75k L potable system design with a few questions. « Alternative Technology Assn Forums

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75k L potable system design with a few questions.

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Started 5 years ago by Ikanuba
Latest reply from Diver

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Ikanuba
Member

Hello,
I'm currently building a 75000 L potable rain harvesting system in rural Oregon. Due to many building mistakes (that's a whole other nightmare) I've had to move my (4) 18927 L tanks farther down hill from my house. This has now raised many questions I wasn't originally figuring into the design.

I've been reading the posts here for the last few months as I try and deal with the many questions I have and was hoping some of the experts here could help me with a few of the remaining questions.
Below is my current design setup: (i've tried to keep it metric but excuse me for any mistakes)

- 167 sq.m house with 185 sq.m roof

- 1:20 ARI for this area is about 177 mm in 24 hour period

- (4) 18927 L x 3.65 m high tanks on an 203 mm thick concrete slab

- The tanks and slabs are roughly 122 meters from the house downhill with drop of about 6 - 8
meters. The top of the 3.65 m tank is roughly 2 - 3 meters below the bottom of the gutters.

- This is going to be a dry system. I've glued and buried 76 mm pvc running from each of the 6
downpipes,three on each side of the house.The left and right side of the house converge into a
76 mm DWV Y pipe and then a single 76 mm pipe feeds into a 1.2 m x 305 mm inground diverter
then into the top 76 mm inlet of the 4th tank.

- 4 of the downpipes will have leaf filters connected right below the downspouts

- All 4 tanks are to be connected to each other with the following scenario: Tank 4 fills first
and overflows via a 76 mm connection at the top to tank 3. There will be a water quieter
attached to the bottom of the pipe in tank 3. Tank 3, 2, 1 will be connected by the bottom
inlets via a 50 mm pvc pipe. Tank 1 will be the tank connected to the pump and pressure tank,
it will also have a 100 mm overflow pipe.

- Regardless if I use flexible or rigid pvc at the bottom of the tanks, each tank will have it's
own discharge pipe that will be operated by independent ball valves and will discharge over
the hill in front of the tanks. My thought here is that in the event I need to empty a tank
due to contaminants etc. I want to be able to still access and fill the other tanks. (See
diagram)

Questions:
1. I know it's best to have flexible connections at the base of tanks, but I'm having a heck of
a time trying to find potable, flexible, weather resistant tubing. What do you guys use? If I
were to use 50 mm rigid PVC for the connections they would be on the cement slab, so I
believe the only thing that would break or upset them would be a jolt from the cascadia fault
Oregon is next to.

2. Since the top of my inlet tank is about 2 - 3 meters below my gutters I've figured I should
have enough head pressure to fill the tank?

3. Will the 50 mm pipe connecting tanks 3,2,1 be large enough to accommodate the 76mm inflow
from tank 4?

4. I was planning on having my 450 L pressure tank, pump and pressure switch in the pump house
right next to the tanks. Would it be better to have the pressure tank and pressure switch in
the house which is 122 m up the hill or should I leave the pressure switch next to the pump
and put just the pressure tank in the house?

I'm attaching a hand drawn schematic of my proposed setup. Hopefully it works.

https://www.dropbox.com/s/9u7ivvajqtdw393/Setup.JPG?dl=0

Posted Monday 17 Oct 2016 @ 8:30:28 am from IP #
Johnnojack
Member

Good idea to have the pressure switch and pressure tank next to, not inside the house. Would give you quicker flow at the taps as the inertia of the water in 122m of piping does not need to be overcome before you get flow from the taps. Will let others answer the rest of your questions.

Posted Monday 17 Oct 2016 @ 9:56:50 am from IP #
David
Member

Hmm, looks a fair bit over complicated from systems I've installed both myself and others. My suggestion is pretty KISS (Keep It Simple, S ). Since the system is a DRY system ie the pipes that take water to the tanks do not stay full of water, the simple effective solution, I've used in the past that works and is SIMPLE is all the down pipes from the house roof are combined to common pipe of X size, with simple low pressure vertical drop gate valves at the inlet of each tank.

