Hi All,
I have seen some great threads regarding rainwater harvesting systems, so was hoping for some help to plan/design our system before I go about building it.
Our builder is basically providing the downpipes only, we are connecting them all to the water tank.
Our tank:
Positioned approx 20m from the house
250,000L
x2 inlet baskets
x2 150mm overflows
Brass firefighting outlet as required
Location:
Perth. 1:20 ARI is 140 mm/h which is based on an average rain intensity of 2.33 mm/minute over a 5 minute duration
House:
Roof area is 496m2 (flat) or 550m2 (pitched) 25* pitch
x12 downpipes (builder has listed them as 75mm PVC)
Heights:
Water tank is 2.18m (inlet pipe would likely end up 100-150mm higher than tank)
Bottom of gutters is 2.9m
Shed:
At some point in the future we are planning to add in a shed, which will add a further 240m2 of catchment area, and will be positioned right next to the water tank. Gutters will likely be 3.6m+
That's about all the information I think I can provide at this stage, however if I have missed something important please let me know.
Hoping for advice to basically make it work the best I can.
What pipe (DWV?) and size to connect all the downpipes with?
How many downpipes to have on each run back to the tank (2x6, maybe 3x4?)
What additional items do I need in the system (leaf baskets, first flush, sediment traps?)
Do I have enough head height?
Appreciate any help I can get there!
Rainwater harvesting system - Perth
Page 1 of 1
Sorry for the delay but I am restricted at the moment.
You have provided great information that also indicates you have done your homework. I will provide information much of which I think you will already know but I am mindful of the benefit to others who will also have interest in the thread.
It is good that you are connecting the pipes as practically all charged (wet) systems are substandard when organised by builders and their plumbers, even when tank companies or their dealers organise their own plumbers.
BASICS: The system's foundations!
Eaves gutter compliance is determined by a region's 1:20 ARI intensity but it must firstly be realised that the roof drainage calculations used for compliance are the minimum qualifying average intensities over a 5 minute duration. You could for example experience a 1:20 intensity that is just short of qualifying as a 1:50 intensity which is well above the minimum qualifying intensity for a 1:20 event on which other roof drainage calculations are based. Knowledgeably designed rainwater harvesting systems have pipe flow calculations that include a safety margin to allow for rain heavier than the minimum qualifying 1:20 ARI intensity figure.
Your 496 sq m roof plan area is factored by 1.23 to allow for wind driven rain on the 25 degree sloped roof when calculating the subsurface pipe sizes. I need a diagram showing the building perimeter and the approximate location of the downpipes.
During your region's minimum qualifying 1:20 rain intensity, the average 2.33 mm/min over the 5 minute duration falling on your roof plan area will yield an average of 1,156 lpm.
At this point, it is also important to understand that eaves gutter roof drainage regulations/compliance is based on the region's 1:20 ARI but those regulations finish at the bottom of the downpipe. Downpipes usually divert to stormwater pipes which have their own regulations (sub surface drainage) that use 1:100 ARI calculations because sub surface also has to capture surface drainage (the third lot of stormwater drainage) and ag pipe discharge to silt pits. Pipes diverting rainwater to a tank are not regulated by either roof drainage or subsurface drainage regulations except for the tank's overflow pipe when it connects to the stormwater system.
If you were to use 100mm DWV pipe, a velocity of 1 metre per second is 510 lpm but if you designed the (total) system at let's say 30% greater than 1,156 lpm, you will have a flow design of 1,503 lpm or 751.5 lpm for each pipe.....but remember that 23% of that 30% increase is the multiplier for the roof slope during wind driven rain that the carrier pipe on the weather side has to manage. For rainwater harvesting diversion, I usually recommend calculating 20% over the factored roof slope which then calculates as 1156 x 1.23 x 1.2 = 1,706 lpm or 853 lpm for each pipe. Two 150mm pipes would be chosen and not 100mm DWV pipe.
