_g{\overline{v}}_g^2}{2}} \left[\mathrm{Pa}\right],$$

(11)

where:

• K_g—The grille loss coefficient [-],
• ${\overline{\rho }}_g$—The moist air density at the grille obtained from Equation (4) at T_g [kg/m³].

The major losses in the horizontal tube linking the grille with the vertical stack duct are obtained from the Darcy–Weisbach equation:

$$\Delta p_t=f^{″}{\displaystyle \frac{L_t}{d_t}}{\displaystyle \frac{{\overline{\rho }}_g{\overline{v}}_g^2{F}_g^2}{2F_t^2}} \left[\mathrm{Pa}\right],$$

(12)

where:

• L_t—The tube length [m],
• d_t—The tube diameter [m],
• and f″ is the friction factor coefficient for non-stabilized flow, as the tube is short, so the turbulent velocity profile has yet not fully developed:

$$f^{″}=k^{″}f \left[-\right],$$

(13)

where f is the friction factor determined by the Colebrook–White equation:

$${\displaystyle \frac{1}{\sqrt{f}}}=-2.0\mathit{lg}\left({\displaystyle \frac{\mathsf{\epsilon }}{3.7}}+{\displaystyle \frac{2.51}{\mathit{Re}\sqrt{f}}}\right) \left[-\right],$$

(14)

where ε is the relative roughness; further on, ε_d denotes the relative roughness of the stack duct, and ε_t denotes the relative roughness of the tube; k″ is a coefficient of non-stabilized flow [34]:

$$k^{″}\approx 1.36{\displaystyle \frac{{\mathit{Re}}_t^{0.05}}{{\left(\frac{L_t}{d_t}\right)}^{0.2}}} \left[-\right]$$

(15)

where the Reynolds number for the flow in the tube is obtained as follows:

$${\mathit{Re}}_t={\displaystyle \frac{4{\overline{v}}_g{F}_g}{\mathsf{\pi }{d}_t{\overline{\nu }}_g}} \left[-\right],$$

(16)

where the kinematic viscosity of moist air at the grille ${\overline{\nu }}_g$ is determined as follows:

$${\overline{\nu }}_g={\displaystyle \frac{{\overline{\omega }}_g{\overline{\mu }}_{vg}+\left(1-{\overline{\omega }}_g\right){\overline{\mu }}_{air g}}{{\overline{\rho }}_g}} \left[{\displaystyle \frac{{\mathrm{m}}^2}{\mathrm{s}}}\right],$$

(17)

where:

• ${\overline{\omega }}_g$—The hourly mean of the specific humidity at the grille $\left[{\displaystyle \frac{\mathrm{kg} {\mathrm{H}}_2\mathrm{O}}{\mathrm{kg} \mathrm{dry} \mathrm{air}}}\right]$,
• μ_vg—The dynamic viscosity of the water vapour at the grille [Pa·s],
• μ_air g—The dynamic viscosity of the dry air at the grille [Pa·s].

The minor losses of the outflow from the horizontal tube to the vertical rectangular stack duct Δp_t-d are as follows:

$$\Delta p_{t-d}=K_{t-d}{\displaystyle \frac{{\overline{\rho }}_g{\overline{v}}_d^2}{2}} \left[\mathrm{Pa}\right],$$

(18)

where:

• K_t-d—The loss coefficient of the outflow from the tube to the duct [-],
• v_d—The velocity in the vertical rectangular stack duct, obtained from the following equation:

$$v_d={\displaystyle \frac{{\overline{v}}_g{F}_g}{F_d}} \left[{\displaystyle \frac{\mathrm{m}}{\mathrm{s}}}\right],$$

(19)

where:

• F_d—The surface area of the stack duct [m²].

The major losses of the vertical rectangular stack duct are obtained from the Darcy–Weisbach equation Δp_d:

$$\Delta p_d=f_d{\displaystyle \frac{h}{d_h}}{\displaystyle \frac{{\overline{\rho }}_g{v}_d^2}{2}} \left[\mathrm{Pa}\right],$$

(20)

where:

• d_h—The hydraulic diameter of the stack duct [m].

