Underfloor Heating System Research Articles

A new approach on the management of landfill leachate reverse osmosis concentrate: Solar distillation coupled with struvite recovery and biological treatment

The management of reverse osmosis (RO) concentrate remains a challenging task for operators of Landfill Leachates Treatment Plants. In this article we suggest an integrated treatment scheme for RO concentrate that combines solar distillation, struvite precipitation to reduce ammonia content of the distillate and biological treatment of the supernatant either with mixed cultures of bacteria or with microalgae. Experiments in a pilot-scale solar still, equipped with underfloor heating system, showed that the production rate of the distillate ranged up to 3.17 L/d m2. The distillate was characterized by elevated average concentrations of ammonium nitrogen; 2028 mg/L and 1358 mg/L in the two experiments conducted, respectively. A decreasing trend on concentrations of NH4+-N was noticed during these experiments, while the opposite was observed for COD. Struvite recovery experiments showed that the optimum Mg:NH4:PO3 ratio was that of 2:1:5.8. Under these conditions, the NH4+-N removal reached 88%. Further treatment of the process supernatant into a 4-L hybrid sequencing batch reactor with biocarriers and activated sludge achieved NH4+-N removal higher than 98% in Phases C and D, where 450 and 600 mL of supernatant were added, respectively. Similar removal was also observed in a 2-L bioreactor with microalgae Chlorella sorokiniana when 150 mL of struvite supernatant were added (Phase B) while further increase of the amount of added supernatant to 200 mL resulted to a sharp stop of NH4+-N consumption (Phase C). Calculations for a landfill serving 20,000 inhabitants and a daily RO concentrate production of 6 m3/d showed that the required area for the construction of the solar still was 1893 m2 and the volumes of the hybrid and the microalgae reactor were 54 m3 and 60 m3, respectively. The recovered solid material of struvite process, after characterization for heavy metals and organic micropollutants, could be reused to the fertilizers industry.

Numerical study using the finite volume method on the thermal and energy performance of a regulated underfloor heating system incorporating PCM in a ventilated room

A physical model is performed to assess the thermal and energetic advantages of using PCM in controlling and regulating the indoor temperature of a ventilated room with an underfloor heating system incorporating a PCM. The heating source is regulated to keep the cavity air temperature in a small interval assuring a certain level of comfort without wasting too much energy. By contrasting our numerical results with numerical data from the literature, the suggested model was validated. Physical processes are solved numerically using computational fluid dynamics by a detailed 2D transient simulation integrating real climatic data of Agadir, Tangier and Casablanca. The simulations carried out justified the suitability of using the PCM with Agadir and Casablanca climate types by a saving of heating power reaching 18.80 % and 17.33 %, respectively.

Model predictive controls for residential buildings with heat pumps: Experimentally validated archetypes to simplify the large-scale application

Exploiting the energy flexibility resulting from thermal loads management in buildings is one of the most promising solutions to contribute to the energy transition targets. To offer energy flexibility to the grid, the building should meet the requirements: (i) it needs electrically powered generation (e.g., through Heat Pumps) and (ii) advanced control techniques (e.g., Model Predictive Controls) must be implemented. In recent years, the scientific community has produced many studies demonstrating the potential of Model Predictive Controls combined with Heat Pumps to exploit energy flexibility in buildings. However, a large-scale deployment of such control techniques is still far off, both because of the not yet widespread use of Heat Pumps and the computational challenges involved in implementing them. The aim of this study is to contribute to the deployment of advanced control techniques for Heat Pumps systems in buildings by simplifying their implementation. At this aim, validated archetypes of Model Predictive Controls for Heat Pumps in residential buildings are proposed. The availability of archetypes can greatly facilitate the practical application of Model Predictive Control. In fact, they are adaptable to the characteristics of different buildings and Heat Pump installations and their structure is designed to have an acceptable trade-off between calculation time and prediction reliability. The archetypes cover three different types of heating systems: low temperature radiators without (i) and with (ii) integrated heat storage devices and (iii) underfloor heating system. All archetypes are applied to a real Heat Pump and validated through experimental campaigns. During the experimental test all the archetypes proved to be effective in controlling the real system and the results showed good reliability of the prediction model in the control (for all archetypes a Root Mean Square Error lower than 0.44 °C was obtained) and an optimizer success rate in Model Predictive Controls greater than 91 %. The archetypes proposed are provided as open-source tools that can be reused for similar cases to facilitate Model Predictive Controls implementation in heat pump systems.

