Thermally Activated Building Systems Research Articles

Comparison of different control methods on the thermally activated building system (TABS) with large energy flexibility

Thermally Activated Building Systems (TABS) has great energy flexibility potential for the effective demand response, but the inherent large thermal inertia creates challenges for the control. Model Predictive Control (MPC) can improve the control efficiency while achieving certain objectives. However, the modeling mechanism of the TABS thermal behavior can lead to the difference in the controller performances. In this study, the white-box model, grey-box model, and black-box model based MPCs (referred to as W-MPC, G-MPC, and B-MPC) are developed and analyzed in depth for a case TABS with high heat flexibility potential. The performances of MPC strategies are investigated together with the baseline Rule Based Control (RBC) strategy under normal conditions as well as a variety of uncertainty events. In general, MPC strategies show better performance compared to the RBC. The prediction-based control can effectively maintain the indoor temperature within the constraints considering the uncertain disturbances and the gradual outdoor climate change. Moreover, MPC strategies help to increase the cost savings due to the effective load shifting by 30%-50%, and enhance the flexible energy utilization by 14%-29%. In terms of the comparison among the different MPC strategies, W-MPC shows better performance in the room temperature control, which reduces the violation of the indoor temperature constraint by 30% and 15% compared to G-MPC and B-MPC, respectively. G-MPC shows slight superiority concerning the economy and flexible energy usage. The normalized cost saving of G-MPC is approximately 3% and 8% lower compared to the W-MPC and B-MPC, respectively, while the utilization efficiencies of the flexible energy are approximately 6% and 12% higher.

Performance verification of pipe‐embedded wall system in school building and proposal of its optimal control strategy

AbstractIn this study, a thermally activated building system (TABS) installed on the exterior wall as the pipe‐embedded wall (PEW) system in a school building was investigated. The basic performance of the PEW system utilizing well water cascade is verified by unsteady CFD analysis and field measurements. Moreover, in order to improve the utilization efficiency of the thermal potential from well water, the MPC‐based optimal control method with the PEW system to maximize the heat extraction is proposed and verified by unsteady CFD analysis. The analysis results showed that: (1) The PEW system can reduce the peak load from the exterior wall facing different directions at different times. In addition, the PEW system has the effect of stabilizing the indoor thermal environment. (2) The proposed optimal operation strategy improves the energy efficiency, extracting up to 30% more heat and reducing the total heat transmission, which significantly develops the operation efficiency of the PEW system.

Assessment of thermally activated inner building components or a high temperature stone storage system to utilize surplus renewable electrical energy

In electrical grids with high renewable percentage, the production is less demand-driven, but more dependent on weather conditions. Usually there are periodical weather patterns in the winter period with substantial amounts of wind energy production. Sometimes this results in a shut-off of the wind turbines due to the inability of the grid to use the produced power (overproduction). This paper assesses two thermal storage systems to service space heating and domestic hot water that exploit the overproduction of electricity and thereby bridge periods of lower electricity production. The first system utilizes inner walls and ceilings with a thermally activated building system (TABS) to store and dissipate heat. The second system is a stand-alone high temperature stone storage system (HTSS). Models to simulate such systems within a whole building simulation framework are introduced and the verification with measured data from field measurements is presented. Both models are used to assess the systems with regard to the speed of loading and the potential to bridge time periods without additional heating in high-performance buildings. It is shown that both systems can provide heating and domestic hot water (DHW) up to 13 days without substantial additional electricity.

Development of design calculations for radiant ceiling panels incorporating phase change materials (PCMs)

Thermally active building systems (TABS) show significant benefits such as providing peak load shifting, peak load reductions, and energy savings. Phase change material (PCM) applications with water circulation have benefits similar to TABS, but PCMs can store more heat per unit volume than concrete due to the latent heat exchange. Radiant panels with PCM can be applied in building retrofit, which gives this application a significant advantage compared to TABS. A design methodology for determining heat flux does not exist though for dimensioning a radiant ceiling system that incorporates PCM. Design methods according to standards for TABS – ISO 11855-2 and for radiant panels – ISO 18566-3 were investigated. Five radiant ceiling panels incorporating PCM were selected from Denmark, Canada, Germany, the Czech Republic and Latvia. The resulting heat flux between the panel and conditioned space, i.e. the room, following methods represented in the standards, were compared with the measured or simulated values reported in the literature. The comparison showed that the calculation for TABS (ISO 11855-2) led to similar results to the measured or simulated values.

