Hydronic Heating System Research Articles

Peak Power Minimization for Commercial Thermostatically Controlled Loads in Multi-Unit Grid-Interactive Efficient Buildings

The load profiles of most commercial and industrial consumers are characterized by brief periods of very high power consumption followed by intervals of lower demand. To encourage such consumers to flatten their load profiles, power utilities around the world often levy a monthly demand charge (DC) on the peak demand measured over brief intervals. In this work, we consider the joint optimization of energy costs (EC) and the instantaneous peak power of a multi-unit building which uses a hydronic heating, ventilation and air-conditioning (HVAC) system and responds to a demand response (DR) program. Despite the apparent non-convexity of the control framework, we show how it may be transformed into a convex optimization problem. Next, we study the power demand patterns resulting from our proposed strategy for thermostatically controlled loads (TCLs), and evaluate the strategy’s performance for various climate zones in the US under both typical and atypical weather conditions. The results show that, depending on the ambient conditions and the tariff structure, our strategy can result in utility bill savings of up to nearly 19% compared to the baseline. The results also indicate that our power control strategy can significantly reduce the instantaneous peak power consumption in commercial TCLs.

Heating properties of bridge decks using hydronic heating systems with internal or external circulation tubes

A comparison analysis of the heating properties of the hydronic heating system of bridge decks with external (exchange tubes installed at the bottom of the existing bridge deck with voids inside) or internal (exchange tubes embedded in pavement of the newly built bridge deck) tubes was carried out through field tests. Two heating methods (constant heating power and constant inlet fluid temperature) were used to analyze the heat exchange flux and the temperature increments as well as thermally induced stress of the slab. Numerical simulation was conducted to model the bridge deck heating process to analyze the temperature distribution of the bridge surface. The results shows that the heat exchange flux are the same under the same constant heating powers for the two embedded tube position heating systems; the maximum temperature increment of the bridge deck surface obtained by the external heating system is 0.46 times that obtained by the internal heating system; the maximum thermally induced stress caused by the external heating is 20.4% of the concrete strength (19.1 MPa), which is much higher than that caused by the internal heating under the same heating powers. The thermal efficiencies of the external and internal heating systems are approximately 24.4% and 47.9%, respectively. Under the same constant inlet temperatures, the temperature increment of the bridge deck caused by the external heating is 20.4% of that of the internal heating.

Insulated PEX-pipe loops for deicing on existing bridge deck using geothermal energy: Laboratory tests, modeling, and performance analyses

An external hydronic heating system utilizing geothermal energy is an innovative new method to de-ice in-service bridges that avoids detrimental environmental effects and damage to bridge deck structures stemming from chemical deicers and mechanical traction materials (e.g., sand). However, in these systems, the bottom surface of the bridge deck is usually fully covered by insulation materials and hence not accessible for visual bridge inspection. In this study, a new attached insulated, cross-linked polyethylene (PEX) pipe loop heating system is developed to heat existing bridges while maintaining a partly uncovered deck for visual inspection. The new loop consists of a PEX pipe, an aluminum plate, polyurethane foam insulation, and a high-density polyethylene jacket. Numerical simulations were first performed to determine the optimum shape and thickness of the insulation. Then the pre-made loop system was attached to the bottom surface of a concrete slab in a freezer box, where 62.3% of the slab bottom surface was covered by the system. A heated water bath was used to simulate the ground heat exchanger for heating the system. The heating tests were conducted at room temperatures of −2.78, −3.89, and −6.67 °C, with supplied water temperatures ranging from 24 to 45 °C. A 1-D steady-state thermal resistance model was then created to model the heat transfer processes and to estimate the slab surface temperatures. The results show that the deck surface heat flux fluctuated from 49.6 to 121.5 W/m2, depending on operating conditions and that an average of 16.3% of heat energy was transferred to the deck top surface. The results of misting tests indicate that the new system kept the bridge deck free from ice under mild winter conditions. These results demonstrate that the new insulated PEX pipe loop heating system is feasible for deicing existing bridges while minimizing the hindrance of bridge inspections.

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.

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.

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.

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.

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.

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.

