Search

A building’s energy consumption is assessed considering the energy required for heating, cooling, lighting, and domestic hot water (DHW). Methodologies used to calculate energy certificates in European Union countries consider hot water consumption rates per person or per heated (floor) area, giving wide-ranging values (35–88 dm3/person/day). Using extreme parameters, it is possible to obtain a primary energy index that meets the legal requirements, although unrealistically large proportions of domestic hot water use relative to the total energy balance of the building may marginalize the influence of other components, such as fluctuations in heating, ventilation, or lighting. In the current work, the DHW consumption of three residential buildings was measured to verify the energy consumption for hot water preparation. Investigations were conducted based on the consumption of natural gas for DHW preparation. Experimentally obtained water consumption rates were determined per m2 of a dwelling and per person living in the building. The calculated indicators (0.85 ± 0.005 dm3/m2/day and 27.4 ± 1.4 dm3/person/day) were lower than those used for energy certifications of buildings. The experimentally obtained indicators were used in further theoretical energy assessments of six residential buildings. By adopting the designated indicators, the analyzed buildings met the legally required primary energy value (2/year) when using natural gas as a heat source. Applying more realistic DHW consumption values resulted in more accurate energy certifications.

Efficiency of the earth-to-air heat exchangers depends not only on their thermal performance but also on the total pressure losses that are the cost of harvesting a geothermal heat. In this paper the sensitivity analysis of the flow characteristics to the change of multi-pipe exchanger geometry is presented. Experimental investigation and CFD simulation results present total pressure losses in the considered exchangers and airflows in each branch-pipes. Considered geometrical structures varies in the number of parallel pipes, pipes length, main pipes diameters and supply type. The experimental investigations were conducted on the exchangers models in a scale 1:4. To investigate the real size exchangers, validated CFD flow performance model was used. A costless modification of heat exchanger supply-type from Z-type to U-type structure (change in air inlet location) is verified as a simple method of decreasing total pressure losses by 6–36% and improving airflow division uniformity by 11–80%. It is shown that main pipes diameter that are 1.4 times bigger than parallel pipes diameter can result in diminished total pressure losses by 56–73% and improved airflow division uniformity by 6–59%. The least significant effect on the flow characteristics has the branch-pipe length. Total pressure losses of long branch-pipes exchangers can be 15–32% higher than for short ones and the airflow division uniformity can be 8–35% higher. Results can be used for choosing the proper geometry of multi-pipe earth-to-air heat exchangers from the flow performance point of view. Presented flow characteristics can be used in detailed analysis and energy assessment of exchangers cooperating with the mechanical ventilation system in building.

In this paper the experimentally obtained flow characteristics of multi-pipe earth-to-air heat exchangers (EAHEs) were used to validate the EAHE flow performance numerical model prepared by means of CFD software Ansys Fluent. The cut-cell meshing and the k-e realizable turbulence model with default coefficients values and enhanced wall treatment were used. The total pressure losses and airflow in each pipe of multi-pipe exchangers was investigated both experimentally and numerically. The results show that airflow in each pipe of the multi-pipe EAHE structures is not equal. The validated numerical model can be used for a proper designing of multi-pipe EAHEs from the point of view of the flow characteristics. The influence of EAHEs geometrical parameters on the total pressure losses and airflow division between the exchanger pipes can also be analyzed. Usage of CFD for a designing process of EAHEs can be helpful for HVAC engineers (Heating Ventilation and Air Conditioning). It can also be helpful for optimizing the geometrical structure of multi-pipe EAHEs in order to save the energy and decrease operational costs of low-energy buildings.

Jet impingement is considered to be an effective technique to enhance the heat transfer rate, and it finds many applications in the scientific and industrial horizons. The objective of this paper is to summarize heat transfer enhancement through different jet impingement methods and provide a platform for identifying the scope for future work. This study reviews various experimental and numerical studies of jet impingement methods for thermal-hydraulic improvement of heat transfer surfaces. The jet impingement methods considered in the present work include shapes of the target surface, the jet/nozzle–target surface distance, extended jet holes, nanofluids, and the use of phase change materials (PCMs). The present work also includes both single-jet and multiple-jet impingement studies for different industrial applications.

The cooling energy demand in the buildings is quite large nowadays and it will increase rapidly in the near future. Therefore, capacity of existing cooling devices must be increased. In this paper surface corrugation as a method of capacity enhancement of ceiling panels is theoretically investigated. A subject of the analysis is the effect of corrugation length L and corrugation angle β on the panel’s cooling capacity. It is shown that in the typical conditions the cooling power of the panel with modified surface can achieve even 153 W/m2 and it is about up to 2.5 times higher than the power of a reference panel with flat surface.

