Need help with water storage

[AdironDoc]

Spoke to a few friends who are off grid. One swears his pressure pump keeps up with a 5 gallon pressure tank and that while he uses the shower, the pressure pump is pressurizing his tank. Another recommends a much larger tank which will result in less pressure pump activity. My setup will be off grid running on the battery bank. Any thoughts on ideal pressure tank volume for usually 2 people, sometimes 4, weekend camp? I was thinking at least 10?

Doc

[glenn kangiser]

Depends on source and needs.

What is your water supply?  Spring, rainwater, well?

If you have water available - cistern - tank - spring etc.  you can use a 12v RV type demand pump with integral switch and no tank.  A well requires more.

[AdironDoc]

The neighbor/contractor said I have the option of shallow or deep well, at $3K, or $10K. I will likely go shallow, as my needs are light, use intermittent. Pump will be on propane or attached to an array of batteries, with perhaps 1200AH. Solar fed. Needs will be light water use, 2 adults mostly, averaging 8 gallon showers each, occasionally up to 6 people. I was thinking a cistern of 65 gallons. Without a pressure tank, I'd need to hoist it into a steel tree stand 20-30ft up to get any  pressure, and not much at that.

My friend's 5 gallon pressure tank begins to repressurize after he begins his shower and he notes he has never run out of pressure. Others online have recommended far larger tanks as necessary. Any thoughts?

Doc

[MountainDon]

You mention a cistern, maybe 65 gallons. Does that mean that you intend to have the well pump fill that tank when the sun shines and then you draw water from that tank as you need water, up to 65 gallons total before the well pump refills the tank?

If so Glenns suggestion of a an RV type on demand water pump could be the solution. They have a built in pressure switch. The pump will operate only when a faucet is opened, a toilet flushed, or something leaks. That's precisely what our cabin uses. The pumps are available in 12, 24 VDC and some in 120 VAC. Different models have different GPM capacities.

[AdironDoc]

I'm cobbling together something that will work, but nothing is set in stone yet. I was going to run a solar pump, or draw power from the battery bank into a cistern. 65 gallons seems a reasonable cistern size for 4 people, but I've considered anything from 50 to 100. I have an Eccotemp L10 tankless water heater which will require 40PSI as per the manual. That necessitates a pressure tank and pump.I like the idea of staying with 12V as much as possible, so gutting the appliances from an RV seems like a great idea.

Glenn, is your RV pump with pressure switch pressurizing a tank or just providing pressurized water on demand?

[Source_to_Sea]

That pump can work either way. You'll likely get more lifetime out of if by using a pressure tank, but it's not that big of a deal either way. They're fairly inexpensive, so by a spare when you get one. Make sure to put valves on both sides to facilitate easy replacement.

[AdironDoc]

Thanks for the good info. Would you know what sort of pressure these RV pumps are designed to produce, if RV's use a pressure tank or on-demand system, and if so, how many gallons their tanks usually hold?

Could be, I'll gut an RV for the pump, lines, tank, right down to the shower head!

Doc

[MountainDon]

From the Shurflo website. This is my pump. Other models and makes will vary.
The material that came with this pump stated it was to be used without a pressure tank.

Name :                                                *SHURflo Classic™ Pump
Model NumbersOEM/Aftermarket :    2008-422-144, 2008-422-444
Voltage :                                              12 VDC
Dimensions Inches/Millimeters :        7.84" x 5.0" x 4.62"  [199 x 127 x 117mm]
Flow Rate GPM/LPM :                           2.8 GPM  [10.6 LPM]
Amps (Max.) :                                      7
Shut-Off Pressure :                             45 PSI  [3.1 BAR]

[AdironDoc]

Thanks Don! Sounds like a little workhorse putting out up to 45 PSI. I may snap one up online.

At 7 amps and 12V, thats 84Watts while running full out I assume. 2.8GPM is just over what my tankless heater can run so I would anticipate no problems unless I was using the hot and cold water on full. Anyway, do you suppose the 84W over the course of a shower or two will use up more power than pressurizing a tank with enough water for same? Theoretically, it's the same, no?

[glenn kangiser]

Sorry I was not here for more comment - working out of town long days.

Looks like others got it well covered.

I used one for a horse watering tank uphill on a customer project and one to pressurize an RO filter for higher output at our other house before we drilled a new well.  RO had a small tank -maybe a couple gallons and the horse tank just had a float shutoff.

I think it may use less power without the tank as it will not be working at full pressure during the shower.  The tank will always go to full pressure before shutting off.  84 watts should be at max pressure while flowing at lower pressure should require less.

[MountainDon]

Something just popped into my head, which may or may not matter here.

