Low-temperature Supply Research Articles

Human exposure to respiratory aerosols: Impact of ventilation rates, mixing ventilation configuration, and breathing patterns

This study investigates airborne transmission dynamics between occupants in office rooms equipped with mixing ventilation (MV). The primary aim was to assess how different ventilation configurations, air change rates (ACH), breathing patterns, and supply air temperatures influence cross-exposure and infection risks. The experimental setup involved two thermal manikins simulating an infected and an exposed occupant within a climate chamber. The investigated parameters included four ACH levels (1.2, 2, 4 and 6.6 h⁻1, representing four EN 16798–1 ventilation categories), two MV configurations (near-ceiling and near-floor inlets), two breathing patterns (nose and mouth breathing), and two supply air temperatures (19 °C and 21 °C). Carbon dioxide (CO₂) was used as a tracer gas to simulate exhaled aerosols, enabling precise measurements of effectiveness (εv), intake fraction (IF), and infection probability (P). The findings indicate that higher ACH do not uniformly improve εv but are linked to reduced cross-exposure risk. The near-floor inlet MV configuration significantly outperformed the near-ceiling configuration in reducing IF and P by 15–41 % under most investigated scenarios. Additionally, mouth breathing increased IF and P compared to nose breathing, especially at higher ACH (2, 4, and 6.6 h⁻1). The results also showed that lower supply temperatures do not always correlate with higher IF and P, as MV configuration and breathing patterns significantly influence outcomes. This research provides insights into optimizing ventilation strategies for safer indoor environments, emphasizing the importance of airflow dynamics, breathing patterns, and supply temperature in ventilation design.

Analysis of the impact of convector heaters operating at low supply temperature on the possibility of deterioration of thermal conditions

The increasing use of renewable energy sources reduces the operating parameters of district heating networks. As a consequence, it is necessary to reduce the supply temperature of already existing building central heating systems. Therefore, there is a doubt whether such operations will not cause deterioration of the thermal conditions of rooms, in particular with a large glazing area. A balance of jet momentum fluxes was developed between the cold down draught and warm stream generated by the heater. A mathematical correlation was formulated based on this comparison. It allows to determine the minimum average velocity of convective currents of warm air generated by the heater, which protects the occupants from the undesired local cooling. The article also includes computer code to perform this calculation in a simple and quick way. A number of experimental studies and CFD modelling were performed to determine the characteristics of the convective currents rising above the typical convector heater with widths of 96 mm, 146 mm, 186 mm, and 236 mm. The type and area of the glazing, air temperature conditions, as well as the supply temperature and the size of the convector were analysed. The results of these experiments and computer simulations were presented in the form of graphs showing the impact of the most important parameters on the minimum warm air velocity value.

Influence of a sub-zero metalworking fluid on the tribological behavior of CoCrMo alloys and WC-Co carbides

Cooling strategies have a decisive impact on the performance of cutting processes, especially when machining hard to-cut materials like CoCrMo. A highly efficient cooling strategy is the usage of sub-zero metalworking fluids (MWF). These sub-zero MWF are applied at liquid state but at temperatures well below 0°C. Consequently, high cooling effects in superposition with a beneficial lubrication are realized.In this paper, tribological tests are described, characterizing the cooling and lubrication effects when using two sub-zero MWF at various supply temperatures as well as a cryogenic CO2 cooling as reference. The performance of the cooling strategies is characterized via the occurring temperatures and coefficients of friction at systematically varied tribological loads.The results obtained show, that cryogenic cooling significantly reduces the thermal load but does increase the coefficient of friction in comparison to the dry condition. In contrast, both sub-zero MWF lead to beneficial lubrication effects while simultaneously offering sufficient cooling effects. Decreasing the supply temperatures of the sub-zero MWF improves these cooling effects. However, slightly higher coefficients of friction are observed at lower supply temperatures, due to an increased shear strength of the asperities in the tribological contact.

