Will I need a pressure tank?

System · February 2009

Hello, I am new to this forum and thank you all for the wealth of knowledge on this site. I am learning alot.

A little background:

I am considering buying a cottage on Sproat Lake, Vancouver Island, Canada. I am doing a lot of research into solar power, as it is off grid. I would like to have a small PV system that will run DC CFL lights inside, a few AC plugs for coffee maker, toaster etc and a DC water pump to operate the toilets and a shower. Also a Propane fridge and stove and hot water on demand.

The cottage is lakefront and I am brain storming about using a generator to run a large water pump to fill a holding tank near the cottage when I arrive, then use a small 12v DC water pump to facilitate a propane hot water on demand system.

I have been reading about an electric auto demand pump such as a shurflo [http://www.shurflo.com/pages/RV/rv_categories/potable_water/electric_automatic.html] and have been reading threads about paloma on demand water heaters.

My question is: I have been reading that the sureflo shuts off at 45psi?? so would it not have lots of preasure to run all the water without a preasure tank? I have been searching for answers to this without luck. Is a preasure tank needed in every situation?

I should also add, that this is a two story cabin with one bathroom on the top floor, one bathroom on the main and kitchen on the main floor. The tank would be located beside the cabin, roughly at that level or a bit below. No gravity assitance.

I imagine this little pump would not have the "pushing" power to lift water this far?

All help is appreciated! Thanks

icarus · February 2009

Re: Will I need a pressure tank?

You are probably going to want a Pressure tank.

Also,, you really have to consider your desire to use PV solar for heating appliances, toasters, coffee pots etc. They will require a very big system. 15 minutes of toaster uses as much electricity as I use in a day.

As we say so often,, do your math, figure your loads, and remember that every dollar spent in conservation will save ~ ten in PV.

I'll write more later.

Tony

Cariboocoot · February 2009

Re: Will I need a pressure tank?

What are your water demands? Easy question with difficult answer!

I use a standard water pump to charge a very large pressure tank. For years I ran this off a generator: firing it up and filling the tank while using water for bath/shower/dishes etc. The remaining charge gave about 30 gallons for use when the generator/pump was off. It now runs off solar, with a very expensive pure sine inverter. But I have quantities of water whenever I turn the tap. (A normal pump/well system runs 30-50 psi range.)

Several of my lake neighbors use the Shurflo type pumps and are satisfied, but they don't have the same volume/pressure of water available as I so patience is required when it's time to wash things.

ANY type of heating is better done using propane. Including making coffee. As Icarus says; uses as much in 15 minutes as the rest of your loads would all day!

Generators can be your friend. Especially if you need to produce a lot of wattage for a little while every now and then.

icarus · February 2009

Re: Will I need a pressure tank?

Please describe your current tank set up.

If, for instance, you have a large non pressurized holding tank, you could fill that with a high volume/low pressure pump,, either gas or electric. Quite frankly, if you are going for fuel efficiency, get a gasoline powered Honda pump and fill the tank at say 15gpm instead of running a generator and a electric pump. (Unless you have need to run a big generator for a while every day anyway). Some of it depends on how high you need to pump into the holding tank. You could then pump out of that tank with a small shurflo type pump into a conventional P-tank. If you oversize the p-tank you can do the majority of you pumping during good solar hours,, costing you few whs net/net.

Tony

System2 · February 2009

Re: Will I need a pressure tank?

I had a quick look at a table describing the power demands for each appliance. I was suprised to learn that a toaster uses as much as a microwave! 800-1300 watts. I will start doing the math to calculate my daily load.

Thanks for your advice. What I am thinking about doing is using the PV system for approximately 10 DC cfl lights and the shurflow dc pump. Also a P-tank if I need one. Since I will have to buy a generator for the construction, I will continue to use a gas generator for large loads like the toaster, coffee, charging laptop or what ever. [on a side note, do DC lights require different wiring and sockets? I know they are different bulbs]

I agree that a honda gas powered water pump would be the best way to fill the storage tank when I arrive. I have not done the math yet, but I will be looking for a 330-500 gal tank. Enough to flush toilets, shower, do dishes etc. I don't mind re-filling it while there and would drain it when I leave.

I have also been trying to learn about "direct charging". Not sure if that word is correct. What I mean is charging a battery bank from the generator, in low sunlight conditions. I have even seen home made "lawnerator" - lawnmower alternator frankenstein contraptions that some poeple are using to charge the battery bank. Looks like a good cheap backup??? not sure how safe.

