Natural Cold Source Research Articles

Experiments and simulations of underground artificial freezing with the use of natural cold resources in cold regions

This study proposes an artificial freezing method that consumes low energy by combining air-cooling and a conventional method. The method fully utilizes a naturally low air temperature in a cold region, which reduces freezing costs and avoids environmental influence. A refrigeration experimental platform is designed to study the refrigeration effects of natural cold sources. A mathematical model is built to analyze the evolution of temperature. And the temperature field was simulated by software----ANSYS. The simulated results match the experimental data well and verify the feasibility of the proposed method. Moreover, air-cooling economy and conventional refrigeration are analyzed. The running cost and power of the air-cooling method are respectively reduced by 52% and 53.4% when compared with the values for the conventional method. This approach effectively reduces refrigeration power load and project cost, consumes low energy, and is environment friendly. This study can thus serve as a reference for new ideas on underground artificial freezing.

Effect of natural cold source on groundwater source heat pump according to laboratory and field geotechnical thermal physical tests

This paper uses the numerical method and laboratory and field tests to determine the effect of cold source on groundwater source heat pump (GWHP) in Jiagedaqi. Cold sources are distributed in a scattered pattern, with temperatures ranging from 0°C to 1°C according to temperature field test results. Laboratory tests show that the thermal physical parameters of pebbles and grit present discrete phenomenon with depth and that the parameters of sandstone and granite undergo minimal change. By considering the correlation and discrepancy of laboratory and field tests and by modifying the parameters of the laboratory test via the analytic hierarchy process, this paper selects formation thickness, moisture content, density, and permeability as the main factors that influence the difference in thermal physical parameters. Basing on the geological conditions of the region, this paper constructs a numerical model with the data from modified laboratory tests and in-situ thermal response tests. The model analyzes heat breakthrough and influence radius of cold source in the producing/injecting system of multiple wells. Simulation results show that the influence range of cold source on GWHP is 150m and that heat breakthrough is observed when the influence radius is less than 85m.

Energy and economic analysis of a building enclosure outfitted with a phase change material board (PCMB)

This paper presents energy and economic analyses related to the application of phase change materials boards (PCMBs) in building enclosures during the cooling season. A heat transfer model was developed, which was implemented via a computer program. Simulations were carried out using weather data files from five cities located in five different climate regions in China. Energy savings from using a natural cold source (e.g., outdoor air) and electricity savings from a reduction in electricity by air conditioning systems were evaluated. The energy savings ratio (ESR) and simple payback period (SPP) were used to assess the application of PCMBs in building enclosures. The selection of optimum phase transition temperatures for the PCMs for the various climates was made using indoor and outdoor air temperatures, as well as SPP. For space cooling purposes, it was suggested that phase transition temperatures should be at least 3°C higher than the mean outdoor air temperature. Simple payback period suggested the possibility of the cost effective use of PCMBs in occupied buildings for moderate temperature climates.

A study on the use of phase change materials (PCMs) in combination with a natural cold source for space cooling in telecommunications base stations (TBSs) in China

A technology that combines phase change materials (PCMs) with a natural cold source is proposed to reduce the space cooling energy of telecommunications base stations (TBSs). First, a mathematical model was developed to assess this technology. Then, a full-scale prototype, named latent heat storage unit (LHSU), was designed, built, and tested in an enthalpy difference laboratory. The energy efficiency ratio (EER) and the adjusted energy efficiency ratio (AEER) were used as the criteria to evaluate the performance of this unit and to compare it with conventional air conditioners. LHSU performance simulations were carried out based on the unit’s operation in TBSs located in five Chinese cities with different climates. The simulated average annual AEER was 14.04W/W, which is considerably higher than the limiting value of 3.2W/W for air conditioners with a cooling capacity of less than 4500W. The estimated average energy savings potential of the LHSU was 50%. Based on these results, it was concluded that LHSUs could be used in TBSs to reduce a significant amount of their energy consumed in space cooling.

