Floor Radiant System Research Articles

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.

An analytical method to estimate temperature distribution of typical radiant floor cooling systems with internal heat radiation

Radiant floor cooling systems are increasingly used in practice. The temperature distribution on the floor surface and inside the floor structure, especially the minimum and average temperature of floor surface, determines the thermal performance of radiant floor systems. A good temperature distribution of the floor structure is very important to prevent occupant discomfort and avoid possible condensation in summer cooling. In this study, based on the heat transfer model of the single-layer homogeneous floor structure when there is no internal heat radiation in the room, this paper proposes a heat transfer model of single-layer floor radiant cooling systems when the room has internal heat radiation. Using separation variable methods, an analytical solution was developed to estimate temperature distribution of typical radiant floor cooling systems with internal heat radiation, which can be used to calculate the minimum temperature and the average temperature of typical composite floor structure. The analytical solution was validated by experiments. The values of the measured experiments are in a good agreement with the calculations. The absolute error between the calculated and the measured floor surface temperatures was within 0.45°C. The maximum relative error was within 2.31%. Prove that this model can be accepted. The proposed method can be utilized to calculate the cooling capacity of a typical multi-layer composite floor and will be developed in the future study for design of a typical radiant floor cooling system.

Model Predictive Control Strategies to Activate the Energy Flexibility for Zones with Hydronic Radiant Systems

This paper presents control strategies to activate energy flexibility for zones with radiant heating systems in response to changes in electricity prices. The focus is on zones with radiant floor heating systems for which the hydronic pipes are located deep in the concrete and, therefore, there is a significant thermal lag. A perimeter zone test-room equipped with a hydronic radiant floor system in an environmental chamber is used as a case study. A low order thermal network model for the perimeter zone, validated with experimental measurements, is utilized to study various control strategies in response to changes in the electrical grid price signal, including short term (nearly reactive) changes of the order of 10–15 min notice. An index is utilized to quantify the building energy flexibility with the focus on peak demand reduction for specific periods of time when the electricity prices are higher than usual. It is shown that the developed control strategies can aid greatly in enhancing the zone energy flexibility and minimizing the cost of electricity and up to 100% reduction in peak power demand and energy consumption is attained during the high-price and peak-demand periods, while maintaining acceptable comfort conditions.

Experimental study on the dynamic thermal response of a radiant floor system in an office building

The dynamic thermal performance of radiant terminal plays an important role in the design and control of radiant cooling system, which is shown as the dynamic thermal response of radiant floor system (RFS) under imposed control. In this paper, the field measurement method was used to study the dynamic thermal response of RFS. The RFS was activated in summer and the supply water temperature was regulated in winter to make dynamic change of thermal performance. The floor surface temperature was selected as the characteristic parameter to describe the dynamic heat transfer performance of the system, and response time τ95 and time constant τ63 were used to quantify the dynamic thermal response. The maximum τ95 was 13.5 h and τ95/τ63 was greater than or equal to 2 in the cooling mode, while τ95 and τ63 were both less than 10 h and τ95/τ63 was 1.6 in the heating mode. As a result, there was no significant lessening of temperature change rate, and the thermal response of RFS was faster under intermittent control of supply water temperature in winter. Therefore, the study aims at providing reference for making intermittent control strategy by using the dynamic thermal performance of radiant system.

Performance analysis of horizontal ground source heat pump for building cooling in arid Saharan climate: thermal-economic modeling and optimization on TRNSYS

