Humidity-sensitive, demand-controlled ventilation systems have been in use for many years in regions with oceanic climates. Some attempts have been made to apply this technology in Poland, which has a continental climate. This article evaluates the performance and energy consumption of such a system when applied in an eight-floor, multiunit, residential building, i.e., the virtual reference building described by the National Energy Conservation Agency (NAPE), Poland. Simulations using the computer program CONTAM were performed for the whole heating season based upon the climate in Warsaw. Besides passive stack ventilation, that served as a reference, two ventilation systems were studied: one standard and one “hybrid” system with additional roof fans. This study confirmed that the application of humidity-sensitive, demand-controlled ventilation in multiunit residential buildings in a continental climate (Dfb) led to significant energy savings (up to 11.64 kWh/m² of primary energy). However, the operation of the system on higher floors was found to be ineffective. Ensuring consistent operation of the system on all floors required supplementary fans. The introduction of a hybrid mode reduced carbon dioxide concentrations by approximately 32% in the units located in the upper part of the building. The energetic effect in such cases depends strongly on the electricity source. In the case of the national energy grid, savings of primary energy would be relatively low, i.e., 1.07 kWh/m², but in the case of locally produced renewable energy, the energy savings would be equal to 5.18 kWh/m².

There are many different factors affecting indoor air quality: environmental ones such as temperature, humidity, human activities within the building, smoking, cooking, and cleaning, but also external pollutants such as particulate matter, biological contaminants, and viruses or allergens. This study investigated the indoor air quality (IAQ) of a primary-school classroom in Cracow, Poland, based only on CO₂ concentration levels exhaled by occupants. In the 1960s, over a thousand schools were built in Poland using similar technology. Most of them are still in use, and in many cases, modernization works are being carried out to improve their building envelope and the comfort of their use. The analyzed school is one of several hundred similar ones in southern Poland. Therefore, analyzing the possibilities of improving IAQ is an important topic, and the results can be used in the modernization process for many other buildings. Measurements indicated that the CO₂ levels significantly exceeded acceptable standards, signaling poor air quality during usage time. This problem was connected mainly with the low efficiency of the natural ventilation system being used in the classroom. It is worth emphasizing that this type of ventilation system is the most commonly used ventilation solution in Polish schools. To address this problem, the classroom environment was simulated using CONTAM software, and the model was validated by comparing the simulated measurement data against the collected measurement data. Next, simulations for the entire heating season in Cracow were conducted, revealing that the IAQ remained consistently poor throughout this period. These findings highlight the persistent problem of inadequate ventilation in the classroom, which can have adverse effects on the health and performance of students and teachers. This article shows the usefulness of CONTAM for modeling not only gravity ventilation but also the window-opening process. The validated CONTAM model will be subsequently utilized to simulate annual IAQ conditions under various ventilation strategies in order to identify the most effective methods for maintaining acceptable IAQ while minimizing energy consumption. In our future analysis, the validated model will be used to test the following systems: demand-controlled ventilation (DCV), exhaust ventilation, and DCV/balanced ventilation with heat recovery.

This article proposes new values and geospatial models of winter and summer external design temperatures for designing buildings’ heating, ventilation, and air-conditioning (HVAC) systems. The climatic design parameters applicable in Poland for the sizing of these installations are approximately 50 years old and do not correspond to Poland’s current climate. New values of climatic design parameters were determined following the methods described in European standards and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) Handbook of Fundamentals. The determined climatic design parameters, particularly the winter and summer external design temperatures, were compared with those currently in force by law in Poland. The external air design dry-bulb temperatures presented in the article were developed based on meteorological and climatic data from the years 1991–2020 from two data sources: synoptic data from the Institute of Meteorology and Water Management (IMWM) in Poland and reanalysis models of the ERA5 database of the European Centre for Medium-Range Weather Forecasts (ECMWF). According to ASHRAE, with 99.6% and 0.4% frequency of occurrence, external air design dry-bulb temperatures for winter and summer were used to develop mathematical geospatial models of external design temperatures for the Central Europe area with Poland’s territory in the centre part. Scattered data from 667 meteorological stations were interpolated to 40,000 uniform mesh points using a biharmonic spline interpolation method to develop these models. Linear regression and ANOVA analysis for the ERA5-generated data from 900 checkpoint data items were used to estimate the correctness of these models. Verified models were used to calculate winter and summer external design temperature isolines presented together with colour space representation on Mercator projected maps of Central Europe.

Poor indoor air quality (IAQ) in naturally ventilated school buildings remains a widespread problem, particularly during the heating season, when limited ventilation leads to elevated CO₂ concentrations. At the same time, increasing ventilation rates may significantly increase energy demand, creating a conflict between IAQ and energy efficiency. This study aims to evaluate whether CO₂-based demand-controlled mechanical ventilation, particularly with heat recovery (HRV), can improve IAQ while maintaining acceptable energy performance in existing school buildings. A previously validated CONTAM model of a Polish primary school classroom was used to simulate natural ventilation, mechanical exhaust ventilation, and balanced ventilation with heat recovery. In mechanical systems, CO₂-based demand-controlled ventilation (DCV) was applied. The resulting airflow rates were then used in EnergyPlus simulations to assess seasonal heating and primary energy demand under Kraków climatic conditions. Increasing the outdoor air supply rate significantly reduced indoor CO₂ concentration but led to higher heating demand in exhaust ventilation systems. In contrast, HRV reduced heating energy demand by more than 80% compared with exhaust ventilation while maintaining comparable indoor air quality. Although HRV required additional electricity for fan operation, the total primary energy consumption remained low. The results demonstrate that CO₂-based DCV systems with heat recovery provide an effective balance between indoor air quality and energy performance. These findings support the application of HRV as a practical retrofit solution for improving ventilation in existing school buildings.

This paper presents the airflow characteristics of humidity-sensitive air inlet. This type of air inlets and exhausts are often part of demand control ventilation, especially in dwellings where humidity is an important indicator of ventilation needs. Humidity-controlled ventilation is one of the simplest implementations of smart ventilation, even in the case of a natural ventilation system. This type of solution leads to decreased energy consumption and increases the indoor air quality. A description of airflow characteristics is crucial for resolving these issues. The presented characteristics are based on the measurements of the indoor/outdoor relative humidity, airflow, and pressure drop across the air inlet. The characteristics are described based on a general power law flow model (V = C·∆pⁿ), which is the most suitable, for example, for the CONTAM multizone indoor air quality and ventilation analysis computer program. The characteristics include relationships between the indoor and outdoor relative humidity, hysteresis, and dynamic changes in indoor relative humidity. The simplified and complex formulas are presented. The accuracy of the airflow calculation based on these formulas is discussed.