Hydronic Heating Research Articles

Hydronic Road-Heating Systems: Environmental Performance and the Case of Ingolstadt Ramps

Abstract Snowfall and ice formation on road surface significantly impact the safety of driving conditions. To resolve this, every year salt and de-icing chemicals are sprinkled on roads. However, use of salts and snow ploughing have environmental as well as economical disadvantages. To resolve these problems, hydronic road heating systems are valid alternatives. Heat transfer fluid, i.e. mixture of ethanol and water, is pumped into a tubular circulation system under the asphalt. By this technology, the road and pavements shall stay ice-free even in times of snowfall and temperatures below the freezing point. The system can also be used to cool the asphalt in case of extreme heat, which – besides the heating effect – could also prevent road from damages in extreme summers. This study aims to compare the environmental impact of use of salts and road-heating system in terms of GHG emissions. To assess the environmental impact, an operational road heating system for a ramp in Ingolstadt, Germany, is considered. A cradle-to-grave analysis technique is used to determine the environmental effects based on a life-cycle assessment (LCA) framework. The analysis includes nine components solemnly responsible for hydronic heating of asphalt surface such as local heating pipe, insulation, pumps, and heat meters. Comparison is performed in terms of relative and total impact over 50-year lifetime of three heated ramps having 1989 m2 surface area in total. The results show that the asphalt and heating-circuit causes the major fraction (65 %) of overall GHG emissions, with total life-time emissions of 28.10 kg CO2 eq./m2 of heated surface. During an operational life of 50 years, road heating systems emit 18 % less CO2 eq./m2 as compared to the use of salts.

Grey-Box Modelling and Virtual Sensors Enabling Continuous Commissioning of Hydronic Floor Heating

Grey-Box Modelling and Virtual Sensors Enabling Continuous Commissioning of Hydronic Floor Heating

A2L low GWP HFO based refrigerant solutions in heat pump applications to drive energy efficiency, safety, and sustainability even in building restoration

Driven by energy efficiency requirements and legal restrictions like F-Gas Regulation Heat Pump OEM supplier are looking for alternative refrigerant solutions. HFO based low GWP refrigerants can help increasing the system efficiency, expanding the operating temperature range while reducing CO2 emissions. For building restoration in particular, high flow temperatures (for existing hydronic heating system) are essential for convenient and cost-and energy-efficient replacements of fossil fuel boilers. A2L classified refrigerants provide extended application range at highest safety level versus A3 classified refrigerants, but R-32 still carries a Global Warming Potential (GWP) of 675 making it a transitional solution. This paper compares different relevant parameters and points out the advantages provided by HFO A2L low GWP refrigerants (like R-454B and R-454C) for a wide capacity range of air to water and brine to water heat pumps. A special focus is put on the application of building restoration.

Field tests on the prediction of heating power requirements for deicing in Jiangyin, China

Hydronic heating systems with geothermal heat exchangers are one of the innovative methods for bridge deck deicing in winter, which avoids infrastructure corrosion and environmental pollution caused by chemical methods. This paper focused on field tests on the temperature process of a bridge deck with a hydronic heating system to predict the heat exchange rate needed to keep the bridge deck temperature above 0 °C before snowing. The heating power in the test was kept constant, and three different heating powers of 125 W/m2, 187 W/m2, and 250 W/m2 were considered. The heat exchange rates remained constant under constant heating powers. The slab temperature and thermally induced stress were analyzed, and the heat exchange rate prediction was discussed. The required heat exchange rate is determined by the air temperature and the wind velocity. The minimum temperature in situ is approximately -5 °C in winter. The heat exchange rate should be greater than 178 W/m2 to keep the slab surface temperature above 0 °C under the condition that the wind velocity is less than 3 m/s. The thermally induced compressive stresses caused by operating the system were <5% of the compressive strength of concrete. Operation of the system does not structurally damage the bridge deck and can protect the bridge deck from being damaged by excessive tensile stress caused by low temperatures in winter.