Solar energy utilization for underfloor heating system in residential buildings

In this paper, the thermal performance of a solar energy system for heating a residential building is experimentally investigated. In this system, the solar thermal energy is supplied via a flat plate solar collector that provides the heated water into a small-scale chamber, that represents the residential building. The experimental setup is installed in Jouf University campus (Latitude: 29° 47′ 1.9” N, Longitude: 40° 2′ 42.2” E) located at Al-Jouf Province, Saudi Arabia. In this experiment, the hot water supplied from solar collector is mixed with water in the storage tank, then extracted from bottom of the tank to be circulated in a copper tube loop located underneath the floor tiles of the chamber and hence increases the chamber’s air temperature. Two circulation pumps are installed in the system, one to circulate the water between solar collector and storage tank and the other to circulate the water between storage tank and chamber. Measurements of several parameters were conducted to evaluate the overall thermal efficiency of the system. The experimental results showed an average efficiency of 51 %, when operating the system for eight-hours duration in the winter season. Additionally, an economic assessment was carried out to confirm the system’s feasibility. This assessment demonstrated that the constructed system is economically feasible, with an estimated benefit-cost ratio of 1.42.

Assessing the impact of the dataset’s size and quality on building thermal models for energy flexibility

The demand side is required to increase its energy flexibility to tackle the demand–supply mismatch caused by integration of renewable energy sources into the energy mix. Model Predictive Control (MPC) is one of the promising measures for achieving this goal. MPC requires operational data from the building to train its predictive model. The quality of this data affects the performance of MPC. This paper aims to analyze the impact of a dataset’s size and excitation method on flexibility harnessed by MPC. Five datasets have been generated that differ in their size and excitation method. They are used to train three modeling algorithms on two buildings. Next, generated predictive models are integrated into an MPC framework, to assess the impact of datasets on the performance of MPCs for activating the energy flexibility of a building. The case studies are two similar dwellings where one is equipped with Electric Heaters (EH), and the other uses an UnderFloor Heating (UFH) system. Results show that the flexibility of the EH case is more sensitive to the size of the dataset. Furthermore, it is shown that the suitability of the excitation signal for flexibility activation depends on the modeling algorithm. The results show that choosing an ill-suited dataset might cost the MPC 35 % and 20 % of the potential flexibility for EH and UFH cases, respectively.

Novel approach to remote rural heating: Direct coupled photovoltaic electric heater underfloor heating system with phase change materials

Limited access to grids and the unavailability of traditional energy sources present significant challenges to effective heating in remote rural. This paper proposes a direct coupled photovoltaic electric heater underfloor heating system with phase change materials (direct coupled PVEH-UFHs), which eliminates the reliance on the power grid or conventional energy sources for heating in remote areas. The model of the direct coupled photovoltaic electric heating system (direct coupled PVEHs) and the building model with PCM floor were created and the accuracy of the direct coupled PVEHs model was verified experimentally. The study proposes using the total heating achievement rate (THAR) as the evaluation index and identifies the critical parameters affecting the system performance through sensitivity analysis. The results indicate that the photovoltaic capacity factor (PVCF), PCMs thickness and melting temperature are the key parameters affecting the heating performance of the system. The recommended 1.4 PVCF and PCM melting temperature of 294 K. The minimum payback time for system configuration that achieves 90 % THAR is 16.2 years. In summary, this paper proposes a design method and evaluation criteria for direct coupled PVEH-UFHs suitable for energy-efficient heating in remote areas.