This paper presents a feasibility and performance study of ground source heat pump (GSHP) coupled with horizontal ground heat exchanger (HGHX) used for cooling residential unit equipped with radiant floor system (RFs) under the meteorological conditions of Saharan environment in Ouargla, city located in Southeast Algeria. A dynamic simulation system is developed using TRNSYS software for modeling the performance of the GSHP system. To verify the reliability of GSHP including HGHX system programs, the modeling procedure was validated against experimental data from a horizontal ground source heat pump system (HGSHPs) installed at the Research and Technology Center of Energy (CRTEn), Tunisia, and a good agreement was obtained. Then, to obtain an acceptable balance between system efficiency and total cost of HGSHPs an economic analysis was carried out to determine the optimum design parameters of the HGHX. The simulation results obtained from this study indicated that the HGSHPs could effectively solve cooling problem and reduce traditional energy consumption in the Saharan areas; it is possible to lower the mean indoor air temperature below 27 °C and raise the average relative humidity to reach 73.97%. By concentrating principally on the thermal-economic optimization, the optimized COP of the GSHP that combines the reliability and economy of cooling in long term was found to be 3.89.

Energy saving potential and environmental benefit analysis of application of balcony for residence in the hot summer and cold winter area of China

The increasing fossil energy demand and carbon emissions pose a significant challenge to the world. According to climate adaptability design, the balcony is open type in Changsha. The study evaluates the energy-saving potential and the economic and environmental feasibility of installing the balcony in living rooms, and considering the effect of balcony orientations and air conditioning types. The economic viability is analyzed using the construction cost of the balcony and the extra market price of a residence with a balcony paid by the holder, respectively. Environmental feasibility assessment mainly adopts the CO2 emission payback period as the index. The annual electricity saving percentage of the split-type air conditioner in the living rooms facing four orientations with a balcony is in between 6.7% and 12.3%. And the balcony's investment payback period facing east or west orientation is less than 50 years based on construction cost. It has better environmental benefits with the CO2 emission payback period of the balcony facing four orientations is in between 10.4 and 24.6 years. Considering a living room constructed with a balcony, it is not feasible for dwellers to use a gas boiler, adopting the radiant floor system during the heating from the perspective of economic and CO2 emission.

Performance analysis and instant/delayed characteristics of a solar heating system used in cold regions

Solar energy is widely used to meet the building heating energy demand in the cold region. Performance of the solar heating system is significantly influenced by the heating terminal. This paper firstly makes a comprehensive comparison between the air supply system and the radiant floor system in solar heating circumstance. A hybrid solar heating system combining the advantages of convective and radiant terminals is proposed to achieve 24-h diurnal heating with daytime limited insolation. Hot air heated by a solar collector is firstly delivered to the hollow cores in the radiant floor. After passing through the cores, the air subsequently enters the room, while room air returns to the collector to complete the cycle. Simulation models are built to analyze the performances of different air-based solar heating systems. It is indicated indoor operative temperature (Top) of the proposed system could be controlled between 18.0∼20.9 °C, where the average Top is 3.4 °C and 1.0 °C higher than those in the air supply system and radiant floor system respectively. It's with superiorities in both indoor temperature satisfactory and solar utilization efficiency. Influences of different parameters such as floor structure, solar collecting efficiency and air flow rate are also investigated. This research preliminarily shows the probability of this combined solar heating system for cold regions with sufficient solar radiation.

A dynamic analysis of a SAGSHP system coupled to solar thermal collectors and photovoltaic-thermal panels under different climate conditions

