|
Post by Keith Rhodes on Oct 31, 2014 12:30:46 GMT
Opinion varied on where exactly the low level alarm should kick in.
Some opinion was somewhere above the residual sprinkler requirement -to alarm when domestic use is unusually high and infill is not satisfying the domestic demand. This however might bring about unwanted false alarms and be an irritant to occupiers.
Other opinion was the location of the low level alarm should be at the position where the most favorable demand volume within the tank is reached so that the alarm warns of inadequate water supply for the suppression system. This is unlikely to give out unwanted false alarm but still confirms that the infill is not fulfilling the (unusually high) domestic demand or has been isolated.
Noting that the position indicated in Fig 1 is below the top of the "effective capacity" it might be concluded that in a shared tank the domestic stored supply would all be above the level of item 1.
|
|
|
Post by Keith Rhodes on Dec 9, 2014 13:40:54 GMT
We are just working on a quite large shared tank and pump site. The pump set the contractors are installing is going to over deliver significantly. So we have worked out that the tank needs to store useable 6000 L for our 30 min duration (including over delivery), 2500 litres for the domestic demand over a 30 min duration at which level the low level warning is to be sited AND have an infill capability greater than 2500 L over 30 mins or additional useable stored capacity to make good any shortfall of infill over that 30 min period. The logic of this is- that in the event of a fire AND simultaneous loss of infill the stored water supply could provide both peak demand and fire fighting water for the 30 min duration.
|
|
|
Post by Keith Rhodes on Jan 19, 2015 13:25:15 GMT
Another potential problem here; On systems which have a pump inverter the delivery increases with demand as pressure drops and kicks in more delivery, sometimes more pumps. So lets say we do a flow test on the landing at level 7 -the domestic demand happens to be low at the time as its mid morning. How do we know that the pump curve would meet max domestic demand simultaneous to max sprinkler design demand? So do we now have to put a max domestic demand flow on in the pump room as well as then doing the flow and pressure test at floor 7? This would mean employing 2 flow test rigs (or having a permanent flow meter on the main pump set/s).
|
|
|
Post by Keith Rhodes on Apr 30, 2015 13:02:32 GMT
At the BAFSA technical meeting of the 29th April, tank supplies were discussed and some interesting points were raised.
1. many BAFSA people attending did not realize that a water draw off for domestic demand on a shared supply should be taken at the bottom of the tank, not above the full holding capacity for the sprinkler most favourable supply. after discussion it was agreed that the risk of stagnant water and WRAS requirements to prevent this outweighed any option to have a higher level domestic draw off.This point is confirmed in 5.8.4.4 note 1 and item b).
2. there was much concern about the position of the low level alarm and response to its activation. all agreed the position should be at the high water mark of the most favourable demand. But- clause 5.8.4.4 note 4 tells us that a PDV should shut off upon sprinkler activation- but what if the water supply was already too low and the low level alarm was sounding but ignored. so the consensus was that this low level alarm should activate the PDV and shut off the domestic demand.
|
|