Radiant Floor Research Articles

Heating Industrial Buildings with Heat Pump Air Systems: Is It Always the Most Advantageous Option?

According to extant Italian legislation implementing the Renewable Energy Directive, the mandatory renewable quota for a new building is 60% referring to a single service (e.g., heating during winter) or to multiple services (e.g., heating during winter and air conditioning during summer), depending on which services are actually present. The obligation to satisfy this minimum value often leads heating and ventilation plant designers to provide heat pump systems in industrial buildings, typically air/water or direct expansion type coupled with air terminals (air heaters or ventilation units) or radiant floors. The question is: Is this always the most advantageous option for industrial buildings? A typical industrial building was modeled by Trnsys® in two different climates. Based on the calculated thermal heating loads, the condensing radiant tubes and heat pump coupled with the air heaters systems were analyzed through dynamic simulation, evaluating their performance from an energy, environmental impact, and economic point of view. The analysis carried out revealed that a heat pump system is not always the most advantageous solution depending on the climate, the characteristics of the building (less or more thermal insulation, which corresponds to existing buildings rather than new ones), and the size of the photovoltaics system eventually installed on the roof.

Experimental analysis of a radiant floor system incorporating phase change materials: Thermal performance and energy efficiency

The incorporation of Phase Change Materials (PCMs) in radiant floors has the potential to improve the thermal and energy performance of the system. PCMs can act as thermal batteries, providing additional thermal energy storage capacity to Radiant Floor Systems (RFS). However, in the case of wet construction, when PCMs are incorporated into the enveloping mortar surrounding the RFS water pipes, the resulting specific heat and thermal conductivity can pose a challenge to system performance. The objective of this paper is to evaluate the impact that the incorporation of microencapsulated PCM (mPCM) in the RFS mortar has on the thermal and energy performance of the system. To tackle this objective, an experimental setup was constructed consisting of two RFS specimens: one reference and the other with mPCM within an innovative mortar. The two specimens were then tested under different heating strategies controlled by: i) timer, and ii) floor surface temperature setpoint. The thermal performance of the PCM-RFS and operating time were compared with the reference RFS. Timer-controlled intermittent heating has proven beneficial when the heating strategy is established to combine renewable solar energy and off-peak electricity tariffs. Thermal fluctuation was reduced and the PCM phase change process was mobilized twice in 24 h, maintaining surface floor temperatures of the PCM-RFS within comfort levels throughout the test period. When the heat source is controlled by floor surface temperature setpoint, the thermophysical properties of the PCM-RFS led to longer operating times, however mitigating high intermittency of the heat source activations, resulting in more regular operation mode, easier control and avoiding peak heating loads.

Calculating the local and overall view factors of a multi-segment human model

In non-uniform environments, such as spaces with radiant ceilings or floors, or with hot or cold windows, view factors (VFs) of a person towards these surfaces are needed for calculating the heat exchanges between the person and the surroundings. Multi-body segmented human models can simulate the heat exchanges of individual body parts with the environment. Simulating heat transfer at the local body parts is important for assessing comfort in non-uniform environments. These models require VFs for each individual body part. Accurately determining these VFs is time-consuming, often requiring methods such as ray-tracing techniques. A fast calculation method to accurately determine the view factor (VF) for each segment has yet to be investigated. This study employed a 16-segment human model into various architectural radiation scenarios. The surface-to-surface model in computational fluid dynamics was utilized to simulate VFs for the 16 body segments in relation to radiant surfaces at different locations. Through a series of simulations, comprehensive formulas for VFs were derived for each individual at various positions within a room, encompassing 16 body segments and computing parameters for 24 building surfaces. The accuracy of these general formulas was validated by comparing the whole-body VF with results from several available studies. Additionally, this study developed a visualization tool for calculating VF and mean radiant temperatures with different room space dimension and embedded radiant surfaces. The users can use this online tool to easily calculate VFs and mean radiant temperatures for each body parts, and for the whole-body. The tool offers valuable insights for predicting thermal comfort in asymmetric radiant environments and facilitating control over building environments.

