Greenhouse heating by solar air heaters on the roof

A solar air heater (SAH) system was investigated experimentally for heating an innovative greenhouse in Baghdad, Iraq (33.3 °N, 44.4 °E). The innovative greenhouse combined a traditional greenhouse and a bank of solar air heaters on the roof as one structure. This arrangement did not affect the required solar radiation inside the greenhouse for winter heating when compared with a conventional greenhouse. An energy balance method was used to calculate the heating load. This differs from the previous standard method which does not include soil heat storage. The soil surface heat gain was considered in the present work and was found to contribute 13-19% of the heating load required. Six solar air heaters with a single glass cover and a 'V' corrugated absorber plate connected in parallel were mounted on the greenhouse roof. Tests were carried out in the winter season of 2012. The mass flux of air through the collectors was varied from 0.006 to 0.012 kg/s.m2. An air mass flux of 0.012 kg/s m2 was found to provide about 84% of the daily heat demand to keep the greenhouse inside air temperature at 18 °C. The summation of a would be stored energy from the SAHs and a stored free solar heat inside the greenhouse can cover all the daily heating demand with an excess of approximately 46%.