A Case Study of Nine Post-Hydrocarbon Ready Homes

A typical 2bed dwelling at Howgate Close, after 16months of occupation, has a daily average energy bill of 10pence/day/dwelling [1] It is proffered that Howgate Close may be the most energy efficient group of dwellings of its type, in the UK [2]. Howgate Close is a residential neighbourhood of nine single storey dwellings, operating free of fossil fuels, they are post-hydrocarbon ready. The development is located in Nottinghamshire, UK, and was completed in June 2022. All nine homes are a net annual generator of surplus renewable energy, with little to no heating demand. Six of the nine homes remain naturally heated, with no resort to the electric underfloor heating system. Exceptionally high levels of energy efficiency have been achieved with third-party verification, the As-Built SAP Rating of 143A [3] Such a rating places these homes in the top 0.01% of the 12million registered UK Energy Performance Certificate‘s (EPC) [4]. This paper provides a building Case Study that evidences performance standards making comparisons with the UK Building Regulation Compliance Standards [5] Howgate Close’s exceptional energy efficiency can be described as an aggregation of marginal gains [6] This paper is a prelude to more forensic analysis of Howgate’s in-use building performance, with the installation more advanced monitoring equipment in May 2024 for a period of two years. EWI Pro, Dr Harrall and Nottingham Trent University (NTU) are to undertake further data dissemination, providing a more forensic Howgate Case Study for ISEC 2025.

Comparative numerical study of floor heating systems using parallel and spiral coil

This article presents a comparative numerical study aimed at determining the optimal pipe layout solution for the heating benches of traditional steam baths, with the goal of ensuring an optimal temperature distribution for customer comfort. This layout incorporates insulation on the lower side to direct most of the emitted heat upwards. The temperature distribution across the floor surface varies depending on the configuration of the buried pipes. Calculations were performed using the CFD software "COMSOL Multiphysics" to investigate the thermal behavior of an underfloor heating system. The results were used to discuss certain critical parameters that require control for the proper operation of the system. These parameters include the flow velocity inside the pipes, inlet temperatures, and pipe configuration. A new parameter designed to measure the thermal homogeneity of the floor was introduced and evaluated. In general, the findings demonstrated that the modulated spiral configuration is the best solution, minimizing pressure losses while ensuring optimal thermal homogenization across the entire floor surface.

Correction of the thermal power calculation in the lightweight floor heating based on NT VVS127:2001 standard

There are many possibilities for determining the thermal power (thermal output) of underfloor heating systems. These may be mathematical, experimental, and numerical methods. Some of them are described in standards, manufacturers’ guides (e.g. charts or tables based on experimental research), as well as programs with numerical calculations. This article concerns the issue of correct calculation of the thermal power only in lightweight underfloor heating without any screeds. It considers the correct entry of the formula for calculating heat power given in the Norwegian standard NT VVS127:2001, relating to a lightweight floor system with metal lamellas. According to the author of this article, there is a significant error in one of the formulas of this standard, which leads to an incorrect final result. This view was based on the results of the author’s calculations and the calculations and conclusions of other scientists. The correction of the incorrectly written formula of the NT VVS127:2001 standard confirms the correctness of the thermal power calculations in a lightweight underfloor heating system with metal lamellas without screeds.

Economic viability of under floor heating system: a case study in Beirut climate

This paper explores the economic feasibility of the underfloor heating system for the climatic conditions of Beirut. A case study of a typical residential room (150 m2 ) is selected to compare its heating energy requirement when using either the conventional convective heating system or the underfloor heating system at similar comfort and indoor air quality conditions. Two mathematical models are developed, a steady space thermal model to establish the energy consumption at the peak load and a transient simulation model to find the energy consumption during the winter heating season. In addition, the economic feasibility of the underfloor heating system is assesd when integrated with solar energy. Based on the steady space model, the calculated peak heating load is reduced by 20% when the test space is heated by the underfloor heating system and a thermal comfort level of PPD 18.3% is achieved for a floor temperature of 27.4 ºC. The simulation results of the transient space model indicates that the seasonal heating energy consumption is reduced by 18% and that the yearly energy savings is $104 for an on-off control strategy that maintains a PMV comfort level greater than -0.5. The pay back period of the underfloor heating system is 10 years for an initial incremental cost of $850. When integrated with 10 solar collector units, the yearly energy savings of the integrated system is increased to $350 and the pay back period is 14 years.