Experimental study on the operating characteristic of a combined radiant floor and fan coil cooling system

Experimental study on the operating characteristic of a combined radiant floor and fan coil cooling system

Classification of radiant and convection time series for cooling load calculation of radiant cooling systems

Radiant cooling systems have the potential for energy saving, better thermal comfort, and space-saving. The lack of cooling load calculation methods limits the engineering application of radiant cooling systems. A universal radiant and convection time series (RCTS) set is indispensable in radiant cooling system design. In this study, an RCTS dataset with 100,000 sample rooms is generated based on the combinations of 9 room characteristic parameters. Extreme gradient boosting (XGBoost) is used to grade the room characteristic parameters and classify RCTSs. Gaussian mixture model (GMM) is used to extract the representative RCTSs for each category. The RMSE is used to measure the accuracy of the representative RCTS. The results indicate that XGBoost and GMM perform very well. Non-solar radiant time series (RTS), convection time series (CTS), solar RTS for radiant ceiling panel systems and solar RTS for radiant floor cooling systems are classified into 12, 8 and 1 categories, respectively. The representative RCTSs of all categories constitute a universal RCTS set. Fifteen room characteristic parameters are taken into account to construct sample rooms for Changsha. The accuracy of the representative RCTS was compared with the self-RCTS and heat balance method. The relative deviations of the design cooling load calculated using the representative RCTS and self-RCTSs were within ±3 % for 90 % cases of the sample rooms. The relative deviations between the design cooling load calculated using the representative RCTS, self-RCTSs, and theoretical design cooling load are within ±7 % for 90 % cases. The universal RCTSs set is applied for radiant cooling systems design.

Performance investigation of a solar-driven cascaded phase change heat storage cross-seasonal heating system for plateau applications

The mismatch between solar radiation resources and building heating demand on a seasonal scale makes cross-seasonal heat storage a crucial technology, especially for plateau areas. Utilizing phase change materials with high energy density and stable heat output effectively improves energy storage efficiency. This study integrates cascaded phase change with a cross-seasonal heat storage system aimed at achieving low-carbon heating. The simulation analyzes heat distribution and temperature changes from the heat storage system to the heating terminal. The results indicate that although the solar collectors operate for 26.3% of the total heat storage and heating period, the cumulative heat stored is 45.4% higher than the total heating load. Heat transferred by the cross-seasonal heat storage system accounts for up to 61.2% of the total heating load. Therefore, the system reduces fuel consumption by 77.6% compared to conventional fossil fuel heating systems. Moreover, radiant floor heating terminals, with a wide range of operating temperatures, match well with cascaded phase change heat storage and can reduce operation time by 19.5% and heat demand by 5.2% compared to conventional radiators. In addition to demonstrating the feasibility of applying cascaded phase change technology in cross-seasonal heat storage heating, this study reveals the lifecycle sustainability due to the shortened heat storage period. The configuration, parameters, and simulation results provide a reference basis for system application and design.

A Novel Direct-Expansion Radiant Floor System Utilizing Water (R-718) for Cooling and Heating

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author’s knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application.

Heating performance of PCM radiant floor coupled with horizontal ground source heat pump for single-family house in cold zones

