Adsorption Beds: The Significance of Thermodynamic Properties and Particle Size on System-Level Heat Pump Performance

The performance of an adsorption heat pump is a function of the equilibrium uptake and diffusion resistances of a particular system, which determine the refrigerant throughput during a cycle. Previous studies have sought improved sorption bed performance by increasing heat transfer; however, some of the proposed heat exchanger enhancements represent costly alterations to the system. This work instead investigates a method for optimizing sorption bed mass transfer, which can be implemented as a low-cost alternative to heat transfer enhancement or in addition to it. The objective is to balance the intra-particle diffusion resistance, which increases with adsorbent particle diameter, with the inter-particle pressure drop, which decreases with adsorbent particle diameter. A silica gel-water system model is used to show that the optimal particle geometry in a packed bed yields a 48% improvement in cooling duty and over 50% increase in COP compared with larger particles (dp = 1.42 mm).

Modeling and Simulation of Combined Heat and Mass Transfer in Zeolite SAPO-34 Coating for an Adsorption Heat Pump

Heat and mass transfers inside an adsorbent bed of an adsorption heat pump (AHP) are considered poor; consequently, they can cause low system performance. They should be enhanced so as to increase the coefficient of performance of the cooling machine. The aim of this work is to study an adsorbent bed coated with the zeolite SAPO-34. A simulation model based on governing equations for energy, mass, and momentum transfers is developed using COMSOL Multiphysics software. The system zeolite SAPO-34/water has been considered. Modeling results are validated by experimental database available at the Institute for Advanced Energy Technologies “Nicola Giordano,” Italy. It has been shown that the adsorption heat pump performance is affected by both heat and mass transfer. The enhancement of heat transfer solely is not sufficient to attain high values of specific cooling power. In the case of water vapor/SAPO-34 pair, mass transfer has a significant impact on the duration of the cooling step which should be shortened if one would want to increase the specific cooling power. The sole way to do it is to enhance mass transfer inside porous adsorbent.

Composite MWCNT/ MIL-101 (Cr)/CaCl2 as High-Capacity Water Adsorbent for Long-Term Thermal Energy Storage

Mil-101 (Cr) material is considered to be one of the most potential thermochemical energy storage materials in recent years. It has the advantages of a typical S-type water adsorption isotherm. Has low working temperature and large water adsorption amount. However, the adsorption properties of the material need to be improved under low water pressure. To improve the performance, the acidified MWCNTs were added before the hydrothermal reaction of mil-101 (Cr) materials to optimize the micropore structure. After the preparation, the new composite thermochemical energy storage materials were prepared by impregnation with a certain concentration of calcium chloride aqueous solution. The effects of multi-walled carbon nanotubes and calcium chloride on the physical and chemical properties of the materials were discussed. Through X-ray diffraction experiment, scanning electron microscope, microstructure analysis, nitrogen adsorption capacity test, water adsorption capacity test, and other means, the micro characteristics, pore structure, crystal morphology, and chemical composition of the materials were characterized, and the water adsorption performance of the materials was synthesized. The experimental results show that the addition of carbon nanotubes can improve the pore properties of the materials so that the porous organic skeleton can accommodate more calcium chloride particles. The composite materials with calcium chloride can provide excellent hydrophilicity and high water adsorption capacity. Also, the water absorption rate and adsorption-desorption cycle capacity of the material have been significantly improved. The experimental results show that when the mass fraction of calcium chloride reaches 30% when 90 mg acidified MWCNTs are added into every four chromium nitrate crystals, the hydrophilicity and adsorption capacity of the composite can reach a high equilibrium state. At the same time, the experimental yield of the material is high, the product is easy to obtain, the environmental friendliness is also reflected, so it is expected to become the adsorption heat pump thermochemical energy storage material with research potential.

