Radiant Slab Research Articles

Incorporating two-dimensional conduction modeling techniques into an energy simulation program: The EnergyPlus radiant system example

Due to the inherent complexity of multi-dimensional solutions for transient conduction in a multilayered building element, most heat balance-based algorithms assume that conduction occurs only in one dimension—through the building element between the inside and outside environments. Usually, since the length and width of the elements are much greater than the thickness of the element, this is a valid assumption. However, there are some cases such as hydronic radiant slabs where this assumption may not lead to an accurate estimate of the energy consumption of the system. In a hydronic radiant slab, water tubes are embedded in a slab, and hot or chilled water is circulated to meet any heating or cooling loads. The energy consumption of such a system will depend highly on the temperature of the water being sent to the slab (i.e., produced by the boiler or chiller). The temperature of the water that must be sent to the slab will depend on the spacing of the tubes, the multilayer construction of the building element, and the boundary conditions to which the construction is exposed. Thus, to accurately predict the energy consumption of such a system, a transient two-dimensional heat conduction model must be integrated with a heat balance-based simulation. This paper demonstrates the potential loss of accuracy associated with the one-dimensional radiant system models by providing a comparison of one- and two-dimensional solutions using EnergyPlus.

An evolving learning method —growing Gaussian mixture regression—for modeling passive chilled beam systems in buildings

Although chilled beam systems are considered as one of the best performing HVAC systems, few studies have looked into data-driven-based modeling for chilled beam systems. Furthermore, no learning-based data-driven methods have been applied to chilled beam systems in buildings. In this study, we used an evolving learning method, growing Gaussian mixture regression (GGMR), to predict cooling rates for passive chilled beam (PCB) systems where the training, evolution, and validation were carried out using data from real system measurements and from building energy simulation. GGMR updates key parameters such as weight coefficients, means, and covariance matrices of Gaussian components to adapt to changes in system operation beyond training data. This case study demonstrated that GGMR is an effective evolving learning-based data-driven method for accurately predicting cooling rates of PCB systems. The selection of key performance parameters of GGMR models including the number of components, training data size, and the learning rate was discussed in this paper. It is recommended that GGMR models could be further explored for predicting the performance of other complex HVAC systems such as radiant slab or mixed-mode ventilation systems.

Towards multifunctional building elements: thermal activation of a composite interior GFRP slab

Modular multifunctional building elements can overcome major disadvantages of the traditional sequential design and become prospective design solutions for sustainable construction. Thus, this work explores lightweight glass fiber-reinforced polymer (GFRP) profiles capabilities as multifunctional load-bearing slab modules in buildings. By adding water channels in a cellular structure of pultruded GFRP elements, hydronic radiant thermal conditioning of the indoor space can be enabled. Additionally, the water channels can protect critical slabs in case of a fire. A preliminary design of a multifunctional GFRP slab is performed for an office case study building by modifying a commercial slab profile with triangular channels. The thermal design load of the slab unit is determined using Rhino 6, and heat conduction and convective heat transfer for ceiling cooling and floor heating/cooling cases are investigated using ANSYS Fluent. The results show that a commercial GFRP profile can be modified to accommodate water channels and provide adequate heating and cooling at the upper or lower face. In addition, Serviceability Limit State is verified and required water flow adjustment in case of a fire outbreak scenario is discussed. Thus, the GFRP radiant slab has the potential as a pre-fabricated alternative for traditional embedded radiant systems.

Studies on how to counteract overheating caused by sun patch exposure in ventilated highly glazed spaces heated by floor heating systems

Enhancing the glazing areas in buildings could save energy by increasing solar gain and thus decreasing the demand for heating and artificial lighting during the cold season. However, relatively large glazed buildings often cause thermal discomfort to occupants due to the midseason heating, especially in the case of inertial heating systems. This study was conducted to examine the impact of direct solar radiation on the dynamic thermal behavior of a floor heating system. A series of experiments were conducted on a monitored full-scale controlled test cell facility simulating a dynamic sun patch on a radiant heating slab. A previously published bi-dimensional dynamic model based on the finite difference method was extended and validated to consider the additional heat flux brought by the sun patch. The findings show that the overheating time induced by the sun patch exposure was approximately 8.5 h after the disappearance of the solar patch. The average heating floor surface temperature attained 33.91 °C, whereas the indoor air temperature reached 26 °C. The conducted numerical parametric study revealed that when the sun patch occurs, ventilation remarkably decreases the indoor air temperature but keeps the average surface temperature almost unchanged and primarily over the standard upper limits. In contrast, water-based cooling technique appeared to be efficient under sun patch exposure since the average surface temperature and indoor air temperature can be decreased and maintained under acceptable limits in the average comfort zone.

