Water-flow Window Research Articles

Experimental study on thermal performance of finned tube water flow window

Water flow window is an advanced energy-saving building façade, and the design of the heat exchanger affects the thermal performance directly. A novel finned tube water flow window (FTWFW) applying a finned tube heat exchanger is proposed. Its thermal performance, with regard to energy savings and the thermal environment created under various operating conditions, is studied experimentally. The reduction in indoor heat gain reached 88.1% compared with insulated glazing unit, and the average daily water heat gain efficiency was 65.2% during the summer testing. The inner glazing surface temperature of FTWFW was more stable and closer to the comfort room temperature, especially under non-air-conditioning condition in winter, resulting in enhanced thermal comfort. Moreover, increasing the flow rate or decreasing the temperature of feed water can improve the thermal performance of FTWFW in summer. In winter, compared to increasing the feed water flow rate, raising the feed water temperature was more effective in increasing the room temperature. The advantages of FTWFW in cooling/heating energy saving, thermal collection, and thermal comfort enhancement were well demonstrated. Its large-scale application is expected to make contributions in green and low-carbon building development. The findings of this study can helpful in decision making of real projects.

Investigating the annual energy-saving and energy-output behaviors of a novel liquid-flow window with spectral regulation of ATO nanofluids

Building envelopes with energy-generation from renewable sources are highly promising for the green development of buildings. Recently, a new concept of energy-efficient window i.e., the water flow window (WFW), that can capture solar energy for domestic water heating, was reported. However, the output heating capacity of the WFW is inferior due to the limited absorption bandwidth of water. In this study, the ATO-based liquid filled window (LFW) was newly conceived for broadband solar harvesting and effective indoor solar regulation, and then a transient model was developed to figure out the annual performance of ATO-based LFW. By comparing the performance of ATO-based LFW with different ATO concentrations, it was found that an ATO mass fraction of 100 ppm is a positive solution for feasible luminous transmittance about 52%, and excellent monthly output heating capacity between 19 and 60 MJ/(m2·month) in Beijing. With the 100 ppm ATO-based LFW nanofluids, the output heating capacity and the annual solar heat gain coefficient (SHGC) of the ATO-based LFW in four cities with different climatic conditions were discussed. The results indicate that the 100 ppm ATO-based LFW shows the highest level of output thermal energy in Hong Kong, the highest output water temperature in Beijing, the lowest output heating capacity in Harbin, and the lowest cooling energy-saving potential in Chengdu. We believe that the ATO-based LFW is a feasible and applicable solution for achieving carbon neutrality in buildings, especially for buildings in hot regions.

Performance analysis of triple glazing water flow window systems during winter season

Water is circulated in the space between glazing as part of the Water Flow Window (WFW) technology. This idea may have an impact on the energy consumption of HVAC (heating, ventilation, and air conditioning) equipment. WFW is commonly used to remove excess heat; the excess heat can be stored. The purpose of this study is to compare the performance of triple glazing WFW under environmental conditions of Turkey during the winter. To compare the electrical energy consumption of the HVAC devices of testing cabinets, three identical testing cabinets with three different glazing types; standard (air-filled) window, WFW system with energy storage tank and domestic water supported WFW system are employed. The Thermal Energy Storage (TES) tank is a water tank that contains two distinct Phase Change Materials (PCM). PCMs are positioned all around and crammed inside water-filled pistol-style tubes. The TES tank volume is 5.675 L (42% water, 46% RT18 HC, 12% RT22 HC). The windows' surface area is approximately 0.3 m2. Visualization of the melting process in the TES tank is obtained with the numerical study. Results show that the consumption ratio of cooling devices can fall under 21% for daytime and heating devices can fall under 79% for nighttime.

Energy saving performance testing of vacuum water flow window under hot summer and cold winter climate

By applying vacuum glazing (VG) to water flow window, a novel vacuum water flow window (VWFW) is raised in the current study. Its advantages in reducing thermal transmission through windows and enhancing thermal utilization against common double layer water flow window (DWFW) and triple layer water flow window (TWFW) are tested in a hot summer and cold winter climate. The impacts on room heat exchange and water pre-heating performance, as well as the thermal utilization efficiency are compared. In cooling season, room heat gain through the VWFW is found reduced greatly comparing to DWFW, the reduction is in the range of 6%–38%. While those of VWFW and TWFW are comparable because of the high supply water temperature. The other benefit of VWFW is the increased water heat gain. A higher water heat gain efficiency in the range of 34%–70% is achievable with VWFW, this is 7%–30% and 3%–12% higher than those of DWFW and TWFW. In heating season, the VWFW is advantageous in reducing heat loss to ambient and increasing the thermal utilization efficiency. This is more promising under the cloudy day and higher supply warm water temperature conditions.