Multi-criteria comparison of various drinking water installations for low-temperature supply systems in apartments

Rules to prevent from legionnaires disease gain importance as the building sector, esp. multi-family houses, needs to be decarbonized with temperature sensitive heat pumps. As legionella grow often in the peripheries of the pipe networks, we carried out dynamic simulations with TRNSYS of four different piping designs with composite pipes inside a reference apartment (T-piece, in-series, ring and a mix of T-piece for potable hot water (PWH) and ring for potable cold water (PWC)). We applied PWH and PWC tapping profiles for each tap, investigated two different supply temperatures of potable hot water 60 °C and 45 °C, and compared the results using hygienic, comfort and energy efficiency performance indicators. Based on the indicators and the boundary conditions used, classical T-piece and the mix installation show the best results, followed by series and ring, especially when using decentral water heaters with 45 °C.

Thermal and structural response of a pavement solar collector prototype

Thermal and structural response of a pavement solar collector prototype

Technical and economic assessment of a hybrid heat pump system as an energy retrofit measure in a residential building

Air to water electric heat pumps are one technological solution to achieve energy defossilisation goals for heating of residential building stock. Nevertheless, they may not necessarily be the only solution for all residential building stock. A case in point is where extensive fabric refurbishment is impracticable or where electric heat pumps are installed where low ambient temperatures prevail and/or high water delivery temperatures must be utilised. For such instances, hybrid (gas and electric) heat pumps offer an alternative option by facilitating fuel source switching between electricity and gas, when ambient temperatures are low or high water supply temperatures are required. In the current study, the effectiveness of an air-to-water electric heat pump and hybrid heat pump are examined for different building retrofit scenarios for a residential dwelling located in Ireland. This is achieved by means of a sensitivity study of a validated building simulation model, incorporating both heat pump systems, subject to different building retrofit scenarios. Relative to a conventional oil-fired boiler, for a deep building retrofit scenario, the hybrid and electric heat pumps achieve primary energy savings of 73% and 70%, respectively. For a minimal building retrofit scenario, the respective primary energy savings are 57% and 52%. For the deep retrofit scenario, compared to the baseline building with no retrofit measures, the carbon footprint reductions were found to be (8.5 gCO2e/m2/year or 44%) for the hybrid heat pump, (10.31 gCO2e/m2/year or 45%) for the electric heat pump, and (17-21 gCO2e/m2/year or 43-53%) for oil or gas boiler systems. Finally, the deployment of either an electric heat pump or hybrid heat pump for deep building fabric retrofit achieves approximately half heating system capital cost return within 20 years.

Efficiency comparison between defrosting methods: A laboratory study on reverse-cycle defrosting, electric heating defrosting, and warm brine defrosting

Frost on the evaporator of a cold storage refrigeration system reduces cooling capacity and COP (Coefficient of Performance). Hence an energy-efficient defrosting process is crucial for economical operation. Various defrosting methods have been proposed in literature and their defrosting efficiency has been assessed. However, differing experimental conditions, e.g., variations in evaporator geometry and diverse air conditions, hinder accurate comparison across literature. Further, while electric heating defrosting (EHD) and reversed cycle defrosting (RCD) methods are widely studied, warm brine defrosting (WBD) method is rarely investigated. Despite this, WBD offers the potential to use low-temperature waste heat for defrosting, which reduces energy consumption drastically. Therefore, this study experimentally assesses the defrosting efficiency for EHD, RCD, and WBD on a single experimental setup, thus ensuring comparability. For the first time, low brine supply temperatures (10 °C/20 °C/30 °C) for WBD are investigated. Our results show that RCD reaches the highest defrosting speeds and has the highest defrosting efficiency between 56% and 61%, depending on air conditions. WBD at10 °C and 20 °C exhibit low efficiencies of 16–29%. However, WBD at 30 °C has comparable efficiency to EHD (40–45%). The reported results can serve as a decision criterion in the design process of refrigeration systems.