Energy, exergy, environment and techno-economic analysis of hybrid solar-biomass systems for space heating and hot water supply: Case study of a Hammam building

The main goal of this study is to assess the thermodynamic performance, environmental benefits and economic feasibility of using a new hybrid solar-biomass system (HSBS) for the production of domestic hot water at 60 °C and for the provision of space heating via an underfloor heating system in a Hammam building located in Marrakesh-Morocco. The HSBSs consists of small biomass pellet boilers in combination with three types of solar thermal systems (evacuated tube, flat plate and parabolic trough collectors). A TRNSYS simulation model of a biomass heating system was developed and validated against experimental data. Performance comparisons of the biomass system with various optimal HSBSs were then conducted, and their results evaluated in terms of energy, exergy, environmental, and economic perspectives. Comparisons between various collectors’ technology revealed that the optimum collector areas of 204 m2, 224 m2 and 300 m2 are responsible for the lowest Levelized Cost of Heat (LCOH) corresponding to about 0.0755 $/kWh, 0.0696 $/kWh and 0.0642 $/kWh when using PTC, FPC and ETC, respectively. Furthermore, the optimal HSBS with evacuated tube collectors is the most effective configuration with a solar fraction of 57 %, and a total life-cycle saving cost of 0.509 M$ for a total annual heat demand of 533 MWh. Moreover, the total energy and exergy efficiencies are calculated equal to 40 % and 3.9 %, respectively. The payback period is found to be around 4.9 years, the levelized cost of heat 0.0642 $/kWh, while the annual CO2 avoidance amounts to 656 tons.

Analysis of solar underfloor heating system assisted with nano enhanced phase change material for nearly zero energy buildings approach

Analysis of solar underfloor heating system assisted with nano enhanced phase change material for nearly zero energy buildings approach

Application of a pilot-scale solar still for wine lees management: characterization of by-products and valorization potential

Wine lees is a heavily contaminated by-product of wine making process. A pilot-scale solar still, equipped with an underfloor heating system, was used for dewatering the wine lees and recovering the evaporated water. Two solar distillation experiments were conducted, and the average distillate productivity rate ranged between 1.43 L/d·m2 and 3.86 L/d·m2. The higher productivity was observed at Experiment B when the daily maximum wine lees temperature in the still was 34.3 °C. The collected distillates were characterized by acidic pH and low conductivity while the average concentrations of COD and total phenols were ranged up to 82.5 g/L and 10.7 mg/L, respectively. UPLC-QToF-MS analysis revealed the existence of eighteen and five bioactive compounds in the wine lees and produced distillate, respectively, at concentrations up to 183 mg/kg and 12 mg/L for ethyl hydrogen succinate. Target screening analysis of the solid residuals allowed the quantification of seven bioactive compounds while four extra substances were identified via suspect screening. Ethyl hydrogen succinate was measured at the highest concentration (10.8 mg/kg) while the highest recovery was observed for 4-hydroxy-benzaldehyde (23.8%). The calorific values of the solid residuals exceeded 28 MJ/kg indicating their potential use as solid biofuels. Batch experiments showed that Chlorella sorokiniana can be grown in diluted distillates of the still. The higher average biomass productivity was observed for a dilution factor of 1:5 and it was equal to 31.4 mg/L per day. Analysis of the collected biomass indicated high lipid and starch content ranging up to 38.8% and 56.9%, respectively.

An analysis of the effectiveness of new generation self-levelling lightweight composite screed for underfloor heating systems

Energy saving has become a significant concern in recent years due to increasing carbon emis- sions and environmental pollution. When examined from a global perspective, it is known that the energy consumed for heating and cooling of buildings is relatively high. In this regard, researchers attach great importance to energy efficiency issues. In recent years, an issue that has been given priority in heating buildings more efficiently is underfloor heating systems. Underfloor heating systems are composite structures of slab concrete, insulation material, hot water pipes, and screed. Here, the thermal performance of the screed is vital as the hot water pipes remain embedded in the screed. This study has produced a new composite and self-leveling screed type that can transfer heat easily. For this purpose, nine screed mixtures were prepared, including a reference (nearly conventional) screed mortar. The screed mortars’ flowability, density, and compressive strength were determined regarding physical properties. Thermal properties, thermal conductivity, specific heat, thermal diffusivity, and heat storage analyses were carried out. In the second stage of the study, a basic underfloor heating system was installed, and the temperatures of the water circulating in the system, the outer surface of the pipe carrying the water, and the outer surface of the screed were measured at specific peri- ods. According to the study results, it has been observed that depending on the thermal prop- erties of the screeds produced within the scope of this study, when used in underfloor heating systems, it can transfer heat from the hot water pipes to the surface with minimum losses.