Targeted occupant surveys: A novel method to effectively relate occupant feedback with environmental conditions

Occupant satisfaction surveys are widely used in laboratory and field research studies of indoor environmental quality. Field studies pose several challenges because researchers usually have no control over the indoor environments experienced by building occupants, it is difficult to recruit and retain participants, and data collection methods can be cumbersome. With this in mind, we developed a survey platform that uses real-time feedback to send targeted occupant surveys (TOS) at specific indoor environmental conditions and stops sending survey requests when collected responses reach the maximum surveys required. We performed a pilot study of the TOS platform with occupants of a radiant heated and cooled building to target survey responses at 16 radiant slab surface (infrared) temperatures evenly distributed from 15 to 30 °C. We developed metrics and ideal datasets to compare the TOS platform against other occupant survey distribution methods. The results show that this novel method has a higher approximation to characteristics of an ideal dataset; 41% compared to 23%, 19%, and 12% of other datasets in previous field studies. Our TOS method minimizes the number of times occupants are surveyed and ensures a more complete and balanced dataset. This allows researchers to more efficiently and reliably collect subjective data for occupant satisfaction studies.

A frequency domain transfer function methodology for thermal characterization and design for energy flexibility of zones with radiant systems

This paper presents a frequency domain transfer function methodology for thermal characterization and design for energy flexibility of zones with hydronic radiant heating/cooling systems and significant thermal mass. The modeling methodology is validated with experiments in an environmental chamber. Using the developed frequency domain model of the zone, key transfer functions are calculated for a case study. By means of transfer functions, the effect of different levels of thermal mass on the zone thermal response and quantification of the energy flexibility in response to grid signals is studied. The model is used to evaluate different design and operation options on a relative basis to enhance energy flexibility for different scenarios. It is shown how transfer function analysis provides insight into the building thermal dynamics without the need for simulations. The transfer function that relates the radiant floor heat source at the bottom of the slab to the zone air temperature is derived and the delay between the heat input of the radiant slab and zone air temperature is calculated. Experimental measurements in an environmental chamber are used to validate the key design parameters obtained from the frequency domain transfer function regarding the operational strategies for energy flexibility of the thermal zone. Finally, it is shown how to utilize the quantified energy flexibility that is possible with the floor thermal mass through application of appropriate control strategies while maintaining satisfactory comfort conditions.

A novel approximate harmonic method for the dynamic cooling capacity prediction of radiant slab floors with time variable solar radiation

The incident solar radiation from glass curtain walls shinning on the radiant floor cooling system enlarges its cooling capacity. In this study, an analytic expression using a novel approximate harmonic method is derived for the dynamic thermal response of the radiant slab floor with time variable solar radiation. The characteristic parameters, namely the decay rate and time lag which could be calculated by the thermal properties of the multi-layered radiant slab floor, are introduced to characterize the thermal response of the solar radiation waves. We compared the results calculated using the novel approximate harmonic method with that using a three-dimensional model of the radiant slab floor to evaluate the deviation of the novel approximate harmonic method. The results indicated that the dynamic heat transfer process calculated through the novel approximate harmonic method accords well with the three-dimensional model. Specifically, the transient floor surface temperature and cooling capacity in a design day calculated using the novel approximate harmonic method were close to that by the three-dimensional model with Root Mean Square Errors below 0.25 °C and 1.6 W/m2, respectively. According to the novel approximate harmonic method, the augment of the specific heat of the radiant floor increases the decay rate and decreases the fluctuation range of the cooling capacity influence by the time variable solar radiation.

A COMBINED USE OF FDM AND DOE METHOD TO DERIVE A NEW TRANSIENT SIMPLIFIED SEMI-ANALYTICAL MODEL: A CASE STUDY OF ANHYDRITE RADIANT SLAB

Radiant floor heating systems (FHS) are considered as reliable heating systems since they ensure maintaining inside air temperature and reduce its fluctuations more efficiently than conventional heating systems. The presented study investigates the dynamic thermal response of an experimental FHS equipped with an anhydrite radiant slab. A new simplified model based on an analytical correlation is proposed to evaluate the heating radiant slab surface temperature and examine its thermal behavior under dynamic conditions. In order the validate the developed analytical model, an experimental scenario, under transient conditions, was performed in a monitored full-scale test cell. 2D and 3D numerical models were also developed to evaluate the accuracy of the analytical model. The method of Design of Experiments (DoE) was used to both derive meta-models, to analytically estimate the surface temperature, and perform a sensitivity study.