A novel concept for energy-efficient floor heating systems with minimal hot water return temperatures

The study proposed and investigated a new concept for hydronic floor heating in dwellings with the aim of reducing hot water temperatures toward a more robust and energy efficient operation. Modern heating systems often rely on low return temperatures to improve operation efficiencies through reduced heat losses from return pipes, greater utilisation of condensation heat from boiler flue gases or from the increased COP of heat pumps. Our study investigated the potential of using an apartment heating substation (or ‘flat station’) to supply space heating through two mixing loops using hot water supply temperatures of 30°C to bathrooms and 24°C to all non-bathrooms. The concept sought to minimise hot water supply temperatures to utilise a self-regulating effect while ensuring low return temperatures. In the first iteration of the concept, the high-temperature return water from the bathrooms was cascaded to the non-bathrooms to heat these rooms and provide further cooling of the hot water. The calculated energy-weighted return temperature under this original concept was 25.6 °C for the example case of a new energy-efficient apartment building. However, there was limited potential to utilise the cascaded coupling, so considering the complexity of its configuration and controls, the authors simplified the proposed concept to two mixing loops without a cascaded coupling. The calculated return temperature with the updated concept was 25.7 °C. The control of the floor heating included some aspect of self-regulation because the heat transfer strongly depended on the indoor temperature. Based on the results of this preliminary investigation, the concept may provide a robust and energy-efficient option for configuring floor-heating systems in situations that rely on low hot-water return temperatures.

Digital Twins of Building Physics Experimental Laboratory Setups for Effective E-learning

Hands-on experiments in laboratories are fundamental educational tools for technical sciences. However, laboratories are expensive and not always accessible to students: lockdown and in-person meeting restrictions due to the ongoing Covid-19 pandemic, distant location of teachers and students, facilities used for higher-priority purposes. Moreover, creating specific experimental setups for teaching only can be costly. In that context, digitalizing laboratory setups provides an attractive teaching alternative for remote e-learning. Digital twins are not meant to replace real-world experiments but should enable flexible teaching and effective learning at a lower cost. They complement physical setups and can be virtual extensions, allowing for larger and more complex study cases. e-learning is now popular and many educational institutions provide open-access videos of entire courses. However, the digitalization of practical exercises for engineering is yet limited. The e-learning effort presented in this paper aims to establish a series of digital twins of experimental setups for teaching building physics, energy in buildings and indoor environment. The development of the two first digital twins is detailed here. They are designed for teaching operation and balancing hydronic heating systems. Their numerical models and graphical user interfaces are created with the LabVIEW programming environment.

A numerical and experimental study of hydronic heating for road deicing and its energy flexibility

The use of deicing salts and other anti-skid measures typically adopted by highway maintenance services have many limitations such as applicable temperatures, location of storage facilities, ease of access to road section and, in the case of salts, infrastructure and environmental damage. An alternative solution that offers several advantages is the implementation of hydronic heating systems implemented under the road surfaces. Hydronic deicing may eliminate the need to add salts to road surfaces, thus prolonging the lifetime of infrastructure and significantly reducing maintenance costs. This article presents a methodology to develop low-order models for hydronic deicing slabs with significant thermal mass along with validation in an environmental chamber. The models are utilized to analyze the thermal dynamics of different pipe depths for hydronic deicing slab of a transportation infrastructure in Montreal, Canada. A key objective of the presented study is preheating the slab to reach a surface temperature of about 2 °C before the precipitation to greatly reduce the risk of ice formation. The magnitude of time delay to reach the required surface temperature for deicing for different slab piping configurations and system capacity is evaluated by means of a reduced-order lumped parameter model. The model is then utilized to study an energy flexibility strategy based on thermal response delay of the slab as a function of piping distance from surface to significantly reduce the heating load during the peak demand period.

An experimental investigation on the effect of use of nanofluids in radiant floor heating systems

Hydronic radiant heating systems are widely being run particularly in association with low temperature heat sources. These thermal units are capable of providing high energy saving potential as well as improvement in thermal comfort. Thus, focus on such systems have considerably ascended recently. In this context, augmentation methods have been employed to enhance heat transfer performance of many thermal systems. The use of ultrafine particles in the fluids is considered to be one of the passive techniques, and hence physical properties have been improved compared to the base fluid. Currently, four working fluids’ inlet temperatures are varied from 30 °C to 60 °C, while the mass flow rates are 0.056 and 0.09 kg/s for the heating from floor, and heating from floor along with cooling from walls. Consequently, the examined nanofluids having multi wall carbon nanotube (0.7% vol. cont.) and aluminium oxide (1.26% vol. cont.) have demonstrated better heat transfer performance compared to pure water for similar operating conditions. Nanofluids of greater concentrations such as (0.7% vol. cont.) and (1.26% vol. cont.) have resulted in improvements within the range of 1.7% and 4.9%. Given the improvement in heat transfer acquired, a promising evaluation can be inferred with respect to nanofluids being operated as working fluids in such systems.

