Regression models of transpiration (T) based on global radiation inside the greenhouse (G), with or without energy input from heating pipes (Eh) and/or vapor pressure deficit (VPD) were parameterized. Therefore, data on T, G, temperatures from air, canopy and heating pipes, and VPD from both a lysimeter experiment and from a cut rose grower were analyzed. Based on daily integrals, all T models showed good fits due to the dominant effect of global radiation G (solar + supplementary radiation) inside the greenhouse on T. Similar G-T relations on high-light and low-light days indicated identical effects of solar radiation and radiation from supplementary light on T. For both data sets, similar regression coefficients of 0.3 l/MJ were obtained with models including G and VPDair, G and Eh, or G and a constant intercept. Including the difference between saturated pressure at leaf temperature and air vapor pressure (VPDleaf-air) did not improve the regression models. G accounted for 74% of latent heat transfer. The contribution of heating underneath the canopy on T was investigated by switching off the heating on days during the winter period, and was on average 13% or 0.2 l/m².day for an extra energy input by heating pipes of 3 MJ/m².day. Therefore, the efficiency of sub-canopy heating was smaller than 0.07 l/MJ, less than 23% of the efficiency of global radiation.
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