SprinklerDesigner2
Mechanical
In 45 years I've never used one but if I understand what they are correctly then this could be my first time.
Storage building exceeds 500,000 sq ft so it isn't a small project.
ESFR system using K16.8 heads discharging at 52 psi so the total amount of water I need, with hose streams, is 1,710 gpm.
City water supply isn't the greatest with 80 psi static, 34 psi residual flowing 2,100 gpm. In this jurisdiction RPZ backflow is required and I must maintain 20 psi residual with the pump flowing 150% at the fire pump suction or downstream the backflow. Using the Ames Maxim Series M500 it appears I will have 7 psi loss through the backflow and if we add to that the loss through the suction line I will end up with around 25 psi at 1,875 gpm at the pump suction flange.
I can do this with a standard 1,250 gpm @ 80 psi fire pump which, and I did examine the curves, should leave me with a churn of under 175 psi but the available pressure at 1,750 gpm is about 100 psi.
I can make this happen but all my cross mains need to be 6" and with 6,000 feet of 6" schedule 10 that ain't cheap no more. Last price I got I have nearly $80,000 in 6" pipe alone which isn't counting the 7.5% sales tax With pipe and fittings I figure I can save over $60,000 in total material cost if I can get a pump that will give me 140 to 150 psi discharge @ 1,710 gpm.
Will a variable speed pump do the job for me? I know they cost more, a lot more, but I already have $33,000 figured in the cost of a 1,250 gpm @ 80 psi pump. Even if the the variable speed pump boosts the price by $40,000 (which I doubt it is that much) the cost savings would still be substantial not counting the savings on labor running 4" instead of 6".
Am I correct in thinking a variable speed pump has a larger motor but the controller controls the motors rpm which would keep the total discharge pressure around 160 psi regardless of how much water I am using?
What am I missing or misunderstanding?
Storage building exceeds 500,000 sq ft so it isn't a small project.
ESFR system using K16.8 heads discharging at 52 psi so the total amount of water I need, with hose streams, is 1,710 gpm.
City water supply isn't the greatest with 80 psi static, 34 psi residual flowing 2,100 gpm. In this jurisdiction RPZ backflow is required and I must maintain 20 psi residual with the pump flowing 150% at the fire pump suction or downstream the backflow. Using the Ames Maxim Series M500 it appears I will have 7 psi loss through the backflow and if we add to that the loss through the suction line I will end up with around 25 psi at 1,875 gpm at the pump suction flange.
I can do this with a standard 1,250 gpm @ 80 psi fire pump which, and I did examine the curves, should leave me with a churn of under 175 psi but the available pressure at 1,750 gpm is about 100 psi.
I can make this happen but all my cross mains need to be 6" and with 6,000 feet of 6" schedule 10 that ain't cheap no more. Last price I got I have nearly $80,000 in 6" pipe alone which isn't counting the 7.5% sales tax With pipe and fittings I figure I can save over $60,000 in total material cost if I can get a pump that will give me 140 to 150 psi discharge @ 1,710 gpm.
Will a variable speed pump do the job for me? I know they cost more, a lot more, but I already have $33,000 figured in the cost of a 1,250 gpm @ 80 psi pump. Even if the the variable speed pump boosts the price by $40,000 (which I doubt it is that much) the cost savings would still be substantial not counting the savings on labor running 4" instead of 6".
Am I correct in thinking a variable speed pump has a larger motor but the controller controls the motors rpm which would keep the total discharge pressure around 160 psi regardless of how much water I am using?
What am I missing or misunderstanding?