Evaluation of model predictive control (MPC) of solar thermal heating system with thermal energy storage for buildings with highly variable occupancy levels

The presence or absence of occupants in a building has a direct effect on its energy use, as it influences the operation of various building energy systems. Buildings with high occupancy variability, such as universities, where fluctuations occur throughout the day and across the year, can pose challenges in developing control strategies that aim to balance comfort and energy efficiency. This situation becomes even more complex when such buildings are integrated with renewable energy technologies, due to the inherently intermittent nature of these energy source. To promote widespread integration of renewable energy sources in such buildings, the adoption of advanced control strategies such as model predictive control (MPC) is imperative. However, the variable nature of occupancy patterns must be considered in its design. In response to this, the present study evaluates a price responsive MPC strategy for a solar thermal heating system integrated with thermal energy storage (TES) for buildings with high occupancy variability. The coupled system supplies the building heating through a low temperature underfloor heating system. A case study University building in Nottingham, UK was employed for evaluating the feasibility of the proposed heating system controlled by MPC strategy. The MPC controller aims to optimize the solar heating system’s operation by dynamically adjusting to forecasted weather, occupancy, and solar availability, balancing indoor comfort with energy efficiency. By effectively integrating with thermal energy storage, it maximizes solar energy utilization, reducing reliance on non-renewable sources and ultimately lowering energy costs. The developed model has undergone verification and validation process, utilizing both numerical simulations and experimental data. The result shows that the solar hot water system provided 63% heating energy in total for the case study classroom and saved more than half of the electricity cost compared with that of the original building heating system. The electricity cost saving has been confirmed resulting from the energy shifting from high price periods to medium to low price periods through both active and passive heating energy storages.

Experimental Study of Photovoltaic-thermal Integrated Heat Pump Building Heating System

Photovoltaic-thermal (PV/T) systems and hydronic radiant floor heating systems can enhance energy efficiency and economic viability. This study investigates their integration through experimental research and designs an experiment to test their performance under typical winter conditions. The heat pump system achieves an average COP of 5.66 and an average photovoltaic power output of 107.5 W. The underfloor heating system quickly reaches and maintains 20.47°C with a water supply temperature of 50°C.

Intermittent Exothermic and Self-Healing Hydrated Salt Gels for Advanced Thermal Management of Underfloor Radiant Heating System.

Phase change materials (PCMs) have great prospects in thermal management applications because they can store and release latent heat. However, they are not suitable for on-demand heating as they can only release heat once. Herein, this work reports the intermittent exothermic of PCMs based on a supersaturated salt solution, exhibiting fully controlled long-term storage of energy, releasing and suspending heat on demand. Due to the high energy barrier, it is difficult for the supersaturated salt solution to nucleate; thus, it can store energy for a long time. Contact with seeds or other foreign objects can destroy the metastable state of the supersaturated salt solution and promote the formation of crystal nuclei, enabling crystallization and heat release on demand. The release of crystallization heat can be interrupted using scissors dip in water. Additionally, self-healing behavior allows it to be recycled and last longer, due to the presence of Fe3+ , inducing strong dynamic reversible non-covalent crosslinking through metal coordination bonds. Furthermore, the hydrated salts gels are applied for thermal management of underfloor radiant heating system, demonstrating four types of intermittent exotherms sequences amazingly. Further, the intermittent exothermic hydrated salts gels provide a more user-friendly thermal management of underfloor radiant heating systems.

