•An alternative indicator of thermal response of radiant systems is studied (HSE).•HSE allows comparing systems with complex thermal behaviour by a single value.•HSE ranged from 3% for fast systems ...to 56% for slow systems.•Effective thermal output (ETO) that considers the thermal response is introduced.•ETO was up to 57% lower than nominal thermal output for thermally active systems.
An alternative indicator of thermal response of radiant heating and cooling systems called heat storage efficiency (HSE) has been tested. The heat storage efficiency was compared with established indicators represented by the time constant τ63, response time τ95, and thermal energy stored (TES). The comparison was performed for three wall cooling systems with various combinations of pipe location, configuration of material layers, and materials of the thermal core. Considering the whole response curve (HSE) instead of focusing on one specific point on the curve (τ63, τ95) allowed comparing the thermal response of complex systems by a single value. It also permitted predicting thermal response consistently regardless of the system and core material. Thermal energy stored predicted the thermal response of certain systems, but it may not be suitable for comparing the thermal response of radiant systems with different thermal admittance. Besides, a novel indicator of thermal output called effective thermal output (ETO) has been proposed. The effective thermal output considers both the steady-state thermal performance represented by the nominal thermal output and dynamic thermal performance represented by the heat storage efficiency. For thermally active building systems (TABS), effective thermal output was up to 57% lower than the nominal thermal output.
Radiant systems are being increasingly used for space heating and cooling of buildings. The contemporary research of radiant systems addresses mainly floor and ceiling structures. Research regarding ...the possibilities of their incorporation in wall structures is lacking, despite their potential advantages. This study addresses a radiant wall system manufactured according to a patent. The patented design involves panels that consist of pipes arranged in milled channels in thermal insulation. The potential advantage of this system is the fact that the thermally active panels can be attached to the facades of existing buildings as a part of their retrofit. Thereby, only minor interventions on the interior side of the retrofitted buildings are needed. To test and improve the design of the wall system, laboratory measurements and computer simulations were performed on a wall fragment for its operation under summer conditions. The results indicate a significant potential for improvement of the patented design by addressing the imperfections in the contact between pipe and wall. Inserting a metal fin between pipe and wall enhanced the cool distribution within the wall fragment considerably. From the three materials of the metal fin considered, using copper led to highest values of the cooling output, followed by aluminium. For these two metals the effect of increasing the thickness of the fin on the cooling output was small. On the contrary, the fin made of steel was the least efficient in terms of cool distribution. In this case the cooling output was most sensitive to the thickness of the fin.
In the following years and decades the increase in cooling capacity will put tremendous pressure on the energy infrastructure and severely increase the environmental impacts. In a moderate climate ...and well thermally insulated buildings like, e.g., in Europe, installation of low-exergy radiant systems could help alleviate these negative effects. Wall systems may be especially suitable for installation in existing buildings, however, their possible applications in buildings retrofit have not been fully explored. We therefore investigate the possible applications of wall cooling in existing buildings by numerical simulations of two-dimension heat flow through a wall fragment. Three wall systems are proposed and compared in terms of thermal response and heat transfer. The effect of various parameters is investigated to facilitate the design of the wall systems.
Using two layers of phase change material (PCM) instead of one to improve the thermal energy storage of PCM is a promising way to minimize thermal loads in buildings. This study aimed to maximize the ...latent heat utilization by splitting the PCM into two layers and adjusting their location and melting temperature. Seven scenarios were created using one or two PCM layers on the inner side, outer side or both sides of an external wall. Energy savings analysis was carried out using a verified numerical model. The results indicated that the monthly optimum PCM melting temperature ranged from 5 °C to 30 °C. Two PCM layers, one on the outside side of the wall with a melting temperature of 17 °C and the other on the interior side with a melting temperature of 25 °C, resulted in higher annual energy savings (17.2%), compared to a single PCM layer (16.8%). With two PCM layers, the energy saving due to latent heat activation increased from 2.5% to 3.2%. Furthermore, this design reduced CO2 emissions by up to 18.4% and caused the surface temperature to approach the comfortable room temperature thereby decreasing thermal loads and improving thermal comfort.