The use of multi-source energy systems is a promising technical solution for the reduction of greenhouse gases emissions and, at the meantime, for enhancing the exploitation of renewable energy sources.The present paper analyses a Solar Assisted Ground Source Heat Pump system and tries to fill the gap in the literature, where a direct comparison between the consolidated solar thermal technology and the emerging and widely discussed photovoltaic thermal technology is missing. Indeed, the two different devices for the exploitation of solar energy have been analysed through dynamic simulations carried out in TRNSYS environment. Through this approach, it is possible to investigate and predict in detail the thermal and electrical behaviour of the energy system, composed by a water-to-water heat pump, which withdraws from two thermal reservoirs that are connected to a solar loop, composed either of solar thermal collectors or of photovoltaic thermal panels and to a ground loop.The heat pump is used to provide space cooling and space heating to a residential building, through fan coil terminal units or radiant floor system. Furthermore, the heat pump system assists the solar field in the production of domestic hot water.This study looks at the development of a flexible system able to work in different operating conditions. The model’s boundary conditions can be changed for simulating a variety of case studies as the weather condition, the building load and the domestic hot water profile can be easily changed, together with specific components’ parameters. The control strategy makes it possible to vary the setpoint temperatures for simulating different operating conditions and management choices. In this way, the user can easily adapt the model functions to a specific plant system.The operating conditions of the two systems layouts have been compared and the energy performances evaluated for three case studies characterised by the weather conditions of the European cities of Berlin (mild-cold climate), Venice (mild climate) and Barcelona (mild-warm climate), and the corresponding thermal load profile of a two-storey building with a useful floor area of 170 m2.The study shows the possibility to directly exploit the solar energy for the domestic hot water production and as a heat source for the heat pump. The results from the comparison between the two systems’ configurations, with photovoltaic thermal panels and with solar thermal collectors, prove that there is the possibility to obtain a relevant improvement in the efficiency of the heat pump using photovoltaic thermal panels. The investigated multi-source energy system, moreover, allows an optimal employment of the available renewable heat sources and could easily be applied to case studies characterized by different boundary conditions.

Experimental investigation on the thermal performance of double-layer PCM radiant floor system containing two types of inorganic composite PCMs

Double-layer radiant floor systems that consist of two inorganic phase change layers placed at different positions, were first explored for regulating the indoor thermal comfort in winter and summer climates. Specifically, two hydrated salts having different melting points were respectively compounded with expanded graphite to obtain enhanced thermal conductivity. In the floor systems, Na2HPO4•12H2O-based composite (31.3 °C) and CaCl2•6H2O-based composite (20.2 °C) were used for the heat storage layer and the cold storage layer, respectively. It is found, in the winter climate, the room equipped with a radiant floor system consisting of an upper heat storage layer and a lower cold storage layer, realizes a thermal comfort duration of 2.2 times that of the reference room containing pebbles in the floor. Significantly, the radiant floor system constructed by just exchanging the positions of the two layers endows the room with a thermal comfort duration of 8.1 h in the summer climate, which is 1.7 times that of the reference room. Moreover, appropriately enhancing the thermal conductivity of the composites can promote energy savings by reducing the operating time of the active system. It is estimated that the double-layer radiant floor systems can save economic costs by shifting the peak load.

A novel radiant floor system: Detailed characterization and comparison with traditional radiant systems

ABSTRACTRadiant floor systems have the potential to reduce energy consumption and the carbon footprint of buildings. This study analyzed a novel radiant panel configuration comprising a metal plate with small spikes that can be pressed into cement board or wood. The behavior of this configuration was simulated for different materials for the metal plate, spike dimensions, and varying spacing between spikes. An annual energy simulation model compared the radiant panel configuration with the traditional concrete-based system. Simulations were run under heating dominant, cooling dominant, and neutral conditions; significant cost savings and greenhouse gas emission reduction were seen across all scenarios.

Optimization of Control Strategies for the Radiant Floor Cooling System Combined with Displacement Ventilation: A Case study of an Office Building in Jinan, China

The radiant floor cooling system, as a thermally activated building system, has attracted significant attention as it can save energy consumption and shift the building load. However, due to its characteristic that building thermal mass has a significant influence on the system performance and indoor environment, the control strategies should be seriously accounted for. Moreover, its performance is highly related to the shift condition of cooling load during the daytime and different weather conditions, therefore, realistic operation will cause the increments of peak load if the control strategy is neglected. This study presented two common strategies including intermittent operation and weatherforecast-based control strategies. The radiant floor cooling system combined with displacement ventilation system in a typical office building located in Jinan was established using the TRNSYS program. The results showed that the energy consumption decreased by 3.3% to 7.5% when the different intermittent operation strategies were applied. The weatherforecast- based control strategy can improve indoor thermal environment by increasing/deceasing the water supply flow rate by up to 25% in advance. This study concluded that the application of intermittent operation and weather-forecast based control strategies can regulate the operation of radiant floor system and reduce the building energy use.