Semi-analytical model for thermal response of anhydrite radiant slab

The choice of heating systems in buildings is primarily guided by the desired comfort level and energy saving concerns. Radiant floor heating systems are suitable for satisfying these requirements by considering the trade-off between minimizing the thermal inertia of the radiant slab and maintaining the surface temperature below a certain value. In this study, a new simplified model based on an analytical correlation is proposed to evaluate the heating radiant slab surface temperature and examine its thermal behavior under dynamic conditions. A full-scale test cell, monitored by a set of sensors, was used to obtain measurements under transient conditions. In addition, numerical models based on the finite difference method and the finite volume method were developed and validated under transient conditions. The design of experiments method is used to derive meta-models for the time constant and the delay time in order to compute the surface temperature. The sensitivity analysis indicated that the specific heat capacity of the slab material and the heating water flowrate significantly affect the time constant as opposed to the insignificant effect of the thermal conductivity and the heating water pipe inner diameter. In addition, it was found that all of these parameters, except for the heating water flowrate, have a significant impact on the delay time. Compared to the experimental results, the maximum relative deviations on the computed surface temperature were within 2% for the numerical model and 4% for the semi-analytical model.

New transient simplified model for radiant heating slab surface temperature and heat transfer rate calculation

A new simplified model based on a semi-analytical correlation is proposed in this paper to evaluate the heating radiant slab surface temperature and to examine its thermal behavior under dynamic solicitations. In fact, the surface temperature is a normative design parameter and shall be kept under an upper limit whatever are the running conditions. Experimental measurements and a two-dimensional finite difference model (2D FDM) were carried out to validate the developed simplified model based on two characteristic parameters that are the time constant and the delay time. A Design of Experiments (DoE) method is employed to derive meta-models for the time constant and the delay time in order to compute the surface temperature. The sensitivity analysis shows that the specific heat capacity of the slab material and the heating water flow rate affect significantly the time constant compared to the thermal conductivity and the heating water pipe inner diameter. Moreover, it was found that all these parameters, except the heating water flow rate, have a substantial impact on the delay time. Compared to the experimental results, the maximum relative deviations from the computed surface temperature are within 2.4% for the numerical model and 1.75% for the simplified semi-analytical model. Consequently, the proposed simplified model may be utilized by engineers and designers to quickly estimate the radiant slab surface temperature and heat flux as well as to study its thermal behavior under dynamic running conditions. This model may also be integrated in the thermal building simulation software.

Testing and demonstration of model predictive control applied to a radiant slab cooling system in a building test facility

Radiant slab systems have the potential to significantly reduce energy consumption in buildings. However, control of radiant slab systems is challenging. Classical feedback control is inadequate due to the large thermal inertia of the systems and heuristic feed-forward control often leads to unacceptable indoor comfort and may not achieve the full energy savings potential. Model predictive control (MPC) is now attracting increasing interest in the building industry and holds promise for radiant systems. However, an often-cited barrier to its implementation in the building industry is the high computational cost and complexity relative to the feedback controls used in conventional systems. The objectives of this study were to (i) verify the correct operation of an open source MPC toolchain developed for radiant slab systems, and (ii) demonstrate its efficacy in a test facility. A matched pair of cells in the FLEXLAB building test facility at the Lawrence Berkeley National Laboratory was used in the study. The proposed MPC toolchain was implemented in one cell and the performance compared to that of the other cell, which used a conventional heuristic control strategy. The results showed that the simplified MPC approach applied in the toolchain worked as expected and realized energy savings over the conventional control strategy. The MPC yielded 42% chilled water pump power reduction and 16% cooling thermal energy savings, while maintaining equal or better indoor comfort.