Impact of indoor heat load and natural ventilation on thermal comfort of radiant cooling system: An experimental study

Construction and operation of buildings are responsible for about 20% of the global energy consumption. The embodied energy of conventional buildings is high due to the utilization of energy-intensive construction materials and traditional construction methodology. Higher operational energy is attributed to the usage of power-consuming conventional air-conditioning systems. Therefore, moving to an energy-efficient cooling technology and eco-friendly building material can lead to significant energy savings and CO2 emission reduction. In the present study, an energy-efficient thermally activated building system (TABS) is integrated with glass fiber reinforced gypsum (GFRG), an eco-friendly building material. The proposed hybrid system is termed the thermally activated glass fiber reinforced gypsum (TAGFRG) system. This system is not only energy-efficient and eco-friendly but also provides better thermal comfort. An experimental room with a TAGFRG roof is constructed on the premises of the Indian Institute of Technology Madras (IITM), Chennai, located in a tropical wet and dry climate zone. The influence of indoor sensible heat load and the impact of natural ventilation on the thermal comfort of the TAGFRG system are investigated. An increase in internal heat load from 400 to 700 W deteriorates the thermal comfort of the indoor space. This is evident from the increases in operative temperatures from 29.8 to 31.5 °C and the predicted percentage of dissatisfaction from 44.5% to 80.9%. Natural ventilation increases the diurnal fluctuation of indoor air temperature by 1.6 and 1.9 °C for with and without cooling cases, respectively. It reduces the maximum indoor CO2 concentration from 912 to 393 ppm.

Small-scale experiments on the operational performance of a lightweight thermally active building system

Thermally active building systems (TABS), which are integrated with the structure of a building, provide a robust approach for utilising renewable energy. However, reinforced concrete, where TABS are typically placed, is responsible for a significant proportion of initial embodied energy and related greenhouse gas emissions. Therefore, combining lightweight structural elements and thermal systems reduces initial embodied energy usage while retaining the active material’s thermal storage and heat transport benefits. The present experimental work explores the operational performance of a prototype of a lightweight TABS at ceiling level. A small-scale climate chamber was constructed and equipped to evaluate the prototype in the key operating modes. The study investigated the relationship between the supply temperature of the lightweight TABS and the climate chamber’s internal air temperature for active heating, active cooling and natural ventilation modes. The experiments compared the reaction time in active heating mode for a range of supply temperatures. In addition, we examined the dynamic characteristics of the thermal mass of the lightweight TABS in passive natural ventilation mode and passive cooling mode in the presence of an internal thermal load. The results provide insights into the dynamic performance in operation. In heating mode, we identified the time lag between the radiant surface achieving a steady state and the conditioned air reaching its target temperature. This feature emphasises the significance of refining control strategies when designing comfortable environments with low-temperature heating systems at ceiling level. Further, we highlighted the importance of balancing decisions on minimising embodied energy with the suitability of the selected material to leverage renewable energy sources. The experimental data can be used for validating high-resolution numerical models, which support the development of multifunctional elements with renewable energy sources for building heating and cooling.

Topology optimization of thermally activated building system in high-rise building

The building sector accounts for nearly 1/3 of global energy end-use and associated carbon emissions. Fulfilling buildings' thermal demand in an efficient way is critical for decarbonizing the building sector. Therefore, this paper introduces the thermally activated building system (TABS) as an energy retrofit solution. A TABS floor-by-floor return water temperature control approach is proposed to reduce buildings' energy use and carbon emissions. The approach includes the topology optimization of TABS and flow control. The bypass pipe connections of the TABS to each floor, namely, the floor-by-floor pipe network topology, have been optimized by using genetic algorithms to achieve the lowest total cost. A case study of a high-rise building located in Beijing demonstrates that the proposed approach can improve the system's energy efficiency compared to the conventional TABS without optimization. The reduction of energy cost can be up to 11.21% with a 13.53% annual emission reduction. In general, the proposed TABS floor-by-floor return water temperature control approach can significantly improve the building efficiency comprehensively, therefore can be considered as a promising energy retrofit solution for the decarbonization of high-rise buildings.

