A Calibration of the Solar Load Ratio Method to Determine the Heat Gain in PV-Trombe Walls

The Trombe wall is a passive system used in buildings that indirectly transfers thermal energy to the adjacent environment by radiation and convection, and directly by the thermo-circulation that arises in the air cavity delimited between a transparent and an absorbing surface. Nevertheless, the latter is painted black to increase the energy gains, but this produces a negative visual impact and promotes the overheating risk in summer. To mitigate these aspects, a hybrid Trombe wall equipped with PV panels can be employed. The PV installation results in a more pleasing wall appearance and the overheating risk reduces because part of the absorbed solar radiation is transformed into electricity. To determine the actual performance of a such system, transient simulation tools are required to consider properly the wall thermal storage features, variation of the optical properties, air thermo-circulation, and PV power production. Alternatively, regarding the traditional Trombe wall, the literature provides a simplified empirical method based on the dimensionless parameter solar load ratio (SLR) that allows for preliminary evaluations and design. In this paper, the SLR method was calibrated to determine the monthly auxiliary energy to be supplied in buildings equipped with PV-Trombe walls in heating applications. The SLR method was tuned by a multiple linear regression by data provided by TRNSYS simulation that allowed to obtain the energy performances in actual conditions of PV-Trombe walls installed on the same building but located in different localities. The comparison between the TRNSYS results and the calibrated SLR method determined average errors ranging between 0.7% and 1.4%, demonstrating the validity of the proposed methodology.

Contrastive Analysis on the Ventilation Performance of a Combined Solar Chimney

A combined solar chimney is proposed in this paper that integrates an inclined-roof solar chimney with a traditional Trombe wall. The ventilation performance of the combined solar chimney is analyzed numerically and then compared with the Trombe wall and the inclined-roof solar chimney. The feasibility of different operation modes and the ventilation effect under different environment conditions are also discussed. The results show that when the ambient temperature ranges from 298 to 303 K in the summer, a natural ventilation mode is appropriate. Otherwise, an anti-overheating mode is recommended. When the ambient temperature is lower than 273 K in the winter, a space heating mode has a better heating effect. A preheating mode can be employed to improve the indoor air quality when the ambient temperature is higher than 278 K. The simulation results indicates that the ventilation effect of the combined solar chimney is better than that of the Trombe wall and the inclined-roof solar chimney, and the problem of overheating can be avoided. The study provides guidance for the optimal operation of a combined solar chimney.

Analytical model for the simulation of Trombe wall operation with heat storage

Passive solar systems, such as the Trombe wall, are cost-effective ways to reduce the energy consumption of buildings for heating, cooling, and ventilation. The operation of these systems can be simulated either with Building Energy Simulation Tools—BES like TRNSYS, EnergyPlus, etc either with Computational Fluid Dynamics—CFD. In both cases, the purchase of special software and/or special programming skills are required. In parallel analytical calculating tools are being developed, which also require some programming to solve an implicit system of non-linear equations but with fewer software requirements. The majority of analytical models concerns energy balance models for steady-state conditions with the result that heat storage is not taken into account, which in the case of a Trombe wall has a significant effect on the developed transport phenomena. In the present work, an analytical energy balance implicit model was developed for the simulation of the transient operation of a Trombe wall taking into account the heat storage. Using this model, the operation of a Trombe wall for 7 typical days of the year was simulated. The results are presented in terms of the daily evolution of the temperature with which the air enters the room served by the passive system, of the temperature of the Trombe wall surface adjacent to the served room, and of the airflow rate inside the air gap. These results are compared with the results that a system without heat storage would give. Both systems are assessed based on annual performance as calculated by a quasi-steady explicit model. The developed model can be used to calculate the operation of a Trombe wall as well as to supply explicit quasi-steady models with values for airflow rate inside the air gap for Trombe wall operation without mechanical ventilation. Feeding these values to a quasi-steady model developed by authors it was found that the increase of storage wall heat capacity, either changing the storage wall material, either using phase change materials, can offer better utilization of Trombe wall heat gains up to 35% yearly. Background: The present work aims to develop an analytical model for simulating the operation of a Trombe wall in a transient state taking into account the heat storage in the wall. Methods: A closed system of equations is developed, based on 5 energy balances and a series of assumptions and auxiliary relations, to calculate the operation of a wall Trombe with heat storage with an hourly time step. Results: Characteristics Trombe wall temperatures and mass flow rate through the air gap are calculated for typical days of 7 winter months. These are used for the calculation of utilizable heat gains from Trombe wall. Conclusions: The model that does not take into account heat storage predicts higher temperatures and air mass flow rate in the gap than the present model by 10%. However heat storage increase the utilizable heat gains by 35% compared with a system without heat storage.

Trombe Walls – Characteristic, Overview and Simple Case Study for Different Climate Conditions

Currently, when we spend a significant part of the day indoors, paying attention to indoor air quality and thermal comfort rise to prominence. Sometimes, improving these issues could be really simple and possible by using passive solar systems like Trombe walls. Because the implementation of solar walls is still problematic due to numerous barriers connecting with a system management or effectiveness in summer or winter period, many of researchers try to find the solutions, which could optimize them. This paper characterizes the main issues of Trombe walls, presents the current state of research on solar walls and provides a simple simulation of a building with a Trombe wall performed in TRNSYS software, for 3 variants of the system and 4 locations with different climatic conditions. It was estimated that system with Trombe wall and control strategies allows the building to maintain thermal comfort for more than 20% of the year, but effectiveness of Trombe walls depends largely on the climatic conditions and they should be considered only as an auxiliary support for HVAC systems.