Experimentally-determined characteristics of radiant systems for office buildings

Radiant heating and cooling systems have significant energy-saving potential and are gaining popularity in commercial buildings. The main aim of the experimental study reported here was to characterize the behavior of radiant cooling systems in a typical office environment, including the effect of ceiling fans on stratification, the variation in comfort conditions from perimeter to core, control on operative temperature vs. air temperature and the effect of carpet on cooling capacity. The goal was to limit both the first cost and the perceived risk associated with such systems. Two types of radiant systems, the radiant ceiling panel (RCP) system and the radiant slab (RS) system, were investigated. The experiments were carried out in one of the test cells that constitute the FLEXLAB test facility at the Lawrence Berkeley National Laboratory in March and April 2016. In total, ten test cases (five for RCP and five for RS) were performed, covering a range of operational conditions. In cooling mode, the air temperature stratification is relatively small in the RCP, with a maximum value of 1.6 K. The observed stratification effect was significantly greater in the RS, twice as much as that in the RCP. The maximum increase in dry bulb temperature in the perimeter zone due to solar radiation was 1.2 K for RCP and 0.9 K for RS – too small to have a significant impact on thermal comfort. The use of ceiling fans was able to reduce any excess stratification and provide better indoor comfort, if required. The use of thin carpet requires a 1 K lower supply chilled water temperature to compensate for the added thermal resistance, somewhat reducing the opportunities for water-side free cooling and increasing the risk of condensation. In both systems, the difference between the room operative temperature and the room air temperature is small when the cooling loads are met by the radiant systems. This makes it possible to use the air temperature to control the radiant systems in lieu of the operative temperature, reducing both first cost and maintenance costs.

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.

Performance analysis of pulsed flow control method for radiant slab system

We present a novel pulsed flow control method (PFM) using a two-position valve to regulate the capacity of radiant slab systems. Under PFM, the on-time duration of the valve is short (compared to all prior work, e.g. 4-minute), and fixed, while the off-time varies. We present a novel, open-source, finite difference model that assesses three-dimensional transient slab heat transfer, accounting for the transient heat storage of the pipe fluid. Sensitivity analysis results indicate the dominant factors influencing energy performance of the PFM are: on-time duration; pipe diameter; and spacing. We experimentally validated both the new control strategy and model in full-scale laboratory experiments. Compared with previous intermittent control strategies (with on-time durations over 30 min), at 50% part load the PFM reduces 27% required water flow rate and increases supply to return water temperature differential. Compared with the variable temperature control method, at 50% part load the PFM reduces 24% required water flow rate. The energy performance of PFM is comparable to that of a conventional variable flow rate control. However, it has more accurate capacity control, achieves a more uniform surface temperature distribution, and reduces initial investment by substituting two-position for modulating valves, thus showing promise for engineering applications.

Marquage CE pour les dispositifs médicaux et nouveau règlement européen : évolutions et outils d’aide à la « personne qualifiée »

The choice of heating systems in buildings is primarily guided by the desired comfort level and energy saving concerns. Radiant floor heating systems are suitable for satisfying these requirements by considering the trade-off between minimizing the thermal inertia of the radiant slab and maintaining the surface temperature below a certain value. In this study, a new simplified model based on an analytical correlation is proposed to evaluate the heating radiant slab surface temperature and examine its thermal behavior under dynamic conditions. A full-scale test cell, monitored by a set of sensors, was used to obtain measurements under transient conditions. In addition, numerical models based on the finite difference method and the finite volume method were developed and validated under transient conditions. The design of experiments method is used to derive meta-models for the time constant and the delay time in order to compute the surface temperature. The sensitivity analysis indicated that the specific heat capacity of the slab material and the heating water flowrate significantly affect the time constant as opposed to the insignificant effect of the thermal conductivity and the heating water pipe inner diameter. In addition, it was found that all of these parameters, except for the heating water flowrate, have a significant impact on the delay time. Compared to the experimental results, the maximum relative deviations on the computed surface temperature were within 2% for the numerical model and 4% for the semi-analytical model.

Cooling capacity and acoustic performance of radiant slab systems with free-hanging acoustical clouds

Radiant slab systems have the potential to achieve significant energy savings, yet, when applied in the ceiling (e.g., thermally activated building system) the exposed concrete may also create acoustical challenges due to the high reflectivity of the hard surface. Balancing all of the building indoor environmental quality factors is important in the design of an effective workspace for the occupants, and so we need to consider the interactions between thermal and acoustic comfort. We assessed the cooling capacity in a hydronic test chamber and the sound absorption in a reverberation chamber to study the effects, for an office room, of different coverage areas of free-hanging acoustical clouds below a radiant chilled ceiling. The cooling experiments showed that for 47% cloud coverage of the ceiling area, we measured only an 11% reduction in cooling capacity caused by the blockage of radiant exchange between the ceiling and the room. The acoustical results showed that if the cloud covered 30% of the ceiling in a private office or 50% in an open plan office, acceptable sound absorption at the ceiling was achieved. We showed that good acoustic quality can be achieved with only a minor reduction of cooling capacity.