Granulation of ibuprofen/isonicotinamide co-crystals by continuous spray granulator (CTS-SGR)

The importance of granulation is paramount for tablet manufacturing, and is based on the fact that granulated powders are characterized by improved flowability, compressibility, segregation, and dust reduction. The aim of this study was to prepare and characterize continuous granules of high drug content by using a continuous-spray granulator (CTS-SGR). Ibuprofen (IBU), a drug of low-flowability, was selected as the model drug. As IBU has a low melting point and cannot easily granulate on its own, we employed isonicotinamide (INA) as a coformer that would allow us to prepare co-crystal granules containing 60 % IBU. The results of the undertaken differential scanning calorimetry and powder X-ray diffraction revealed that the IBU and the INA in the granules formed co-crystals. The granulation conditions affected the particle size and the yield of the granules; in fact, a low air supply temperature, a low atomizing air rate, and a high solution flow rate ensured a high granulation efficiency. Moreover, continuous granulation increased the yields of the formulations compared to those obtained through a short-run granulation, and high yields were obtained after applying a low atomizing air rate. The circularity of the granules exceeded 90 %, and their flowability improved when compared to that of the IBU bulk. The undertaking of dissolution studies revealed no change in the elution amount of IBU as a result of the co-crystallization. Our study shows that it is possible to produce high-content IBU granules in a direct and continuous manner through the co-crystallization of IBU and the use of a CTS-SGR.

Sub-zero milling of Ti-6Al-4V—impact of the cutting parameters on the resulting forces, tool wear, and surface quality

Due to an excellent ratio of high strength and low density, Ti-6Al-4V is suitable for many industrial applications, especially in the aerospace industry. However, Ti-6Al-4V is also characterized by a very low thermal conductivity and high chemical reactivity which is why the titanium alloy is considered to be a hard-to-cut material. Machining Ti-6Al-4V leads to high cutting temperatures, which leads to a rapidly progressing thermo-chemical induced tool wear. To reduce the thermal load and to enhance the cutting performance, suitable cooling strategies are a necessity. A novel, highly efficient cooling approach is to apply sub-zero metalworking fluids (MWF) at liquid state but at supply temperatures well below 0 °C. These sub-zero MWF inhibit high cooling effects due to their low supply temperature in superposition with a beneficial wetting behavior. In this work, the application of a sub-zero cooling strategy is investigated when milling Ti-6Al-4V. The influence of both down milling and up milling is investigated under a systematic variation of the cutting speed and feed per tooth. For comparison, the experiments are also conducted using a cryogenic CO2 cooling. The performance of both cooling strategies in dependence of the milling process is described on the basis of the occurring forces, the resulting tool wear, and the surface quality achieved. The results show that the sub-zero cooling can successfully improve the machinability of Ti-6Al-4V even at elevated cutting parameters and unfavorable cutting conditions. As a result, sub-zero milling clearly outperforms the cryogenic CO2 cooling, since less tool wear and an overall lower surface roughness are observed. Consequently, when using a sub-zero cooling strategy, higher metal removal rates, longer tool life, and better surface qualities are achievable.

Comparison of Suitable Business Models for the 5th Generation District Heating System Implementation through Game Theory Approach

Abstract District Heating and Cooling (DHC) technology is widely recognised as a promising solution for reducing primary energy consumption and emissions. The 5th Generation District Heating and Cooling (5GDHC) network is the latest DHC concept characterised by low-temperature supply, bi-directional heating network operation, decentralised energy flows, and surplus heat sharing. Unlike the 4th Generation District Heating (4GDH) technology, the 5GDHC technology switched to a consumer/prosumer-oriented perspective. The introduction of 5GDHC solutions requires high investments, an important barrier to further developing DHC systems. Therefore, a novel pricing and business model could include introducing co-owners or energy managers into the system. Three different local market business models for 5GDHC at the community level have been tested. The reverse technical and economic simulation has been used for a feasibility study to determine the resources, business models, and combinations closest to the break-even point with lower costs and higher gains for all involved stakeholders.