Only the over flow from the farthest tank on the line is open by default to allow excess water to overflow from the system, the overflow from every tank is connected to common overflow pipe work again with simple vertical drop gate valves, the overflow pipes should be at the top of tanks at the highest point water is going to reach in the tanks each overflow should be the same size as the inflow pipe. The output for each tank with a ball valve at each tank outlet and connected to a common output pipe of whatever is deemed to required depending on the distance to the house but lets say for now 38mm (1 1/2") to suitable pump that gives say 400kpa at the height of the highest floor of the house is above the pump at whatever number of litres per minute is deemed to be required for the house or better yet use a hydro controller based water pump, this will vary the speed of the pump based on water flow demand to keep the water pressure constant to X number taps decided on and you can still use a pressure tank if you wish which can be ideally located at the house, not essential but handy.

The pump house/room you show can be reduced to simple large cover or a "large dog house" for want of better way of putting it.

Install the leaf filters low enough on the downpipes so you don't need a ladder to clean them, you WILL need clean to from time to time, it would be real pain to have get a ladder every time to clean them, mine can be reached while still standing on the ground, it makes the job safe and quick to do.

Typical in-flow pipes are simply pointed into the very basic filter basket of each tank the top of the tank/s, in Aus they are screwed in but that became a pest so I always remove the stainless screws so they can easily be lifted out to give them belt against the side of the tank to knock out any debris they collect put back quickly, takes about 15secs for each one a few times a year. ( I have 4 tanks 62kL's takes under 5 mins typically when it's required.)

Works, simple to setup, very simple to maintain, if or when it might be required, which for us its been 10+ years on the system here and there's still not much crap in the bottom of the tanks, just the leaf collectors ever few months and the tank filter baskets every so often depending on the time of year.

BTW way first flush systems are wildly overrated if your in an area where there is not much rubbish in the air I would not bother. I've never used one, they tend to waste a lot of water, I do use water filters but only because I'm in builtup area (In Town) Dandenong, Victoria, Australia.

If in the unlikely event you really do need to clean out a tank siphoning a tank of the water is as easy a way as any and if you have the siphon hose attached to suitable swimming pool rod and vacuum attachment then you can move the pipe around the bottom of the tank sucking up debris on the bottom while emptying it at the sametime, there's no need to install a specific drain system, it's just not needed.

6-8 metres below ground level of the house is long way below and completely unnecessary, can you have the tanks considerably closer to the house worst case the top of the tanks can be level with the ground at the house. Mine are only lower than the gutters by about 500mm (approx 1.5') there is no issue with flow to the tanks provided you use a say 80mm+ for each down pipe connected to say a common manifold pipe of say 100mm and each tank has say an 80mm inflow pipe with lets say an 80mm overflow pipe.

All pipes from each of the bottom of the water tanks ball valves to the pump intake should be black polyethylene pressure blue stripe pipe and from the pump to the house it's rated to 1200kpa and is fully UV stabilised is also semi-flexible and pretty easy to work with, far better choice compared to PVC pressure pipe.

Posted Monday 17 Oct 2016 @ 10:41:09 am from IP #
Diver
Member

Ikanuba said:

- 1:20 ARI for this area is about 177 mm in 24 hour period

Our 1:20 ARI is based on a 5 minute average rainfall intensity, for example, a 1:20 180mm/hr ARI is an average of 3mm per minute over the 5 minute duration. So long as 15mm falls in 5 minutes, it is a 180mm/hr 1:20 ARI.

I am confused by your reference to the 1:20 ARI being 177mm over a 24 hour period as this is only drizzle. Can you clarify thanks as I need to know what the rainfall intensity is to do the necessary hydraulic calculations. For these next answers, I will assume a rounded 3mm per minute over a 5 minute duration.

There are a lot of things wrong with your intentions. I'll give some basics and you should then be able to work out what is best.

Ikanuba said:

- 167 sq.m house with 185 sq.m roof

I've glued and buried 76 mm pvc running from each of the 6 downpipes,three on each side of the house.The left and right side of the house converge into a 76 mm DWV Y pipe and then a single 76 mm pipe feeds into a 1.2 m x 305 mm in ground diverter then into the top 76 mm inlet of the 4th tank.

A 185 sq m roof will collect 555 litres per minute if your ARI 5 minute duration is 3mm/min.