As the energy demand for space heating increases, the necessity for innovative and energy-efficient heating technologies has become more urgent. This study proposes and evaluates a heating system that integrates a phase change material radiant floor with a horizontal ground source heat pump (PCM floor-HGSHP, Case 1), intending to maintain indoor comfort temperatures and enhance energy efficiency through the utilization of renewable energy sources. Despite the considerable potential of PCM floors, their combination with HGSHP requires further research to fully unlock their benefits. The study involved simulating the PCM floor using a validated TRNSYS component and developing an advanced rule-based control strategy with time-of-use tariffs as a key input to optimize system operation. To elucidate and quantify the advantages of the PCM floor-HGSHP system and verify its applicability in cold regions of China, a single-family house was used as a case study building, four representative cities were selected, and two comparative simulation cases were defined, along with three key performance indicators. The results indicate that, compared with the radiant floor heating system with HGSHP (RFHS-HGSHP, Case 2), the incorporation of PCM in the floor of Case 1 improves the indoor temperature stability by 8.6 %, enhances the load flexibility by 18.1 %, and reduces the total operating costs by 13.8 %. Furthermore, relative to the PCM floor with air-to-water heat pump system (PCM floor-AWHP, Case 3), the proposed system which substitutes the AWHP with the HGSHP, extends the duration of indoor comfort temperatures by 9.6 % and decreases the system electricity consumption by 33.7 %. The proposed system demonstrates excellent thermal and energy performance across all selected cities, proving to be both technically feasible and significantly beneficial for maintaining indoor comfort temperatures and reducing operational costs. This study offers valuable insights and technical support for designing and optimizing residential heating systems in cold regions, thereby promoting the development and application of renewable energy sources.

Influence of hot water pipe position on the performance of radiant floor heating systems integrated with PCM

To address the slow heating and low efficiency issues of traditional macro-packed phase change material (PCM) radiant floor heating systems, this study innovatively explores the impact of altering the eccentric positions of hot water pipes within the PCM encasement, based on computational fluid dynamics (CFD) numerical simulations. Starting with a concentric case as a baseline, the investigation extends to six different configurations achieved by displacing the hot water pipes vertically (upward and downward) and horizontally. The analysis encompasses the PCM's thermal state, temperature dynamics, spatial distribution, and heat flux. The results indicate that the arrangement of hot water pipes with upward and horizontal displacements demonstrates a more positive impact on improving the thermal performance of the PCM radiant floor heating system, with the effect becoming more pronounced as the displacement distance increases. Cases with upward eccentric movement of r/4 (where r is the encasement radius) and r/2 reached the optimal floor temperature of 297.15 K faster than the concentric case by 2 h and 3.8 h, respectively, during the heating phase. Cases with horizontal eccentric movement advanced by 0.5 h and 2.5 h, respectively. Cases with horizontal displacements of r/4 and r/2 caused smaller temperature fluctuations and provided greater comfort and energy efficiency than those with upward displacements, with average heat flux values being 4.75 % and 11.82 % lower, respectively. These findings offer theoretical support for the optimization and application of macro-packed PCM floor heating systems.

Development and thermal performance testing of radiant conditioning ceiling panels

The past decades have seen an advancement from heavyweight radiant floors to lightweight conditioning ceiling systems. However, the performance of these lightweight systems are seldom comprehensively discussed in an informative manner for designers. This paper reviews lightweight radiant ceiling panel designs and conducts instrumental experiments to examine the thermal performance of different designs. Four distinct capillary hydronic panels have been designed and developed to assesses their thermal performance via empirical testing and measurement. Prototypes were built and integrated into a suspended ceiling system where they were tested in cooling mode. The response time, surface temperature, and energy transfer of the different panel designs were investigated. The experiment results show that higher thermal mass yields higher heat transfer and better surface temperature, but longer response time. A better thermal connection between the capillary tubes and the radiant surface also results in better conduction, faster response times, and improved surface temperature.

Preparation and characterization of innovative cement mortar incorporating fatty acid/expanded graphite composite phase change material for thermal energy storage

To explore the application of phase change energy storage materials in building energy conservation, in this study, an innovative composite thermal energy storage cement mortar (CTESCM) was developed using lauric acid–palmitic acid/expanded graphite (LA-PA/EG) as the composite phase change material (CPCM). Seven different CTESCM test blocks with different CPCM mass contents were prepared. The thermal characterization of the CTESCMs was achieved using a differential scanning calorimeter (DSC), a thermogravimetric analysis (TGA), thermal conductivity tests, and heat storage/release tests. The physical behavior was assessed using density, mechanical performance was assessed using compressive strength, and the microstructure was observed using a scanning electron microscope (SEM). The results indicate that the phase transition temperature of the CTESCMs was lower than that of the LA-PA/EG CPCM, and the latent heat consistently decreased with the decrease of the CPCM mass content. With the addition of the CPCM, which had a low-density porous structure, the thermal conductivity, density, and compressive strength of the CTESCMs decreased. CTESCM with a mass fraction of 20%C (20% cement) CPCM can be used for building energy conservation such as floor radiation heating systems.

