Header tank and pressure

[BangCrash]

Hi
I have an off-the-grid self-sustainable-type home. I am currently pressurizing my water mains with a pump from harvested rainwater tanks. Nothing too exotic: when one opens a tap the pressure-drop switches on the pump and water flows.

The issue: since my electricity is from a solar-fed battery array, I don't want the pump switching on and off every time a tap is opened (or the loo flushed) and especially not at night.

The solution: a largish header tank. I'll run the pump to fill it when the sun is shining and I have electricity to spare. Then I'll have water whenever I want it without depleting my batteries.

So far so good.

I'm now just stumped for a rather simple question that, I am sure, a plumber would know the answer to.

How high must the header tank be above the level of the household taps (and the shower-head) in order to have acceptable pressure?

I realize I am asking a "how long is piece of string" type question as there are many, many variables. But assuming:
a single-story house
a header tank on a "tower" (it can be any height, not restricted to being in a loft)
a 1500l size header tank that will usually be more than 50% full (that will increase the pressure, right?)
a 32mm pipe from the header to ground-level feeding the cold mains
a 32mm pipe from the header to the geyser in the roof.
The cold mains and the geyser feed out of the geyser are 22mm.

What is confusing me is that I read on the 'net that decent pressure for a home is considered to be around 3 bar... but you only get about 0.1 bar per meter of head, right? So for 3 bar I need a 30 meter high header!?! That's just silly. But even 1 bar of pressure needs 10 meters. Even this can't be right many city homes use a header in their loft and that's not going to be 10 meters above the upstairs taps.

So I'm a little confused and I hope someone here can point me in the right direction before I buy tanks etc.

 

[sooey]

What is confusing me is that I read on the 'net that decent pressure for a home is considered to be around 3 bar... but you only get about 0.1 bar per meter of head, right? So for 3 bar I need a 30 meter high header!?! That's just silly. But even 1 bar of pressure needs 10 meters. Even this can't be right many city homes use a header in their loft and that's not going to be 10 meters above the upstairs taps.

So I'm a little confused and I hope someone here can point me in the right direction before I buy tanks etc.

Those figures are correct, yet many homes have gravity systems which perform perfectly well because they have good flow rate.
As much height as you can reasonably get helps but more important is pipe restriction. In general the larger the bore of the pipe the less restriction in flow, elbows are also more restrictive than formed bends and outlets come in high and low pressure versions, you need to use low pressure outlets. If you want really powerful showers then the water needs to be pumped.
I'd be worried about legionella in this 'tank on a tower' you propose, especially in summer when the sun is shining as you say.

 

[BangCrash]

Thank you so much for the feedback, Sooey.

So bottom line: as high as I can go and then as large pipes as I can put in. Got it.

Fortunately the shower is very close to where the tower will be so and also where the geyser is so the pipe runs are short. That will help.

Thank you also for your concern about legionnella. I am aware of this. All my neighbors in this part of the world use harvested rainwater and I have never heard of any health issues ever. But, for all that, I am more cautious than anyone else around here. My harvest goes in through a rainhead (a system that discards the first run-off that carries contaminants) and then I also do chlorinate my water.

I chlorinate the large collector tanks alternately and aim for a residual level of no less than 0.5ppm when collected from the taps. This doesn't adversely affect taste but gives me that extra bit of comfort knowing my water is safe.

Thanks again for the feedback!