Abiotic stresses and ways to overcome them on <I>Achillea millefolium</I> L. in conditions of the Western Precaucasus

Relevance. An important place in the extensive assortment of ether-oil cultures belongs to the common yarrow (Achillea millefolium L.), phytopreparations produced on its basis are widely used in the treatment of inflammatory processes, the normalization of the gastrointestinal tract.Methodology. To provide the pharmaceutical industry with this type of medicinal raw materials, it is necessary to create adapted technologies, where an important link will be the development of techniques for adapting the culture to unstable weather conditions.Results. The studies were carried out in the conditions of the North Caucasus branch of VILAR (West Ciscaucasia) in 2019-2021, by conducting small-scale experiments. The indicators of growth and development of yarrow of the II-V years of vegetation, the yield of raw materials, the content of essential oil and its collection per hectare under unstable weather conditions were studied. It was found that with sufficient moisture supply and a comfortable level of air temperatures in 2021, a high yield of medicinal raw materials of this crop is observed. At the same time, low water supply and high temperatures in 2020 had a negative impact on plant development, a drop in yield of 1.35-1.65 t/ha was established, which led to losses in the collection of essential oil per hectare by 3.23-4.32 kg/ha. A decrease in the degree of negative impact of drought on yarrow plants of the II-IV years of vegetation was achieved through the use of silicon-containing microfertilization Siliplant. Double treatment with this drug contributed to a decrease in the yield of raw materials to 5-6% and the collection of essential oil per hectare to 5-7%. in the control – 21-24% and 22-24%, respectively. Despite the high yield of raw materials in the III-III years of yarrow vegetation, the use of Siliplant allows collecting ether-oil raw materials for 4 years. Thus, the inclusion of Siliplant microfertilization in cultivation technology allows plants to adapt to hydrothermal stress conditions and makes it possible to obtain stable yields of raw materials with a high collection of essential oil per hectare, regardless of weather conditions.

Experimental study on radiant cooling with double-skin infrared-transparent membranes

Radiant cooling is an energy-efficient space cooling technology in built environments to achieve high thermal comfort. However, there are technical bottlenecks of condensation risk and insufficient cooling capacity in hot and humid climates. The use of double-skin infrared-transparent membranes (DIMs) to separate the radiant cooling surface from the air-contact surface can improve the cooling capacity while preventing condensation. Current research focuses on theoretical analysis and reduced scale experiments, and the lack of measured operational and performance data creates a key limitation on DIMs use. Therefore, the verification of radiant cooling system with DIMs in a full-scale experimental space and its radiant cooling performance need to be further studied. In this study, two full-scale radiant cooling chambers (one with DIMs and one without DIMs) were constructed. The effect of DIMs on radiant cooling performance was studied by monitoring surface temperature, condensation risk and cooling capacity. The results indicated that the air-contact surface temperature in radiant cooling with DIMs was always maintained above the dew point temperature for condensation-free safety at a low water supply temperature of 8 °C. In contrast, the conventional radiant cooling without DIMs had severe condensation. Moreover, the cooling capacity of radiant cooling panel with DIMs was 105.5 W/m2 at water supply temperature of 8 °C, 24.4 % improved compared to radiant cooling panel without DIMs at water supply temperature of 14 °C. This study provides prototype experimental verification for new technology with DIMs to improve radiant cooling performance and provides experimental data as a reference for related theoretical and model studies.

Requirements for renovating residential buildings in the Netherlands towards lower temperature supply from district heating.

In the Netherlands, district heating with a lower temperature supply (<70°C) will play a crucial part in accomplishing the energy transition goals of delivering natural gas-free sustainable heating to dwellings. The existing dwellings often require energy renovations to make them suitable for lower temperature heating. However, choosing renovation strategies that promote the transition to lower temperature district heating while improving energy efficiency and thermal comfort is challenging. This study aims to identify minimum renovation requirements for comfortably heating homes using lower temperature heat from district heating. Identifying minimum renovation strategies to prepare existing dwellings for lower temperature district heating would be vital in addressing the European Renovation Wave’s target of improving worst-performing buildings. For the same, the study uses a typical intermediate terraced house built before 1945 as a case study to investigate renovation strategies based on four levels of renovation intervention (no renovation, basic, moderate and deep). The impact of renovations on space heating demand and thermal comfort was tested with medium (70/50°C) and low supply (55/35°C) temperatures against key performance indicators (KPIs) using dynamic simulation. The study found that for the case study dwelling, moderate renovation strategy of upgrading the building envelope insulation by 0.40 W/m2K for opaque parts and 1.5 W/m2K for glazing, improving the airtightness by 0.3h-1 and replacing existing radiators with LT radiators can be considered as a no-regret solution for comfortably heating homes with both medium and lower temperature supply from district heating.

