This paper investigates the integration of geothermal storage into state-of-the-art CO2 trans-critical booster systems. The objective is to evaluate the impact of this integration on energy efficiency. Three scenarios of integration are studied including stand-alone and integrated supermarket building systems.The results show that for a stand-alone average size supermarket, heat recovery from the CO2 system should be prioritized over a separate ground source heat pump. Extracting heat from the ground by an extra evaporator in the CO2 system has also little impact on this supermarket annual energy use. However, in the case of supermarket integration with a neighboring building where the supermarket provides heat to the neighbor, geothermal storage integration can reduce the total annual running cost of the two non-integrated buildings by 20–30% with a payback time of less than 3.5 years. The results also show there is no need for a separate ground source heat pump.
Hunting causes a poor operational safety and efficiency of a direct expansion (DX) air conditioning (A/C) system when it is variable speed (VS) operated to output different sensible and latent cooling capacities. An existing dynamic model was further developed by adding the equations for evaluating temperature sensor dynamics and air side operating parameters. After experimentally validated the model, the temperature sensor dynamics and VS operation on stability were numerically examined. Simulation results showed that due to the temperature sensor dynamics, actual system hunting could be much more serious than what was measured, and increasing the thermal resistance between temperature sensor and refrigerant pipeline would mitigate hunting. The mixture-vapor transition point in the DX evaporator would move closer to its exit at a smaller output equipment sensible heat ratio (E SHR) or a larger output total cooling capacity (TCC), consequently, leading to a higher chance to instability.
A new model is developed to predict the heat transfer coefficients (HTCs) of pure refrigerants and refrigerant mixtures condensing within horizontal microfin tubes. A 1312-point experimental database from 22 sources was compiled for this purpose. The data comprise CO2, R1234yf, R1234ze(E), R134a, R22, R407C, R404A, and R410A, 2.64-8.98 mm diameter tubes, -25 degrees C to 50 degrees C saturation temperatures, vapor qualities from 0.02 to 0.98, reduced pressures from 0.16 to 0.81, and heat and mass fluxes ranging from 1.79 to 98.1 kW/m(2) and 49.0 to 872.5 kg/m(2) s, respectively. To develop the model, one hundred twenty unique dimensionless parameters pertinent to condensing flows in microfin tubes were first selected. Multi-variable regression analysis was then applied to identify the most significant of these variables influencing the condensation Nusselt number. On an overall basis, the new model performs significantly better than any of six extant correlations. The new model was then assessed for different refrigerants, and many ranges of diameter, heat and mass flux, vapor quality, and reduced pressure. Generally, the new model is reasonably accurate, with mean absolute deviations generally smaller than 20-25%. The model also predicts annular flow HTCs fairly accurately. Parameter ranges in which Cavallini et al. (2009), the best of the extant correlations, gives better predictions than the new model and those in which more data would be useful for further analysis are also identified. In general, the new model can be recommended for a large variety of refrigerants under practically significant operating conditions. (C) 2019 Elsevier Ltd and IIR. All rights reserved.
Previous researches have proved that newly introduced parameters such as void velocity and others can be successfully used for correlating the heat transfer and pressure drop parameters. In order to establish a reliable procedure for estimation of air pressure drop, experiments on plate finned tube heat exchangers have been conducted, as well as the extensive investigation of the open literature. Using own and previously published experimental data, new correlation for estimation of air pressure drop have been established, covering a wide range of parameters of industrial importance. New correlation is comprehensive and statistically superior to any other pressure drop correlation.
In this paper, the current state of the art on a new adsorptive cycle (the so-called "Heat from Cold" or HeCol), recently suggested for upgrading the ambient heat (Aristov, 2017), is surveyed. The survey includes theoretical and experimental parts. In the first one, the cycle efficiency and an optimal adsorbent are discussed. Requirements to the adsorbent optimal for this cycle from thermodynamic and kinetic points of view are formulated in terms of the Dubinin–Polanyi adsorption potential. The experimental part includes the dynamic study of the adsorbent regeneration stage and testing of a first lab-scale HeCol prototype to prove the feasibility of the HeCol concept. Advanced composite sorbents of methanol on the base of inorganic salts confined to porous matrices are synthesized and studied, including their testing in the first HeCol prototype. Finally, future development of the HeCol concept is discussed.