In the cold and moderate climates the energy demand for heating of fresh ventilation air is crucial. The mechanical ventilation systems with heat recovery are used to decrease the peak power of the heating system and to save the energy. In a case of wall-type heat recovery units there is a doubt about the possibility of mixing fresh and exhausted air in the combined intake-outtake device. In this paper experimental investigations were conducted to assess their hygienic safety. The original set-up containing test chamber and the equipment for CO2 concentration measuring has been used. Visualization of airflows mixing with the usage of smoke is presented. The results show that the risk of the exhausted air return to the building is low. At the same time the ventilating efficiency of such systems is high. The analysis of the annual energy demand for the sample single-family and multi-family buildings has been conducted to present the possible energy benefits of usage such devices. Concluding, the wall-type heat recovery units should be considered as hygienic safe and helpful devices in achieving the standard of low energy buildings in a case of existing and refurbished ones.

In multi-pipe structures of earth-to-air heat exchangers (EAHEs), the airflow distribution between parallel pipes is not uniform and depends on many geometrical parameters, primarily the relation between the diameters of parallel pipes and manifolds, and the length of branch pipes. The phenomenon of airflow non-uniformity is usually neglected in the thermal performance calculations. This report investigates the influence of airflow distribution patterns on the thermal performance of multi-pipe EAHEs in order to bridge this knowledge gap. The calculations have been performed for a winter-time season for exchangers located in the climatic conditions of Central Europe. Analysis was conducted for different airflow conditions characterized by an airflow distribution uniformity coefficient. Results show that the thermal performance calculated for real EAHEs, with branch-pipes of a length L = 76d and diameters equal to the main pipe diameters, can be up to 28% lower than for ideal (uniform) distribution of air in an analogous exchanger. For EAHEs with branch-pipes of a length L = 300d and main pipes 1.4 times larger in diameter than parallel branch-pipes, the differences are much lower, i.e., less than 13%. The correlation between the airflow distribution uniformity coefficient and the EAHE seasonal heat gains is presented for exchangers consisting of 3, 5, 7, or 10 parallel branch-pipes. These results can be applied in various energy and economic analyses to estimate the potential energy savings from designing energy efficient building HVAC systems equipped with EAHEs characterized by better airflow distribution.

In this paper surface corrugation as a method of capacity enhancement of ceiling panels is presented. The triangular corrugation shape was analyzed. Influence of corrugation length L and corrugation angle β on panel cooling capacity was investigated theoretically. The calculation model was validated experimentally. In calculations the range of corrugation length L was from 30 mm to 120 mm, and the range of corrugation angle β was from 30° to 180°. In experiments the values of the above parameters were: L = 0.04 m, β = 90°, and β = 180°. A special cuvette-type-laboratory panel was used to obtain nearly uniform temperature distribution at the entire cooling surface. The width and length of the laboratory panel were 380 mm and 1502 mm, respectively. The panel surface emissivity was ɛ = 0.9. Calculations have shown that in the typical room conditions the cooling power of the panel with small values L = 30 mm and β = 30° can achieve even 121 W/m2 and it can be up to 90% higher than the specific power of a reference panel with a flat surface. For geometry more desirable from an operating point of view: L = 40 mm and β = 90°, both experimental and theoretical results have shown that the cooling power of the corrugated surface increased by 15÷20% compared to a traditional flat surface. A physical interpretation of the regularities found is presented.

Due to the low emissivity of raw metal surface (i.e. aluminum), the specific heating or cooling performance of non-painted surfaces is powered mainly on the natural convection and is relatively small. It can be sufficient for low energy buildings but not for the traditional ones. To increase the heat exchange through the radiation one can cover the raw surface with paint to increase its emissivity. To investigate the influence of paint cover on the heating and cooling performance of the ceiling-oriented flat aluminum surface the experimental investigations were done. The experiment was conducted on the aluminum ceiling panel with heat exchange surface of the dimensions 0.32 ⨯ 3.0 m. Heating performance of painted surface increased from 2.3 to 2.8 times and cooling performance increased from 1.5 to 1.7 times in the comparison to the non-painted one.

In this paper the experimentally obtained flow characteristics of multi-pipe earth-to-air heat exchangers (EAHEs) were used to validate the EAHE flow performance numerical model prepared by means of CFD software Ansys Fluent. The cut-cell meshing and the k-ε realizable turbulence model with default coefficients values and enhanced wall treatment was used. The total pressure losses and airflow in each pipe of multi-pipe exchangers was investigated both experimentally and numerically. The results show that airflow in each pipe of multi-pipe EAHE structures is not equal. The validated numerical model can be used for a proper designing of multi-pipe EAHEs from the flow characteristics point of view. The influence of EAHEs geometrical parameters on the total pressure losses and airflow division between the exchanger pipes can be also analysed. Usage of CFD for designing the EAHEs can be helpful for HVAC engineers (Heating Ventilation and Air Conditioning) for optimizing the geometrical structure of multi-pipe EAHEs in order to save the energy and decrease operational costs of low-energy buildings.