Choice Criteria of Adsorbents for Heat Energy Converters in Ventilation Systems

Abstract

The criteria of adsorbent selection for adsorption transformers of thermal energy in ventilation systems are considered. The main characteristics of adsorbents that affected the structural parameters of the adsorption module are revealed. The method of determining the mass of the adsorbent and the volume of the adsorption unit in ventilation systems has been developed. The main factor affecting the volume of adsorbent is confirmed to be maximal adsorption. The advantages of ‘salt in the porous silica gel matrix’ composites are compared with traditional silica gels. On the example of an adsorption regenerator of low-potential heat and moisture, the greater effectiveness of the composites "silica gel-sodium sulphate" is shown in comparison with the composite 'silica gel - sodium acetate'. According to the experimental data on the operation of the adsorption regenerator of heat and moisture on the basis of the composite 'silica gel – CH3COONa', the adequacy of the proposed algorithm for determining the temperature efficiency factor has been confirmed. 
 Suggested algorithm includes the calculation of the air volume passed through the layer of heat-storage material, water concentration in the air at the exit from the heat accumulator, adsorption, heat of adsorption, the final cold air temperature, air temperature after mixing cold air from the street and the warm air in the room at the inlet, the calculation of the concentration of water in the flow at the exit from the heat regenerator, the adsorption and heat of adsorption, the final temperature of the warm air, the air temperature after mixing the cold air from the street and the warm air from the room during the discharge, determination of the temperature efficiency factor, total adsorption and time to achieve the maximal adsorption. The efficiency of the processes of operating adsorption regenerators based on composites 'silica gel - sodium sulphate' and 'silica gel-sodium acetate' in the conditions of the typical ventilation system of housing premises was compared. 
 The parameters that correspond to the maximum value of the temperature efficiency factors: the humid air velocity is about 0.22 - 0.32 m/s and the time of switching of the flows up to 5 minutes. The influence of meteorological conditions on the efficiency of the adsorption regenerator has been confirmed. The higher efficiency of adsorption regenerators based on 'silica gel - sodium sulphate' composites is explained, which is explained by higher values of maximal adsorption, which results in increasing the heat of adsorption. The results of the research can be used for the selection of adsorbents for energy-efficient heat energy converters in ventilation systems for residential and warehouse premises.

Performance of adsorptive heat-moisture regenerator

“…The heat regeneration factor i.e. temperature efficiency factor is determined by the formula [13,14]:…”

“…According to algorithm described in [14], temperatures of inflowing and outflowing air are determined as a temperatures after mixing the cold supplied air and the warm internal air during inflow and cold external air and warm exhausted air from the room. Final temparatures of inflowed and outflowed air are described by thermal balance equations.…”

“…adsorption [11,12]. Mathematic model of performance of adsorptive heat-moisture regenerator suggested in [13,14] allows evaluating only temperature efficiency factor. Nevertheless, the energy performance of the heat-moisture regenerators is characterized not only by temperature efficiency factor, but humidity efficiency factor.…”

“…Experimental. The design of the adsorptive regeneration unit is presented in [13,14]. Length of laboratory prototype of heat regenerator is 0.6 m [15].…”

“…The device is operated in two-phase mode which involves alternating modes 'inflow' and 'outflow' [13,14]. When inflowed, ambient air is intaken by inner ventilator and got through the adsorbent layer into premise, air flow being heated and water excess being adsorbed.…”