Experimental investigation on cooling surface heat transfer behavior of a thermally activated building system in warm and humid zones

Thermally Activated Building System (TABS), is one of the alternative cooling methodology, due to the numerous advantages it provides the building industry. This system consists of encapsulated pipes within the building structure to control the surface temperature, which helps to remove the sensible heat from the indoor. The objective of this investigation is to experimentally evaluate the influence of cooling surface area and the effect of cooling water inlet flow velocities on the TABS performance in the warm and humid zone under natural ventilation, and the experimental results were compared with the conventional building (CB), which does not have any cooling arrangements. An increase in water inlet velocity from 0.35 to 1.5 m/s substantially removes the thermal energy stored in the TABS, and reduces the average indoor temperature by 3 °C. In a CB, the average heat gain of all surfaces varies from −3 W/m2 to 13 W/m2. Moreover, in all surface cooling (ASC), it varied from −2 W/m2 to 24 W/m2. This resulted in increased surface cooling, which increased the surface heat gain and indoor cooling capacity. There are no significant thermal behaviour and heat transfer variations at 1 m/s and 1.5 m/s of inlet water flow velocities.

Influence of cooling surface area on indoor air and surface heat transfer characteristics of a thermally activated building system in warm and humid zones: An Experimental study

Several alternatives have been introduced in recent years to enhance the thermal comfort levels within buildings. Thermally Activated Building Systems (TABS), one of the above alternatives, have gained interest because of the huge benefits this technology offers the building sector. This type of system consists of encapsulated pipes within the building structure to control the surface temperature. This study explores the thermal behavior of the cooling surface and fluctuations in indoor air temperature (IAT) of TABS under various cooling scenarios. Only limited number of investigations has been carried out to study the heat transfer behavior of TABS. Hence, the building indoor thermal properties such as air temperature, surface temperature and rate of heat transfer between the indoor air and inner surface of the TABS has been evaluated experimentally by enhancing the cooling surface area. Moreover the results were compared with the conventional building (no cooling provides). The thermal energy stored in the TABS is significantly removed by the increase in cooling surface area, resulting in a 2°C decrease in the average indoor air temperature. The average heat gain of all wall surfaces in the case of no cooling (WOC) ranges from −3 to 13 W/m2. The amount of heat gain on the walls was not significantly affected by only roof and floor cooling (R+F) activities. Moreover, it ranged from −2 to 24 W/m2 in all surface cooling (ASC) scenarios. As a result, there was additional surface cooling, which increased surface heat gain and indoor cooling capacity.

Multi-objective optimization of intermittent operation schemes of thermally activated building systems using grey relational analysis: A case study

The thermal storage of thermally activated building systems (TABS) demonstrates the advantages of intermittent operation, however, the existing studies rarely compared different intermittent schemes to determine the optimal one. Therefore, this study presented a case study on the multi-objective optimization of intermittent operation schemes of a TABS system equipped in a typical residential building in Xi'an. Three objectives including thermal comfort, energy conservation and economic efficiency were balanced. The comparison of the 6-h, 8-h, 12-h, and 24-h cooling durations were presented. The optimal cooling duration was determined, which further optimized the cooling time distribution, and the effects of different time-of-use (TOU) electricity prices were analyzed. The results show the 8-h cooling duration is the optimal one. When the 8-h duration is designed such that to include five cooling time distributions (i.e., 8-h daytime cooling, 8-h nighttime cooling, 2-h cooling + 1-h intermittence, 1-h cooling + 1-h intermittence, and 30-min cooling + 30-min intermittence), it is found that the optimal cooling time distribution under the TOU electricity price of Xi'an is the 1-h cooling + 1-h intermittence. In addition, the TOU electricity price greatly affect determining the optimal scheme. The results can provide references for the operation of TABS.