Investigation of issues affecting thermal comfort in water system underfloor heating applications of buildings with Bayesian networks

Thermal comfort is related to the stability of the ambient temperature. Constant changes in ambient temperature appear as a situation that negatively affects comfort. The selected build-ing systems must be arranged to maintain this stability for the continuity of thermal comfort. In this study, issues affecting thermal comfort in water system underfloor heating applications of buildings are handled and analyzed using the Bayesian Network modeling methodology. Visual examples of the problems encountered in field applications are also given. Three dif-ferent scenarios are tested with the constructed Bayesian Network model. In the first scenario, assumed that mechanical project failures were prevented. In this case, it was observed that the failure rate decreased by about 5%. In the second scenario, assumed that mechanical applica-tion failures are prevented along with mechanical project failures. The failure rate decreased by 11% compared to the first situation. The third scenario assumed that the mechanical proj-ect preparation phase was concluded without any problems, the mechanical project was im-plemented without any failures, and the mechanical system was commissioned without any problems. In the last scenario, the failure rate decreased by 14% compared to the first case, and the probability of not providing thermal comfort remained at 2%. As a result of these three scenarios, the possibility of not providing thermal comfort in the underfloor heating system is detailed and interpreted.

Experimental study and numerical simulation of a floor heating system in a three-dimensional model: Parametric study and improvement

In recent years, the installation of underfloor heating systems has increased considerably in many countries, due to their ability to be connected to a solar thermal collector in order to benefit from clean and renewable energy. This promising technology allows for reduced energy consumption, achieves a higher level of comfort, and ensures a more homogeneous temperature distribution than conventional heating systems. A huge loophole is detected in research works concerning the three-dimensional numerical modelling of the thermal behavior of underfloor heating by COMSOL Multiphysics software. The present study aims to reduce these knowledge gaps and to analyze the thermal behavior of the direct solar floor numerically and experimentally under the specific climatic conditions of Casablanca, Morocco. Visualize the thermal behavior of the underfloor heating system and the heating circuit as a 3D model using COMSOL Multiphysics software, based on the finite element method by investigating the influence of various design and operational parameters to select the best parameters that guarantee thermal comfort in the case of installing this heating system in traditional bathrooms.The results obtained by numerical simulation are then compared with those of the experimental measurements in order to verify the validity of the numerical model. The average deviation between the simulated and measured surface temperatures is approximately 1.04%, while the deviation in pipe temperature is around 3.13%, which shows a very good agreement between the numerical and experimental results. In addition, the results of the parametric study indicate that the key elements for enhancing the floor heating system are primarily a floor covered by tile with a minimum thickness of 5 mm, a pipe spacing of approximately 15 cm, a PER pipe diameter of 16/20 mm, and a thermal insulation layer with a thickness of 50 mm made of XPS or polystyrene. The incorporation of these improvements in the standard model ensures a surface temperature within the thermal comfort range of a less warm bathroom, approximately 34.13 °C, and a high heat flux emitted at the surface around 502.07 W compared to the standard model. In the literature, it was found that the comparison of architectural characteristics of direct solar floors receives minimal attention, with most studies only comparing systems in terms of thermal comfort or energy efficiency. In this study, the analysis and interpretation of the results obtained can be used to help engineers and designers select the type and dimensions of the best materials for heating floors installed in traditional bathrooms in Morocco.

Hammam from Khankurgan

The authors publish the results of architectural and archaeological research of the medieval bath house carried out on the territory of the settlement Khankurgan in 2015–2016. During the excavations, six rooms were unearthed, two of which were built of burned bricks and turned out to be “steam rooms” with an underfloor heating system, the remaining four were frame rooms – “washing rooms”. All rooms are covered with waterproof mortar and plaster. Their original layer was decorated with red-brown drawings, carved stucco and moldings. The plaster has been updated more than twenty times in the course of multiple repairs. Two major reconstructions of the bathhouse were recorded, which did not affect the "hot" rooms, due to which their original layout was preserved. The stages of restructuring and repair work for the entire period of operation of the hammam are determined. The Khankurgan bath house is well preserved and is a unique example of medieval architecture of the Samanid era, it belongs to rather early examples of such structures that arose at the middle of the 9th century. Functioning until the middle of the 11th century, it gives us a represent of the features of the architectural and construction techniques used in the building of the baths of the pre-Mongolian era in Kazakhstan. Hammam Khankurgan, being a vivid example of the medieval architecture, allows to determine the time of the emergence of this culture in the Ispidzhab historical and cultural region, clarifying its planning, constructive and shaping principles, reflecting in general the cultural and economic connection of the region with the Muslim world.