The biggest crunch however is that rainwater harvesting system pipe sizes are invariably wrongly designed to sub surface drainage regulations. In your case, also having 150mm pipes at the head of the system as would normally be plumbed will build up sediment because there will be no flushing velocity in a 150mm charged pipe flowing full of water with minimal velocity. It also means that a large volume of water will be retained in the wet system between rain events plus the larger pipes and fittings are expensive, something best minimised.
The subsurface pipe at the head of a charged system needs to occasionally flush bed load to prevent constant accumulation. Stronger but smaller pvc DWV pipe is the best choice.
Note that unlike flooded wet system pipes, sub surface drainage pipe design require a minimum slope which generates a good flushing velocity with minimal water flowing as a narrow stream along the curved bottom. Chalk and cheese.
The builder has referenced the NCC Part 2 (BCA) roof drainage regulations (which he is entitled to do) rather than reference the superior Deemed To Satisfy (DTS) Australian Standards AS 3500.3. I know this because your average roof harvest area (factored by 1.23 for wind driven rain) serviced by the 12 downpipes is 50.84 sq m. The Australian standards do not allow the use of 75mm downpipes for this roof area size in a 140 mm/hr ARI region but the laxer NCC Part 2 regulations do.
I recommend fitting leaf diverters to the top of downpipe to prevent debris entering a charged system plus they also prevent mosquitoes breeding. They also serve as air gaps (emergency overflows) during torrential rain to allow the gutter to drain unimpeded.
The only leaf diverter I recommend is the ICON Leaf and Debris Controller but the 75mm pvc downpipes specified by your builder makes it difficult to connect to a suitable sub surface rainwater diversion pipe. You should tell him you want 90mm round pvc downpipes because the leaf diverter's bottom fitting which takes a 90mm pvc stormwater pipe can then be easily adapted to 100mm DWV and then downsized to a smaller DWV pipe.
If the roof area servicing the downpipe is your average of 51 sq m (already factored by x 1.23 for the slope) plus a 20% margin, you would be designing for 51 x 1.2 x 2.33 = 143 lpm per downpipe.
Flushing is generated by velocity and/or turbulence. DWV pipe sizes jump from 40mm to 50mm to 65mm to 80mm and greater.. The 65mm DWV internal diameter is generally 63.6mm which is a volume of 3.17 litres per metre. If this pipe was to flow with a velocity of 0.7 metres per second, its flow rate would be 3.17 x 0.7 x 60 = 133.1 lpm. It should move bed load along with a tad lesser velocity and would be my choice as the pipe size to use at the head of the system.
Tried and tested:
1. If you increase the volume by 1% and the hydraulic head and all else remains the same, you will increase the flow rate by nearly 1.5% for each 1% increase.
2. A pipe loses pressure along its path but each downpipe acts as a water tower does on a subsurface pipe to replenish pipe friction losses. See the two videos below.
https://www.youtube.com/watch?v=_hSL9_eo4n8&t=8s
https://www.youtube.com/watch?v=933XNdClFrc
The next larger DWV pipe size is 80mm which has an internal diameter of 76.2mm, giving an internal volume of 4.56 litres per metre, a volumetric increase of 44%. It would be suitable to upsize to this pipe immediately before the second downpipe.
The carrier pipe would then be upsized before the 3rd downpipe to 100mm DWV (104mm ID) which holds 8.5 litres per metre. The 100mm pipe would upsize to 150mm DWV before the 5th downpipe and continue to the 6th downpipe and the tank. The 100mm DWV pipe's maximum design flow after the 4th downpipe would be 143 x 4 = 572 lpm which is a velocity of 1.1 metres per second.. This is ok but I would use 45 degree junctions to connect the downpipe to the carrier pipe at the 4th, 5th and 6th downpipes to reduce turbulence but also consider using them at the 2nd and 3rd downpipes.
The 150mm DWV pipe has an inside diameter of 151.6mm and a volume of 18 litres per metre.
