In a PPS project under the flag of "de topsector Tuinbouw & Uitgangsmateriaal", Wageningen University & Research, the supply industry, LTO Glaskracht Nederland and NEN have developed new NEN standards.
These standards are for determining light transmission and scattering of greenhouse covering materials and screens and also for a sampling procedure for checking the transmittance of glass delivered to the client. Since the introduction of diffuse glass the previous standards were no longer appropriate and no standard was available for horticultural screens and seasonal coatings.
The new NEN2675 describes, next to the PAR transmittance, also transmittance for Ultraviolet (UV), near-infrared (NIR) as well as the solar factor. For light scattering a new term is introduced: the Hortiscatter. This is much more appropriate for greenhouse glass and has to replace the Haze measurement which comes original from the plastics industry.
Also the sampling procedure (NEN2674) has been revised thoroughly. The previous standard requires measuring according to the previous NEN2675 (only applies for clear glass) which makes it practically unusable. Likewise, the old sampling procedure requires a large number of samples, even at small batches. For this reason the standard was used barely.
At current greenhouse construction sites batches are even larger and would require even more samples. In the revised sampling procedure a limited amount of panes are selected by the supplier as well as the client and stored properly. In a later stage these could be measured according to the new standard. Currently the consortium agrees about both revised standards. NEN2675 is expected to take effect in the beginning of 2018, followed by NEN2674 a few months later.
An important condition for a successful introduction is the availability of proper measurement equipment. For this Wageningen University & Research is working together with a commercial company.