Performance Evaluation of an Adsorption Heat Pump System Using MSC-30/R1234yf Pair with the Impact of Thermal Masses

In this study, we evaluated the performance of low Global Warming Potential (GWP) refrigerant R1234yf on the activated carbon (MSC-30) for adsorption heating applications. The adsorption isotherms of MSC-30/R1234yf were measured using a constant-volume–variable-pressure (CVVP) method from very low relative pressure to the practical operating ranges. The data were fitted with several isotherm models using non-linear curve fitting. An improved equilibrium model was employed to investigate the influence of dead thermal masses, i.e., the heat exchanger assembly and the non-adsorbing part of the adsorbent. The model employed the model for the isosteric heat of adsorption where the adsorbed phase volume was accounted for. The performance of the heat pump was compared with MSC-30/R134a pair using the data from the literature. The analysis covered the desorption temperature ranging from 60 °C to 90 °C, with the evaporation temperature at 5 °C and the adsorption temperature and condensation temperature set to 30 °C. It was observed that the adsorption isotherms of R1234yf on MSC-30 were relatively lower than those of R134a by approximately 12%. The coefficient of performance (COP) of the selected pair was found to vary from 0.03 to 0.35 depending on the heat source temperature. We demonstrated that due to lower latent heat, MSC-30/R1234yf pair exhibits slightly lower cycle performance compared to the MSC-30/R134a pair. However, the widespread adaptation of environmentally friendly R1234yf in automobile heat pump systems may call for the implementation of adsorption systems such as the direct hybridization using a single refrigerant. The isotherm and performance data presented in this work will be essential for such applications.

Thermal Performance of Heat Exchanger Using Zeolite/vapour Adsorption

About 60% of the energy input in the chemical industry is discarded from the plant. Energy saving can be achieved in the entire plant by recovering these waste heats and reusing them as power and heat sources in the power plant. An adsorption heat pump has been developed for the purpose of regeneration of such unused energy. In this study, saturated humid air was supplied to a device packed with 13X zeolite particles of 4 mm in diameter. The time variation of temperature in the apparatus was measured experimentally. Then, the maximum temperature was estimated from the relationship between heat balance and adsorption equilibrium. The trend of the maximum temperature calculated from the heat balance is consistent with experiment. Further, it was found from the result of the heat balance equation that the sensible heat of the humid air supplied and the heat of adsorption of the zeolite are mainly distributed to the sensible heat of the zeolite. In the future, it is important to make effective use of the sensible heat of this zeolite. In order to extract more thermal energy from the device, it is necessary to improve the heat transfer between the packed bed and medium. A double pipe heat exchanger having a zeolite packed bed on the annular side was proposed as an apparatus. Flow direction of the humid air supplied to device was changed in two different ways. The one of them is supplying humid air radial flowly to the device and another is supplying the air in parallel flow. The influence of flow direction on heat transfer between packed bed and medium is studied with numerical simulation.

A hybrid district heating substation with an adsorption chiller and PCM storage units: a concept and preliminary study

Development of the district heating system (DHS) is needed to achieve the Renewable Energy Directive goals. To maintain the economic profitability of DHN, the increase of intensity of heat production/consumption has to be ensured. Well, a known method is a cold production using an adsorption heat pump. However, developing a system suitable for implementation in the district heating companies is very difficult. As a solution, the authors propose a composite substation equipped with the adsorption heat pump and the heat/cold storage system based on a PCM.

Facility Energy Management Application of HBIM for Historical Low-Carbon Communities: Design, Modelling and Operation Control of Geothermal Energy Retrofit in a Real Italian Case Study

The highest challenge of energy efficiency of building stock is achieving improved performance in existing buildings and, especially, in heritage buildings which per se are characterized by massive limitations against the implementation of the most sophisticated solutions for energy saving. In Italy, historical buildings represent more than 30% of the building stock and the vast majority require energy retrofit, while ensuring the preservation of the heritage value and acceptable comfort conditions. In this context, historical buildings must be retrofitted and re-functioned by introducing innovative technologies aimed at reducing energy consumption and improving human comfort, health, and safety. To this aim, this study implements the Historic Building Information Modeling (HBIM) approach for the integrated modeling, monitoring, management, and maintenance of a novel geothermal system involving horizontal ground source heat exchangers (GHEXs) coupled to an adsorption heat pump for the energy refurbishment of historical buildings. In detail, a rural building part of a medieval complex in Perugia, Central Italy, is considered as a pilot case study. The analysis stresses the potential of the Facility Management (FM) applications of HBIM to provide a tool for the human-centric operational management control of the building energy performance and indoor comfort when combined with the building monitoring and supervision system. Therefore, this integrated HBIM approach may drive the path towards the user-centric re-functioning of heritage buildings.