Experimental and Numerical Study of Newly Assembled Lightweight Radiant Floor Heating System

In this study, the heating capacity of a new prefabricated assembled hot water radiant modular heating system made from a recycled waste building masonry structure is investigated through experimental and numerical simulation methods. The heating capacity of the system in different working conditions (a water supply temperature of 48 °C, 51 °C, 56 °C, and 61 °C; a flow rate of 0.49 m3/h, 0.35 m3/h, and 0.21 m3/h) is analyzed and verified. A three-dimensional steady-state heat transfer numerical model of the floor heat transfer of the module is established, and the accuracy of the model is verified through the measured results to investigate the heating capacity of this system under different water supply temperatures, flow rates and coil spacings. The results show that the new prefabricated hot water radiant module heating system has a 0.9 °C higher air temperature and 2.1 °C higher average floor surface temperature than the traditional wet floor radiant heating system under the same experimental conditions, and the response time is 44% shorter. The water supply temperature can significantly change the heating capacity of the system, while the water supply flow rate has little effect on the system. The established three-dimensional steady-state numerical model can be in good agreement with the measured results. This study can provide an experimental and theoretical basis for the design and application of such systems.

A method for setting room temperature of district heating in northern China based on local thermal comfort

Currently, the district heating system in northern China primarily employs two types of terminals, namely radiators and radiant floors. The heating design temperature is set for the center of the room without considering local thermal comfort for individuals. As the real thermal environment within buildings is non-uniform, variations in thermal sensation across different parts of the body will affect whole-body thermal comfort. Therefore, it is crucial to prioritize local thermal comfort when setting room temperatures for heating purposes. In this study, we analyzed the data from the chamber experiments and Chinese Thermal Comfort Database, focusing on the district heating environments of residences, office buildings, and university classrooms in severe cold and cold zones. We developed a thermal sensation evaluation model for analyzing the most uncomfortable body part, investigated the lower limit of acceptable air temperature for this specific body part and inferred appropriate setpoint based on both this limit and head-ankle temperature difference. The results indicate that ankles are the most uncomfortable part with an estimated lower limit of acceptable air temperature at approximately 18 °C. Consequently, we recommend setting room temperatures of 20 °C for radiator heating (RH) and 19 °C for floor heating (FH) to ensure ankle thermal comfort. The findings of this study can provide theoretical basis for reasonable settings of heating room temperature for the aforementioned three types of buildings in northern China, thereby further achieving energy conservation.

A Comparative Analysis of Machine Learning Algorithms in Predicting the Performance of a Combined Radiant Floor and Fan Coil Cooling System

Machine learning algorithms have proven to be practical in a wide range of applications. Many studies have been conducted on the operational energy consumption and thermal comfort of radiant floor systems. This paper conducts a case study in a self-designed experimental setup that combines radiant floor and fan coil cooling (RFCFC) and develops a data monitoring system as a source of historical operational data. Seven machine learning algorithms (extreme learning machine (ELM), convolutional neural network (CNN), genetic algorithm-back propagation (GA-BP), radial basis function (RBF), random forest (RF), support vector machine (SVM), and long short-term memory (LSTM)) were employed to predict the behavior of the RFCFC system. Corresponding prediction models were then developed to evaluate operative temperature (Top) and energy consumption (Eh). The performance of the model was evaluated using five error metrics. The obtained results showed that the RF model had very high performance in predicting Top and Eh, with high correlation coefficients (>0.9915) and low error metrics. Compared with other models, it also demonstrated high accuracy in Eh prediction, yielding maximum reductions of 68.1, 82.4, and 43.2% in the mean absolute percentage error (MAPE), mean squared error (MSE), and mean absolute error (MAE), respectively. A sensitivity ranking algorithm analysis was also conducted. The obtained results demonstrated the importance of adjusting parameters, such as the radiant floor supply water temperature, to enhance the indoor comfort. This study provides a novel and effective method for evaluating the energy efficiency and thermal comfort of radiant cooling systems. It also provides insights for optimizing the efficiency and thermal comfort of RFCFC systems, and lays a theoretical foundation for future studies integrating machine learning algorithms in this field.