143 lpm x 6 = 858 lpm and a velocity of a tad less than 0.8 metres per second at that flow rate. Looking good.
If you have leaf diverters (highly recommended), you will lose head but we can draw on some lessons learnt from our Supadiverta research and development program by using supplementary low inlets to boost the flow rate and which are a good idea for other reasons anyway.
The Icon leaf diverter is the best currently on the market but it is large (the result of prioritising good design). You should buy one and gauge how much head you will sacrifice.
We are now going into ball park mode with guesstimated lengths and measures; Let's say the mid point of the vertical riser's socket above the tank is 2.35 m above the ground. Now let's say that we lose another 300 mm head by fitting leaf diverters. That makes 2.65m height. The gutter's sole is 2.9m high, leaving a 250mm head.
It is 20 metres from the house to the tank but we need to know the distance from the nearest two downpipes to the tank. There will also be some elbows between those two downpipes and the top of the vertical riser that need factoring as equivalent pipe lengths. Lets assume two 90 degree elbows as 4.5 metres of equivalent pipe length each (x30 the pipe's internal diameter). The length of the vertical riser also needs to be included. To make it easy as we are ball park and not on site, let's say each pipe length is 33.33 metres but I expect it to be more..
Remember how downpipes act as water towers? We are not calculating the head as being from the system's furthest downpipe because all downpipes are continually restoring pressure losses along the subsurface carrier pipe(s).
We can use a friction loss calculator to calculate the head required to gravity feed 858 lpm through 33.33 metres of pvc pipe with an internal diameter of 151.6mm. A chosen calculator needs to use the Hazen-Williams formula for gravity fed pipelines.
https://www.engineeringtoolbox.com/hazen-williams-water-d_797.html
Note that 100 metres was entered as the pipe length. If our pipe length friction losses are 33.33 metres, we divide the head loss figure (380mm) by 3 otherwise we divide the calculations by 100 and then multiply by the pipe's length expressed as friction loss.
Head loss is the same as required head, i.e. 127mm is the required head but it isn't quite this simple, for example, the tee (but much preferably the 45 degree junction) at the last downpipe also needs calculating as an equivalent length of pipe plus I don't know the actual pipe length. Regardless, even if we used 50 m as the pipe's length, dividing the calculations by 2 would still be in range but final verification is needed..
Also note that the earlier selected 65mm (63.6mm ID) DWV pipe requires 9.4mm head per metre to flow at 2.38 L/s, a velocity of 0.749 m/s.
Using leaf diverters also allows you to plumb directly into the tank and this gains additional head by not having the inflow pipe higher than the tank.
Fitting a smaller branch line from a reducing junction on the carrier pipe to a low inlet fitted 100-200mm above the bottom of the tank reduces the amount of water retained in the wet system between rain periods plus the incoming oxygen rich water oxygenates the anaerobic zone. Rainwater is naturally acidic, oxygenating the higher density water also helps correct the pH imbalance. Fitting a large low restriction inlet significantly boosts the inflow capacity.
Water is best diverted to the bottom of a tank and taken by the pump from the top of the tank, the opposite to current archaic practices. Make sure that the water isn't being dropped into the tank from a height that is overhead the outlet valve that supplies the pump. Many tanks are plumbed like this.
Water discharges faster the higher it is above a horizontal pipe's invert or a vertical drain pipe's crest. Vertical pipes also drain much more efficiently than horizontal pipes but having a suitable height of water above the invert or crest is vitally important.
An unmeshed 150mm horizontal outlet with 150mm, 175mm and 200mm of water above the invert (the bottom of the pipe) will discharge at 770 lpm, 890 lpm and 996 lpm but take 20% off those figures if the overflow outlet is meshed. The unmeshed figures for a vertical pipe are 1090 lpm, 1178 lpm and 1260 lpm. These figures and many others for different horizontal and vertical unmeshed pipe sizes and water levels can be found in AS/NZS 3500.1 Section 8.