Thermal performances of porous snow by a hydronic heating system at different weather conditions

The snow on the road in the cold regions is easy to cause slippery conditions, which are dangerous for vehicles and people. To remove the slippery conditions, the hydronic snow melting system has been applied to remove the snow on the road. This study proposed a transient finite volume model with snow porous characteristics, to analyze the snow melting performances by a hydronic heating system. Three primary environmental parameters (snow thickness, wind velocity, and air temperature) were selected to compare the average road surface temperature and snow melting ratio. Then, the snow melting performances using a hydronic road heating system were analyzed. The results showed that the snow melting ratio was rapidly dropped as the snow thickness was increased from 10 to 90 mm. The snow thickness had a slight influence on the average road surface temperature in the melting process, whereas it had a significant impact after the snow was completely cleared. When the wind velocity was increased to 5 m s−1, the critical melting ratio appeared at around 0.7. The wind velocity had a significant influence on average road surface temperature when the average road surface temperature increased more than 273.15 K. There is a critical air temperature existed between 263.15 and 258.15 K, which limits the snow melting process at current supplied fluid temperature (313.15 K), indicating that more energy was need to supply to overcome cold weather. This study offers a good reference for the design of a hydronic snow melting system in severely cold regions.

Heating performance enhancement for a road unit by using sectorial-finned pipe

This study proposes a sectorial-finned pipe in the hydronic road heating system with a three-dimensional road model to enhance the road heating performance. Three primary fin parameters, including sectorial fin angle, height, and spacing, were analyzed. The range analysis and ANOVA (analysis of variance) of the final average road surface temperature (Tasf), the maximum temperature difference of road surface (Tds), and the overall utility (Ut) were conducted through the orthogonal test method. The results showed that compared with the bare pipe, Tasf and Tds of the finned pipe increased by 0.63–1.37 K and 0.27–0.66 K, respectively, and ts0 of the finned pipe decreased by 0.22–0.44 h when the fin parameters were changed in specific ranges at the average air temperature of 258.15 K. The fin angle of 210° had the most suitable performances for road heating in terms of the thermal and economic targets. The range analysis revealed that the ranks of influence degree for Tasf, Tds, and Ut were height > spacing > angle, height > spacing > angle, and angle > spacing > height, respectively. ANOVA indicated that the parameters of height, spacing, and angle contributed Tasf in proportions of 80.56%, 10.25%, and 9.19%, those contributed Tds in proportions of 98.58%, 1.29%, and 0.13%, and those contributed Ut in proportions of 60.06%, 36.20%, and 3.74%, respectively. The optimum parameter combination for Ut was 210°, 20 mm, and 45 mm for the fin angle, height, and spacing, respectively. The results can provide a good guide for the design of sectorial-finned pipes in the hydronic road heating system.

Numerical study on thermal performances of bare, circular and rectangular finned pipes for road heating

The hydronic road heating system based on embedded finned pipes is a new application that can improve the thermal performances of heat conduction in concrete. When the embedded pipe layouts were studied and determined, the thermal performances of three embedded pipe geometries (bare, circular finned and rectangular finned) were detailed. The variables including supplied fluid temperature and flow velocity were used for different pipe geometries. The results indicated that the pipe layout of 80 mm depth and 200 mm spacing was the most suitable one for heating road among all the pipe layouts (depths of 80, 120 and 150 mm and spacings of 200, 300 and 400 mm). This was because it had the highest average heating rate (2.77 K h−1) for a heating period of 6 h with a supplied fluid temperature of 308.15 K and a flow velocity of 0.9 m s−1. Rectangular finned pipe showed the highest thermal performance among the three embedded pipe geometries, due to its shortest preheating time (1.2 h) and highest preheating rate (6.67 K h−1) at the same conditions. When the road was preheated from the initial road surface temperature (265.15 K) to the critical temperature (273.15 K), the preheating time difference between rectangular finned and bare pipes decreased from 4.81 to 0.66 h when the supplied fluid temperature was increased from 298.15 to 318.15 K, and it decreased from 1.61 to 0.94 h when the flow velocity was increased from 0.05 to 0.9 m s−1. It was also observed that the flow velocity had slight effects on the heating performances of the three pipes when it was higher than 0.2 m s−1.