Search

A novel radiative cooling and solar collection concept is presented, and the combination of these two technologies and its energy integration in residential and commercial buildings is evaluated. This innovative concept, herein named Radiative Collector and Emitter (RCE), allows for supplying both cooling and Domestic Hot Water (DHW) demands. First, the RCE concept is introduced by presenting its background, with special attention to the overlapping and switching between radiative cooling and solar thermal collection. Then the DHW and cooling demands for four building typologies, two residential and two commercial, are compared with the energy production of the RCE. The analysis is performed for representative cities of the world climates according to Köppen‐Geiger classification. The RCE concept showed suitability in some of the studied cities (San Francisco, Cape Town, Johannesburg, London, and Ottawa) with C (temperate) and D (continental) climates in residential and tertiary buildings. Suitable technology! A new concept, the Radiative Collector and Emitter (RCE), combining radiative cooling and solar collection is analyzed. The RCE concept showed suitability in some of the studied cities (San Francisco, Cape Town, Johannesburg, London, and Ottawa) with C (temperate) and D (continental) climates in residential and tertiary buildings, covering more than 25 % of the cooling demand and more than 75 % of the domestic hot water demand. [ABSTRACT FROM AUTHOR]

Abstract: An exergy analysis, which only considers the unavoidable exergy destruction, is conducted for single, double, triple and half effect Water–Lithium bromide absorption cycles. Thus, the obtained performances represent the maximum achievable performance under the given operation conditions. The coefficient of performance (COP), the exergetic efficiencies and the exergy destruction rates are determined and the effect of the heat source temperature is evaluated. As expected, the COP increases significantly from double lift to triple effect cycles. The exergetic efficiency varies less among the different configurations. In all cycles the effect of the heat source temperature on the exergy destruction rates is similar for the same type of components, while the quantitative contributions depend on cycle type and flow configuration. Largest exergy destruction occurs in the absorbers and generators, especially at higher heat source temperatures. [Copyright &y& Elsevier]

Abstract: The optimum allocation of the heat exchange area considers both running and investment cost. The structural method of thermoeconomic optimization is used to derive a simple equation for the estimation of the economic optimum of the area of a heat exchanger integrated in a more complex system. The obtained equation is generally valid for thermal systems. The optimum heat exchange area can be estimated in a straightforward calculation once operation and cost parameters, the overall heat transfer coefficient and the Coefficient of Structural Bonds (CSB) are known. The CSB quantifies the interactions between the units of the thermal system and is obtained from an exergy analysis. Therefore, compared to former work, the proposed equation has the advantage of considering interactions between the units of the system. A case study is presented for an ammonia-water absorption chiller. The optimum area from the proposed formulation is compared with the results obtained from the integrated optimization algorithm of EES (from F-Chart) and the base cases for different annual operation time. [Copyright &y& Elsevier]

First and second law analysis have been conducted for three low temperature driven ammonia-water absorption cooling cycles with increasing internal heat recovery. Based on the results of exergy analysis the structural analysis has been achieved. The obtained Coefficients of Structural Bonds (CSB) consider how the irreversibility of the whole cycle is affected by a change in the irreversibility related to an efficiency improvement of a single component. Trends for the different configurations are similar, while quantitative differences among the main heat exchangers are considerable. The highest values of the CSB are found for the refrigerant heat exchanger. Also the evaporator, the condenser, the generator and the absorber show values higher than unity. The lowest CSB's are obtained in the solution heat exchanger. In general, CSB's decrease with increasing efficiency. That means that for very efficient heat exchangers, a further improvement looks less attractive. The dephlegmator is an exception as it shows a singularity of the CSB value due to its complex interactions with the other components. Once the CSB's are obtained for the main components, they can be used in the structural method of the thermoeconomic optimisation. This method enables us to find the optimum design of a component in a straightforward calculation. [ABSTRACT FROM AUTHOR]

Most water–lithium bromide (LiBr) absorption chillers have a purge system to remove non-absorbable gases that cause a reduction in cooling capacity. Generally, the non-absorbables are originated in corrosion/passivation processes inside the machine, but leaks can also be a source of concern. However, since leaks must be corrected immediately to avoid machine deterioration, this study is mostly aimed at the non-absorbables evolved during operation. This paper analyses the effect of inlet non-absorbable air concentration, outlet purge velocity, absorber pressure and cooling water temperature on the falling film absorption process inside a vertical tube absorber, based on a simple transport coefficient model. This model consists of three ordinary differential equations solved with as method for initial-value problem, and a set of auxiliary equations. The study shows that the effect of non-absorbables can be significant, and furthermore provides a quantitative framework to aid in purge design. The nominal working conditions in this study were a solution Reynolds number of 100, an absorber pressure of 1.3 kPa, a cooling water temperature of 35 °C and an inlet solution concentration of 62% LiBr by weight. The results indicate that a minimum vapour velocity is required to sweep the non-absorbables along the absorber towards the purge, thus preventing reduced absorption fluxes. At a cooling water temperature of 35 °C, an inlet air concentration of 20% (by mole) resulted in a 61% reduction in mass absorption flux. [Copyright &y& Elsevier]

Abstract: In air-cooled water–LiBr absorption chillers the working conditions in the absorber and condenser are shifted to higher temperatures and concentrations, thereby increasing the risk of crystallisation. To develop this technology, two main problems are to be addressed: the availability of new salt mixtures with wider range of solubility than water–LiBr, and advanced absorber configurations that enable to carry out simultaneously an appropriate absorption process and an effective air-cooling. One way of improving the solubility of LiBr aqueous solutions is to add other salts to create multicomponent salt solutions. The aqueous solution of the quaternary salt system (LiBr+LiI+LiNO3 +LiCl) presents favourable properties required for air-cooled absorption systems: less corrosive and crystallisation temperature about 35 K lower than that of water–LiBr. This paper presents an experimental study on the absorption of water vapour over a wavy laminar falling film of an aqueous solution of (LiBr+LiI+LiNO3 +LiCl) on the inner wall of a water-cooled smooth vertical tube. Cooling water temperatures in the range 30–45 °C were selected to simulate air-cooling thermal conditions. The results are compared with those obtained in the same experimental set-up with water–LiBr solutions. The control variables for the experimental study were: absorber pressure, solution Reynolds number, solution concentration and cooling water temperature. The parameters considered to assess the absorber performance were: absorber thermal load, mass absorption flux, degree of subcooling of the solution leaving the absorber, and the falling film heat transfer coefficient. The higher solubility of the multicomponent salt solution makes possible the operation of the absorber at higher salt concentration than with the conventional working fluid water–LiBr. The absorption fluxes achieved with water–(LiBr+LiI+LiNO3 +LiCl) at a concentration of 64.2 wt% are around 60 % higher than those of water–LiBr at a concentration of 57.9 wt%. [Copyright &y& Elsevier]