Schlussbericht
(Englisch)
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Energy storage In winter time the heat energy and hot water need can be supplied by a saisonal stor-age tank. For this application sorbate storage tanks can be used. High energy density The alkali alumino-silicate = zeolite are used in a lot of different technological areas. Zeolites are promising natural materials with a high potential of heat energy storage capacity. In literature, it is reported that the energy density of sorption energy storage tanks (Silica gel 230 kWh/m3) is a factor of up to four higher than in hot water tanks (57 kWh/m3). We want to apply these materials in solar systems for heat storage and extend our research activities to transfer the know how into the education of engineers at University of applied Science of Rapper-swil HSR. Zeolite 13X The energy is stored in the two separate natural materials - water and zeolite (sor-bate). The high heat of adsorption of maximum 4200 kJ/kg water is released by adsorbing the polar molecule of water on zeolite which acts on the basis of it's polarisability. Zeolites with a high ratio of Al/Si are needed and the molecular sieves 3A, 4A and 13X can be applied for this assignment. For regeneration of the saturated zeolite at elevated temperature solar energy can be used. According to literature the zeolites 4A and 13X are most applied in heating or cooling systems. For the first experi-ments we will apply the sorbate 13X in our experimental setup. Real energy density For dry zeolite, values for the theoretical density of energy of 177 kWh/m3 are reached. Compared to the energy density in a hot water storage tank, this value is higher by a factor of 3 to 4, depending on the temperature difference in the water tank. In an open system with zeolite 13X ZAE-Bayern measured a energy density of 120 to 130 kWh/m3. System type Sorbate storage tanks are designed in open and closed system configurations. The closed system operates in the pressure range of water vapour p(T) of several mbar. The sorbate mod-ule contains a heat exchanger, which is physically in contact with the granular sorbate material. A water reservoir tank is connected to the storage tank by a pipe. Out of this tank water is evaporated through the connecting pipe into the sorbate tank. The water vapour is adsorbed on the sorbate which is heated up because of the release of the heat of adsorption. The heat of evaporation is supplied by a heating device into the water reservoir tank (solar in a technological realisation, electrical in a labora-tory design). In case of drying, heat is fed into the zeolite module by the built in heat exchanger. The saturated sorbate is heated up and the water vapour is released. In the heat exchanger following the zeolite module the water vapour is condensed and the liquid water is fed back into the water tank. In the open configuration, air is the medium for transporting heat and water. A ventilator transports the medium through the system. The operating pressure is in the range of 1 bar. Water vapour is ad-sorbed by the Zeolite out of the humid air and both air and zeolite are heated up. The hot and dry air is transported through a heat exchanger and is cooled down. After leaving this heat exchanger the venti-lator transports the air through the moisturizer back into the sorbate/zeolite module and a new process cycle starts. Price per kWh In a saisonal sorbate storage tank, for a one family house, a extra heat energy of ap-proximately 2000 kWh is needed, which can not be supplied by a solar hot water system. Approxi-mately 10 t of zeolite are needed. So, the estimated price per 1 kWh is in the range of CHF 4.- to 6.-, depending on the price of the zeolite and on the number of loading cycles. In a hot water storage tank 1 kWh has a slightly higher price. In case of several loading cycles in a sorbate tank the above men-tioned price is divided by the number of cycles. Optimum design According to literature for sorbate material zeolites are used for most applica-tions. This is contradictory under the view point of the heat density of the sorbate materials zeolite (120 – 130 kWh/m3) and silica gel (230 kWh/m3). For the design of a system, the coefficient of heat transfer and water transfer, which are the limiting parameters, have to be known. In the planed ex-perimental setup this factors can be measured depending on the sorbate material and the heat ex-changer (closed system) as well as on the distribution of the particle size of the sorbate.
Auftragnehmer/Contractant/Contraente/Contractor:
Hochschule Rapperswil HSR
Autorschaft/Auteurs/Autori/Authors:
Frei,Ueli
Gantenbein,Paul
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