Advancements in design of radiant floor heating systems with an innovative simplified calculation method

The calculation accuracy of existing simplified methods for radiant floor heating systems (RFHS) is far from meeting the growing demand for energy saving. Therefore, an innovative steady-state simplified method is proposed based on conduction shape factors, equivalent thickness, and mirror principle. The new model is validated by experimental data and compared with an equally simple simplified method. Meanwhile, the effects of the total heat-transfer coefficient of radiant surfaces and fluid flow rate in heating pipes on the calculated results are discussed. The calculation flowchart is given. Parameter influence and sensitivity analysis are then performed. The results show that the new simplified model agrees well with experimental data, and the maximum relative error is 7.9% for heat flux and 2.0% for surface temperature. Standard deviation reduces by 68.5% and 66.8% for the heat flux and surface temperature, respectively, compared to the equally simple existing simplified method. With the same absolute increment of pipe pitch, the smaller the pipe spacing, the faster is the heat flux and surface temperature change. The order of importance of influential parameters is mean water temperature > indoor air temperature > pipe pitch > thermal conductivity of filling layer > thermal conductivity of pipe wall.

On the mitigation of the overheating caused by floor heating systems exposed to long direct solar radiation and high occupation rates

This study investigates the effects of solar radiation and human metabolic heat due to occupation on the dynamic thermal response of glazed building's floor heating system (FHS), which may entail an indoor thermal discomfort. A full experiment was conducted on a real test cell to measure various parameters such as surface and floor-depth temperature, ambient and operative temperature, and relative humidity. The sun patch was experimentally simulated with a moving heating film placed on the surface of the radiant floor. The performance of the radiant floor was simulated using a TRNSYS® model in conjunction with SketchUp®. Once validated, the model was used to predict the test cell surface, ambient, and operative temperatures under four different scenarios related to the presence or absence of shading and/or occupant gains. Under the realistic climatic data of the city of Troyes (France), the results show that when the solar and occupants gains are considered on the heating slab, the indoor temperature reach the high value of 33.9 °C. A statistical approach based on Design of Experiments (DoE) method was used to perform sensitivity analysis and evaluate the effects of factors/design parameters such as heating pipe thickness, heating slab conductivity, specific heat capacity and density on surface and indoor air temperatures. Findings indicates that heating slab with 6 cm thickness, and with low conductivity and diffusivity leads to better FHS performances with no overheating/discomfort periods. The developed model could serve as a basis for any predictive adaptive control to mitigate the overheating problem.

Optimizing the characteristic cooling curves of PCM-integrated thermally active buildings: Experimental and numerical investigations

Phase change materials (PCMs) exploit their cyclic phase change (solidification and melting) to enable latent heat storage. While incorporating them in thermally activated building systems can potentially enhance energy savings and thermal comfort, they can introduce significant challenges to the building energy management system. This work first reports the result of small-scale side-by-side experiments on two thermally active cuboids with and without BioPCMs at different supply water and PCM melting temperatures, as well as irradiance levels. Next, a dynamic model is developed in TRNSYS v18.05 for a typical design of an office space under hot desert climate conditions. The model is then integrated into a multi-objective optimization routine using NSGA-II algorithms to identify the optimal characteristic cooling curves, melting temperatures, and PCM thicknesses that simultaneously minimize energy consumption and maximize the percentage of comfortable hours. The experimental observations of the PCM-integrated cuboid highlighted energy savings between 80.45 and 84.56 %, compared to the reference cuboid, at nearly the same levels of indoor temperatures. The PCM panels reduced the cooling capacity of the radiant floor but also dampened air temperature variations by up to 83.17 %. Besides, higher solar irradiance levels, encountered in desert areas, were found to enhance the cooling capacity by up to 46.8 %. The Pareto solutions highlighted the possibility of achieving acceptable unmet hours of 3.16 % using PCMs and without the need for an assisting air system, compared to 14.1 % without PCMs. Besides, at the same unmet hours of the reference system, the PCMs reduced the total energy consumption and the peak cooling power by 9.75 and 41.2 %, which translates into substantial operation and capital investments, respectively. Moreover, the study demonstrated by example the importance of calibrating the commonly used cooling curves of thermally active buildings when planning for PCM integration.