Examining a Non-Mixing Concept for Hydronic Heating Systems: A Simulation Study

While buffer tanks are common to address the short-cycling concern of hydronic heating systems, they involve water mixing, where the boiler’s hot water is mixed with the system’s return water. This water mixing condition brings concerns of the performance of the boilers and the in-space heating equipment (e.g., radiant floors and terminal units) due to the reduced temperature differences (ΔT) through these devices. Then, a non-mixing concept is introduced by putting a movable separation plate in a buffer tank, which can store supply hot water and return cold water separately. To examine this non-mixing concept, a simulation study is conducted by developing two hydronic system models with mixing and non-mixing concepts. After simulating these models under continuous heating loads, it is observed that the non-mixing model can achieve better system efficiency (e.g., 86.7% versus 82.0% for low heating loads) due to better boiler’s efficiency and less system cycles. In addition, it is noted that the non-mixing concept allows better control of supply water temperature, which can better support the outdoor reset control of boilers.

Experimental Study on the Use of Enhanced Coconut Oil and Paraffin Wax Phase Change Material in Active Heating Using Advanced Modular Prototype

The use of phase change materials in buildings as a thermal energy storage system gained the attention of researchers all over the world. In the current study, coconut oil bio-based PCM is macro-encapsulated with enhanced thermal conductivity containers and coupled with hydronic radiant floor heating system. The study follows experimental aspect utilizing two identical small scale modular test prototypes. Investigations are directed toward studying the effect of the active CO-PCM system under different weather conditions, effect of combining active and passive systems, effect of PCM choice/type and effect of PCM location within the active floor, on the thermal and energy storage performances. Results revealed that coupling CO-PCM to active floor, passive wall and passive roof is capable of achieving load shifting and energy savings; and is affected by the control method, weather conditions, electricity tariff policy and PCM position and type. Further discussions, conclusions and perspective recommendations are summarized within the article.

The performance of geothermal passive heating and cooling for asphalt and concrete pavement

Hydronic pavement heating and cooling applications have been well established to provide road safety over the past two decades. However, most of the systems run on asphalt, only a few are tested with concrete, and there rarely is a comparison between those two common materials in their heating and cooling performance. In this work, a field study was carried out using asphalt and concrete as pavement material for pavement heating and cooling under the climatic conditions of the city Erlangen, Germany. Both heating performance in winter and cooling performance in summer were tested with similar setups and a low inlet temperature of 10 °C. The results indicate that asphalt's heating performance is worse than that of concrete, showing slightly lower surface temperatures and limited snow melting capabilities. During heavy snowfall, concrete's surface remained snow-free, while asphalt's surface was covered under a thin layer of snow, indicating that snow is melted not fast enough. However, in summer, asphalt, due to its lower albedo, had a significantly higher energy output of 450 W/m2 compared to 290 W/m2 of concrete. Therefore, asphalt showed good cooling perfomance, compared to concrete. Thus, it is concluded that both materials have advantages and disadvantages in geothermal passive heating and cooling, which leave the decision on appropriate material to match the specific planned parameters and environmental requirements.

Study on thermal performance of a PCM enhanced hydronic radiant floor heating system

Radiant floor systems enhanced with Phase Change Materials (PCMs) could achieve significant energy savings while improving the thermal comfort of occupants in lightweight buildings. Effective integration of PCMs typically requires customised solutions based on a comprehensive analysis due to their complex nature. The objective of the present study is the experimental and numerical investigation of a hydronic radiant floor heating system integrated with macroencapsulated PCM. Experimental tests were carried out on a laboratory-scale by the University of Ferrara, Italy, within the H2020 European project IDEAS. A 2D model was then implemented in COMSOL Multiphysics and calibrated in steady as well as in transient state according to the experimental tests. The behaviour of the system, including temperature distribution and heat flux, were analysed under different conditions. The impact of using dry and wet sand, as well as the effect of the position of PCM – above or under heating pipes – on thermal performance, were investigated. Results showed that the use of high thermal conduction in mortar increases much faster the overall performance of the PCM integrated underfloor heating system. Furthermore, the coupling technology with PCM containers installed under piping significantly enhances the positive effect of wet sand.