Bellmouthing a standing pipe lengthens the weir wall which substantially increases the pipe's flow capacity.
Don't use leaf baskets!
Our DIY sediment trap design works wonders and is super simple to make with off the shelf parts. Just fit it about 4 m past the last area of turbulence to trap the bed load. We now use invert tapers rather than pipe reducers.
Collecting first flush is worthwhile, particularly after a dry period but try to use the captured water. Rather than have large first flush collectors on every downpipe, you could simply run a small pipe from a short collector pipe to a common larger carrier pipe that drained directly into a sealed remote tank. The collected water can then be used for outdoor use and you can even have outlets at the base of some of the smaller vertical pipes rather than draw from the tank. The tank will need a small diameter vent pipe higher than the house gutter and the pressure increase caused by the pipe will demand a strong sealed tank.
You have provided great information that also indicates you have done your homework. I will provide information much of which I think you will already know but I am mindful of the benefit to others who will also have interest in the thread.
Our builder is basically providing the downpipes only, we are connecting them all to the water tank.
Location:
Perth. 1:20 ARI is 140 mm/h which is based on an average rain intensity of 2.33 mm/minute over a 5 minute duration
House:
Roof area is 496m2 (flat) or 550m2 (pitched) 25* pitch
x12 downpipes (builder has listed them as 75mm PVC)
What pipe (DWV?) and size to connect all the downpipes with?
How many downpipes to have on each run back to the tank (2x6, maybe 3x4?)
Location:
Perth. 1:20 ARI is 140 mm/h which is based on an average rain intensity of 2.33 mm/minute over a 5 minute duration
House:
Roof area is 496m2 (flat) or 550m2 (pitched) 25* pitch
x12 downpipes (builder has listed them as 75mm PVC)
What pipe (DWV?) and size to connect all the downpipes with?
How many downpipes to have on each run back to the tank (2x6, maybe 3x4?)
It is good that you are connecting the pipes as practically all charged (wet) systems are substandard when organised by builders and their plumbers, even when tank companies or their dealers organise their own plumbers.
BASICS: The system's foundations!
Eaves gutter compliance is determined by a region's 1:20 ARI intensity but it must firstly be realised that the roof drainage calculations used for compliance are the minimum qualifying average intensities over a 5 minute duration. You could for example experience a 1:20 intensity that is just short of qualifying as a 1:50 intensity which is well above the minimum qualifying intensity for a 1:20 event on which other roof drainage calculations are based. Knowledgeably designed rainwater harvesting systems have pipe flow calculations that include a safety margin to allow for rain heavier than the minimum qualifying 1:20 ARI intensity figure.
Your 496 sq m roof plan area is factored by 1.23 to allow for wind driven rain on the 25 degree sloped roof when calculating the subsurface pipe sizes. I need a diagram showing the building perimeter and the approximate location of the downpipes.
During your region's minimum qualifying 1:20 rain intensity, the average 2.33 mm/min over the 5 minute duration falling on your roof plan area will yield an average of 1,156 lpm.
At this point, it is also important to understand that eaves gutter roof drainage regulations/compliance is based on the region's 1:20 ARI but those regulations finish at the bottom of the downpipe. Downpipes usually divert to stormwater pipes which have their own regulations (sub surface drainage) that use 1:100 ARI calculations because sub surface also has to capture surface drainage (the third lot of stormwater drainage) and ag pipe discharge to silt pits. Pipes diverting rainwater to a tank are not regulated by either roof drainage or subsurface drainage regulations except for the tank's overflow pipe when it connects to the stormwater system.
If you were to use 100mm DWV pipe, a velocity of 1 metre per second is 510 lpm but if you designed the (total) system at let's say 30% greater than 1,156 lpm, you will have a flow design of 1,503 lpm or 751.5 lpm for each pipe.....but remember that 23% of that 30% increase is the multiplier for the roof slope during wind driven rain that the carrier pipe on the weather side has to manage. For rainwater harvesting diversion, I usually recommend calculating 20% over the factored roof slope which then calculates as 1156 x 1.23 x 1.2 = 1,706 lpm or 853 lpm for each pipe. Two 150mm pipes would be chosen and not 100mm DWV pipe.