Multivariable optimization of PCM-enhanced radiant floor of a highly glazed study room in cold climates

Hydronic radiant floor systems enhanced with phase change materials (PCMs) could achieve significant energy savings while improving the thermal comfort of occupants in lightweight buildings. However, successful integration of PCMs typically requires comprehensive numerical analysis due to their complex nature. This study aims to investigate two scenarios for optimal integration of PCM into the hydronic floor heating system of a highly glazed study room exposed to cold weather conditions. Scenario 1 includes optimization of two design variables, including PCM melting temperature and thickness. Scenario 2 encompasses optimization of seven design variables, including PCM melting temperature and thickness, insulation thickness and thermal conductivity, floor thickness, thermal conductivity, and solar absorbance. Both scenarios are optimized for the six supply water temperatures, ranging from 35.6 °C to 45.6 °C with a 2 °C step. The overall findings suggest that successful integration of PCMs into the hydronic heating system requires a comprehensive solution tailored for the specific application. Thus, scenario 1 and scenario 2 achieved the highest total energy savings of approximately 17.7% and 20.5% for the lowest supply water temperature of 35.6 °C, whereas under both scenarios the supply water temperature of 43.6 °C provided the best thermal comfort. Furthermore, scenario 1 achieved more substantial cooling energy savings over the wider temperature range (41.6-35.6 °C) compared to scenario 2 (39.6-35.6 °C). The findings also suggest that the addition of the insulation layer in the second scenario reduced the thickness of PCM and payback period for more than 70% compared to the first scenario.

Underfloor Heating Using Ceramic Thermal Panels and Solar Thermal Panels in Public Buildings in the Mediterranean: Energy Savings and Healthy Indoor Environment

Radiant floor air conditioning systems based on capillary tube mats, in addition to offering high comfort standards, generate significant energy savings. They allow the use of renewable energies such as thermal solar panels and combine them with solar cooling systems based on lithium chloride or absorption systems with lithium bromide in summer, cooling water down to 15–16 °C through solar thermal panel energy collection. Thus, in addition to energy savings from the transport of low water flows, annual energy demand is also reduced. This research analyses the application of thermal ceramic panels (TCP)—containing polypropylene (PPR) tube capillary mats—to public buildings in the Spanish Mediterranean. A case study of the Museum of the University of Alicante (MUA) is presented. Water was distributed individually from a split system heat pump inside the building combined with a thermal solar panel system on the roof. The MUA’s annual energy demand was quantified using thermal simulation tools and was monitored during the entire one-year cycle. Simulations were conducted both for the radiant floor system and an all-air conventional convective system, as well as with solar thermal panel applications. The reduction in annual energy demand was 24.91% when TCP panels are used on the floor. This is a considerable value, but lower than others results obtained in Central Europe due to the higher values of humidity. When solar thermal panels are installed on the rooftop the energy savings can increase to 60.70%.

A model predictive control strategy to optimize the performance of radiant floor heating and cooling systems in office buildings

This paper introduces a smart operation strategy based on model predictive control (MPC) to optimize the performance of hydronic radiant floor systems in office buildings and presents results from its implementation in an actual building. Our MPC approach uses dynamic estimates and predictions of zone loads and temperatures, outdoor weather conditions, and HVAC system models to minimize energy consumption and cost while meeting equipment and thermal comfort constraints. It includes data-driven building models estimated and validated using data from an actual building, and deploys an optimizer based on constraint linear/quadratic programming with hard comfort bounds that yields a global minimum with predicted exogenous disturbances. The MPC results show 34% cost savings compared to baseline feedback control during the cooling season and 16% energy use reduction during the heating season. Also, the radiant floor system with the predictive controller shows 29–50% energy savings when compared with a baseline air delivery system serving two identical thermal zones located in the same building.

