scholarly journals Modelling and testing a passive night-sky radiation system

2017 ◽  
Vol 28 (1) ◽  
pp. 76 ◽  
Author(s):  
G.D. Joubert ◽  
R.T. Dobson
Keyword(s):  
Storage Tank ◽  
Cold Water ◽  
Water Storage ◽  
Heating System ◽  
Hot Water ◽  
Theoretical Simulation ◽  
Water Storage Tank ◽  
Heating And Cooling ◽  
Night Sky ◽  
Radiation Cooling

The as-built and tested passive night-sky radiation cooling/heating system considered in this investigation consists of a radiation panel, a cold water storage tank, a hot water storage tank, a room and the interconnecting pipework. The stored cold water can be used to cool a room during the day, particularly in summer. A theoretical time-dependent thermal performance model was also developed and compared with the experimental results and it is shown that the theoretical simulation model captures the experimental system performance to within a reasonable degree of accuracy. A natural circulation experimental set-up was constructed and subsequently used to show that under local (Stellenbosch, South Africa) conditions the typical heat-removal rate from the water in the tank is 55 W/m2 of radiating panel during the night; during the day the water in the hot water-storage tank was heated from 24 °C to 62 °C at a rate of 96 W/m2. The system was also able to cool the room at a rate of 120 W/m3. The results thus confirmed that it is entirely plausible to design an entirely passive system, that is, without the use of any moving mechanical equipment such as pumps and active controls, for both room-cooling and water-heating. It is thus concluded that a passive night-sky radiation cooling/heating system is a viable energy-saving option and that the theoretical simulation, as presented, can be used with confidence as an energy-saving system design and evaluation tool. Keywords: passive cooling and heating, buoyancy-driven fluid flow, theoretical simulation, experimental verification Highlights:Passively driven renewable energy heating and cooling systems are considered.Time-dependent mathematical simulation model is presented.Experimental buoyancy-driven heating and cooling system built and tested.Experimental results demonstrate the applicability of the theoretical simulation model.Saving and evaluation design tool.

Thermal modelling of a night sky radiation cooling system

2005 ◽  
Vol 16 (2) ◽  
pp. 20-31 ◽  
Author(s):  
RT Dobson
Keyword(s):  
Storage Tank ◽  
Cooling System ◽  
Water Storage ◽  
Design Tool ◽  
Thermal Modelling ◽  
Water Storage Tank ◽  
System Components ◽  
Mathematical Equations ◽  
Night Sky ◽  
Radiation Cooling

The thermal modelling of a night sky radiation cooling system suitable for a room situated in the Namib Desert at Gobabeb, Namibia, is considered in this paper. The system consists of the following components: radiator panels, a single water storage tank, room air-to-water natural convection heat exchangers or convectors, circulating pump(s), interconnecting pipe work and temperature sensors and controls. The mathematical equations describing the thermal behaviour of the various system components are given. These equations are solved using an Excel spreadsheet and the hourly panel surface, water storage tank and room temperatures are calculated for a given internally generated heat load and weather pattern. Given the maximum allowable room temperature, the sizes of the system components may be calculated. The results obtained compared favourably with values reported in the literature. It is thus concluded that the thermal model presented can be used with confidence as a design tool for the sizing of a night sky radiation cooling system.

THE EFFECT OF UPPER-HEATING SYSTEM IN SOLAR WATER STORAGE TANK

2014 ◽  
Vol 22 (04) ◽  
pp. 1450027 ◽  
Author(s):  
HYO SEOK SON ◽  
JAE-WOOK KWON ◽  
SEONG HOON LEE ◽  
CHUL KIM ◽  
HIKI HONG
Keyword(s):  
Storage Tank ◽  
Thermal Stratification ◽  
Collection Efficiency ◽  
Water Storage ◽  
Side Wall ◽  
Heating System ◽  
Substantial Improvement ◽  
Solar Heating ◽  
Hot Water ◽  
Water Storage Tank