Impact of a Weather Predictive Control Strategy for Inert Building Technology on Thermal Comfort and Energy Demand

The sun’s total radiation alone exceeds the world population’s entire energy consumption by 7.500 times and ignites secondary renewable energy sources. The end energy consumption buildings use for heating amounts to 28% of Germany’s total energy consumption. With the ongoing trend of digitalization and the transition of the German energy supply away from fossil fuels and the consequent political dependency, electric heat pumps and photovoltaic (PV) systems have become increasingly important to the discussion. This has led to an increasing demand for smart control strategies, especially for inert systems such as thermally activated building systems (TABS). This paper presents and analyses a weather predictive control (WPC) strategy using a validated thermodynamic simulation model. The literature review of this paper outlines that the current common control strategies are data intense and complex in their implementation into the built environment. The simple approach of the WPC uses future ambient temperature and solar radiation to optimize the control of the heating, cooling, ventilation, and sun protection system. The thermal comfort and energy demand evaluate the concept. We show that with a WPC for TABS, thermal comfort can improve without increasing the energy demand for the office building in the moderate climate of Munich. Furthermore, this paper concludes that the WPC works more effectively with more thermal mass. This simplified building control strategy promotes the European roadmap goal of climate neutrality in 2050, as it bridges the phenomenon of the performance gap.

Numerical comparison of an office cooled with and without a ventilated slab using a model predictive controller

Ventilated slabs are Thermally Activated Building Systems (TABS) that use the supply air as the heating/cooling medium for taking advantage of the thermal inertia of a slab. The objective for the ventilated slab is to maintain the indoor temperature within the desired range for a minimal energy consumption, at least equal or lower than with a regular (non-ventilated) slab. To achieve such objectives, an efficient control is required but the latter is challenging for TABS because of the delay brought by their thermal inertia. While advanced control techniques are available and suitable with TABS, it is not always clear if the final performances are driven by the control technique itself or the inherent thermal potential of the ventilated slab. The present paper numerically analyses the behaviour of the ventilated slabs controlled with a Model Predictive Controller, and provides a comparison with a non-ventilated slab combined with the same controller. This comparison was extended to four other airflow rates, since it significantly changes the thermal dynamic of a ventilated slab. The indoor temperature requirements were satisfied most of the time and energy demand differences observed between the two systems were minor. However, a lower airflow rate is preferable as it decreases the consumption of the fans, which was significant for this test case. The most important improvement brought by the ventilated slab was the smoothed temperature variation at the outlet of the slab, resulting in a smaller blown air – room air temperature difference with ventilated slabs and thus favouring indoor comfort.

Development and Verification of Novel Building Integrated Thermal Storage System Models

In electrical grids with a high renewable percentage, weather conditions have a greater impact on power generation. This can lead to the overproduction of electricity during periods of substantial wind power generation, resulting in shutoffs of wind turbines. To reduce such shutoffs and to bridge periods of lower electricity production, three thermal energy storage systems (TESs) have been developed for space heating and domestic hot water. These include a water-based thermal system (WBTS), a thermally activated building system (TABS), and a high-temperature stone storage system (HTSS). The paper explains the development of computer models used to simulate the systems and their successful verification using field measurements. Target values to cover about 90% of building heating demand with excess electricity were found to be achievable, with performance ratios depending on storage size, particularly for WBTS and HTSS. The TABS’ storage capacity is limited by building geometry and the available inner ceilings and walls.

Hydronic flow path analysis on the thermal comfort performance of radiant cooling system