The friction factor of the stack duct is obtained from Equation (14) after substituting ε = ε_d; the Reynolds number is as follows:

$${\mathit{Re}}_d={\displaystyle \frac{d_h{v}_d}{{\overline{\nu }}_g}} \left[-\right],$$

(21)

The minor losses of the outflow from the stack duct are as follows:

$$\Delta p_{out}=K_{out}{\displaystyle \frac{{\overline{\rho }}_g{v}_d^2}{2}} \left[\mathrm{Pa}\right],$$

(22)

where K_out is the overall loss coefficient of the outflow from the stack duct to outside:

$$K_{out}=k_{\Delta }{\displaystyle \frac{4.06}{{\mathit{Re}}_d^{0.118}}}{C}_{1}A{K}_o \left[-\right],$$

(23)

where:

• k_Δ depends on the relative roughness of the duct [-],
• C₁ is the correspondence of the relative elongation that is the ratio between the height and width of a rectangular duct (for a circular or square shape C₁ = 1) [-],
• A is the function of the bend angle from the original straight pipe [-],
• K₀ is the minor losses coefficient [-].

Table 2. The data to determine pressure losses.

The Name of a Quantity	Symbol	Units	Value	Uncertainty	Comments
the function of the bend angle (a)	A	[-]	1.2	1
the correspondence of the relative elongation (a)	C1	[-]	0.97	0.1
the discharge coefficient of the window crevice (a)	Cd	[-]	0.6	1
the hydraulic diameter of the stack duct	dh	[m]	0.1853	0.0007584
the tube diameter	dt	[m]	0.13	0.0005
the surface area of the window crevice	Fc	[m2]	0.05762	0.0008626	April–October
			0.04128	0.0008613	November, December
			0.03268	0.0008608	January–March
the surface area of the grille opening	Fg	[m2]	0.009727	0.0002042
the gravitational acceleration	g	[m/s2]	9.807	0.0001
the height of the stack duct	h	[m]	7.3	0.01
the grille loss coefficient (a)	Kg	[-]	0.9068	0.00001
the outlet loss coefficient (a)	Ko	[-]	0.99	0.1
the loss coefficient of the outflow from the tube to duct (a)	Kt-d	[-]	4.418	0.00001
the function of the relative roughness of the duct (a)	kΔ	[-]	1	1
the tube length	Lt	[m]	0.13	0.001
the gas constant of air	Rair	[J/(K·kg)]	287.2	0.0001
the gas constant of vapour	Rv	[J/(K·kg)]	461.5	0.0001
the relative roughness of the stack duct (a)	εd	[-]	0.01619	0.00000001
the relative roughness of the tube (a)	εt	[-]	2.308 × 10−5	0.000000001

^(a) According to the handbook [34].

shows the data for performing the computations.

3. Measurement Uncertainty Estimation

Estimation of the measurement uncertainty is carried out according to Moffat [35] at a 95% confidence level. When the result is a function F (of n quantities), the following is obtained:

$$F=F\left(X_1, X_2, X_3, \dots ,X_n\right)$$

(24)

The uncertainty is obtained from the following formula [35]:

$$\delta F=\sqrt{{{\displaystyle \sum _{i=1}^n\left(\frac{\partial F}{\partial X_i}\delta X_i\right)}}^2},$$

(25)

where:

• δF—The total uncertainty of a determined quantity F,
• δX_i—The overall fixed error uncertainty.

The uncertainty of a temperature-depended physical property whose values are tabulated is the root-square sum of the uncertainty of a value in the table δX_tab and the impact of the temperature measurement uncertainty:

$$\delta X\left(t\right)=\sqrt{{\left(\delta X_{tab}\right)}^2+{\left({\displaystyle \frac{\partial X\left(t\right)}{\partial t}}\delta t\right)}^2},$$

(26)

where the function X(t) is approximated with third-degree polynomial from the values in the range between the lowest and highest measured temperature:

$$X\left(t\right)=a{t}^3+b{t}^2+ct+d.$$

(27)

The uncertainty δX_tab is assumed to be equal to 10 units of the least significant digit; eventually, one obtains the following:

$$\delta X\left(t\right)=\sqrt{{\left(\delta X_{tab}\right)}^2+{\left[\left(3a{t}^2+2bt+c\right)\delta t\right]}^2}.$$

(28)

When $\overline{F}\left(X\right)$ is the arithmetic mean and the measurement uncertainties dX_j differ in their values, Equation (25) simplifies to:

$$\delta \overline{F}={\displaystyle \frac{1}{n}}\sqrt{{{\displaystyle \sum _{j=1}^n\left(\delta X_j\right)}}^2},$$

(29)

When the measurement uncertainties are uniform, the following is obtained:

$$\delta \overline{F}={\displaystyle \frac{\delta X}{\sqrt{n}}}.$$

(30)

A detailed description of the uncertainty estimation is provided in Appendix A.

