5.5m between heads rule vs 25SQM max per head

With regard to distribution of the density it has to be recognized that complete even distribution is not going to be met.

Taking the commercial rules of a 4 x 3 max spacing grid some areas will get marginally more, others less but the heads are designed to deliver in theory at least the density over each metre.

Spacing does however need to be carefully considered to try to achieve an even distribution overall. This argument is further confused by wall wetting patterns and it can be said that with "over pressure" maybe too much wall wetting is achieved. counterbalance that argument with over delivery of density overall and a picture of some sort of pragmatic balance can be drawn.





So if each head is covering an area 5.5 long x 4.5 wide (nominally) you are just inside the 25 M2 rule per head. To meet the density you will need 100.98 LPM @2.04 mm/M2.

Using say VK457 heads you will need 64.4 LPM per head @0.83 bar to meet cat 1 or cat 1 a)a)this being 128.8 LPM and a little bit more for the more favorable head. That's quite a high demand and where you might consider using 6 x low flow heads such as VK488 where at a max spacing of 3 .7 x 3.7 you would need 30.3 LPM @0.49 bar. That's just 60.6 LPM and a little bit more again. The clear trade off is number of heads over water stored volume/ flow and pressure available off town mains.

there could be a counter argument that with low flow heads the area of operation is reduced from what perhaps was envisaged E.G. some 50 M2 capability for a 2 head operation might become only 27.38 M2 within a larger room



If you go to cat 2 on this room size you will need 138.6 LPM to meet the 2.8 mm density this can only be achieved by using 4 heads as to the 5.5 spacing VK457 heads only give 64.4 LPM- however- you could use manufacturers data and go to 6.1 spacing with 75.7 LPM @1,15 bar with 2 heads as this would give you the density- at some significant hydraulic cost though.



For a corridor there's no reason why you cannot use 5.5 max spacing's as the reduced widths will give you the density overall - again the density is going to be much higher on the wall sides near each head -counter argument might be the wall wetting bounces off the nearer walls onto the furthest coverage of that head. in all probability though a 4.9 spacing that keeps pressure down is more likely to be employed- or low flow heads as mark noted. 30 LPM over 3.7 metres is more economical on water that 49 LPM over 4.9 metres by some 20% - but are the extra heads worth it?

Bear in mind to always to use the "next area up" to cover the actual area using manufacturers proven data sheet so you know at 2.04 that under max area with responsible spacing = compliance. For 2.8 mm / 4 mm get your thinking caps on!