The biggest crunch however is that rainwater harvesting system pipe sizes are invariably wrongly designed to sub surface drainage regulations. In your case, also having 150mm pipes at the head of the system as would normally be plumbed will build up sediment because there will be no flushing velocity in a 150mm charged pipe flowing full of water with minimal velocity. It also means that a large volume of water will be retained in the wet system between rain events plus the larger pipes and fittings are expensive, something best minimised.
The subsurface pipe at the head of a charged system needs to occasionally flush bed load to prevent constant accumulation. Stronger but smaller pvc DWV pipe is the best choice.
Note that unlike flooded wet system pipes, sub surface drainage pipe design require a minimum slope which generates a good flushing velocity with minimal water flowing as a narrow stream along the curved bottom. Chalk and cheese.
The builder has referenced the NCC Part 2 (BCA) roof drainage regulations (which he is entitled to do) rather than reference the superior Deemed To Satisfy (DTS) Australian Standards AS 3500.3. I know this because your average roof harvest area (factored by 1.23 for wind driven rain) serviced by the 12 downpipes is 50.84 sq m. The Australian standards do not allow the use of 75mm downpipes for this roof area size in a 140 mm/hr ARI region but the laxer NCC Part 2 regulations do.
I recommend fitting leaf diverters to the top of downpipe to prevent debris entering a charged system plus they also prevent mosquitoes breeding. They also serve as air gaps (emergency overflows) during torrential rain to allow the gutter to drain unimpeded.
The only leaf diverter I recommend is the ICON Leaf and Debris Controller but the 75mm pvc downpipes specified by your builder makes it difficult to connect to a suitable sub surface rainwater diversion pipe. You should tell him you want 90mm round pvc downpipes because the leaf diverter's bottom fitting which takes a 90mm pvc stormwater pipe can then be easily adapted to 100mm DWV and then downsized to a smaller DWV pipe.
If the roof area servicing the downpipe is your average of 51 sq m (already factored by x 1.23 for the slope) plus a 20% margin, you would be designing for 51 x 1.2 x 2.33 = 143 lpm per downpipe.
Flushing is generated by velocity and/or turbulence. DWV pipe sizes jump from 40mm to 50mm to 65mm to 80mm and greater.. The 65mm DWV internal diameter is generally 63.6mm which is a volume of 3.17 litres per metre. If this pipe was to flow with a velocity of 0.7 metres per second, its flow rate would be 3.17 x 0.7 x 60 = 133.1 lpm. It should move bed load along with a tad lesser velocity and would be my choice as the pipe size to use at the head of the system.
Tried and tested:
1. If you increase the volume by 1% and the hydraulic head and all else remains the same, you will increase the flow rate by nearly 1.5% for each 1% increase.
2. A pipe loses pressure along its path but each downpipe acts as a water tower does on a subsurface pipe to replenish pipe friction losses. See the two videos below.
https://www.youtube.com/watch?v=_hSL9_eo4n8&t=8s
https://www.youtube.com/watch?v=933XNdClFrc
The next larger DWV pipe size is 80mm which has an internal diameter of 76.2mm, giving an internal volume of 4.56 litres per metre, a volumetric increase of 44%. It would be suitable to upsize to this pipe immediately before the second downpipe.
The carrier pipe would then be upsized before the 3rd downpipe to 100mm DWV (104mm ID) which holds 8.5 litres per metre. The 100mm pipe would upsize to 150mm DWV before the 5th downpipe and continue to the 6th downpipe and the tank. The 100mm DWV pipe's maximum design flow after the 4th downpipe would be 143 x 4 = 572 lpm which is a velocity of 1.1 metres per second.. This is ok but I would use 45 degree junctions to connect the downpipe to the carrier pipe at the 4th, 5th and 6th downpipes to reduce turbulence but also consider using them at the 2nd and 3rd downpipes.