•Research of effective use of latent heat by separating PCM into two layers.•Optimizing melting temperature and location of one or two PCM layers.•Analysing annual energy saving, CO2 emissions, and room temperature stability.•Greatest yearly saving with one PCM at outer and one at inner side of the wall.•Optimum melting temperature was 17 °C for outer and 25 °C for inner PCM layer.
•PCM layer 23 mm thick and located near the interior saves 12.8% of energy.•Contribution of latent heat utilization in overall energy saving can be up to 73.4%.•Optimum phase transition temperature ...equals the upper temperature setpoint.•Proper phase transition temperature prevents adverse effects of latent heat storage.•Using PCM reduces the number of air conditioner operation cycles.
An optimization study was conducted for an external office wall containing a phase change material (PCM) layer under intermittent cooling operation. The design parameters such as location, PCM layer thickness and phase transition temperature were optimized to maximize energy savings by efficient use of latent heat. Moreover, simulations were performed for a representative week of each summer month to evaluate the effect of incorporating PCM into the wall on thermal comfort and air conditioner operation. PCM located near the exterior did not save energy and might even increase the energy demand. It is advisable to locate the PCM layer near the interior. The optimum phase transition temperature was 25 °C irrespective of the PCM layer thickness, which equaled the upper temperature setpoint. At this phase transition temperature, the room and wall surface temperature was reduced before working times and during lunch breaks which enabled reducing the number of operation cycles of the air conditioner. Also, energy savings of up to 12.8% were attained for the PCM layer thickness of 23 mm as compared to a wall without any PCM. Any phase transition temperature above 26 °C negatively affected the energy savings due to the adverse effect of latent heat usage.
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•Water-based wall systems for heating and cooling and thermal barriers are reviewed.•A classification scheme is proposed for heating/cooling systems and thermal barriers.•Benefits and ...drawbacks are summarized, design recommendations are provided.•Alternating between heating, cooling, and thermal barrier is perspective operation strategy.•Incorporating PCM in the wall and use in building retrofit are research opportunities.
This study reviews water-based wall systems for space heating and cooling and thermal barriers (TB) for the reduction of buildings’ thermal load. The review gives a general overview of the research and groups it into subtopics that are discussed in detail. For space heating and cooling, the subtopics entail thermal performance, thermal comfort, renewable energy sources, use for building retrofit, and combination with phase change materials (PCM). For TB, especially the working principle, types and designs, and performance are discussed. A classification system is proposed separately for wall heating and cooling systems and TB based on the designs found in scientific literature. Benefits and drawbacks are summarized, and design recommendations are provided for the wall systems.
It was shown that in certain cases, radiant wall systems can be preferable to radiant floors and ceilings, but further comparisons would be useful to provide conclusive evidence. For TB, the studies uniformly declare that TB reduce buildings’ thermal loads and energy demands. Few studies focused on the economic and environmental aspects of using TB. Most of the studies about TB are based on calculations. Measurements to quantify the benefits of TB under real operation and refine the conditions under which various types of TB are feasible are lacking. Enhancing the wall performance by PCM in the active layer, application of the wall systems in building retrofit, and alternating between the functions of heating, cooling, and TB present the biggest research opportunities and challenges.
► Air distribution and ventilation effectiveness studied in room heated by warm air. ► No serious thermal discomfort due to vertical air temperature differences or draught. ► Buoyancy forces ...important for ventilation effectiveness when room heated by warm air. ► Depending on position of air terminal devices ventilation effectiveness from 0.4 to 1.2. ► Ventilation effectiveness about 1 for combination of cold air and floor heating.
Air distribution, ventilation effectiveness and thermal environment were experimentally studied in a simulated room in a low-energy building heated and ventilated by warm air supplied by a mixing ventilation system. Measurements were performed for various positions of the air terminal devices and at different simulated outside conditions, internal heat gains and air change rates. Floor heating was also simulated and compared with the warm air heating system. Vertical air temperature profiles, air velocity profiles and equivalent temperatures were derived in order to describe the thermal environment. Contaminant removal effectiveness and air change efficiency were used to evaluate ventilation effectiveness. No significant risk of thermal discomfort due to vertical air temperature differences or draught was found. When the room was heated by warm air, buoyancy forces were important for ventilation effectiveness at low air change rates. The effect of increasing air change on the ventilation effectiveness depended on the position of air terminal devices. Depending on the position of air terminal devices, the ventilation effectiveness varied between 0.4 and 1.2, where 1 is complete mixing. When a radiant floor heating system was simulated, the cooler ventilation air introduced to the room mixed well and created uniform conditions with a ventilation effectiveness of about 1.