4. Results and Discussion

Since the total pressure losses correspond to the flow rate through the grille, their minimal and maximal values occur at the same time.

Table 3. The measured extremal IAQ parameters in the workroom.

	Minimum						Maximum
	CO2	Date	ti	Data	φ	Date	CO2	Data	ti	Date	φ	Date
	[ppm]		[°C]		[%]		[ppm]		[°C]		[%]
October	322	19 11:00	13.8	21 07:00	45.94	21 21:00	419	21 05:00	19.9	17 16:00	45.94	18 17:00
November	394	15 05:00	−5.3	19 21:00	58.64	17 12:00	520	19 20:00	10.9	14 21:00	58.64	21 20:00
December	410	1 05:00	4.9	2 20:00	53.72	2 15:00	486	1 00:00	11.2	1 00:00	53.72	6 21:00
January	356	24 15:00	16.3	19 02:00	39.33	24 15:00	452	19 11:00	18.6	26 00:00	39.33	24 22:00
February	348	19 14:00	17.2	14 19:00	34.65	19 18:00	431	14 11:00	18.9	19 09:00	34.65	17 23:00
March	340	15 14:00	17.4	12 17:00	31.31	9 19:00	495	8 22:00	19.1	14 22:00	31.31	14 21:00
April–May	312	3 11:00	11.3	6 07:00	25.11	7 11:00	416	1 05:00	21.4	3 11:00	25.11	2 16:00
June	281	10 18:00	19.0	15 06:00	50.88	12 19:00	380	13 01:00	22.4	10 16:00	50.88	9 00:00
July	278	26 15:00	19.0	28 05:00	54.18	26 10:00	471	31 00:00	24.1	26 10:00	54.18	28 22:00
September	274	23 13:00	16.8	20 04:00	57.55	22 07:00	335	16 20:00	21.6	17 08:00	57.55	23 20:00

shows that the relative humidity and temperature values satisfy the regulation [36] as they are in the permitted range; temperatures that are too low are measured only during airing. The maximal CO₂ mole fraction in the workroom does not exceed the outer mole fraction by more than 700 ppm; this parameter is also within the acceptable limits [37].

4.1. Moderate Tightness in Autumn

In October, the lowest total pressure losses of 0.92 Pa and the lowest flow rate through the grille of 32.1 m³/h were observed on the 17th at 16:00; whereas their highest values of 7.82 Pa and 95.28 m³/h were observed on the 19th at 14:00. The lowest stack pressure difference of −1.11 Pa was observed on the 18th at 10:00; its highest value of 5.56 Pa was observed on the 20th at 5:00. The lowest ratio between the stack pressure difference and the pressure losses of 15.30% was observed on the 21st at 10:00; its highest value of 154.37% was observed on the 17th at 17:00; this ratio was in the range of 90–110% for 6.51% of the experiment’s duration; its negative value was observed for 0.59% of the experiment’s duration. Figure 3 shows the hourly changes in the stack pressure difference, pressure losses, and the flow rate through the grille.

The lowest uncertainties of the pressure losses of 1.96 Pa and the air flow rate of 4.86 m³/h were observed on the 17th at 16:00; their highest values of 5.62 Pa and 6.06 m³/h were observed on the 19th at 14:00. The lowest uncertainty of the stack pressure difference of 1.2 Pa was observed on the 18th at 10:00; its highest value of 1.26 Pa was observed on the 21st at 6:00. Figure A1 shows the detailed results of the uncertainties.

The lowest relative uncertainties of the pressure losses of 71.91% and the volume flow rate of 6.36% were observed on the 19th at 14:00; their highest values of 213.04% and 15.13%, respectively, were observed on the 17th at 16:00. The lowest relative uncertainty of the stack pressure difference of 22.58% was observed on the 20th at 5:00; its highest value of 489.79% was observed on the 18th at 12:00.

