Glossary · Snow and wind
Operating conditions factor Ce
The snow load factor for clearing and melting; without data on how the roof is operated C_e = 1 (cl. 8.9).
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Definition
Ce is part of the factor C = μ · Ce · Calt in formula (8.4) of DBN V.1.2-2:2006. Under clause 8.9 it accounts for how operation affects snow build-up on a roof — clearing, melting and so on — and is set by the design brief.
The norm names one specific reduction: uninsulated roofs of workshops with high heat release, a slope over 3 % and proper meltwater drainage take Ce = 0.8. Without data on how the roof is operated, Ce may be taken as one.
Can C_e be reduced for panels?
Snow often slides off module glass, and owners sometimes clear the array by hand. But no clause of the DBN ties that to a number, and clearing cannot be guaranteed over the whole service life. For a solar plant it is sensible to keep Ce = 1 and let the tilt reduce the snow through the shape coefficient μ.
Example for Kyiv at 30°: Sm = 1.00 · 1,550 · 0.857 · 1 · 1 = 1,329 Pa. Taking Ce = 0.8 without grounds would give 1,063 Pa — 20 % less, and the rails or trusses could fall short in exactly the snowy winter.
How Solispec applies it
The Solispec engine always takes Ce = 1, as clause 8.9 allows when no operating data exist. There is no input for Ce; if a design brief sets another value, that is for the engineer checking the calculation.
Norms and clauses
- DBN V.1.2-2:2006, cl. 8.6, formula (8.4); cl. 8.9
Related terms
- Limit design snow load SmThe snow load on the horizontal projection used for strength checks: S_m = γ_fm · S₀ · C under DBN V.1.2-2:2006.
- Snow shape coefficient μThe conversion from ground snow to roof snow: μ = 1 up to 25°, 0 from 60°, linear in between (DBN V.1.2-2:2006, Annex Zh, scheme 1).
- Altitude factor CaltThe correction for altitude: 1.4H + 0.3 for snow from 0.5 km, 2H for wind above 0.5 km, otherwise 1 (DBN V.1.2-2:2006).
- Characteristic snow load S₀The weight of snow cover per 1 m² of ground exceeded on average once in 50 years; under DBN V.1.2-2:2006 Kyiv has 1,550 Pa.
- DBN V.1.2-2:2006 “Loads and actions”: what matters for a solar plantNorms explained
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.