Survey and evaluation of heating technologies for worldwide agricultural greenhouse applications

An overview of innovations introduced in the field of flat solar thermal collectors is presented using information from different literature sources. Despite the large number of publications available about this specific issue, this review is focused on the last ten years period, to underline the actual trend of the scientific and technologic world so far. Bearing in mind this choice, in this study a selection of the most valuable papers has been done, considering different points of view and aspects. Even if this work cannot be considered exhaustive of the complete literature about this field, it can be taken into account as a quick reference to have an overview about new materials, geometries, heat transfer fluids etc., available and tested in the last decade.

Innovation in flat solar thermal collectors: A review of the last ten years experimental results

Energy saving techniques for reducing the heating cost of conventional greenhouses

The evacuated tube solar collector assisted heat pump for heating greenhouses

Conversion of solar energy via thermal route is highly efficient, more environmental friendly and economically viable. Integrated Collector Storage Solar Water Heaters (ICSSWHs) convert the solar radiation directly into heat at an appreciable conversion rate and in many cases that happen under concentrated form. These systems are compact, aesthetically attractive and reasonable in construction. They have the potential to reduce environmental impact up to 40% and also have high collection efficiency factor. Despite many advantages, ICS solar water heaters suffer from high thermal losses in the night/overcast sky conditions. Performance of ICSSWH systems is influenced by various parameters such as reflector and absorber types, energy collection and storage arrangements and design parameters of the systems. In this article, various concentrating and non-concentrating ICSSWHs, systems with PCM (Phase Change Material) and heat retention strategies are reviewed. Recent development in the ICSSWHs indicates the potential of reliability of these systems for domestic hot water application at lower cost. The concentrating type ICSSWHs show better collection efficiency at reduced cost, but suffer high night time thermal losses. Further research is needed, especially in CPC-ICSSWHs, for minimizing night time thermal losses.

Recent developments in integrated collector storage (ICS) solar water heaters: A review

Performance of a solar storage collector

The use of solar energy for greenhouse heating has gained an increasing acceptance during the last years. Active solar systems applied to greenhouses can supply a significant part of the heating requirements. However, there are some problems related to the cost of the heat collection unit and the heat storage methods. In this context several techniques were born. The most famous of these techniques is the seasonal storage of thermal heat in soil. The objective of our work is to study a system of thermal energy storage conceived in our Laboratory (LEPT, Tunisia). The system is composed of a vat having a large dimension (6 m 3 ) filled with fin sand. Inside the vat three batteries of capillary exchangers are buried at three different levels. To heat the accumulator soil, we use a solar collector with a surface equal to 6 m 2 . In order to size the heat accumulating system, a numerical study is started. It allows evaluating the soil temperature as well as the energy cumulated inside the accumulator during the charging and the discharging period.

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Thermal Performance of a Solar Heat Storage Accumulator Used For Greenhouses Conditioning

Comparison between a solar system and a fuel boiler for greenhouse air-conditioning

The problem of temperature inversion is one of solar origin principal problems about which the cultures under shelters complain. Indeed, for the winter period, the temperature under greenhouse is very low at night and it is rather high during the day in summer. Consequently, the heating of the greenhouses is essential. In this work, we studied the advisability of using two exchangers coupled between them to manage thermal energy in a greenhouse. The first system is a battery of plaits with capillary tubes buried under ground with a depth of 70 cm. The second is an air exchanger based on plastic tubes black known as agrotherms suspended with two meters and half height. The hot water, which circulates in the exchangers, is provided by the hot-water tank of the electrosolar power station of the Center of Energy Researches and Technologies (CRTEn) from Tunisia.

Mejdi Hazami

Papers

Performance of a solar storage collector

Thermal Performance of a Solar Heat Storage Accumulator Used For Greenhouses Conditioning

Comparison between a solar system and a fuel boiler for greenhouse air-conditioning

Thermal Energy Storage in the Ground of a Greenhouse by the Polypropylene Capillary Heat Exchanger

Heat transfer characteristics of a capillary heat exchanger based air conditioning cupboard