A hybrid TEG/Thermal radiator system for space heating and electric power generation

In this work, a hybrid thermoelectric generator/thermal radiator unit is examined with the aim of producing electricity while heating a cold space. A mathematical model was constructed for the thermoelectric generator, TEG, under steady-state conditions linked with a hydronic heating system. The TEGs were installed on the two sides of the aluminum sheet of the radiator to utilize the temperature difference between hot water inside the radiator and surrounding air. In addition to the TEG parameters, temperature and velocity of hot water and air were considered in assessing the performance of the hybrid system. The performance of the hybrid system was studied and compared under free and forced convection conditions. It was found that a typical radiator produces about 0.849 W of power in addition to the normal heating effect at an air velocity of 0.5 m/s, in addition to the normal heating effect of 1092 W at hot water temperature of 365 K. Ambient air velocity was the most influential on power with optimum value of 0.5 m/s. Moreover, it was found that the power produced decreased by 15.39 % for an increase of 5 K in ambient temperature while the power increased by 24.6 % as the temperature of hot water increased by 5 K. The power generated by such a system may be significantly increased by utilizing large radiation units in addition to enhancing the TEG performance.

Radiant heating floors with PCM bands for thermal energy storage: A numerical analysis

Radiant heating floors with phase change materials (PCMs) for thermal energy storage (TES) represent an opportunity to achieve improvements in energy efficiency in buildings. In radiant floors that include PCM in macro-capsules the thermal energy is stored during melting and subsequently released during solidification. This paper presents a CFD study for hydronic radiant heating floors with PCM bands embedded in a concrete core in accordance with several arrangements depending on the bandwidth and position with respect to the heating pipes. The heat transfer solutions are compared with those obtained for radiant floors without PCM. Other effects analysed are: the thickness of a wooden cover, which represents the main thermal resistance of the floors, the indoor air temperature and the heating pipe surface temperature. The results show that PCM radiant floors increase thermal energy storage up to 243% and decrease the maximum heat flux between 10 and 18% according to the case. They also release the heat slowly when the heating is off. The time-averaged heat fluxes during the solidification process are between 31.4 and 44.6 W/m2and the solidification last for more than 24 h, allowing time to start a new charge using for instance solar energy.

Optimization of Hydronic Heating Pavement Design Using Geothermal Hot Water in Western North Dakota

Hydronic heating pavement (HHP) is considered to be more sustainable and environmentally friendly for deicing. Using deep direct-use geothermal energy provides a more efficient heat source. In western North Dakota, several aquifers have been identified that provide geothermal hot water ranging from 34 ° to 140 °C within 2300 m below the ground surface. The current technique has made it feasible to utilize the hot water for power generation. The water temperature exiting the power plant is still up to 70 °C. This temperature enables valuable applications and cascading use for other purposes such as space heating, snow melting for transportation infrastructure, etc. This paper mainly focuses on studying the how the geothermal water can be used more efficiently for HHP using finite element analysis. Considering the high heat demand in western North Dakota due to extreme weather, the parametric studies were conducted based on reasonable water temperatures, pipe layouts, heating process, volumetric flow rates, and thermal conductivity of pavement. The optimization of the HHP design subjected to different weather conditions is discussed and conclusions drawn.

Thermal characteristics of porous concrete in a hydronic road heating system

Porous road concrete is an important part of the hydronic road heating system to avoid icing on the road. The thermal characteristics of porous concrete are obtained in the heating process to evaluate the microstructure effects and predict the road conditions. This study applied the Monte Carlo method to generate a two-dimensional heterogeneous porous concrete model. The porous concrete is a mixture of aggregates, bonding interfaces, cement pastes, and air voids. The thermal characteristics (average road surface temperature and road surface temperature distribution) of porous concrete were simulated. The average road surface temperatures were validated with the experiment results. The thermal characteristics of porous concrete as affected by the aggregate areal ratio, air void size, and air void ratio were compared and analyzed. The results indicate that the average road surface temperature at 8 h increased by 1.07 K and the preheating time decreased by 1.05 h when the aggregate areal ratio was increased from 40% to 60%. The road surface temperature fluctuation for the aggregate areal ratio of 50% was the highest (274.34~275.96 K). The average road surface temperature at 8 h decreased by 0.39 K and the preheating time increased by 0.51 h with the air void size changing from 1~3 mm to 1~5 mm. The road surface temperature fluctuation for the air void size of 1~5 mm was the highest (273.80~274.50 K). The average road surface temperature at 8 h decreased by 4.48 K and the preheating time increased by 4.03 h with the air void ratio increasing from 0 to 10%. The road surface temperature fluctuation of none air void was the lowest (277.88~278.12 K), indicating that the air void had a significant impact on the road surface temperature.