We have 80mm DWV pipes here and the internal diameter is 76.2mm. They are the same pipe as yours and they hold 4.56 litres per metre. A flow rate of 555 lpm is a velocity of a 2.03 metres per second. The pipes are not pressure rated but they are ok for this scenario.

You have 6 downpipes but are only fitting 4 leaf diverters...why is that?

The leaf diverters are a good idea but if you are going to infeed directly into tank 4, then you should have mosquito proof leaf diverters on every downpipe to prevent dead birds etc from being washed into the tank.

The 122 metre run will have additional friction losses (3 elbows at the vertical riser for starters) so let's say that the total friction loss is equivalent to 150 metres. A quick calculation tells me that for the 76.2mm ID DWV pipe, you will need a 7 metre head to achieve 550 litres per minute and even a straight 122 m run would require nearly 6 metres of head.

Another consideration is expense. Over here, 100mm DWV is much cheaper than 80mm DWV. Have you priced the pipe?

Using 100mm DWV also lets you have a good sized sediment trap that can also double as a first flush diverter if you choose to do so. It also allows you to fit a low restriction inlet that would have priority flow over the vertical riser but you would need leaf diverters on every downpipe to do this. A low restriction inlet oxygenates the bottom of the tank but it would need to be fitted to a valve that was 100mm above the bottom of the tank at the valve's lowest point.

A 76mm overflow fitted to the top of tank 4 would be totally inadequate to handle the overflow. Torricelli's law factors the height of water above the pipe's invert (bottom of the pipe) to arrive at the flow rate and the proposed pipe if un-meshed would only flow at 2.27 lps with the water level at the very top of the pipe. Totally inadequate and even more so if it was fitted with mosquito proof mesh which reduces the % of open surface area by nearly 1/2.

For the 550 lpm inflow rate if applicable, I would have a single 100mm overflow on tank 4 and have the overflow elbowed and bell mouthed inside the tank to greatly increase the overflow capacity. The other tanks wouldn't need overflow pipes.

Planning to fill only tank 4 and have the pump connected to tank one is a good idea as it gives you a settling (decant) system. I would just have 40mm or 50mm balance lines about 80mm above the bottom of the tanks at the valve's lowest points connecting the tanks. These valves would cope 99.9% of the time without tank 4 overflowing before the others filled.

We use black corrugated UV stabilised flexible pond hose and nut and tails to connect the hose to the tank valves.

If you have a remote pressure tank, it is much better to have it at the house than at the tank but you should factor the pressure tank's elevation Vs the pump's cut in - cut out pressure settings. Also be aware that you need a pump's pressure controller that can be set to the pressure tank's setting. You can buy adjustable electronic pressure controllers now.

To make cleaning the tank's top meshed inlet easier, we use an oversized round piece of shadecloth. To clean, you just lift it out and give it a shake.

Posted Monday 17 Oct 2016 @ 4:33:26 pm from IP #
Ikanuba
Member

Hey Guys,

Really appreciate all the advice and info. as this project seems a little overwhelming at the moment and I can't seem to find anyone local to help with this rainwater catchment system.

David said:

6-8 metres below ground level of the house is long way below and completely unnecessary, can you have the tanks considerably closer to the house...

All pipes from each of the bottom of the water tanks ball valves to the pump intake should be black polyethylene pressure blue stripe pipe and from the pump to the house it's rated to 1200kpa and is fully UV stabilised is also semi-flexible and pretty easy to work with, far better choice compared to PVC pressure pipe.

David -

Ans: Tanks are so far down hill due to the contractor we hired pouring our old tank pad at the
incorrect height. So the tanks sat too high up and were basically blocking the view from many
of the windows in the house.

I am working to locate this black poly pipe which I could use to connect. If I'm understanding
you and Diver correctly, I could just use this pipe as the balance lines between tanks and run
that straight to the pump?

To answer a few of Diver's questions:

- the 1:20 ARI is just an estimate due to no reliable current data from local weather or NOAA for this area. I recently did find an old publication citing in inches per hour based on a storm of 1 hour duration and 100 year return period. It stated 1.5 inches per hour and following your math example would equate to right about 0.6mm/min or 3mm/5min.

-

Diver said:

You have 6 downpipes but are only fitting 4 leaf diverters...why is that?