In November, the lowest total pressure losses of 4.9 Pa, flow rate through grille of 73.51 m³/h, and stack pressure difference of 3.34 Pa were observed on the 15th at 10:00; the highest total pressure losses of 10.86 Pa and flow rate of 109.95 m³/h were observed on the 18th at 20:00; the highest stack pressure difference of 7.67 Pa was observed on the 19th at 6:00. The lowest ratio between the stack pressure difference and the pressure losses of 38.77% was observed on the 16th at 12:00; its highest value of 102.30% was observed on the 19th at 21:00; this ratio was in the range of 90–110% for 8.80% of the experiment’s duration. The detailed data are plotted in Figure 4.

The lowest uncertainty of the pressure losses of 4.29 Pa was observed on the 15th at 10:00; its highest value of 6.89 Pa was observed on the 18th at 20:00. The lowest uncertainty of the volume flow rate of 3.37 m³/h was observed on the 14th at 21:00; its highest value of 6.46 m³/h was observed on the 18th at 20:00. The lowest uncertainty of the stack pressure difference of 1.24 Pa was observed on the 15th at 3:00; its highest value of 1.28 Pa was observed on the 19th at 21:00. Figure A2 shows the detailed results of the uncertainties.

The lowest relative uncertainty of the pressure losses of 63.42% was observed on the 18th at 20:00; its highest value of 87.44% was observed on the 15th at 10:00. The relative uncertainty of the volume flow rate of 4.11% was observed on the14th at 21:00; its highest value of 7.92% was observed on the15th at 10:00. The lowest relative uncertainty of the stack pressure difference of 16.69% was observed on the 19th at 6:00; its highest value of 37.24% was observed on the 15th at 10:00. Figure A2 shows the detailed results of the uncertainties.

4.2. Increased Tightness in Winter

In December, the window tightness in the house was increased. The lowest total pressure difference of 4.35 Pa and flow rate of 69.66 m³/h were observed on the 7th at 15:00; their highest values of 10.08 Pa and 105.31 m³/h were observed on the 5th at 8:00. The lowest stack pressure difference of 5.53 Pa was observed on the 7th at 20:00; its highest value of 8.02 Pa was observed on the 2nd at 22:00. The lowest ratio between the stack pressure difference and the pressure losses of 65.09% was observed on the 5th at 8:00; its highest value of 132.85% was observed on the 7th at 15:00; this ratio was in the range of 90–110% for 48.51% of the experiment’s duration. Figure 5 shows the detailed data.

The lowest uncertainty of the pressure losses of 4.00 Pa was observed on the 7th at 15:00; its highest value of 6.58 Pa was observed on the 5th at 8:00. The lowest uncertainty of the volume flow rate of 2.37 m³/h was observed on the 1st at 00:00; its highest value of 6.26 m³/h was observed on the 5th at 8:00. The lowest uncertainty of the stack pressure difference of 1.25 Pa was observed on the 1st at 00:00; its highest value of 1.27 Pa was observed on the 2nd at 22:00. Figure A3 shows the detailed results of the uncertainties.

The lowest relative uncertainty of the pressure losses of 65.30%% was observed on the 5th at 8:00; its highest value of 91.98% was observed on the 7th at 15:00. The relative uncertainty of the volume flow rate of 3.02% was observed on the 1st at 00:00; its highest value of 7.98% was observed on the 7th at 15:00. The lowest relative uncertainty of the stack pressure difference of 15.86% was observed on the 2nd at 22:00; its highest value of 22.67% was observed on the 7th at 20:00.

4.3. The Highest Tightness in Winter

In January, the lowest total pressure losses of 2.86 Pa and flow rate of 54.80 m³/h were observed on the 19th at 8:00; the highest total pressure losses of 13.51 Pa and flow rate of 120.08 m³/h were observed on the 21st at 8:00. The lowest stack pressure difference of 4.77 Pa was observed on the 19th at 10:00; its highest value of 7.00 Pa was observed on the 25th at 7:00. The lowest ratio between the stack pressure difference and the pressure losses of 47.14% was observed on the 21st at 8:00; its highest value of 178.76% was observed on the 25th at 15:00; this ratio was in the range of 90–110% for 8.88% of the experiment’s duration. The comprehensive data are plotted in Figure 6.

