I've been planning a water system of some kind now for years, but got sidetracked by a freeze that hit us. Our neighbors discovered they had a sprinkler system installed in their over-grown yard only when it froze hard and long enough for the entire feed pipe to freeze and bust the valve . . . for the first time in 50 years. My plans called for a pump house, but I figured no way to isolate the pump from freezing conditions, so I put that plan on hold.
I'm curious. What kind of pressure do you have from your header tank? That's one limitation living where we are; not much space to build things like elevated tanks and main tank farms. Three thousand liters of storage would eat up half my yard. I have a solution in mind, but need to run some more numbers and make some more tests.
0.4335 psi per foot of head.
So, if you have a tank in your attic that's five feet tall, and the water level is a foot below the top, and you have a shower head that's two feet below the base of the tank, you'll have 2.6psi. A shower head on the floor below might have almost 7 psi. You need an appreciable rise to make "real" water pressure.
One option would be to use a pump and pressure tank, as standard. Doesn't take much of a pump to make 20-30psi, if it only has to produce enough flow for a shower or two. The low-pressure side is enough for bulk-flow systems like toilets (as long as the right fill valve is used), so the pressure pump could be sized to only supplying pressure to showers and such.
Another option is to use a whole-house pressure pump, like a Grundfos SQE. Even if you have high enough demand to justify a 3/4hp pump, the SQE pumps soft-start (spin up slowly from zero, rather than trying to jump immediately to thousands of RPM), so they don't draw the kind of current that other pumps do.
Just designed a system for a neighbor. He has a 1250-gallon Roth septic tank (Roth "multi-tanks" are potable-safe), which actually holds over 1400 gallons, since he's not limited to leaving septic air space. The tanks can be buried, or installed above-ground in a basement or mechanical room (51"x62"x177", HxWxL). The tank is filled by a conventional well pump that runs on solar power, only when the sun is shining (so the battery system does not need to account for starting/running that pump), and the house is pressurized by a Grundfos SQE that is submerged in the tank. The batteries can easily run the SQE. The result is that inexpensive water replaces a lot of additional, expensive batteries that would otherwise be needed to run the well pump when the sun isn't shining. If money is no object, the first well pump could also be replaced with a high-efficiency unit, which would allow it to run on dedicated panels with a small inverter, rather than having to draw through the main inverter.
I've neither a solar system nor a need for low-pressure water. I do have a Grundfox pump ready for installation, though. All I need are the reservoir and some pipes.
That Roth looks about 2 times too big for my house. 1400 would work, but that would take a lot of space, unless I buried it. A possibility. I would have to see how much the budget allows. Probably much less than a dollar/gallon. Much.
It's not that there might be a "need" for low-pressure water. It's just that you can do certain things, like fill toilets, without having to waste a lot of energy getting the same sort of pressures that are used for comfortable showers.
There are a variety of other sizes: http://www.roth-usa.com/PDF_Download_Files/RGP_Brochure_Combined.pdf
Probably much less than a dollar/gallon
We bought 1000 litre tanks like these:-http://www.eaauctions.com.au/catalogue/details.php?itemId=1735
(Not that we're in Australia, but the same design of tank is used the world over.)
They cost us 75 euros each, delivered, and had been used to ship soft drink syrup (so they are food grade). They're recycled packaging.
Each tank has an outlet at the bottom, and came with a screw cap. I drilled the screw cap and fitted a 3/4" tank fitting to each, then plumbed them together to make one 3000 litre store.
Since they're square and stackable, boxing them in should be easy enough. And since they're metal-framed, the foundation is a stand for each corner -- and where the tanks are next to each other, one stand can be shared by two or more tanks.
3000 litres for 225 euros is 7 1/2 cents per litre, or about 28 cents per US gallon. I guess that's less than half a dollar per gallon. :-)
Our system is designed to freeze without injury. The pump and external tube are both soft plastic, and there is an air-valve above the UV steriliser so the system drains back when the pump goes off. In very cold weather the pipe is cold in the morning and the water freezes the first time the pump comes on, but the flexible pipe is easily removed and put in a pan of hot water on the range. It's a 10-minute chore at breakfast time.
The external tanks don't freeze solid, because they're big. I am planning to box them in with polyurethane board, but with the high winds over Christmas I didn't get a chance.
The pressure is low: the header tank is on a bit of a platform in the loft, but it's only a single-storey cottage. We knew this would be the case, and bought plumbing fittings accordingly. The shower is a thermostatic mixer system that works down to 0.1 bar (1 1/2 psi). I would think we have double that when the tank is full. The header tank is a 250 litre (65 US gallon) affair, since the filter, pump and steriliser deliver less than 4 litres (1 gallon) per minute.
But all our hot taps have thermostatic mixers because our hot water comes from a solid fuel range. The heating comes on before the range properly boils (12v again -- the pump came from a yacht store) but with boiling hot water and a three-year-old, my wife wanted thermostatic mixers for safety.
When we plumb the bathroom (it's going to be in the as-yet-unbuilt extension) we'll be using 3/4 inch pipe to get a decent flow rate. The shower and the sinks are plumbed with 1/2" pipe, which is adequate.
Gravity fed hot water systems are quite common in Ireland and the UK, so appropriate plumbing fittings are available.
Edited at 2012-01-17 09:31 am (UTC)