Simulation and experimental validation of soil cool storage with seasonal natural energy

For the purpose of reducing energy consumption by summer air conditioning and utilizing renewable resources, this paper presents a new type of soil cool storage system with seasonal natural cold source In the cool storage system, the natural cool energy is stored in soil by ground heat exchanger during the cold season and is extracted for space cooling in the summer. Based on film moisture migration theory, a moisture-heat transfer coupling mathematical model is brought up to describe the charging and discharging processes of freeze-thaw phase change of the soil. Besides, a new method is presented that variable time step size is used to solve nonlinear phase change problems numerically. Moreover, a comparison of the model predictions and experimental data shows that the model has good prediction accuracy. The parametric studies indicate that the soil cool storage system full meets the air conditioning needs and has excellence in economic performance. The research results prove that the feasibility of inter-seasonal cool storage system using shallow soil in severe cold regions.

The Effective Use of the Piston Effect, Natural Cold Sources, and Energy Saving in Beijing Subways

With the development of the subway, the energy consumption of subway ventilation and air-conditioning systems is increasing rapidly. To solve this problem, this paper describes the environment of a subway station in Beijing subway line no. 2 from July to September, 2011, and uses numerical methods to quantitatively analyze and evaluate the contributions of the subway piston effect and natural outdoor cold sources to energy saving in the air-conditioning system and improvement of the subway environment. The results show that the piston effect can be used for ventilation in each area of the subway station. During summer, part of the subway air-conditioning season, a natural cold source can introduce a cold capacity of 5,100 GJ to the subway station.

Development and Validation of Mathematical Model for Tailrace Tunnel Ventilating Process in Hydropower Station

When outdoor air flowing through the tailrace tunnel, it will be handled and its thermodynamic conditions will change under the differences of temperature and water vapor pressure between air and water surface, air and tunnel wall. Utilizing the handled air for space cooling in hydropower station is an energy saving, environmental protection and renewable application of natural cold source. In this paper, a detailed quasi-three-dimensional mathematical model of heat and moisture transfer of tailrace tunnel ventilating was developed and validated against the field test data from Yingxiuwan hydropower station, and the validation shows that the model predicts the test results very well. The model can be used to predict the heat and moisture performance of tailrace tunnel ventilating system.

The Air-Conditioning Rtilization of Natural Cold Resource of Lakes and Reservoirs

In the reservoir water temperature conducted annual test, test data shows that water temperature perennial remain in 9 ~ 10 in certain depth below. Reservoirs and lakes are huge natural cold source. In an air conditioning engineering, the reservoir cold water was directly used as cooling source. The air conditioning effect is good and to gets good energy-saving and environmental benefits. It suggests that solar energy, natural ventilation and natural cold and heat storage in water should be widely used in the western tourist architecture in order to achieve low carbon tourism.

Long term immersion corrosion tests on metal-PCM pairs used for latent heat storage in the 24 to 29°C temperature range

Phase Change Materials (PCMs) can be used for heating and cooling in buildings with two applications in mind. First, using natural heat and cold sources, that is solar energy for heating or night cold for cooling. Second, using manmade heat or cold sources more efficiently. In any case, storage of heat or cold with PCMs is necessary to match availability and demand with respect to time and also with respect to power. Depending on where and how the PCM is integrated, PCMs with different melting points are applied. Currently, there is a lack of commercial PCMs in the lower temperature range, that is between 5 and 29°C. The research to develop such materials is bringing new PCMs to the market, but they should be tested before application. Their corrosion behaviour is one of the aspects to be considered. In the present work, we tested the corrosion resistance of five commercial metals in contact with PCMs with a melting temperature in the range of 5 to 29°C in experiments with a duration up to 500 days. The PCMs were a commercial one, TH29 from TEAP (Australia), with a chemical composition of CaCl2·6H2O and an unknown nucleator, and the mixture of this material with MgCl2·6H2O (2:1wt%) to obtain a new PCM with melting temperature around 23°C. The main conclusions to be taken were that aluminum and steel should not be used in combination with these PCMs, but all the other metals have shown no problems. Maybe, only the fact that stainless steel can produce some orange precipitate, together with former literature recommendations to avoid the use of this metal, should be highlighted.