Ecient utilization of energy in buildings and ponds Josef Tanny a, *, Meir Teitel b a Center for Technological Education Holon, P.O.B. 305, Holon 58102, Israel b Agricultural Engineering Institute, Agricultural Research Organization, Volcani Center, P.O.B. 6, Bet-Dagan 50250, Israel Received 21 January 1998 Abstract Thermal strati®cation is often established in heated buildings and ponds. In such cases, the temperature at the bottom is lower than that near the top, resulting in an inconvenient microclimate at the lower region. Thus, it is usually desired to further raise the temperature near the bottom. This can be done in two ways. The ®rst is by providing a surplus of heat without destroying the thermal strati®cation, and the second is by mixing mechanically the medium (while heating) to establish a uniform temperature distribution and hence, to raise the bottom temperature. The objective of this study is to calculate the energy required by each method in an attempt to determine the one which is more economical. A theoretical one-dimensional (1D) model is developed to calculate the energy required by each method and the ratio between them. The model considers enclosures with inclined or vertical side walls. For typical conditions in buildings and ponds, the ratio between the energies of mixing and surplus heating is very small, indicating that mixing is much more economical in raising the temperature of the lower region of the heated enclosure. For the case of inclined side walls, it is shown that the ratio between the energies required for mixing and heating increases with the inclination angle. # 1998 Elsevier Science Ltd. All rights reserved. Keywords: Energy saving; Strati®cation; Heating; Mixing Nomenclature A cross sectional area of the enclosure (m 2 ) c p speci®c heat at constant pressure (kJ kg 1 8C 1 ) E potential energy (kJ) Applied Thermal Engineering 18 (1998) 1111±1119 1359-4311/98/$19.00 # 1998 Elsevier Science Ltd. All rights reserved. PII: S1359-4311(98)00036-2 PERGAMON * Corresponding author.