As I mentioned in the first post. I am considering buying the cottage, but do not own it yet. It is a very big "handy man special" and will need to be gutted and nearly re-built. There is wiring in place to light sockets and switches. It looks like the old owner connected large batteries in the crawl space before. Not sure about he quality of the old wires.

Here's a pic of my project "dream cabin!" haha.

Thanks

BB. · February 2009

Re: Will I need a pressure tank?

Gasoline and diesel powered equipment is something that you should avoid... Noisy, smelly, and expensive to run...

Normally, define your electrical loads for as small as and most efficient devices you can use. LED lighting, CFL lamps, EnergyStar rated fridge or look at the converted chest freezer into a fridge project.

Otherwise, propane powered stove, fridge, hot water, etc.

Running a microwave on solar RE + batteries can be OK--they are pretty efficient and only ran for short periods of time.

Toasters, toaster ovens, coffee makers, etc. on Solar RE is just too expensive.

You can, of course, fire up the old generator to run your large electric appliances--but that entails fuel, oil changes, rebuilds, etc.

My recommendation is that you only start up the generator when you cannot use something else. Running your large power tools, large water pump (low pressure / high volume into a 2,000 gallon tank once a week type stuff). And try to make do with other sources of power for the rest...

I always find it useful to convert my energy costs into $$$/kWhr...

Your costs for power (very rough estimates):

$0.10 per kWhr (utility price)
$0.20-$0.40 per kWhr (grid tied solar)
$1.00-$2.00+ per kWhr (off grid solar with genset backup)

And you can figure out your own power costs.

For example, say your 5kW generator cost $500 and needs to be replaced every two year. And you run it every day for 30 minutes for toast and water pumping. And it takes 1 gph to run, your toaster is 10 minutes at 1,500 watts, and your pump is 30 minutes at 1,500 watts. Fuel costs $3.00 per gallon:

($500 + 0.5g*$3.00pergal*365days*2years) / [(1,500 watts * 10min/60min per hour + 1,500 watts * 30min/hour)*365days*2yrs*1/1,000wperkW]=

=$1,595 2yr costs/730kWhr 2year power generated (2yr life cycle)= $2.18 per kWhr

The above numbers are just made up--but give you an idea of how you can calculate your own costs.

-Bill

machineman · February 2009

Re: Will I need a pressure tank?

Many of the 12v Surflo pumps (including mine) have an adjustable pressure shut-off using a small hex key. They can go higher then 45psi. Problem is your flow will be very low for showers and such. However if you us a pressure tank and the surflo to slowly pressureize it then you can get the flow you want assuming the water is not on very long enough to releve all the tank pressure. Otherwise your GPM will only equal the pump output which might be fine for most stuff anyway. I use a 0.8GPM pump and 65w Solar panel to pump up 75ft to a large 2500gal tank and then gravity feed to the house.

System2 · February 2009

Re: Will I need a pressure tank?

The pump I am considering is a higher flow model.

http://www.shurflo.com/pages/RV/rv_product_sum/rv_sum_docs/potable/premium_water_pump.html

It says it is 3.5 GPM. Would this be enought to pump water through a propane hot water on demand heater and then provide enought pressure for a shower? What if it had to push water up to the second floor?

If not, Can anyone provide examples of a suitable pressure tank? I don't know much about pressure tank systems and if I can get hot water and shower without another piece in the puzzel I would be happier. Maybe this is a pipe dream? (pun intended)

How about DC?

Thanks.

BB. · February 2009

Re: Will I need a pressure tank?

Can you mount a pressure tank (or a large storage tank) on the hill behind the home/cabin? You still will have to pump the water up there--but then you will have static pressure to help move water through the home/plumbing.

Also, do you have a good southern exposure for solar panels (and you should look into solar hot water heating/pre-heating to reduce fuel costs)? Ideally, you want a minimum of 9am-3pm--winter and summer.

You can also get away with an East or West facing system (solar pV and/or hot water)... but power generation will suffer (especially in the winter).

If you have not yet--take a look at Home Power Mag. Will give you good ideas for your own project.

And, your first three steps. Conserve, then conserve, and conserve some more (insulation, double pane windows, energystar/efficient appliances/lighting/pumping, etc.).

And, you have to decide what your fuel availability and pricing will be... But, using less of everything through conservation (even extreme conservation) is almost always a winner.

-Bill

PS: DC or AC--the old age old question. In general, if you can find an efficient 12 volt (or better yet 24+ volt) DC device that meets your needs--that is great.