Efficiency in Heating Operation of Low-Temperature Radiant Systems Working under Dynamic Conditions in Different Kinds of Buildings

In recent years many types of radiant systems have been installed in buildings. Meanwhile, practitioners debate on which thermal inertia of radiant systems fit better and which control strategies should be better in buildings, depending on the insulation level and thermal inertia of the structures. In particular, in new and retrofitted buildings, where the envelope presents high levels of insulation, it is argued if it is better to have low or high inertia radiant systems for controlling the indoor operative temperature and avoid overheating, especially in mid-seasons when the outdoor temperature is mild and solar radiation is high. For this purpose a room with three types of insulation level has been analysed combining different types of structures (masonry, and light and timber walls) and three types of radiant systems (classic wet floor, dry floor, and ceiling). Two operation modes have been simulated: fixed supply temperature and variable temperature according to the outdoor temperature. The results looked at the embedded and control efficiency, the energy performance in case of coupling with a water to water heat pump and the long-term possible overheating analysis. The embedded and control efficiency in dynamic conditions has been evaluated and compared with different possible definitions, in particular with steady state conditions, former EN15316-2-2007, and current EN15316-2-2017. New values for the current standard are suggested based on the results of this work, since the former and existing values overestimate the seasonal losses of floor and radiant systems in heating conditions. The paper shows that working at variable temperature according to the outdoor air temperature leads to longer operation time. The temperature, on average, lowers, and coupling the radiant system with a water to water heat pump leads to lower consumptions in the case of variable supply temperature compared to fixed supply temperature over the season. The seasonal coefficient of performance of the whole system, i.e. the heat pump and auxiliary pumps, leads to overall lower energy consumption in the case of variable supply temperature. The simulations did not show any relevant problem of discomfort from December to February. Overtemperature effects in terms of operative temperatures over the dead band of the control systems are not especially due to the radiant system, but they also occur in any case with ideal convective systems. The paper demonstrates that in general the radiant floor systems perform better than radiant ceilings in heating conditions and there is no evidence that dry floor systems perform better than wet screed systems in all the types of buildings regardless of the level of insulation and thermal inertia.

Radiant heating utilizing conductive concrete tiles

Conductive concrete tiles of thickness 20-mm were subjected to electrical Joule heating tests. The average temperature increased by 51.62 K in 60 min under 36-V AC (alternating current) power. These tiles were subsequently utilized to build an indoor radiant heating system. Electrical heating tests under different conditions in a room, with the window open or closed, were performed. The results show that the floor tiles are effective for radiant heating. The temperature at the center of the room increased by 4.5 K in approximately 10 min. The energy consumption in 24 h is 0.775 kW-h/m2 in a thermally insulated room, corresponding to an average power density of 32 W/m2. This energy consumption is lower than that of typical radiant floor systems with embedded heating cables. A computer model of the room with the heating system is developed to simulate the radiant heating process. The numerical results compare favorably with the test data.

A distributed approach to model-predictive control of radiant comfort delivery systems in office spaces with localized thermal environments

This paper introduces a new multi-agent system approach to optimal control of high performance buildings and presents algorithms for both distributed system identification and distributed model predictive control (DMPC). For the system identification, each thermal zone is divided into sub-systems, and a parameter set for each sub-system is first estimated individually, and then integrated into an inverse model for the whole thermal zone using the dual decomposition algorithm. For the DMPC, a distributed optimization algorithm inspired by the Proximal Jacobian Alternating Direction Method of Multipliers (PJ-ADMM) is deployed and multiple MPCs run iteratively while exchanging control input information until they converge. The developed algorithms are tested using field data from an occupied open-plan office space with a radiant floor system with distributed sensing, control, and data communication capabilities for localized comfort delivery. With this tractable approach, agents solve individual optimization problems in parallel, through information exchange and broadcasting, with a smaller scale of the input and constraints, facilitating optimal solutions with improved efficiency that are scalable to different building applications. Using a data-driven model and weather forecast, the DMPC controller is implemented to optimize the operation of an air-cooled chiller while providing different operative temperature bounds for each radiant floor loop. The radiant comfort delivery system with predictive control is capable of providing localized thermal environments while achieving significant energy savings. For the system and climate under consideration, results from the building operation during the cooling season, show 27% reduction in electricity consumption compared to baseline feedback control.