Restrictions have been imposed on the number of people, the duration of their stay and air conditioning operation in temples to limit the spread of the SARS-CoV-2 pandemic. This work studied how ...restrictions affected energy consumption, thermal comfort, and indoor air quality (IAQ) in mosques. Energy consumption data on lighting, heating and cooling before and during the pandemic were analyzed in six mosques of various sizes located in Yalova city, Turkey. The annual energy consumption for lighting was reduced during the pandemic in all mosques due to less usage, while the annual heating and cooling costs were raised in one mosque despite their restricted use. Besides, experiments were conducted to assess the effect of pandemic measures on thermal comfort and IAQ by measuring indoor temperature, relative humidity, air velocity, CO2 and PM concentrations in a typical mosque. Keeping the windows open and limiting occupancy improved the IAQ. This was evidenced by the lower average CO2 concentration during the pandemic (428 ± 40 ppm) than before the pandemic (661 ± 201 ppm). An acceptable thermal environment was achieved under pandemic measures at night during the summer period. Creating excellent conditions can be difficult without air conditioning even with open windows and prayers performed at night.
•Operation strategies for underfloor heating system (UHS) to reduce energy consumption is studied.•Operating the UHS only during prayer times cannot satisfy thermal comfort.•Operating the UHS only at ...night did not meet the comfort requirements.•Turning off the UHS between morning-noon and night-morning prayers reduced energy consumption.•Fuel consumption and CO2 emission can be reduced by 9% with a proper operation strategy.
This study aimed to reduce fuel consumption and CO2 emissions in a typical neighborhood mosque in Yalova, Turkey, where winters are mild and rainy and the average monthly outdoor temperature can typically drop to 4 °C, by improving the operating strategy of its underfloor heating system (UHS) while maintaining thermal comfort. The mosque has a thick outer wall and a large indoor volume and therefore high thermal inertia. Dynamic computer simulations were performed for each operating strategy employing input data from measurement. Six operation strategies were devised with respect to prayer times. When UHS was operated only during prayer times, energy consumption and CO2 emissions decreased, but thermal comfort was not achieved. When the UHS was operated only at night, comfortable conditions during prayer times were not achieved either. In the scenarios where UHS was used only during the day but not between morning and noon prayers, CO2 emissions increased. In the last scenario, the UHS was turned off between morning-noon and night-morning prayers, considering individual average hot water loop temperatures for each month. In this scenario, an annual saving of 89 kWh (0.81 kWh/m2day) of natural gas and 136 kg/day of CO2 emissions was attained while providing comfortable conditions. This means a 9% reduction in fuel consumption and CO2 emissions by employing an appropriate heating operation strategy in a typical medium-sized neighborhood mosque.
A radiant wall heating and cooling system with pipes attached to thermally insulating bricks was tested using climate chambers and a hotbox. This system is especially suitable for building retrofit ...due to its affordability and ease of installation but can be also applied in new buildings. Besides walls, the design tested can be also used for ceilings. Thermal output and response, wall surface and cross-section temperature, and water temperature were measured under a range of thermal loads. The thermal response was fast despite the coupling of the pipe with the bricks; the time constant τ63 was 0.5 h. The low-conductivity core substantially reduced thermal losses meaning that the system can properly function even without thermal insulation. These qualities may present an advantage compared to systems with pipes coupled to a conductive core which require insulation and have longer response times. The difference between water and average surface temperature was small, up to 7.0 °C at the peak output of 100 W/m2, which benefits the energy source efficiency. However, the surface temperature was non-uniform, which should be considered to prevent local condensation. Numerical simulations at room level showed that locating the system at one wall leads to a non-homogeneous thermal environment. Installation at multiple walls can be preferable to attain more uniform conditions.
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