Construction and operation in the building sector account for more than 1/5th of global energy consumption. Moving on to an energy-efficient cooling technology and eco-friendly building material can lead to energy savings and a reduction in associated CO2 emissions. In the present study, an energy-efficient thermally activated building system (TABS) is integrated with eco-friendly building material, namely, glass fibre reinforced gypsum (GFRG). The proposed hybrid system is termed as thermally activated glass fibre reinforced gypsum (TAGFRG) system. This system is not only energy-efficient and eco-friendly but also provides better thermal comfort. An experimental room is constructed with the TAGFRG roof within the Indian Institute of Technology Madras campus, Chennai, i.e., in a tropical warm and humid climate zone. The TAGFRG roof has reinforcement in every third cavity with cooling pipes, while in the other two cavities, cooling pipes are embedded with air gap and partial reinforcement. The TAGFRG roof has four parallel loops of cooling pipelines, and each loop consists of one reinforcement zone (RZ) and two air gap zones (AZ1 and AZ2) in series. According to the water flow path in a single loop, various combinations of the flow path, i.e., RZ → AZ1 → AZ2, AZ1 → RZ → AZ2 and AZ1 → AZ2 → RZ, have been analyzed. According to the adaptive thermal comfort model, the water flow path has a negligible effect on thermal comfort. The average operative temperature for all the cases investigated varies between 28.1 and 29.2 °C. The operative temperature is always within the 90% band of thermal comfort, as per the adaptive comfort model.

Experimental investigation of thermally activated building system under the two different floor covering materials to maximize the underfloor cooling efficiency

This paper aims to investigate the impact of different floor coverings on thermally activated building systems (TABS) to maximize underfloor cooling. The effects of a floor surface and room operating temperature, heat flux, thermal response time, and time constant were experimentally investigated through a side-by-side comparison between vinyl and granite floor coverings of the TABS built environment. The real-time dynamic thermal performance of TABS for different floor coverings is investigated with the aid of thermal response time (Ʈ95) and time constant (Ʈ63.8). The indoor air temperature and heat flux in the granite floor covering were maintained uniform and steady for most of the time, however, in the case of vinyl flooring, there were irregular variations and approximately similar to the outdoor ambient conditions. Also, it was observed that for the granite floor, the thermal response time is 4 h, the and time constant (t) is 2 h; however, the vinyl floor has a thermal response time of 6 h. And the time constant (t) is 4 h. Granite floor covering cooling efficiency is 64% better than that of vinyl floor covering. Therefore, for the TABS, it is desired to use granite floor covering for its lower operative temperature, maximum heat dissipation, and cooling efficiency.

Feasibility study of simplified pipe modeling for analyzing thermal performances of radiant heating and cooling systems

Energy-efficient radiant heating and cooling require surface temperature and thermal capacity analysis. Simplified pipe modeling is applied to save time and resources for numerical analysis when evaluating the radiant system. Therefore, this study investigated the surface temperature distribution and thermal capacity of a radiant system using simplified pipe modeling. To do this, a steady-state heat transfer simulation was performed using Physibel BISCO. The difference between detailed (circular) and simple (rectangular) pipe models and the effect of material thermal conductivity of various layers were analyzed in three types of radiant heating and cooling systems: Embedded Surface System (ESS), Thermally Activated Building System (TABS), and Cooling Radiant Ceiling Panels (CRCP). The simple and detailed ESS and TABS simulation results showed similar surface temperature and heat capacity in various materials. Also, the CRCP simple and detailed models for materials differed in surface temperature and heat capacity, especially when the pipe thermal conductivity was high. The CRCP simple model overstated surface temperature and thermal capacity, which needs heat resistance to solve this overestimation. Further studies are necessary to investigate the discrepancy with different dimensioning and operation conditions, such as water temperature and flow rate.

Impact of placement and design of phase change materials in thermally activated buildings

Phase change materials (PCMs) and thermally activated building systems (TABSs) are two candidate technologies for reducing the energy consumption of modern buildings due to their favorable thermal storage features. However, the existing relevant studies do not specify the optimal integration schemes of PCMs when used in radiant cooling systems. Hence, this paper reports the first attempt to parametrically optimize the PCM-TABS system integration, considering typical open office space in the hot and dry climate zone of Cairo, Egypt. Using dynamic system simulations, four system configurations are examined, regarding the relative positions of the activated slab and Bio-PCM layer (ceiling or floor), and compared to active ceiling or floor systems (without PCMs). The results demonstrate the feasibility and favorableness of using PCMs in TABS, with energy and cost saving up to 18.80 and 19.78 %, respectively. The largest cost savings are achieved when PCMs are incorporated into the radiant ceiling, with a melting temperature of 22.0 °C and thickness of 6.0 cm. Energy savings also increase as the volume of PCMs increases, with melting temperatures closer to the building's setpoint. The percentage of comfortable hours decreases slightly from ~100 % to >95.5 % when using some PCM designs due to their thermal inertia, but PCMs result in generally lower variations of indoor thermal comfort. By mapping the performance of such system configurations, the study can be valuable for researchers and practitioners alike to determine the optimal integration scheme of PCMs in radiant cooling systems.