Research on optimization of the heating system in buildings in cold regions by energy-saving control

Building heating is an indispensable part of people's winter life in cold regions, but energy conservation and emission reduction should also be taken into account during the heating process. This paper provides a concise overview of the heating system based on air-source heat pump radiant floor and its control strategy. It also optimizes a control system based on thermal comfort and energy efficiency ratio, and analyzes a room in Xining City, Qinghai Province, to test the heating system performance under two control strategies. The final results show that under the traditional control strategy, the cumulative working time of the heating system within a day was 15 hours, the average indoor temperature was 17.36℃, the temperature standard deviation was 2.08℃, and the average power consumption was 189.6 kWh. Under the improved control strategy, the cumulative working time of the heating system within a day was reduced to 10 hours, the average indoor temperature was 18.56℃, the temperature standard deviation was 0.92℃, and the average power consumption was 132.5 kWh.

Quantifying the energy flexibility potential of a centralized air-conditioning system: A field test study of hub airports

Centralized air-conditioning systems are widely considered a major energy consumer with high energy flexibility, contributing to renewable penetration and power system regulation. Nevertheless, a lack of understanding of their system components' abilities limits the utilization of their full potential. Hereby, we took the centralized air-conditioning systems of two hub airports as typical examples and quantified their energy flexibility potential by cooling load reduction potential (qmax), cooling energy storage capacity (Q), based on field test. Cooling plants had the highest potential (qmax = 70–110 Wc/m2; Q = 500∼1500 Whc/m2), followed by terminal devices with building thermal mass (qmax = 2–11 Wc/m2; Q = 10–40 Whc/m2) and transmission & distribution networks (qmax = 50–200 Wc/m2; Q = 10–20 Whc/m2). Various air-conditioning terminal devices utilize building thermal mass to different degrees. During the investigation, the conventional all-air system used 7.8 %∼18.7 % of the building's thermal capacity, whereas that of the radiant floor system significantly increased to 38.9 %∼48.3 %. Consequently, the systems of the hub airports can participate in demand response programs with a cooling load reduction of 2∼15 MWe, for 6–20 h using different operating strategies. These findings shed light on demand-side flexibility characterization and exploitation to support a decarbonized energy system.

Optimizing Heat Pump Operation of Residential Buildings Using Calibrated R-C and Deep Learning Models and Electricity Costs Forecasts

The aim of this research is to improve the efficiency of energy systems using the mass of the building as thermal storage. We present a case study of a residential building, in which a detailed monitoring system was installed to measure, among other parameters, the electricity consumption, the indoor air quality, and the operation of the heating system, consisting on a Heat Pump (HP) and a radiant floor. Based on the data collected, both a lumped parameter model (R-C Model) and a Deep Learning (DL) Model have been calibrated to simulate the apartment analyzed. Both models provide a significantly accurate simulation of the apartment under real operating conditions. Then, using the simulation models, different operation scenarios have been analyzed. One of the scenarios considers the thermal inertia of the apartment and the electricity costs forecast to optimize the operation of the HP. Within this scenario, energy savings up to a 35.1%, and electricity costs savings up to a 47.3%, may be achieved during a winter season, when compared to the standardized operation of the HP.