The 150mm DWV pipe has an inside diameter of 151.6mm and a volume of 18 litres per metre.
143 lpm x 6 = 858 lpm and a velocity of a tad less than 0.8 metres per second at that flow rate. Looking good.
Our tank:
Positioned approx 20m from the house
250,000L
x2 inlet baskets
x2 150mm overflows
Brass firefighting outlet as required
Heights:
Water tank is 2.18m (inlet pipe would likely end up 100-150mm higher than tank)
Bottom of gutters is 2.9m
Do I have enough head height?
Positioned approx 20m from the house
250,000L
x2 inlet baskets
x2 150mm overflows
Brass firefighting outlet as required
Heights:
Water tank is 2.18m (inlet pipe would likely end up 100-150mm higher than tank)
Bottom of gutters is 2.9m
Do I have enough head height?
If you have leaf diverters (highly recommended), you will lose head but we can draw on some lessons learnt from our Supadiverta research and development program by using supplementary low inlets to boost the flow rate and which are a good idea for other reasons anyway.
The Icon leaf diverter is the best currently on the market but it is large (the result of prioritising good design). You should buy one and gauge how much head you will sacrifice.
We are now going into ball park mode with guesstimated lengths and measures; Let's say the mid point of the vertical riser's socket above the tank is 2.35 m above the ground. Now let's say that we lose another 300 mm head by fitting leaf diverters. That makes 2.65m height. The gutter's sole is 2.9m high, leaving a 250mm head.
It is 20 metres from the house to the tank but we need to know the distance from the nearest two downpipes to the tank. There will also be some elbows between those two downpipes and the top of the vertical riser that need factoring as equivalent pipe lengths. Lets assume two 90 degree elbows as 4.5 metres of equivalent pipe length each (x30 the pipe's internal diameter). The length of the vertical riser also needs to be included. To make it easy as we are ball park and not on site, let's say each pipe length is 33.33 metres but I expect it to be more..
Remember how downpipes act as water towers? We are not calculating the head as being from the system's furthest downpipe because all downpipes are continually restoring pressure losses along the subsurface carrier pipe(s).
We can use a friction loss calculator to calculate the head required to gravity feed 858 lpm through 33.33 metres of pvc pipe with an internal diameter of 151.6mm. A chosen calculator needs to use the Hazen-Williams formula for gravity fed pipelines.
https://www.engineeringtoolbox.com/hazen-williams-water-d_797.html
Note that 100 metres was entered as the pipe length. If our pipe length friction losses are 33.33 metres, we divide the head loss figure (380mm) by 3 otherwise we divide the calculations by 100 and then multiply by the pipe's length expressed as friction loss.
Head loss is the same as required head, i.e. 127mm is the required head but it isn't quite this simple, for example, the tee (but much preferably the 45 degree junction) at the last downpipe also needs calculating as an equivalent length of pipe plus I don't know the actual pipe length. Regardless, even if we used 50 m as the pipe's length, dividing the calculations by 2 would still be in range but final verification is needed..
Also note that the earlier selected 65mm (63.6mm ID) DWV pipe requires 9.4mm head per metre to flow at 2.38 L/s, a velocity of 0.749 m/s.
Using leaf diverters also allows you to plumb directly into the tank and this gains additional head by not having the inflow pipe higher than the tank.
Fitting a smaller branch line from a reducing junction on the carrier pipe to a low inlet fitted 100-200mm above the bottom of the tank reduces the amount of water retained in the wet system between rain periods plus the incoming oxygen rich water oxygenates the anaerobic zone. Rainwater is naturally acidic, oxygenating the higher density water also helps correct the pH imbalance. Fitting a large low restriction inlet significantly boosts the inflow capacity.