Evaluation of energy conservation potential and complete cost-benefit analysis of the slab-integrated radiant cooling system: A Malaysian case study

The energy-efficiency aspects and cost-saving features of various radiant cooling systems have been reported in many previous studies. However, the available literature on the analysis of initial investment and maintenance costs is scanty, especially for the slab-integrated one. A field survey was carried out in a green building in Malaysia that was installed with a combined radiant-convective system. The performance of this multi-floor radiant slab cooling system was studied and the energy conservation potential was evaluated by comparing the data obtained from the building energy management system (BEMS) with the estimated energy consumption of a conventional convective air system. Also, price quotations and service maintenance contracts were obtained for a complete cost-benefit evaluation of both systems. It was found that the radiant slab cooling system was able to reduce 34% of the energy consumption compared to the conventional variable air volume system while providing the same level of air conditioning. Despite its higher initial cost, the payback period for the investment cost is about 2.5 years. These findings are particularly useful for design engineers in the tropics to consider an alternative cooling technology for large office buildings which is more energy efficient and cost effective.

Analysis of Integrated Radiant Slab Heating and Cooling Systems for Residential Buildings

ABSTRACTThis paper presents a simulation environment developed to assess the energy use specific to integrated radiant heating and cooling systems. The developed simulation environment combines a transient finite difference solution for the two-dimensional model of an integrated radiant slab heating and cooling system with a resistance capacitance (RC) thermal network model for a multifloor building. The developed model of the integrated radiant system is able to account for thermal bridge effects on the energy performance of multifloor buildings. The predictions of the developed simulation environment are verified against those obtained from a detailed whole-building energy simulation tool under specific conditions. The developed simulation environment is then used to investigate the impact of thermal bridge effects on the performance of an integrated radiant heating and cooling system. Thermal bridging can affect significantly the energy performance of the integrated radiant systems by up to 8%. Several...

Lessons Learned from Field Monitoring of Two Radiant Slab Office Buildings in California

In this paper we present the results from field studies of two low-energy office buildings in California, both using radiant slab ceiling systems (thermally activated building systems, TABS) for primary cooling and heating in the buildings. Both buildings are certified LEED Platinum and incorporate a wide range of energy efficient technologies and design strategies, including TABS, advanced shading systems, underfloor air distribution, chilled beams, ceiling fans, natural ventilation, and photovoltaic panels. Findings and analysis from the following building performance assessment techniques will be discussed.•Occupant satisfaction survey. Occupant surveys are an invaluable source of information for describing how well the building is providing a high quality indoor environment for the occupants. In addition, the survey results are also compared against a large benchmark survey database of over 50,000 occupants.•Wireless measurement system. A network of wireless sensors was installed in selected zones of the buildings to provide additional more detailed information about the operation and control of the radiant slab system. This data was combined with trend data from the building management system (BMS) to examine the performance of the buildings during both winter and summer conditions. Some control issues were identified and corrected based on these measurements.•Energy performance analysis. We collected utility data for 2014 in one of the buildings and used this information to determine the building's Energy Star rating.

Model predictive control of radiant slab systems with evaporative cooling sources

Buildings that use radiant slab systems with evaporative cooling sources have shown to be energy efficient. However, control of the systems is challenging because of the slow response of the slab and the limited capacity of cooling sources. The objectives of this paper are to: (1) create a simplified dynamic model of radiant slab system for implementation in real-time model predictive controller (MPC); and (2) test the MPC energy and thermal comfort performance in a case study building. A calibrated EnergyPlus model of the building was developed as the testbed. The MPC is compared with the existing rule-based control method for a cooling season in a dry and hot climate. The results indicated that the MPC controller was able to maintain zone operative temperatures at EN 15251 Category II level more than 95% of the occupied hours for all zones, while with the rule-based method, only the core zone were maintained at this thermal comfort level. Compared to the rule-based method, MPC reduced the cooling tower energy consumption by 55% and pumping power consumption by 25%.