Grey-box modelling and virtual sensors enabling continuous commissioning of hydronic floor heating

Operating district heating systems with low supply and return temperatures improves heat production and distribution efficiency, permitting greater integration of renewable heat sources. Low-temperature district heating is viable without compromising comfort, but faults in end-users’ heating systems constrain temperature reductions. Such faults include malfunctioning valves, improper hydronic balancing, and excessive supply temperature setpoints. Occupants lack the resources to detect and diagnose these faults, so there is a need for automated solutions without requiring additional hardware. This paper proposes a method for improving the operation of an apartment's hydronic floor heating system using data from room thermostats, a heat meter and a circulation pump to identify a grey-box model of the system. The resulting model virtually senses each room loop's heat flux, flow, return temperature, and flow coefficient. The authors tested the model on a low-energy apartment in Denmark, using it to diagnose causes of high return temperatures, including poor hydronic balancing and an excessive supply temperature setpoint and pump setting. The authors also used the model to predict the minimum permissible supply temperature maintaining comfort, yielding a reduction in the energy-weighted supply and return temperatures of 8.6 °C and 6.5 °C, respectively.

Thermal performance of a controllable pavement solar collector prototype with configuration flexibility

Solar energy harvesting as a renewable and sustainable energy source has been widely investigated in recent years across engineering fields. The use of Pavement Solar Collectors (PSC) can lead to clean energy production, an increase in road safety, prolong the service life of asphalt pavement, and can mitigate the Urban Heat Island (UHI) effect. This study describes a controllable large-scale research PSC prototype with high configuration flexibility, and full monitoring capability at the University of Antwerp, Belgium. Since small- or laboratory-scale setups do not reflect the behavior of actual projects, the present paper investigates the thermal response of a large-scale PSC in the Western European climate, including heating load, heat extraction capacity, and asphalt surface and profile temperature changes during heating and cooling experiments.The study shows that a low supply temperature compared to high (14 °C vs. 28 °C) can reduce the depletion rate of the stored thermal energy in borehole thermal energy storage up to 7 times. The sensitivity analysis indicates that an increase in flow rate from laminar to transient regime requires twice as much thermal power compared to the same flow rate changes within transient and turbulent regimes. The maximum average daily efficiency of the PSC could reach 34% with a flow rate of 4 l/min. The experimental results showed that increasing the pipe length from 50 m to 200 m reduces the cumulative power extraction capacity by up to 48%. Furthermore, the PSC system shows great potential in reducing the asphalt surface temperature (up to 12 °C) to mitigate the UHI effects. Finally, the PSC system effectively controls the temperatures of the interface zones to reduce the rutting distress in the summertime and lower the potential of cold thermal crack developments and brittle shear failure behavior in wintertime.

Thermodynamic investigations on an integrated heat pump with thermal storage for wind-solar hybrid heating

Heating with wind and solar energy is an effective way to reduce carbon dioxide emissions. Vapor Compression Heat Pumps (VCHP) were generally used to improve the utilization rate of wind power. However, normal VCHP driven by wind power or solar energy has low performances in low temperature environment and low supply temperature of heating water, and it is also difficult to achieve continues and stable heating because of the intermittence of wind power. The present paper introduces a new integrated heat pump system, in which a VCHP absorbs heat from the environment and sends it to an Absorption Heat Pump (AHP) as its low temperature heat source after temperature lift. Thermal storage system is also equipped for continues heating and it serves as the driving force of the AHP. The results show that the integrated heat pump can produce heating water at 50 °C or even higher with a COP of about 1.42 when the environment temperature is as low as −30 °C. Also, the power consumption of the VCHP accounts for only 5%–18% of the total energy input. This indicates that the energy consumed by the integrated heat pump can be mainly from off-peak electricity produced by the wind turbine.