Heat transfer and thermal comfort analysis of thermally activated building system in warm and humid climate – A case study in an educational building

The thermally activated building system (TABS) is the most promising energy and eco-friendly cooling technique. These cooling methods consist of pipe encapsulated building surfaces, and it has been used in this work. The objective of this study is to develop a sustainable cooling system for an education institution. In this work, indoor thermal parameters and comfort indices of TABS was experimentally evaluated and compared with the building without cooling (WOC). The results from the investigation indicates that the average floor temperature decreased by 1.5 °C, and the average heat flux is increased by 8 W/m2 in TABS compared to the WOC. While considering the comfort indices, the operative temperature in the case of the TABS envelope is well within the 90% adaptive comfort band as per ASHRAE standards. The TABS has the most significant advantage of maintaining uniform indoor air temperature, reducing the operative temperature, and improving indoor thermal comfort.

Thermal comfort of a radiant cooling system in glass fiber reinforced gypsum roof – An experimental study

• Thermal comfort is achieved in a low embodied energy building with low energy cooling. • A high supply water temperature of 20 °C provided thermal comfort in a warm climate. • Radiant cooling of all surfaces provided thermal comfort even in hot weather. • Regression equations are developed to quantify the comfort in similar structure. • Air cavities in glass fiber reinforced gypsum roofs reduce penetration of solar heat. A holistic energy conservation approach that reduces the operational and embodied energy of the building is the need of the hour. A novel system that integrates the energy-efficient thermally activated building system (TABS) with the eco-friendly glass fibre reinforced gypsum (GFRG) reduces both operational and embodied energies. This system is termed a thermally activated glass fibre reinforced gypsum (TAGFRG) system, and research publications on this novel system are scarce. TAGFRG system is in the development stage; hence, its thermal comfort performance must be investigated extensively. A good understanding of the influence of operating parameters of the TAGFRG system can help in achieving the required thermal comfort by controlling these parameters. Therefore, the influences of supply water temperature and cooling surfaces are investigated experimentally and quantified using Fanger and adaptive thermal comfort models. An experiment room (3.46 m × 3.46 m × 3.46 m) with a TAGFRG roof in a warm and humid climate is used for this study. The proposed system can achieve 90% thermal comfort throughout the day, even at a high supply water temperature of 18 and 20 °C. An increase in supply water temperature from 18 to 26 °C increases the diurnal average operative temperature from 24.1 to 26.1 °C. An increase in the cooling surface area increases the cooling output and improves thermal comfort. The average predicted percentage dissatisfied is 22% if the roof alone is cooled directly with TABS. It reduces to 6% if all surfaces are cooled. The regression equations developed can quantify the thermal comfort indices for buildings with similar conditions at various water temperatures.

A Review of Thermally Activated Building Systems (TABS) as an Alternative for Improving the Indoor Environment of Buildings

Among the alternatives for improving the thermal comfort conditions inside buildings are the thermally activated building systems (TABS). They are embedded in different building components to improve the indoor air temperature. In this work, a review and analysis of the state of the art of TABS was carried out to identify their potential to improve thermal comfort conditions and provide energy savings. Furthermore, this study presents the gaps identified in the literature so that researchers can develop future studies on TABS. The articles found were classified and analyzed in four sections, considering their implementation in roofs, walls, floors, and the whole envelope. In addition, aspects related to the configuration of the TABS and the fluid (speed, temperature, and mass flow rate) were analyzed. It was found that when TABS are implemented in roofs, walls, and floors, a reduction in the indoor temperature of a building of up to 14.4 °C can be obtained. Within the limitations of the TABS, the complexity and costs of their implementation compared to the use of air conditioning systems are reported. However, the TABS can provide energy savings of up to 50%.