Performance analysis of water flow window systems with thermal energy storage tank includes phase change material in autumn season

When it comes to solar energy systems, the phase change materials (PCM)s latent heat storage (LHS) capacities can be advantageous for thermal energy storage (TES). The Water or Liquid Flow Window (WFW-LFW) Systems are notions that have just recently gained popularity. Solar energy is dissipated and stored by water flow between the glazing panes. The experimental analysis of the WFW system, as well as solar energy storage using PCM acts like a heat exchanger numerically, are made in this research (The volumes are around 2.4 L for water and 3.3 L for PCM in the tank). The experiment is carried out in a controlled environment, similar to prototype testing. Three identical test cabinets are used to assess the heating and cooling systems’ electricity consumption of test cabinets. These are WFW with PCM tank, mains water-supported WFW, standard window (commercial air-filled). Two distinct PCMs are mounted in a water tank; they are filled in the tubes are positioned like a pistol-type. The windows have a surface area of about 0.3 m2. After comparison, the outcomes demonstrate that the ratios of cooling device consumption can be as low as 66% for daytime and the heating device consumption ratio can be as low as 12% for nighttime. The time of around 6 h for melting and 12 h for solidification of PCM is adequate.

Investigation of water flow window with/without energy storage tank during winter season

The Water Flow Window (WFW) system includes water circulation in the gap between glazing. This circulation takes away the undesirable heat. What if this waste heat is stored? This concept can affect the electricity consumption of the Heating Ventilating and Air Conditioning (HVAC) devices. The WFW system's performance analysis with/without an energy storage tank during the winter is investigated in this study's scope. The experiments are conducted in Turkey's natural winter environment. Three identical testing cabinets have different glazing types; these are standard (air-filled) windows (SW)s and WFW with/without energy storage tanks are used. The test cabinets' HVAC devices' electricity consumption is compared. A water tank includes two different Phase Change Materials (PCM)s called Thermal Energy Storage (TES) tank. PCMs are placed around and stuffed tubes as pistol-type inside water. The PCM-TES tank volume includes 2.4 L of water; PCMs are 2.6 L RT18 HC and 0.7 L RT22 HC. The numerical analysis is made to visualize water temperature between glazing in the ANSYS Fluent with Volume of Fluid (VOF) method. It is seen that the ratio of electricity consumption with/without energy storage tank WFWs to SWs drops to 27% for daytime; 45% for nighttime. The minimum flow rate of HTF in the WFW with PCM-TES tank results has the lowest consumption ratio. The thermal energy is stored for 8 h and used for 12 h. 60% of the stored energy can be recovered.

Numerical study on the thermal performance of water flow window fed with air-conditioning condensate

A water flow window (WFW) fed with potable water is deemed as an effective system for absorbing incoming heat energy through the glazing area of a window. In this study, condensate formed in an air-conditioning (A/C) system is applied in a WFW for reducing heat gain and electricity consumption of a building. There is no need to consume any potable water. Through building energy simulations and numerical computation, this study unveils that a fully air-conditioned office building operating under a subtropical climate can produce condensate of sufficient flow rate to absorb heat energy from the glazing panes of an A/C condensate fed WFW system. The surface temperature of an outer glazing pane in an A/C condensate fed WFW system can be dropped by 16.3 °C when compared to a Low-e glass window. Moreover, an A/C condensate fed WFW can offer better thermal performance than a conventional WFW. When comparing to a Low-e glass case, an A/C condensate fed WFW facing four different orientations (N, E, S & W) can give reduction percentages of transmitted heat gain ranging from 57.2% to 63.5%. This A/C condensate fed WFW system shows a promising performance and has good potential for real application in commercial buildings.

Thermal Characteristics Simulation of an Energy-Conserving Facade: Water Flow Window

In this paper, a 3D numerical simulation was completed to explore the thermal characteristics in a water flow window in-depth. CFD was used to carry out the analysis on top of successful validation. By changing the solar intensity, water supply temperature and velocity, the temperature distribution and flow field in the window cavity, as well as the water heat gain, were analyzed and compared. This is meaningful for improving the energy-conserving performance in building applications. Simulation results reveal that the variation of solar intensity and water supply temperature affects directly the temperature distribution and the water heat gain but has little impact on the overall velocity field. Local vortices are generated in the window cavity, and their formation and location are largely affected by the varied temperature rise in the water layer. The water heat gain increases and then decreases with the increase in water supply velocity. In addition, a large-enough water supply velocity can disorder the uniform upward flow. These are detrimental to effective thermal extraction. Therefore, in practical application, the vortex should be eliminated, and the flow velocity should be determined properly to maximize the water heat gain.