The leaf diverters are a good idea but they decrease the available head. The 122 metre run will have additional friction losses (3 elbows at the vertical riser for starters) so let's say that the total friction loss is equivalent to 150 metres. A quick calculation tells me that for the 76.2mm ID DWV pipe, you will need a 7 metre head to achieve 550 litres per minute and even a straight 122 m run would require nearly 6 metres of head.

Another consideration is expense. Over here, 100mm DWV is much cheaper than 80mm DWV. Have you priced the pipe?

Using 100mm DWV also lets you have a good sediment trap that can also double as a first flush diverter if you choose to do so. It also allows you to fit a low restriction inlet that would have priority flow over the vertical riser but you would need leaf diverters on every downpipe to do this. A low restriction inlet oxygenates the bottom of the tank but it would need to be fitted to a valve that was 100mm above the bottom of the tank at the valve's lowest point.

Ans: Two of the downpipes are smaller roofs which would not yield much debris so I thought I
would forgo adding leaf diverters to them.

Ans: Unfortunately, I didn't price out DWV pipe but instead went with 76.2mm sch 40 PVC. If
i'm understanding your calculations correctly about head loss, are you saying that due to head
loss from friction, leaf eaters, pipe fittings, pipe length etc, that the water in the 76.2mm
pipe flowing from the roof gutters will not have enough head pressure to rise up 3.65m to the
tank inflow inlet?

-

Diver said:

I would have a single 100mm overflow on tank 4 and have the overflow elbowed and bell mouthed inside the tank to greatly increase the overflow capacity. The other tanks wouldn't need overflow pipes.

If you plan to fill tank 4 and have the pump connected to tank one...which is ordinarily a good idea for a settling system...then tank 4 would always be full if I understand the diagram correctly. I would just have 40mm or 50mm balance lines about 80mm above the bottom of the tanks at the valve's lowest points connecting the tanks. These valves would cope 99.9% of the time without tank 4 needing to overflow.

We use black corrugated UV stabilised pond hose and nut and tails to connect the hose to the tank valves.

Ans: Great idea about overflow on tank 4 instead of 1. I will def. put in 100 mm. What did you
mean by "elbowed and bell mouthed"? I was planning on installing the overflow slightly below
the level of the water inlet on the side of the tank. Do you have any suggestions of what is
the best location for large tank overflows?

What are your thoughts on having a dedicated outlet for the pump to pull from or have the pump pull from the balance lines between the tanks thus pulling from all three tanks simultaneously?

Thank you again to everyone, help is much appreciated.

Posted Monday 17 Oct 2016 @ 8:16:17 pm from IP #
Greg
Member

There is a good thread on this forum with a complete multiple tank design. I'd have a look at that and the guys will assist with calcs. I like the design that overflows from the bottom of the tank to keep water fresh.
Those large pressure tanks are expensive and if you don't have power outage issues and need the reserve, I'd consider a smaller tank using a "cycle stop valve" (US company) especially useful for irrigation eg garden watering.
As for using shade cloth as additional filter , I purchased drop in stainless steel mesh tank filter product that clips in place makes cleaning easy

Posted Monday 17 Oct 2016 @ 10:20:18 pm from IP #
David
Member

Ikanuba said:
I am working to locate this black poly pipe which I could use to connect. If I'm understanding
you and Diver correctly, I could just use this pipe as the balance lines between tanks and run
that straight to the pump?

Hers one supplier I found in less than a minute in the US. I'm sure there are plenty of others.
http://keithspecialty.com/water.line.pe.htm

Yes, linking all the outlets from the tanks together is very simple and just works.

I've tried other ways in the past, this is the easiest, no hassle solution.

For a dry system. there is and as mentioned the main pipe to the tanks is too small. I'd use as an absolute minimum 90mm storm water pipe as it's known here. If I really wanted to ensure plenty of volume then 2 x 90mm storm water pipes run in parallel, this stuff in OZ very cheap using pairs in parallel is often cheaper than a single 100mm DWV pipe and will flow more water anyway.

