- #1

saxman2u

- 19

- 1

Greetings,

Looking for the best way to calculate TDH for some rainwater catchment systems I am designing in Texas. Some homes we are installing these systems on have large footprints, between 6,000 to 8,000 sq feet. The large rainwater collection tanks we install range between 30,000 and 65,000 gallons and are 7 feet tall. The PVC pipe entering the top of the tank is around 8 feet high. Most soffits/fascia/gutter bottoms are around 8 feet high, so you can see that it is ideal to place a tank for a large home downhill when using 4" PVC pipe. The downspouts for the collection system are all made of PVC pipe, and are primed and glued all the way to the tank so that the system is sealed. The worst case scenario would be to install a tank for a large home and in a heavy downpour, more water backs up into or even our of the gutter rather than goes into the tank because of pipe friction loss. That is a hard repair/fix! I use a 4" rain rate/hr for my calculations to accommodate heavy steady rain but to also not "over design/size" the system for cost.

An example we could use would be 120 GPM that is being collect at the last downspout or closest downspout to the tank, downspout F. The farthest downspout from the tank is downspout A and it only collects 20 GPM from its section of roof area. If the closest downspout to the tank or downspout F is 100 ft from the tank, and the farthest downspout or downspout A is 500 ft from the tank, I get .81 TDH at downspout F and .55 TDH for downspout A.

The downspout that is farthest from the tank has the least amount of water in it but has to travel the farthest. As the conveyance pipes pick up downspouts, more water is flowing in the system. The last downspout (or closest downspout to the tank) has the most water moving past it or in it since it is a culmination of all the downspouts/roof area. My question is, when calculating TDH, what distance do I use? Should I use the distance and elbows from the tank to the tank's closest downspout to figure out how much head will be in the pipes? Or, should I use the distance from the tank to the farthest downspout? Also, what GPM should I use for the farthest downspout? I need to build in some buffer but I also want a CYA for my systems. I was just thinking of using the farthest downspout with max GPM and call it a day, but then again, my mind now wants to know what is actually happening in the pipes but I also want to design my systems appropriately and build tanks at an elevation that is reasonable accurate based on fluid hydraulics. I need some clear PVC pipe I guess!

Thanks!

-S

Looking for the best way to calculate TDH for some rainwater catchment systems I am designing in Texas. Some homes we are installing these systems on have large footprints, between 6,000 to 8,000 sq feet. The large rainwater collection tanks we install range between 30,000 and 65,000 gallons and are 7 feet tall. The PVC pipe entering the top of the tank is around 8 feet high. Most soffits/fascia/gutter bottoms are around 8 feet high, so you can see that it is ideal to place a tank for a large home downhill when using 4" PVC pipe. The downspouts for the collection system are all made of PVC pipe, and are primed and glued all the way to the tank so that the system is sealed. The worst case scenario would be to install a tank for a large home and in a heavy downpour, more water backs up into or even our of the gutter rather than goes into the tank because of pipe friction loss. That is a hard repair/fix! I use a 4" rain rate/hr for my calculations to accommodate heavy steady rain but to also not "over design/size" the system for cost.

An example we could use would be 120 GPM that is being collect at the last downspout or closest downspout to the tank, downspout F. The farthest downspout from the tank is downspout A and it only collects 20 GPM from its section of roof area. If the closest downspout to the tank or downspout F is 100 ft from the tank, and the farthest downspout or downspout A is 500 ft from the tank, I get .81 TDH at downspout F and .55 TDH for downspout A.

__Will the water in downspout A ever rise above .15 ft during a 4" steady rain event?__The downspout that is farthest from the tank has the least amount of water in it but has to travel the farthest. As the conveyance pipes pick up downspouts, more water is flowing in the system. The last downspout (or closest downspout to the tank) has the most water moving past it or in it since it is a culmination of all the downspouts/roof area. My question is, when calculating TDH, what distance do I use? Should I use the distance and elbows from the tank to the tank's closest downspout to figure out how much head will be in the pipes? Or, should I use the distance from the tank to the farthest downspout? Also, what GPM should I use for the farthest downspout? I need to build in some buffer but I also want a CYA for my systems. I was just thinking of using the farthest downspout with max GPM and call it a day, but then again, my mind now wants to know what is actually happening in the pipes but I also want to design my systems appropriately and build tanks at an elevation that is reasonable accurate based on fluid hydraulics. I need some clear PVC pipe I guess!

Thanks!

-S