FM Engineering Bulletin regarding CMSA vs. LD sprinklers?

[Bagge]

It has come to my information that FM has allowed that the K16.8 CMSA sprinkler now can be used as a protection option whereever the K11.2 CMSA sprinkler (Large Drop) can be used.
The same installation and design guidelines apply to both sprinklers, except for the minimum required operation sprinkler pressure. They have announced a pressure conversion table you should use which I have attached.

I have used the different conversions in the table into a calculation. It turns out that there is a big difference in the water demand, if you choose an Ultra K17 (Tyco)sprinkler instead of a Large Drop Sprinkler – but only in the lower commodity though (see calculations below). If you have to use a larger minimum pressure, it seems that the system with the Ultra K17 demands the same amount of water or even less than with the Large Drop sprinkler.

I am now wondering why this is – maybe a mistake in the table or is there a rational explanation? Possibly there is no explanation… but the reason I ask you guys, is that I could use the lower amount of water, if you know what I mean.

Water amount calculation (with pressure conversion from the table):

1.7 bar:
Large Drop:
Q = 160 * (SR)1.7 = 208 l/min
Ultra K17:
Q = 242 * (SR)1.0 = 242 l/min

DIFFERENCE: 34

3.5 bar:
Large Drop:
Q = 160 * (SR)3.5 = 299 l/min
Ultra K17:
Q = 242 * (SR)1.5 = 296 l/min

Difference: (-) 3

3.8 bar:
Large Drop:
Q = 160 * (SR)3.8 = 311 l/min
Ultra K17:
Q = 242 * (SR)1.5 = 296 l/min
Difference: (-) 15

5.2 bar:
Large Drop:
Q = 160 * (SR)5.2 = 365 l/min
Ultra K17:
Q = 242 * (SR)2.4 = 375 l/min
Difference: (+) 10