The lowest uncertainties of the pressure losses of 3.24 Pa and air flow rate of 5.28 m³/h were observed on the 19th at 8:00; their highest values of 8.64 Pa and 6.54 m³/h were observed on the 21st at 8:00. The lowest uncertainty of the stack pressure difference of 1.24 Pa was observed on the 24th at 12:00; its highest value of 1.25 Pa was observed on the 19th at 20:00. Figure A4 shows the detailed results of the uncertainties.

The lowest relative uncertainties of the pressure losses of 63.96% and the volume flow rate of 5.45% were observed on the 21st at 8:00; their highest values of 113.62% and 9.63%, respectively, were observed on the 19th at 8:00. The lowest relative uncertainty of the stack pressure difference of 17.89% was observed on the 25th at 7:00; its highest value of 26.15% was observed on the 19th at 10:00.

In February, the lowest total pressure difference of 2.40 Pa and flow rate of 49.61 m³/h were observed on the 14th at 19:00; the highest total pressure difference of 9.17 Pa and flow rate of 99.22 m³/h were observed on the 19th at 16:00. The lowest stack pressure difference of 3.57 Pa was observed on the 14th at 13:00; its highest value of 6.95 Pa was observed on the 19th at 23:00. The lowest ratio between the stack pressure difference and the pressure losses of 52.93% was observed on the 14th at 13:00; its highest value of 241.06% was observed on the 14th at 19:00; this ratio was in the range of 90–110% for 10.65% of the experiment’s duration. The detailed data are plotted in Figure 7.

The lowest uncertainties of the pressure losses of 3.15 Pa and air flow rate of 5.18 m³/h were observed on the 14th at 19:00; their highest values of 7.78 Pa and 6.13 m³/h were observed on the 19th at 16:00. The lowest uncertainty of the stack pressure difference of 1.23 Pa was observed on the 18th at 12:00; its highest value of 1.25 Pa was observed on the 14th at 20:00. Figure A5 shows the detailed results of the uncertainties.

The lowest relative uncertainties of the pressure losses of 84.80% and the volume flow rate of 6.18% were observed on the 19th at 16:00; their highest values of 131.18% and 10.44%, respectively, were observed on the 14th at 19:00. The lowest relative uncertainty of the stack pressure difference of 18.01% was observed on the 19th at 23:00; its highest value of 34.61% was observed on the 14th at 13:00.

In March, the lowest total pressure difference of 1.74 Pa and volume flow rate of 43.36 m³/h were observed on the 14th at 17:00; the highest total pressure difference of 13.04 Pa and the greatest volume flow rate of 119.47 m³/h were observed on the 11th at 22:00. The lowest stack pressure difference of 1.57 Pa was observed on the 14th at 12:00; its highest value of 8.79 Pa was observed on the 13th at 1:00. The lowest ratio between the stack pressure difference and the pressure losses of 44.88% was observed on the 15th at 4:00; its highest value of 173.87% was observed on the 10th at 18:00; this ratio was in the range of 90–110% for 18.34% of the experiment’s duration. The detailed data are plotted in Figure 8.

The lowest uncertainties of the pressure losses of 2.67 Pa and air flow rate of 4.66 m³/h were observed on the 14th at 17:00; their highest values of 10.42 Pa and 6.51 m³/h were observed on the 12th at 15:00. The lowest uncertainty of the stack pressure difference of 1.21 Pa was observed on the 14th at 10:00; its highest value of 1.27 Pa was observed on the 13th at 1:00. Figure A6 shows the detailed results of the uncertainties.

The lowest relative uncertainties of the pressure losses of 79.86% and the volume flow rate of 5.47% were observed on the 11th at 22:00; their highest values of 152.95% and 11.67%, respectively, were observed on the 14th at 17:00. The lowest relative uncertainty of the stack pressure difference of 14.42% was observed on the 13th at 1:00; its highest value of 77.43% was observed on the 14th at 12:00.