However, as the power requirements go up (more watts, more current) and the distance from the batteries increase (longer than a few tens of feet)--it is almost always better to go with an inverter. Sending 100 amps at 12 volts (1,200 watts) vs sending 10 or 5 amps at 120/240 VAC (also 1,200 watts) is a very costly problem (lots of big copper wires).

Yes, the inverters add loss--but use the savings in copper and DC device costs and put it into more solar panels and slightly large battery bank.

In the end, there is no correct answer--but if you work out the design and costs--you will quickly figure out which works best for your situation.

-Bill

machineman · February 2009

Re: Will I need a pressure tank?

Here's the specs on that pump. http://www.shurflo.com/pdf/rv/product_data_sheets/pds-2088-453-144.pdf
Note that the pump can only draw up 9feet from the inlet. (Like most can)

Here's an installation diagram
http://www.shurflo.com/pdf/rv/911_trouble_shooting/new/911-352-I.pdf

Assuming you have no flow loss due to friction (squeezing thru small pipes and minimal elbows) and the water is pumped and used at the same elevation then you will get 3.5GPM. I don't know how restrictive the water heater is but it will probably add 6ft of elevation becuase the inlet is at the top. 6 feet of elevation is about <3psi (using feet of head conversion = 0.43). So you will actually get about 3.2GPM and draw about 4amps. (See the chart on the spec sheet). For a second story lets say its 16ft from ground floor to the shower head, that would be <7psi at 2.7GPM at the pump and about 4.5amps.

The solar panel you would need is (4.5amps x 12V) = 54 watts Assumiing full sun and no other losses. You should get a 75watt or more. Using Linear current booster will help keep the pump running in low light situations so you should get one of those also. NAWS has one for sale.

When you shut off the faucet the pump will continue to run until it reaches the shut off pressure. Then when you turn it on it will burst water until the presure drops to the operating pressure (7psi for second floor). If the pump is adjustable you might want to reduce the shut off pressure to maybe 30psi or lower to prevent the pressure burst and reduce strain on the water heater.

Is 2.7GPM enough for a shower? I never measured it but you can use a gallon bucked and stop watch with you current shower and time how long it takes to fill up. Back it off to 2.7GPM and see if its OK.

Ecnerwal · February 2009

Re: Will I need a pressure tank?

Eww - the un-handy-man's special gift for the handy-man.

Bid low.

That's one of those fixer-uppers that may cost you more to fix up than to start over...

Will you be using it in freezing weather, or not?

Would it include higher land behind the house, which seems to be set into a hillside?

If not freezing and yes you have higher land you can use, park your storage tank up there and have gravity-feed water. That works well with a variety of solar pumps that just keep plugging away at filling the big tank up the hill - if you don't leave the toilet running, there's nearly always plenty of water in the tank. Can be done with freezing conditions, but suddenly involves a lot more digging to get the tank (aka cistern) and waterlines below frost.

If staying inside the house, you want a pressure tank. They are really not all that complicated, and they do make things work better. Get one described as a bladder tank or captive air tank, they take what mystery there is out of them until the bladder tears. Think of it as a battery for water pressure...not quite correct, but easier for most people to grasp than capacitor, which is the closer electrical equivalent.

Cariboocoot · February 2009

Re: Will I need a pressure tank?

Another consideration with DC lighting is wiring distance: the longer the run the more loss (see wiring loss calculator on this board). If the wiring is there, what size is it? If it needs to be ripped out anyway ... maybe consider an inexpensive MSW inverter and use standard 120 VAC wiring/lighting equipment which is more readily available.

Also, with a remote, off-grid cabin battery power tools are your friend! Although they require pure sine to re-charge, it's a lot nice to just fire up the gen and charge now and then rather than every time you want to cut a board or drill a hole. I've got a nice little Ryobi 18v set which was reasonably priced and has worked well for years.

Regarding pressure tanks, it is sometimes more practical to install two or more small tanks (must be the same and at the same place) than one very large one. Even a small one will help 'moderate' pressure fluctuations with a small pump. Water-saver shower heads flow less than 3 gpm.

It looks like you need to develop a "holistic" cabin plan before deciding to buy or not!

icarus · February 2009

Re: Will I need a pressure tank?

CC,

Not to pick nits,, but it has always been told to me that it doesn't matter where the P-tank(s) are, nor that they have to be the same size. Can you please explain your theory?

In my mind, a P-tanks is only a "wide section of pipe" with the walls of the pipe (the bladder) pushing the water out. 60 psi in one spot is the same as 60 psi somewhere else,, all else being equal.

Tony

BB. · February 2009

Re: Will I need a pressure tank?