Fourth-Generation District Heating and Motivation Tariffs

Abstract Future district heating systems and technologies—also known as fourth-generation district heating—have a potentially important role to play in the green transition of societies. The implementation of fourth-generation district heating involves adjustments in the demand side to allow for low temperature supply. In order to facilitate such changes, district heating supply companies have in recent years introduced tariffs with penalties for high return temperatures and benefits for low return temperatures. This paper describes the case of a housing community of 17 buildings in their attempts to adjust to such tariffs as an integrated part of connecting to district heating. Replacing domestic hot water tanks with instantaneous heat exchangers and introducing smart meters resulted in abilities to lower the return temperature from around 40 °C to around 30 °C. However, the current design of the motivation tariffs does not yet fully compensate the consumers because the supply company provides unnecessarily high supply temperatures. Based on such efforts, this paper discusses the fairness and effectiveness of the tariffs and provides recommendations for improving them.

Research on NH3-SCR reductant technology progress for diesel vehicles

This paper describes the technical principle, research status and application status of four reducing agents (aqueous urea solution, solid ammonium salt, solid ammonia compound and liquid ammonia) which supply NH3 for SCR of diesel vehicles, introduces the replacement methods of solid ammonia, and analyzes the application feasibility of liquid ammonia. A comprehensive comparative study of the four reducing agents is carried out in terms of storage and validity requirements, low temperature performance, ammonia storage capacity, replacement mode, replacement frequency, safety, cost and future application prospect. It is found that the ammonia storage density of solid ammonia and liquid ammonia is 2.5 ~ 3.5 times of that of aqueous urea solution. And there is no significant difference in the theoretical use cost of several reducing agents, however, the actual use cost of aqueous urea solution is higher than the theoretical value on account of its actual decomposition rate less than 100%. The analysis shows that the requirements for NH3-SCR reductant technology in the future are excellent low temperature supply capacity, small space occupation, convenient use, low cost and guaranteed quality, and etc. As a traditional technology, aqueous urea solution is easy to crystallize at low temperature and can not meet the requirements of low temperature performance. Solid ammonium salt also has the problem of crystallization at low temperature. Solid ammonia compounds meet the above requirements, and the market application is gradually mature. If liquid ammonia wants to be applied in large-scale engineering, its safety problem of storage tank should be solved.

Heating the Dutch housing stock without natural gas

This paper studies the level of improvement of building envelopes required to heat the Dutch housing stock using an energy supply without natural gas, such as a district heating network at lower supply temperature or a heat pump. We identified 35 building types to represent the Dutch housing stock of single-family dwellings. A 4R2C building model was used to assess whether the dwellings could be heated at lower supply temperatures after they were renovated according to six renovation packages of different ambition level.

Data driven model for heat load prediction in buildings connected to District Heating by using smart heat meters

An accurate characterization and prediction of heat loads in buildings connected to a District Heating (DH) network is crucial for the effective operation of these systems. The high variability of the heat production process of DH networks with low supply temperatures and derived from the incorporation of different heat sources increases the need for heat demand prediction models. This paper presents a novel data-driven model for the characterization and prediction of heating demand in buildings connected to a DH network.This model is built on the so-called Q-algorithm and fed with real data from 42 smart energy meters located in 42 buildings connected to the DH in Tartu (Estonia). These meters deliver heat consumption data with a 1-h frequency. Heat load profiles are analysed, and a model based on supervised clustering methods in combination with multiple variable regression is proposed. The model makes use of four climatic variables, including outdoor ambient temperature, global solar radiation and wind speed and direction, combined with time factors and data from smart meters. The model is designed for deployment over large sets of the building stock, and thus aims to forecast heat load regardless of the construction characteristics or final use of the building. The low computational cost required by this algorithm enables its integration into machines with no special requirements due to the equations governing the model.The data-driven model is evaluated both statistically and from an engineering or energetic point of view. R2 values from 0.70 to 0.99 are obtained for daily data resolution and R2 values up to 0.95 for hourly data resolution. Hourly results are very promising for more than 90% of the buildings under study.