Here's a rough semi-customized example for you. Ours is similar of what works for us, I don't need the 2 x 90mm storm pipes or 100mm for the overflow. Yes the bottom pipes will always self level the tanks given a bit of time. The overflow pipes will assist in distribution of water if one is full and the other are not. I have not shown any drop gate valves on the inlets or overflow pipes (optional, just handy)

https://drive.google.com/file/d/0B1wBHcE8z_VValdqNmcyaXloVGs/view?usp=sharing

It shows both pipes coming from the house connected in a 4 way combination however one to each pipe that goes the tanks might possibly better, depending. They need to be interconnected up at the house end. The overflow pipe should rise up 100mm before it does a U turn to allow excess water to drain away, the overflow pipe should be open above the drain section of the overflow pipe to ensure it can't create a siphon, with SS mesh screen over the top open end and a self closing flap at the far end of the overflow pipe to stop mosquito's from getting in.

Posted Tuesday 18 Oct 2016 @ 12:16:45 am from IP #
Diver
Member

Ikanuba said:

- the 1:20 ARI is just an estimate due to no reliable current data from local weather or NOAA for this area. I recently did find an old publication citing in inches per hour based on a storm of 1 hour duration and 100 year return period. It stated 1.5 inches per hour and following your math example would equate to right about 0.6mm/min or 3mm/5min.

I have found information about how they calculate roof drainage compliance in the US and it is basically the same as our method except that the US uses what they call a 10 year return whereas we use a 20 year ARI for eaves gutter compliance. Both are based on a 5 minute rain intensity duration. A 1:20 ARI has roughly a 25% greater intensity than a 1:10 and so your flow rate calculations are easy to work out if the local area's 10 year return stats are known.

I have also found a US 1:10 year 5 minute duration rainfall intensity chart (shown as inches and mm per hour) for many areas in the US but Oregon only lists Baker (56mm) and Portland (53mm) which are unbelievably low, I really can't imagine anywhere having such a low 1:10 year 5 minute intensity that is less than 1mm per minute but there are some other similar low intensity places also listed. If your area's 1:10 intensity is as low as this, then the pipes would be more than adequate.

http://img2.timeinc.net/toh/static/pdf/Rainfall-Intesity-Chart-01.pdf

The rainfall intensity is needed to determine both the infeed pipe's required flow capacity, the tank's overflow capacity and the balance line sizing.

Ikanuba said:
If i'm understanding your calculations correctly about head loss, are you saying that due to head loss from friction, leaf eaters, pipe fittings, pipe length etc, that the water in the 76.2mm pipe flowing from the roof gutters will not have enough head pressure to rise up 3.65m to the tank inflow inlet?

The water will go into the tank because there is a hydraulic head but at the required flow rates that I quoted, there would not be enough head to achieve those flow rates but it appears as though your rainfall intensity is much less than the figures I used. Knowing the 1:10 figure is necessary to do proper calculations.

Ikanuba said:
What are your thoughts on having a dedicated outlet for the pump to pull from or have the pump pull from the balance lines between the tanks thus pulling from all three tanks simultaneously?

Having the inflow pipe to tank 4, the pump fitted to tank 1 and the tanks balanced from 4 to 3, 3 to 2 and 2 to 1 will give you a superior settling system. If the valve supplying the pump also has a floating inlet with the entry about 200mm below the water surface, you will draw very clean water and the outlet valve can be fitted lower on the tank. An irrigation outlet will be able to make one up for you if they are not available in the US.

http://www.crystalclearwater.com.au/waterboy/

Re the balance lines, rigid couplings should never be used because tanks flex, only use flexible couplings. We always use flexible black corrugated UV stabilised pond hose and most irrigation shops here have it and cut it to the required length. The 32mm hose is my favourite because it's a good size and the larger sizes are less flexible over short distances but the size of course is determined by the inflow capacity during a major rain event.

http://www.clearpond.com.au/products/all-products/hose-fittings/clearpond-hose-accessories/pondflex-hose-50m-roll-32mm

I really need to post a sketch and some photos with additional information but unfortunately I find this forum's uploading format difficult to use and when I click on the suggested full html tutorial site at http://www.w3schools.com it comes up as error 503. You have however posted the same thread on Homeone and I will concentrate on that thread unless I can find a way around the issue here.

Posted Wednesday 19 Oct 2016 @ 1:57:24 am from IP #

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