Experimental and numerical performance investigation of a water-flow window with vacuum-glazing insulation

Thermal transmission through translucent façades is the primary source of energy consumption in buildings. A vacuum-glazing insulated water-flow window (VWFW) offers improved thermal insulation and enhanced solar water preheating performance. This paper explored the effectiveness of vacuum-glazing (VG) insulation in a water-flow window (WFW) and the energy-saving performance of a VWFW compared to a common double-glazing water flow window (DWFW). This comparison was conducted based on experimental and numerical analyses.The results revealed that with VG insulation, the annual heat gain of a room through the window was reduced by 50.3% compared to that measured with a DWFW. Moreover, the interior glazing surface temperature of the VWFW was more stable and closer to the room temperature set-point. Monthly average water heating efficiencies of 40% and 34% were obtained for the VWFW and DWFW, respectively. WFWs can be applied as energy producers in building. The advantages of VWFWs include improved electricity savings and reduced carbon emissions. These values were found to be 78.34 kWh/m2 and 69.8 kg CO2-eq/m2, respectively, for the VWFW, while those of the DWFW were 33.67 kWh/m2 and 30 kg CO2-eq/m2. The use of VWFW is thus meaningful for further reducing building-related energy consumption and reachingcarbonneutrality.

Clariant ready for faster, smarter catalyst research with high-tech upgrade of site in Japan

Thermal transmission through translucent façades is the primary source of energy consumption in buildings. A vacuum-glazing insulated water-flow window (VWFW) offers improved thermal insulation and enhanced solar water preheating performance. This paper explored the effectiveness of vacuum-glazing (VG) insulation in a water-flow window (WFW) and the energy-saving performance of a VWFW compared to a common double-glazing water flow window (DWFW). This comparison was conducted based on experimental and numerical analyses.The results revealed that with VG insulation, the annual heat gain of a room through the window was reduced by 50.3% compared to that measured with a DWFW. Moreover, the interior glazing surface temperature of the VWFW was more stable and closer to the room temperature set-point. Monthly average water heating efficiencies of 40% and 34% were obtained for the VWFW and DWFW, respectively. WFWs can be applied as energy producers in building. The advantages of VWFWs include improved electricity savings and reduced carbon emissions. These values were found to be 78.34 kWh/m2 and 69.8 kg CO2-eq/m2, respectively, for the VWFW, while those of the DWFW were 33.67 kWh/m2 and 30 kg CO2-eq/m2. The use of VWFW is thus meaningful for further reducing building-related energy consumption and reaching carbon neutrality.

Experimental investigation of water flow window system and numerical modeling of solar thermal energy storage with phase change materials on the way of nearly zero energy buildings

Latent heat storage of Phase Change Material (PCM) is beneficial for Thermal Energy Storage (TES) in solar energy systems. The Water Flow Window (WFW) is a concept that has emerged in the last decade. The circulation of water between glazing dissipates and stores solar-based energy. These two concepts can be brought together on the way of Nearly Zero Energy Buildings. In this study, the experimental investigation of the WFW system and numerical modeling of solar TES with PCM as a heat exchanger has been carried out. The experimental study is performed under environmental conditions like prototype testing. Two equivalent testing cabinets with WFW and standard (air-filled) window are employed to compare the electrical energy consumption of the cooling devices of testing cabinets. Two different PCM, filled in tubes as a pistol type, is mounted in a water tank. The TES tank volume is 5.675 liters (42% water, 46% RT28 HC, 12% RT35 HC). The windows' surface area is approximately 0.3 m2. Results show that the consumption ratio of cooling devices can fall under 85% and 2916 kJ energy can be stored throughout 6 h. Visualization of the melting process in the TES tank is obtained with the numerical study.

