Analytical and Numerical Investigation on Depth and Pipe Configuration for Coaxial Borehole Heat Exchanger, A Preliminary Study

Existing research on the performance of shallow geothermal systems are prone to investigate the ground as a large thermal mass at a constant temperature despite possible temperature increase at depths - otherwise commonly known as the geothermal gradient. Most of the existing analytical models that predict the heat exchange between a borehole heat exchanger with the soil does not allow for the geothermal gradients to be accounted for. The few models that actually does account for the geothermal gradients, on the other hand, does so by enforcing a pre-existing temperature gradient only. We are presenting a bottom up approach in this paper to solve the temperature distribution by accounting for both the convective heat transfer from the working fluid and the conductive heat transfer through both the pipe and the soil. Assuming the heat transfer is entirely axisymmetric, we approach the problem by solving the Navier-stokes equation and energy equation with a finite difference solver that calculates the temporal change of temperature with given diameter, depth of borehole and geothermal gradient. The heat transfer through the pipe and into the ground can therefore be further calculated. We were able to determine a CBHE configuration that allows maximized thermal output by assuming a synthetic heating/cooling load for year-round production of heat

Visualizing the exergy destructed in exergy delivery chain in relation to human thermal comfort with ExFlow

Exergy analysis is an important tool to fully appreciate the usability of energy at different levels and has been widely applied in the building system analysis domain. It has became more useful as low temperature heating and high temperature cooling began to attract more attention both in Europe and the United States. Using low-grade energy to supply for these systems have, in return, led to an increase in awareness of low exergy (LowEx) system designs. The possibility of modeling the last missing link in the system that is to delivery thermal comfort, the human body, have therefore became a topic that increasingly draws the attention of many more researchers. Due to the complexity of these human body exergy models, it is very rare for these models to be linked back to building systems and produce an exergy efficiency for occupants’ thermal comfort. Attempting to fill in the blanks of overall system exergy efficiency on delivery occupant thermal comfort, we have developed a visualization algorithm that could visually assess the exergy efficiency in comfort delivery. Using the ExFlow tool, it is much clearer and easier to determine the relationship of how much primary energy input is eventually converted to the energy that is used to condition for the occupants’ comfort

Liquid Desiccant-Polymeric Membrane Dehumidification System for Improved Cooling Efficiency in Built Environments

We have recently demonstrated a new type of moisture absorber using a silicone-based liquid desiccant and a nonporous hydrophilic membrane. The setup consists of a core-shell structure where the desiccant flows inside the hydrophilic membrane (core) surrounded with humid air and confined inside a larger diameter tube (shell). In this work, we propose to extend the capabilities of this moisture absorber prototype by addressing two additional characteristics in order to fully validate its capabilities in the built environment. In the first section of this study, we developed a new setup to demonstrate the regeneration process of the liquid desiccant. The regeneration process takes into account the following parameters: (i) air temperature and relative humidity level, (ii) desiccant temperature and water saturation amount, (iii) air/desiccant contact length, (iv) air and liquid desiccant flow rates. In the second part of this paper, we extend our earlier work with this absorber and propose to further improve its performance. We investigate in detail the water absorption kinetics to favor water access to the bulk liquid desiccant surface through efficient mixing inside a confined volume

Exploring potentialities of energy-connected buildings: Performance assessment of an innovative low-exergy design concept for a building heating supply system

Abstract Low exergy building systems generate new possibilities for the design of high performance buildings, especially when the design of a new building is considered as part of a district where the relationship between buildings are optimized to minimize the dispersion of energy in the environment and maximize the recovery of waste energy. We present an innovative design concept and the performance assessment of the heating system of the new Embodied Computation Laboratory at Princeton University. The system is demonstrated to be able to match the heat demand without need for backup systems

WATeRVASE: Wind-catching Adaptive Technology for a Roof-integrated Ventilation Aperture System and Evaporative-cooling

The WATeRVASE is a Wind-catching Adaptive Technology for a Roof-integrated Ventilation Aperture System and Evaporative-cooling. Prior research for the adaptive wind catcher technique demonstrates the effective multi-fin design composition for geometry shifting in response to wind directions and speeds (Aviv, Meggers 2018, 186-195; Aviv, Axel, 2017, 1123-1128). Other prior research demonstrates the effectiveness of superporous polyelectrolyte hydrogels for water sorption and diffusion (Smith, 2017, 2481-2488; Ida, 2018). Our team members have also developed a machine-learning platform for testing building technology prototypes for particular environmental conditions and building integration analyses (Smith, Lasch, 2016, 98-105). The new area of research combines the prior work of environmental systems, material science, and electrical and computer engineering for expanding the potential environmental variables that might be addressed simultaneously with the WATeRVASE. Human thermal comfort is one of the most significant challenges in hotarid climate contexts due to energy-intensive building cooling needs, resulting in significant amounts of problematic carbon emissions. Existing experience has shown that passive cooling techniques with natural ventilation and evaporative-cooling provide excellent thermal comfort, together with very low energy consumption (Santamouris and Dionysia 2013, 74-79). The adaptive roof aperture is an advanced passive cooling system that responds to the external airflow thermodynamics by changing its membrane water sorption states to allow either downdraft airflow (saturated top membrane) or nighttime radiation (open top with dry ventilation membrane). In this research, we are developing the adaptive roof aperture functions in the specific hot-arid climate location of Tucson, Arizona. The integration of the hydrogel membrane as an inner surface-lining of the wind-catcher will enable the control of moisture interface with airflow streams via hydropumps with sensors and actuation control, providing evaporative-cooling effects for the daytime downdraft system. Furthermore, the prototype incorporates a lyophilized hydrogel that provides for humidity sorption at the base of the cooling space for water recuperation. The hydrogel membrane may also provide daylighting and thermal conduction mitigation based on saturation states. The project will also explore the potential for rain-water harvesting with the roof-integrated aperture, which is especially necessary for drought-prone hot-arid contexts