Soil Moisture Variations in Frozen Ground Subjected to Hydronic Heating

Full-scale thawing experiments, performed on three types of homogenous, initially frozen soils, were carried out during late winter 2011 and repeated in 2012. An auxiliary heat source (hydronic heating) was employed to initiate and expedite the thawing process. The corresponding phase change, soil temperature increase, and variations in bound and unbound water content were monitored during the experiments. The resulting thermal response have been published in an earlier paper by the authors. In the current paper, the remaining results are presented. This includes spatial and temporal soil moisture variations and resulting thaw rates. Results from both experiments show similar trends. Generally, frost-susceptible soils, such as silty sand, contain more water and thaw slower relative to coarser soils, such as gravelly sand. Very porous soils (uniform gravel) with low water content thaw comparatively slower. Thaw rates compiled from soil moisture records correspond well with similar based on soil temperature. The degree of water redistribution and migration is higher in silty sand compared with coarser soils. These processes are more prominent in the uppermost layer for all soils examined.

Determination of thermal performance of hydronic radiant panel heaters for different fluid flow rates, fluid inlet temperatures and room temperatures

An experimental study of a commercially manufactured ceiling type hydronic radiant heating system has been performed in a test room, under controlled temperature conditions. One of the goals was to investigate how the radiant heater, under various operating conditions, affects the temperature distribution inside an occupied room. Another goal was to study the thermal performance of the radiant heating panel for different fluid inlet temperatures, fluid mass flow rates and test room temperatures. In addition, the temperature distribution on top of a surface placed below the heater, representing an actual application, was investigated. From the relevant literature, it was concluded that insufficient knowledge exists about these characteristics. The working fluid was water, and fluid inlet temperatures between 45 °C and 85 °C and mass flow rates of 97 kg/h and 174 kg/h were analyzed. The results showed that an almost linear increase in heat output arises, with the increase in the inlet water temperature. For lower inlet temperatures the heat output is moderately higher for a mass flow rate of $${\dot{\text{m}}}$$ = 97 kg/h. The fraction of radiation heat transfer to the total heat transfer increases with decreasing water inlet temperature. It was also observed that, a relatively uniform temperature distribution could be obtained on the plate below the radiant panel. Furthermore, lower vertical temperature differences can be obtained inside the test room, for low water inlet temperature conditions. The obtained results of this study, could give information to manufacturers and building engineers, on the appropriate use and regulation of hydronic radiant systems.

Experimental on thermal performance of bridge deck with hydronic heating system

Hydronic heating systems with geothermal heat exchangers are one of the innovative methods for bridge deck deicing in winter, which avoids infrastructure corrosion and environmental pollution caused by chemical methods. This paper focused on field tests of the thermal performance of a bridge deck with a hydronic heating system under heating conditions. The inlet fluid temperatures were kept constant to study the transient heat flux through outlet fluid temperatures under different ambient temperature conditions. Three different inlet fluid temperatures of 30.5 °C, 35.5 °C, and 41.0 °C were considered in the field test. The objective of this paper is to study the influences of the air temperature, slab temperature, and inlet fluid temperature on the heat exchange flux and the thermally induced stresses due to heating. The results indicate that the inlet fluid temperature should be controlled above 2.3 times the absolute value of the air temperature to keep the slab surface temperature above 0 °C when the air temperature is below 0 °C. The thermally induced stresses caused by operating the system are smaller than 5% of the strength of the concrete, which are negligible.

Phase-Change Materials in Hydronic Heating and Cooling Systems: A Literature Review.

When considering the deployment of renewable energy sources in systems, the challenge of their utilization comes from their time instability when a mismatch between production and demand occurs. With the integration of thermal storages into systems that utilize renewable energy sources, such mismatch can be evened out. The use of phase-change materials (PCMs) as thermal storage has a theoretical advantage over the sensible one because of their high latent heat that is released or accumulated during the phase-change process. Therefore, the present paper is a review of latent thermal storages in hydronic systems for heating, cooling and domestic hot water in buildings. The work aims to offer an overview on applications of latent thermal storages coupled with heat pumps and solar collectors. The review shows that phase-change materials improve the release of heat from thermal storage and can supply heat or cold at a desired temperature level for longer time periods. The PCM review ends with the results from one of the Horizon2020 research projects, where indirect electrical storage in the form of thermal storage is considered. The review is a technological outline of the current state-of-the-art technology that could serve as a knowledge base for the practical implementation of latent thermal storages. The paper ends with an overview of energy storage maturity and the objectives from different roadmaps of European bodies.