Thermal performance testing of triple-glazing water flow window in cooing operation

Water flow window is an energy efficient multi-glazing system with water flowing in the window cavity. Proper thermal insulation is crucial to enhance the related energy and cost saving. In this paper, the insulation performance of vacuum glazing (VG) and insulated glazing unit (IGU) in triple-glazing water flow window is explored. Experimental testing was completed during cooling season of Chengdu, China. The benefit of water application in window is also analyzed based on the testing results.The insulation performance of VG and IGU is found comparable when applied to water flow window in air-conditioned space. The additional water stream is quite effective in lowering the glazing surface temperature. Comparing water flow window and those without water supply, the reduction can be as large as 4.81 °C for inner glazing and reaches 10 °C for outer glazing. Also, the inner glazing surface temperature fluctuation can be narrowed with water flow window, and the performance of VG insulation water flow window (VWFW) is more favorable comparing to IGU insulated water flow window (TWFW). Thermal performance of water flow window as thermal collector is also promising. The daily thermal efficiency of VWFW and TWFW are in the ranges of 24.69–45.95% and 21.9–36.13% respectively.

Numerical simulation on year-round performance of water-flow window with different shading control modes

Water-flow window combines the functions of transparent building envelop, solar collector, as well as sun shading. Coloured particles are added to the flowing water within window cavity in order to provide extra shading, prevent indoor glare and enhance solar collection. The energy consumption of both air-conditioning system and water heating device can be further reduced. The aim of present investigation is to predict and analyze the year-round energy performance of a well-insulated water-flow window with different shading control modes. Accordingly, physical model of water-flow window is built up. FORTRAN program is developed and utilized in the numerical simulation. Results show that water-flow window can achieve exceptional sun blocking and cooling load reduction without occupying extra space. The year-round solar energy collection efficiency is within the range of 17.95∼21.06%. At the same time, indoor heat gain through the window can be reduced by around 50% compared with common double-layer window. The water-flow window under discussion has great application potential in buildings with constant hot water demand and high-density air-conditioning cooling load. In practice, the shading control mode should be carefully decided, and factors including climate region, hot water demand, window size and occupants' preference on indoor light environment should be taken into consideration. Numerical simulation proves to be an efficient method in predicting the energy performance of similar innovative-designed windows and a good assist in decision-making of real projects.

Energy performance of water flow window as solar collector and cooling terminal under adaptive control

Renewable energy is extensively utilized in building section for the purpose of energy conservation. In the present study, energy-saving potential of water flow window system under adaptive control is analyzed. The system utilizes geothermal energy for indoor cooling and solar energy for water heating. The window design combines the functions of transparent envelope, thermal insulation, solar collector and cooling terminal. These advantages make the system especially suitable for regions with hot summer and high-density indoor cooling load. As cooling terminal, the temperature of glass surface can be adjusted simultaneously according to indoor and outdoor condition through regulation of water flow rate.Two system control mechanisms are proposed: i) M1, to achieve zero indoor heat gain through the water flow window, and ii) M2, to compensate indoor cooling load from both ambient environment and internal heat sources. Self-developed FORTRAN program is utilized to investigate its application and energy conservation potential as both solar collector and indoor cooling terminal. Thermal and energy performances under both control mechanisms are evaluated. The economic analysis shows a promising annual energy saving of 576.0∼1223.5 MJ for the 9 m2 water flow window. Results demonstrate preferable potential of double-circulation water flow window system application.

Performance of double-circulation water-flow window system as solar collector and indoor heating terminal

Double-circulation water-flow window is a novel-designed solar-building-integrated energy saving system. The window part is composed of four layers of glass panes and 2 layers of flowing water, which contributes to building energy conservation by utilizing solar energy for domestic hot water preheating and regulating indoor heat gain through window. In heating season, warm water is supplied to the water-flow window cavity and it releases heat to the room through the innermost glass pane. Thermal, energy and economic performance of the compact double-circulation water-flow window was numerically analyzed in the present study. Results showed that direct solar transmission could be largely reduced with water-flow window, compared with common curtain wall. The year-round solar collection efficiency was 16.2% for the external water circulation and 4.3% for the internal water circulation. The predicted static payback period was around 7 years, with the extra investment of water-flow window over common curtain wall and the saving in electricity charge taken into consideration. For higher inlet water temperature at the internal window cavity during heating season, the predicted payback period was slightly longer, since part of the heat was lost to the outdoor environment. The results showed preferable potential of double-circulation water-flow window system in buildings with stable hot water demand and high-density energy demand.