~15 PSI per 30 feet of water.

For every 30 feet you can mount the tank higher, that is 15 psi less the tank has to be charged. I presume (and I may be wrong) that the lower the stresses, the longer the bladder will last.

Of course, in terms of energy use, no difference. And a 30 foot lower tank that never freezes is better than a 30 foot higher tank that does freeze (i.e., self destruct) in the winter.

There is the other issue of "water hammer"... I am not sure which is better--having the tank near the pump, or at the end of the pipe run. It may make no difference anyway (still need some sort of air chamber at the end of runs anyway to reduce water hammer).

-Bill

Cariboocoot · February 2009

Re: Will I need a pressure tank?

icarus wrote: »

CC,

Not to pick nits,, but it has always been told to me that it doesn't matter where the P-tank(s) are, nor that they have to be the same size. Can you please explain your theory?

In my mind, a P-tanks is only a "wide section of pipe" with the walls of the pipe (the bladder) pushing the water out. 60 psi in one spot is the same as 60 psi somewhere else,, all else being equal.

Tony

If the pipe runs are short it won't matter much. The longer the runs, the greater the pressure difference between points during actual use. If you have a pressure pump & switch down by the lake & 100+ feet of pipe to the tank the pump will cycle rapidly on/off and the tank won't get filled. This is an extreme case. The same thing happens with multiple tanks if they're too far apart or much different sizes; one tank will charge/discharge more than others and you won't get full storage capacity usage. The closer together the tanks - which is where the switch should be - the better. That's the theory, anyhow. In practice most applications are probably small enough that you wouldn't notice. An extension of this is long pipe runs within a large house: some taps will have lower pressure, especially with another tap open. That's why the 'modern' method is to 'loop' pipes back to the source - much like an electric grid!

I mainly suggest multiple small tanks instead of one big one because it can be easier to find them, cheaper to buy per gallon, and can offer installation advantages if space is tight. But not always.

Oh, and anyone who doesn't use PEX pipe at a cabin is asking for trouble!

Ever notice how for any one, 'simple' question there are often dozens of answers?

icarus · February 2009

Re: Will I need a pressure tank?

CC,

Gotcha,

As for PEX, it IS the best advance in plumbing in the last generation. There are a couple of cautions however. The first is that it will not tolerate sunlight/UV radiation. There have been problems with bulk PEX tubing sitting in wholesale yards in the sun failing in a few years, even though it seemed like new initially. Make sure you protect any installation from the sun. (I even ran my in lake water line INSIDE a piece of 1" poly pipe to keep the sun off it, even in 30' of water!) The other great advance are "shark bite" fittings. They are fittings that will fit PEX, Copper, CPVC all in the same fitting. So if you have to repair a frozen copper pipe, instead of cutting out the piece, draining the pipe, sweating in the new piece with a couple of coupling, all you have to do is cut out the bad section, cut a piece of PEX to fit, slide a shark bite on each end, slip it over the copper ends,, even wet, and bingo, your done. The are also approved for service in the wall! I wouldn't do the whole house with them as they are spendy, but for service and repair work they are the greatest invention since sliced bread!

Second, in any hydronic heating system you must spec and use PEX for the purpose or you will have pump trouble. Some of the PEX comes with an O2 barrier. That without the barrier will cast off something that damages cast iron pump impellers.

I also use PEX tubing for gas line use,, but you must use the gas approved yellow PEX and it also cannot see the sun. (The gas PEX requires very expensive fittings to get from PEX to IP or Flare fittings).

Tony

Ecnerwal · February 2009

Re: Will I need a pressure tank?

PEX without O2 barrier can be used for heat - but it means buying bronze or stainless pumps, and not using any iron pipe. If using a cast iron boiler it should be used with a heat exchanger to keep it separated from the boiler loop. It does not "cast off" anything, it just lets oxygen into the system, which makes iron things rust.

At the time I put tubing in my floor, the larger diameter stuff I could find to buy was not available with O2 barrier, so I simply plan my system around that reality. Having dealt with plenty of "supposedly sealed" boiler loops (all metallic, pre-PEX) that had rusty pumps which failed, I'm not too bothered by it, though it does mean far more expensive pumps. Had I used the small diameter tubing, I'd have significant problems getting adequate flow (too much resistance/dynamic head) - or I'd have had to make a lot more loops and complicate my tubing layout. Now that I still haven't completed the rest of the system, but years after the critical point where the concrete was poured, several sources of oxygen barrier in larger diameters have come on the market.

Will I need a pressure tank?

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