4.4. Moderate Tightness in Spring and Summer

In April–May, the lowest total pressure losses of 1.45 Pa and volume flow rate of 40.44 m³/h were observed on the 1st at 19:00; the highest total pressure losses of 7.62 Pa and volume flow rate of 93.44 m³/h were observed on the 6th at 3:00. The lowest stack pressure difference of −5.99 Pa was observed on the 2nd at 10:00, its highest value of 5.64 Pa was observed on the 1st at 4:00. The lowest ratio between the stack pressure difference and the pressure losses of 13.12% was observed on the 2nd at 8:00; its highest value of 150.57% was observed on the 1st at 19:00; this ratio was in the range of 90–110% for 2.37% of the experiment’s duration; its negative value was observed for 11.83% of the experiment’s duration. The detailed data are plotted in Figure 9.

The lowest uncertainty of the pressure losses of 2.81 Pa was observed on the 1st at 19:00; its highest value of 9.37 Pa was observed on the 6th at 3:00. The lowest uncertainty of the volume flow rate of 2.86 m³/h was observed on the 30th at 21:00; its highest value of 6.02 m³/h was observed on the 6th at 3:00. The lowest uncertainty of the stack pressure difference of 1.17 Pa was observed on the 2nd at 10:00; its highest value of 1.26 Pa was observed on the 1st at 5:00. Figure A7 shows the detailed results of the uncertainties.

The lowest relative uncertainty of the pressure losses of 122.92% was observed on the 6th at 3:00; its highest value of 193.94% was observed on the 1st at 19:00. The relative uncertainty of the volume flow rate of 3.60% was observed on the 30th at 21:00; its highest value of 12.38% was observed on the 1st at 19:00. The lowest relative uncertainty of the stack pressure difference of 19.49% was observed on the 2nd at 10:00; its highest value of 256.08% was observed on the 4th at 12:00.

In June, the lowest total pressure difference of 0.13 Pa and volume flow rate of 11.96 m³/h were observed on the 10th at 9:00; their highest values of 6.44 Pa and 86.84 m³/h were observed on the 14th at 00:00. The lowest stack pressure difference of −4.47 Pa was observed on the 10th at 10:00; its highest value of 2.84 was observed on the 12th at 3:00. The lowest ratio between the stack pressure difference and the pressure losses of 1.33% was observed on the 10th at 19:00; its highest value of 82.95% was observed on the 14th at 22:00; this ratio was not in the range of 90–110% amid the experiment’s duration; its negative value was observed for 35.76% of the experiment’s duration. The detailed data are plotted in Figure 10.

The lowest uncertainties of the pressure losses of 0.95 Pa and air flow rate of 4.50 m³/h were observed on the 10th at 9:00; their highest values of 6.38 Pa and 5.89 m³/h were observed on the 14th at 00:00. The lowest uncertainty of the stack pressure difference of 1.17 Pa was observed on the 10th at 10:00; its highest value of 1.23 Pa was observed on the 15th at 4:00. Figure A8 shows the detailed results of the uncertainties.

The lowest relative uncertainties of the pressure losses of 99.06% and the volume flow rate of 6.78% were observed on the 14th at 00:00; their highest values of 717.87% and 37.62%, respectively, were observed on the 10th at 9:00. The lowest relative uncertainty of the stack pressure difference of 26.08% was observed on the 10th at 10:00; its highest value of 4181.48% was observed on the 10th at 7:00.

At the turn of July and August, the lowest total pressure difference of 0.24 Pa and flow rate of 16.31 m³/h were observed on the 30 July at 19:00; their highest values of 7.94 Pa and 97.20 m³/h were observed on the 29 July at 17:00. The minimal stack pressure difference of −3.80 Pa was observed on the 31 July at 9:00; the maximal stack pressure difference of 3.27 Pa was observed on the 28 July at 4:00. The lowest ratio between the stack pressure difference and the pressure losses of 5.26% was observed on the 1st at 18:00; its highest value of 211.52% was observed on the 30th at 20:00; this ratio was in the range of 90–110% for 8.28% of the experiment’s duration; its negative value was observed for 31.36% of the experiment’s duration. The detailed data are plotted in Figure 11.