Thermal stratification in the water storage tank of solar heating system is essential to increase the collection efficiency. We previously investigated the stratification performance of side-heating system, where the hot water returning from the collector heats up the side wall of storage tank. Subsequently, we studied an evolved heating system for further improvement, where we added an upper-heating to the side-heating. Here we thoroughly examine the stratification performance of the evolved heating system using TRNSYS-based simulation. As the essential result, contrary to expectation, evolved system does not show substantial improvement of collection efficiency compared to side-heating. However, we confirm that evolved system excels in the useful energy.

Evaluation of Thermal Stratification Inside a New Model of Spherical Water Storage Tank Using a Computational Fluid Dynamics 6 Degrees of Freedom Solver

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Mohamed Taher Bouzaher ◽  
Belghar Noureddine ◽  
Charaf-Eddine Bensaci ◽  
Nora Bouchahm ◽  
Belhi Guerira
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Flow Rate ◽  
Storage Tank ◽  
Cold Water ◽  
Fluid Dynamic ◽  
Water Storage ◽  
Hot Water ◽  
Computational Domain ◽  
Water Storage Tank

Abstract In this work, a computational analysis of a spherical solar hot water storage tank during the discharging process is carried out by using the commercial code ansys-fluent.15. The study investigates a new type of spherical heat storage tank. A hinged baffle is fixed at the tank vertical axis to increase the discharge flow rate without a thermocline layer. The dynamic mesh LAYERING technique is used to update the computational domain during the movement of the hinged baffle. The passive pitching of the submerged baffle is due to the fluid-dynamic loads. This model limits the mixture between hot and cold water regardless of the inlet flow rate. A comparative study between tanks with typical diffusers and the hinged baffle model is considered. The comparison of the computational fluid dynamics results with available experimental data showed a good agreement. Examinations of the temperature contours indicate that for the typical models, the interaction between the incoming cold water and the stored hot water gives rise to a thick thermocline layer where its temperature and thickness are related to the intensity of the mixing process. The suggested model shows high stratification efficiency along the discharging process.

scholarly journals Minimum Number of Experimental Data for the Thermal Characterization of a Hot Water Storage Tank

Energies ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4741
Author(s):  
María Gasque ◽  
Federico Ibáñez ◽  
Pablo González-Altozano
Keyword(s):  
Experimental Data ◽  
Water Temperature ◽  
Temperature Profile ◽  
Storage Tank ◽  
Water Storage ◽  
Hot Water ◽  
Experimental Temperature ◽  
Inlet Temperature ◽  
Water Storage Tank ◽  
Minimum Number

This paper demonstrates that it is possible to characterize the water temperature profile and its temporal trend in a hot water storage tank during the thermal charge process, using a minimum number of thermocouples (TC), with minor differences compared to experimental data. Four experimental tests (two types of inlet and two water flow rates) were conducted in a 950 L capacity tank. For each experimental test (with 12 TC), four models were developed using a decreasing number of TC (7, 4, 3 and 2, respectively). The results of the estimation of water temperature obtained with each of the four models were compared with those of a fifth model performed with 12 TC. All models were tested for constant inlet temperature. Very acceptable results were achieved (RMSE between 0.2065 °C and 0.8706 °C in models with 3 TC). The models were also useful to estimate the water temperature profile and the evolution of thermocline thickness even with only 3 TC (RMSE between 0.00247 °C and 0.00292 °C). A comparison with a CFD model was carried out to complete the study with very small differences between both approaches when applied to the estimation of the instantaneous temperature profile. The proposed methodology has proven to be very effective in estimating several of the temperature-based indices commonly employed to evaluate thermal stratification in water storage tanks, with only two or three experimental temperature data measurements. It can also be used as a complementary tool to other techniques such as the validation of numerical simulations or in cases where only a few experimental temperature values are available.

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