Stuck in a stack—Temperature measurements of the microclimate around split type condensing units in a high rise building in Singapore

AbstractThe use of air-conditioning, the largest energy demand for buildings in the tropics, is increasing as regional population and affluence grow. The majority of installed systems are split type air-conditioners. While the performance of new equipment is much better, the influence of the microclimate where the condensing units are installed is often overlooked. Several studies have used CFD simulations to analyse the stack effect, a buoyancy-driven airflow induced by heat rejected from condensing units. This leads to higher on-coil temperatures, deteriorating the performance of the air-conditioners. We present the first field measurements from a 24-storey building in Singapore. A network of wireless temperature sensors measured the temperature around the stack of condensing units. We found that the temperatures in the void space increased continuously along the height of the building by 10–13°C, showing a significant stack effect from the rejected heat from condensing units. We also found that hot air gets stuck behind louvres, built as aesthetic barriers, which increases the temperature another 9°C. Temperatures of around 50°C at the inlet of the condensing units for floors 10 and above are the combined result, reducing the unit efficiency by 32% compared to the undisturbed design case. This significant effect is completely neglected in building design and performance evaluation, and only with an integrated design process can truly efficient solutions be realised

Thermoheliodome Testing: Evaluation Methods for Testing Directed Radiant Heat Reflection☆

Abstract The Thermoheliodome is a prototype experimental pavilion that produces comfort through the manipulation of the mean radiant temperature generated by a combination of evaporative cooling and radiant heat reflection. We present the development of a sensing and analysis method for measuring the impact on radiant temperature and other performance data for the space, along with the initial system measurements. This is an environmental control station through which low cost microcontrollers enable distributed networked nodes to take measurements of relevant system parameters. The system measurements show a reduction of mean radiant temperature by 2-3 °C using evaporative cooling and strategic reflection

Sensing of Indoor Air Quality—Characterization of Spatial and Temporal Pollutant Evolution Through Distributed Sensing

Discouraged by the high-cost and lack of connectivity of indoor air quality (iAQ) measurement equipment, we built a platform that would allow us to investigate what kinds of iAQ evolution information could be collected by a low-cost, distributed sensor network. Our platform measures a variety of iAQ metrics (CO2, HCHO, volatile organic compounds, NO2, O3, temperature, and relative humidity), can be flexibly powered by batteries or standard 5 W power supplies, and is connected to an infrastructure that supports an arbitrary number of nodes that push data to the cloud and record it in real-time. Some of the sensors used in our nodes generate data in standard units (like ppm or °C), and others provide an analog signal that cannot be directly converted into standard units. To increase the relative precision of measurements taken by different nodes, we placed all 6 pairs of the nodes used in our deployments in the same environment, recorded how they reacted to changing iAQ, and developed calibration functions to synchronize their signals. We deployed the comparatively cross-calibrated nodes to two different buildings on Princeton University's campus; a fabrication shop and an office building. In both buildings, we placed nodes at key positions in the ventilation supply chain, providing us with the ability to monitor where indoor air pollutants were being introduced, and when they tended to be introduced—enabling us to monitor the evolution of pollutants temporally and spatially. We find that the occupied space of the first building's fabrication shop and the second building's open-plan office have higher levels of volatile organic compounds (VOCs) than outside air. This indicates that both buildings' ventilation systems are unable to supply enough fresh air to dilute VOCs generated inside those spaces. In the second building, we also find indications that other parameters are being driven by set-backs and occupancy. These first deployments demonstrate the ability of low-cost distributed iAQ sensor networks to help researchers identify where and when indoor air pollutants are introduced in buildings

Extracting Radiant Cooling From Building Exhaust Air Using the Maisotsenko Cycle Principle

Indirect evaporative cooling has exciting implications for air based thermal comfort. With recent advances in the research and commercialization of Maisotsenko Cycle (M-Cycle), or dew-point, evaporative cooling, thermodynamics can be fully leveraged to provide effectively free air cooling. However, few studies seek to generate cool surfaces by evaporation for radiant cooling. As a method to reduce building energy consumption, such an evapo-radiative system would maintain occupant thermal comfort at higher ventilation air temperatures and provide cooling at low cost. This study explores an analytical model for an M-Cycle evapo-radiative cooling system that derives a 1-D temperature profile throughout an experimental module and compares the outputs to experimental data to begin the model validation process