The lowest uncertainties of the pressure losses of 1.17 Pa and air flow rate of 4.57 m³/h were observed on the 30th at 19:00; their highest values of 8.47 Pa and 5.51 m³/h were observed on the 29th at 17:00. The lowest uncertainty of the stack pressure difference of 1.17 Pa was observed on the 31st at 9:00; its highest value of 1.23 Pa was observed on the 28th at 4:00. Figure A9 shows the detailed results of the uncertainties.

The lowest relative uncertainty of the pressure losses of 106.75% was observed on the 29th at 17:00; its highest value of 487.48% was observed on the 30th at 19:00. The lowest relative uncertainty of the volume flow rate of 6.07% was observed on the 28th at 4:00; its highest value of 28.05% was observed on the 30th at 19:00. The lowest relative uncertainty of the stack pressure difference of 30.88% was observed on the 31st at 9:00; its highest value of 3415.61% was observed on the 27th at 17:00.

In September, the lowest total pressure difference of 0.99 Pa and volume flow rate of 33.41 m³/h were observed on the 17th at 17:00; their highest values of 5.67 Pa and 81.62 m³/h were observed on the 20th at 15:00. The lowest stack pressure difference of −1.94 Pa was observed on the 18th at 16:00; its highest value of 3.62 Pa was observed on the 19th at 00:00. The lowest ratio between the stack pressure difference and the pressure losses of 0.61% was observed on the 22nd at 15:00; its highest value of 204.05% was observed on the 23rd at 15:00; this ratio was in the range of 90–110% for 4.73% of the experiment’s duration; its negative value was observed for 16.57% of the experiment’s duration. The detailed data are plotted in Figure 12.

The lowest uncertainties of the pressure losses of 2.10 Pa and air flow rate of 4.88 m³/h were observed on the 17th at 17:00; their highest values of 6.07 Pa and 5.64 m³/h were observed on the 20th at 15:00. The lowest uncertainty of the stack pressure difference of 1.19 Pa was observed on the 19th at 13:00; its highest value of 1.24 Pa was observed on the 19th at 1:00. Figure A10 shows the detailed results of the uncertainties.

The lowest relative uncertainty of the pressure losses of 107.19% was observed on the 20th at 15:00; its highest value of 212.38% was observed on the 17th at 17:00. The lowest relative uncertainty of the volume flow rate of 7.02% was observed on the 19th at 10:00; its highest value of 14.60% was observed on the 17th at 17:00. The lowest relative uncertainty of the stack pressure difference of 34.05% was observed on the 19th at 00:00; its highest value of 10,225.11% was observed on the 22nd at 15:00.

The measurements were performed in the IV climatic zone, which is the second coldest zone in Poland; there is a possibility of achieving a good IAQ in the coldest V zone even at the highest applied airtightness, as when the outside temperature falls, the stack pressure difference rises. The pressure losses remain more or less the same, as the internal temperature is constant; only the pressure loss through the window increases because the outside air density rises. Otherwise, in the I–III zones, a higher tightness might deteriorate IAQ, as the stack pressure difference lowers, whereas the pressure losses change much less.

In multi-storey buildings, the stack pressure difference increases (except on the top floor) because of the higher stack ducts, so a high IAQ might be maintained even at a higher tightness.

Properly adjusting the window crevice size to the outer temperature allows for maintaining a good IAQ whilst simultaneously providing thermal comfort without consuming additional energy, e.g., for driving a fan in a hybrid system.

5. Conclusions

In this study, the impact of changing the airtightness of windows on stack ventilation performance and indoor air quality was studied. Increased window airtightness deteriorated neither the stack ventilation performance nor IAQ parameters; therefore, there is no need to apply a hybrid system.

Although the stack effect enables driving the air flow through rooms, its impact on the flow rate is reduced by wind, which may even cause reverse flow through the stack duct. The stack effect rarely drives the airflow alone, as the relative time periods when the ratio between the stack pressure difference and the pressure losses are in the range of 90–110% change from 0% (in June) to 48.15% (in December); the mean value of this ratio is 11.72%; for the overwhelming majority of the time, the wind dominates over the force due to the specific weight difference.

The determined values are significantly affected by the measurement uncertainties, which influence the pressure losses the strongest because of the highly numerous variables and constants in the final equation; the stack pressure difference and the volume flow rate, which are calculated using much simpler equations, are affected by uncertainties greatly.