Warm climate performance of water-filled double-glazing with submerged heat exchanger

Water-filled double-glazing is a new design in water-flow window technology. With a horizontal heat-transfer tubing dipped at the top end of the water layer in the window cavity, the absorbed solar heat is directly passed onto the domestic water heating system. The design avoids water-tube insertion at the high-pressure region, and hence minimizes the water leakage risk. Its warm climate application helps to reduce the year-round domestic water heating and air-conditioning loads. This paper reports the application of the dynamic simulation model of this new design. The validated model was used to evaluate its energy performance at different tropical and subtropical cities worldwide. The numerical results show that the 24 -h thermal efficiency is in the range of 26%–51% in the selected cities, mainly depending on the seasonal variation in ambient temperature. The degree of electricity saving in air conditioning will depend on the actual site location and the building activity. This innovative technology has wide application potential in zero-energy buildings.

Evaluation on year-round performance of double-circulation water-flow window

The topic of present study is a novel design of double-circulation water-flow window which combines the functions of solar thermal collector, indoor cooling/heating terminal and sun shading. Simulation program is developed and used to evaluate the year-round performance. For cooling dominant region, the window is efficient in solar thermal collection while making use of low-grade geothermal energy to provide additional heating/cooling in winter/summer. With flow rate of 0.005 kg/s, the window is capable of collecting 21.25% of total incident solar energy, which can be further enhanced to 28.76% by utilizing colored water with higher solar absorptance. Meanwhile, the window utilizes 174.27 and 64.76 kWh geothermal energy annually for indoor cooling and heating per unit area.The present work introduces a feasible way to model and evaluate the overall performance of an active window, which combines the utilization of both solar energy and geothermal energy in single building envelop. Moreover, the authors emphasized on beneficial indoor heat gain/loss through window which favors the energy saving in air-conditioning system, rather than the window component itself. The numerical model can be inserted into building energy simulation tools and provide assistance in green building design.

Numerical analysis on the advantages of evacuated gap insulation of vacuum-water flow window in building energy saving under various climates

A novel triple glazing vacuum-water flow window combining the advantages of water medium window and vacuum glazing is proposed in the current study. Its thermal performance as compared to double glazing water flow window was analyzed numerically under various climates. The application of an evacuated gap is proven quite effective in reducing heat flow through the window. In typical cities with cold, hot summer cold winter, and hot summer warm winter climates, room heat gains through the window can be reduced by 43%, 44% and 42% during cooling operation. The contribution is more significant under stronger solar radiation condition. In heating operation, warm water supply is beneficial in reducing room heat loss through the window. Heat loss to ambient from the warm water layer is lessened and heat transfer inward to room space can be enhanced with thermal insulation of the evacuated gap. The benefit of active heating with warm water and evacuated gap insulation is more significant in climate with lower ambient temperature and larger heating demand. Stabilizing the inner glazing temperature and improving the indoor thermal comfort level is another advantage of the evacuated gap insulation.

Pipe-work optimization of water flow window

Water flow window has been demonstrated an energy-efficient product that benefits both air conditioning and hot water systems. Its thermal performance was found affected much by the design geometry and system configuration. For those based on buoyant-driven flow, liquid water is at very slow movement; the magnitude depends on the overall flow-path friction loss and hence the connecting-pipe arrangement. In this study, the impacts of such recirculating pipe-work have been examined extensively. Firstly, experiment tests were executed to evaluate the system performances with and without distribution headers. Then their thermal and flow characteristics were compared using CFD analysis. Further on, the impacts of connecting-pipe dimensions were examined through the use of a validated FORTRAN program. The optimal pipe size was determined accordingly. It was found that without headers, more uniform temperature distribution close to the glazing surfaces could be achieved. The system thermal efficiency could be improved by around 5%. On the other hand, the variation in room heat gain was found around 1%, as a result of the self-regulating nature of the buoyant-driven flow. For the given window system, an optimal pipe size of 20–25 mm is recommended.

Numerical research on thermal performance of water-flow window as hospital curtain-wall

Water-flow window can reduce indoor cooling load from direct solar radiation and preheat domestic hot water at the same time. It is quite suitable for hospital with patient wards and large demand of hot water, especially buildings with large area of glazing curtain-wall. Field measurement was carried out during July 2018 at a major comprehensive hospital in Shenzhen, and the inner surface of the four-storey west-facing glazing curtain-wall reached over 45.6oC in the daytime. The year-round energy-saving potential is investigated by applying water-flow window to the curtain-wall through programme simulation, with a pre-validated FORTRAN programme. The results show that the year-round solar energy utilization rate can reach as high as 9.4%, and the indoor thermal environment is better, compared with conventional window design. The preheated water can be used in wards for showering and help building energy conservation. Water-flow window has great potential for large-scale application within similar buildings.