The specs for that pump state it can lift water up 10 feet or something like that. If you install it higher than the cistern storage tank the flow falls. Badly IMO. I remounted the pump from sitting an inch above the water tank (16" or so tall) to slightly below the tank outlet. I am much happier with the output. The pump sounds happier too, runs more quietly.

[AdironDoc]

The specs for that pump state it can lift water up 10 feet or something like that. If you install it higher than the cistern storage tank the flow falls. Badly IMO.

Thanks for that bit of info, Don. I was looking at the stats on your model and thinking I might upsize slightly to their larger unit. My tankless heater puts out 2.8GPM max, but if the hot water is running wide open, and the cold water tap is opened, the Shur-Flo would struggle. With the info you gave, it might be well to have a slightly stronger pump to allow for faster flow rate, and for a bit more in the suction department. I know that ideally, pumps push, not suck, but my cistern would either sit beside my cabin (unsightly), or be almost buried, under the cabin which will be on 2ft posts. A bit more "oomph" wouldn't be a bad thing, I suppose.

[MountainDon]

After my experience I would buy the pump before installing the tank, run some tests and then decide.

[Nevada Mike]

I have a cabin that I trailer water in as well. I currently use a 2500 gal tank outside of my cabin with a standard 110 shallow well pump under the house and a pressure tank inside under the stairs.  While I don't have the solution for you I have some observations after several years of use.  http://www.countryplans.com/cowan.html

1. Your pressure tank needs to be as large as possible.

I like to shut things down in the evening and not run the generator or inverter.  My pressure tank has proven itself to be too small.  It is a 25 gal or so and a few toilet flushes or so and its done. A 25 gallon pressure tank does not equal 25 gallons of useable water.  My neighbors use a 'booster" pump type of system that works fine but has its limitations. It is the small well pump with a 2.5 gallon pressure tank attached. It only works when the generator is on or it eats the batteries!

2. Larger holding tank is better

While I know how to live "like its an RV" the guests do not.  If they are not running back and forth filling the water tank they don't really get it even though you explain it.  As the host we smile hook up the trailer with the tank on it and go get more. I move 625 gallons at a time.

3. Bury the water lines from the tank and get them under the foundation stem wall.

My cabin is in Alaska and the water tank rarely freezes.  I drain mine in late November after the last trip and some of the locals never drain theirs.  The line from the tank into the cabin is a different story.

4. Insulate the crawl space foundation not the cabin floor.

If I were to do it again I would create an air tight foundation.  That goes against current logic but is gaining in popularity.  It involves spray foam and its easy at your stage.  The floor of the crawl space and the stem walls are insulated.  The earth is covered in plastic first.  There are no foundation vents in this type of system and the floor is not insulated.  It creates a warm floor and a dry crawl space.  I may still do this and I will draw air for my wood stove from the crawl space and I will place a dummy vent in the opposite corner of the cabin to draw warm and dry air into the crawl space.

5. Think about water filters as an integrated part of the system early and possibly UV treatment.

I wish I had figured out where I was going to put my filters earlier.  I still have not installed them.  Even though I haul in treated water a little extra attention is still needed if you intend to drink it.  You cant get all of the water out of a large tank and it does not look good in the spring.

Well I hope that helps and feel free to email.

[Dave Sparks]

Keep in mind if you oversize the pressure tank to a small pump you will stress pump parts and shorten pump life. From the old less is more design school of engineering. 

[wvrammer]

At my Dad's camp in Ontario we start the generator to pump fresh water from a shallow well to pressurize a large pressure tank once or twice a day depending on how many people are using the water. The old leather seal piston pump is a challenge to prime at times. The lake is close so we don't use the pressurized water to wash.  We generally haul a buckets of lake water to use in the toilet.  Hot showers are rare and come from solar hot water bag hung in the sun in the morning.

Opening the camp takes a while but it is not complicated.  Over the years when a low spot in the pipes didn't drain then froze and the pipe busted, Dad fixed the leak with a section of heater hose and clamps. I consider this a very elegant solution.  Hooking up 3 or 4 sections each year is not much of a chore.  Sometimes when the pressure is high or the hose is old and hard, it drips -- so be it.  The next year I replace the hose.  When we close, I loosen the clamp and pull off the hose.  Voila, no low points to freeze.  I am sure I am preaching to the choir here, but I am always amazed at how long 20 lbs of water in the tank will last.

My wife came to this place as an adult.  After some initial culture shock, she loves it as much a I do. Some DARE brand double fudge cookies (rationed of course), home made bread, Canadian ale, and an occasional Northern Pike to fry give us great happiness.  The northern lights make it almost heaven.

Good luck with your water!