I. Seginer, Louis D. Albright
In search for inexpensive heat exchangers for waste-heat utilization in greenhouses, water-filled mats to be placed on top of greenhouse benches were suggested. Such mats were monitored in situ, while exchanging heat with their surroundings through convection of air, conduction to pots, thermal-radiation, and absorption of solar energy. The significant routes of heat transfer were found to be convection to air, solar radiation absorption and conduction to pots, in that order. A pair of simple design formulas evolved:
  • for mature plant canopy Q = 0.19 S + 8 (Ta-Tm)
  • for seedlings Q = 0.42 S + 10 (Ta-Tm)

where Q is the sink (or source) of heat in the mat in W per m length of bench, S is solar radiation above the canopy in Wm-2, Ta is greenhouse air temperature and Tm is mat temperature, both in K.

The absorption of solar radiation was twice as large without canopy as with canopy. The canopy reduced the convective heat transfer coefficient by 20%.

The high transfer coefficient between mat and pots limits the range of Tm, unless precautions are taken.

Seginer, I. and Albright, Louis D. (1981). WATER MAT AS A HEAT EXCHANGER FOR GREENHOUSES. Acta Hortic. 115, 279-292
DOI: 10.17660/ActaHortic.1981.115.30

Acta Horticulturae