Our tank:
x2 inlet baskets
x2 150mm overflows
x2 inlet baskets
x2 150mm overflows
Water is best diverted to the bottom of a tank and taken by the pump from the top of the tank, the opposite to current archaic practices. Make sure that the water isn't being dropped into the tank from a height that is overhead the outlet valve that supplies the pump. Many tanks are plumbed like this.
Water discharges faster the higher it is above a horizontal pipe's invert or a vertical drain pipe's crest. Vertical pipes also drain much more efficiently than horizontal pipes but having a suitable height of water above the invert or crest is vitally important.
An unmeshed 150mm horizontal outlet with 150mm, 175mm and 200mm of water above the invert (the bottom of the pipe) will discharge at 770 lpm, 890 lpm and 996 lpm but take 20% off those figures if the overflow outlet is meshed. The unmeshed figures for a vertical pipe are 1090 lpm, 1178 lpm and 1260 lpm. These figures and many others for different horizontal and vertical unmeshed pipe sizes and water levels can be found in AS/NZS 3500.1 Section 8.
Bellmouthing a standing pipe lengthens the weir wall which substantially increases the pipe's flow capacity.
What additional items do I need in the system (leaf baskets, first flush, sediment traps?)
Don't use leaf baskets!
Our DIY sediment trap design works wonders and is super simple to make with off the shelf parts. Just fit it about 4 m past the last area of turbulence to trap the bed load. We now use invert tapers rather than pipe reducers.
Collecting first flush is worthwhile, particularly after a dry period but try to use the captured water. Rather than have large first flush collectors on every downpipe, you could simply run a small pipe from a short collector pipe to a common larger carrier pipe that drained directly into a sealed remote tank. The collected water can then be used for outdoor use and you can even have outlets at the base of some of the smaller vertical pipes rather than draw from the tank. The tank will need a small diameter vent pipe higher than the house gutter and the pressure increase caused by the pipe will demand a strong sealed tank.
SaveH2O - thanks for that great information! I actually forgot I made this post and I apologize for not thanking you sooner. I'm about to start plumbing up the system and started researching again.
I think I am going to go for a system similar to what you suggest, however instead of having x6 downpipes on each run that end up with a 150DWV, I'll only run x4 downpipes for each run but only end up at 100DWV. This is just a cost decision, as x3 runs of 100DWV is quite a bit cheaper than x2 runs of 150DWV.
Basically:
Downpipe 1-2 = 65mm DWV
Downpipe 2-3 = 80mm DWV
Downpipe 3-4 = 100mm DWV
Downpipe 4-tank = 100mm DWV
This should maintain adequate flow rate at all points and satisfy total flow. I assume this is fairly equivalent to the system you proposed? Main difference being my 3x100DWV will flow at 1.1m/s as opposed to the 2x150DWV at 0.8m/s
I think I am going to go for a system similar to what you suggest, however instead of having x6 downpipes on each run that end up with a 150DWV, I'll only run x4 downpipes for each run but only end up at 100DWV. This is just a cost decision, as x3 runs of 100DWV is quite a bit cheaper than x2 runs of 150DWV.
Basically:
Downpipe 1-2 = 65mm DWV
Downpipe 2-3 = 80mm DWV
Downpipe 3-4 = 100mm DWV
Downpipe 4-tank = 100mm DWV
This should maintain adequate flow rate at all points and satisfy total flow. I assume this is fairly equivalent to the system you proposed? Main difference being my 3x100DWV will flow at 1.1m/s as opposed to the 2x150DWV at 0.8m/s
Even better!
Related
1/10/2023
3
There is a whole lot more to know than just the answers you seek but they are a good start. Overflow outlets have a mosquito proof mesh. These…
13/02/2024
2
Once you know the basics, the rest is easy. Read my post in the thread linked below. viewtopic.php?p=1919271#p1919271
23/05/2023
3
DIY, Home Maintenance & Repair
But if it is a ground level open pit, then it is not a charged system. No surprises there. The pipes have obviously been altered and there would be a reason for this.…