Novel method for the design of radiant floor cooling systems through homogenizing spatial solar radiation distribution

The local and mobile incident sunlight from skylight and side windows shining on the floor surface increases the cooling capacity of the radiant floor cooling system. In this study, a novel method of homogenizing spatial solar radiation distribution over the entire radiant floor surface is proposed to the design of the radiant floor with a conventional circuit pattern of counter flow. A verified three-dimensional numerical radiant floor model is utilized to evaluate the deviation of the novel method in steady and transient states. The simulation results indicate that the relative error for local sunlight with a width over two pipe spacing is less than 1.0%. With a solar radiation intensity of 300 W/m2, the deviation of the simulated floor surface heat flux via the novel method is less than 0.3 W/m2 for any sunlight size in steady states. Furthermore, under transient and mobile sunlight, the simulated water side and floor surface heat fluxes via the novel method agrees well with the 3D model. As a result, the homogenizing treatment significantly simplifies the dynamic analysis of radiant floor system under temporal and spatial solar radiation distribution with enough accuracy in engineering applications.

Experimental comparison of thermal comfort during cooling with a fan coil system and radiant floor system at varying space heights

With the development of the economy, architectural space forms and air conditioning systems have become more and more diverse. This paper presents a comparative study on thermal comfort in spaces of varying heights using a fan coil system and a radiant floor system for cooling in the “Comprehensive Experiment Platform of Variable Building Space” located in Tianjin, China. A total of 30 subjects participated the questionnaire survey under 8 different experimental conditions, and the indoor thermal environmental parameters were collected for these two systems at varying space height by instrument monitoring. Results indicated that space height had a significant effect on thermal comfort for both the fan coil system and the radiant floor system. The neutral temperature at space height of 3, 5, 7, and 9 m were 24.8 °C, 24.2 °C, 23.8 °C, and 23.5 °C, respectively. The neutral temperature gradually decreased with height of the ceiling when using a fan coil system, which means that participants had greater requirements for cooling at greater heights. In contrast, the neutral temperature at heights of 3, 5, 7, and 9 m were 23.5 °C, 23.8 °C, 24.1 °C, and 24.5 °C, respectively. The neutral temperature gradually increased when using the floor radiant system with increasing height, indicating that participants had lower requirements for cooling at greater heights. Furthermore, the results of this study demonstrate that the floor radiant system had an advantage over the fan coil system for thermal comfort in a space of greater height.

Full scale laboratory experiment on the cooling capacity of a radiant floor system

Direct solar radiation on a cooled radiant floor increases its cooling capacity. There is limited measured evidence of this phenomenon reported in the literature. We assessed the effect of solar radiation, increased air movement, and carpet on the cooling capacity of the radiant floor in a laboratory exposed to the outside environment. We performed experiments for different chilled water supply temperature. The cooling capacity of the chilled radiant floor was measured to increase from 32 up to 110 W/m2 under direct solar radiation. The surface temperature region exposed to solar radiation reached a peak temperature of 26 °C while the unexposed areas were between 20 and 21 °C. Increasing the chilled water supply temperature from 12 to 18 °C caused a decrease in cooling capacity from ∼110 to ∼95 W/m2. Higher air speeds along the floor created by ceiling fans increased the radiant slab cooling capacity by ∼12% (from 32 to 36 W/m2) when the operative temperature was 24 °C and, up to ∼19% (40 W/m2) when it is increased to 26 °C. The presence of thin carpet tiles reduced the radiant floor cooling capacity for ∼5% compared to an exposed floor slab.