Gravity fed or pressurized system ?

treefrogtreefrog Posts: 7Registered Users
I have read a lot on this forum but this is my first post.

My family has a cabin on an island that is off the grid. We have a propane fridge/freezer and stove/oven. Heating of cabin is by wood fire stove. I want to setup a solar/battery/inverter/genset system but am first trying to work out how many watt hours we require. So to figure that out, I first need to work out our water system to see if it needs to be pressurized (requiring electricity). I will save my electricity questions for another post.

Currently we are drawing water from a creek. We are going to add a water tank (1100 US gallons, 4100 litres). The spot we were planning on putting it would give us about 6 psi (0.4 bar) of pressure from gravity alone. I know that in the UK you can buy showers and taps that are made specifically for low pressure (0.1 to 0.5 bar) so that is not a problem. Now I was hoping this would be enough to run through I tankless hot water heater so that we would not need to have a pressurized system (to save money, electricity and to just eliminate one more piece of equipment that could fail). I found a tankless heater than will activate with 8 psi made by Marey but that is still too high. For that to work I would want 10 psi to be sure it would not cut out, and that means an extra 8 feet (2.5m) of height which would require either a structure or making a flat spot much further back in the woods on a slope, both being difficult but could be done if really needed. So does anyone know of any tankless heaters that will activate on 5 psi? To explain more, we want to be able to supply hot water to a shower, bathroom sink and kitchen sink. Not all needs to be able to be used all at once, one at a time would be fine.

Am I putting too much thought into all of this? or would it be better to just go with an electric pump to pressurize the system? In that case how many watts does one of these use? and does it make any difference then if I put this water tank above the house to get 6 psi or under the house where it would have a negative psi?

Or any other suggestions?

Thanks

Comments

  • BB.BB. Posts: 27,350Super Moderators admin
    Re: Gravity fed or pressurized system ?

    You can use an RV pump (12 or 24 VDC)... Should work nice. Something like less than ~100 Watts @ 12 volts (~9 amps maximum).

    Suggest that, if possible, you have a screen and positive pressure on the pump inlet. The more lift you require of the pump (~20 feet is about the absolute operational maximum), the less reliable it will become (drawing a vacuum, air leaks in lift pipe, screen clogging, etc.).

    Also, will you have problems with freezing temperatures?

    http://www.solar-electric.com/solar-water-pumping-guide.html

    http://www.solar-electric.com/wind-and-water-products/sodcwapu/shacdcwapu.html

    And welcome to the forum Treefrog!

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    An RV water pump is the way to go. We've used one in our cabin for many years with no problems at all. The pumps have a pressure switch built in; no need for a pressure tank. We use a Shurflo here in the USA running a 12 VDC model through a 24/12 converter. I went 12 VDC because those are easy to pick up at any RV dealer if a replacement is needed. The 24 VDC would most likely need to be ordered.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    Thanks for the replies and suggestions.

    Just to clarify. Water from creek to water tank (1100 Gal) is gravity fed, so no pump is needed there, and I will be adding filters in the pipe before it enters the tank, since bits do make it through at the moment. Its just whether I can get away with not adding a pump between the water tank and the house. I thought it would be less hassle to not added one and just use gravity from the water tank to the house. But you have both suggested little inexpensive 12v/24v pumps to pressurize the line. I assume it would need to run every time the tap was opened if I do not add a little tank to act as a capacitor? and is a 24v to 12v converter recommend over a 115v pump from the inverter? I assume so because I can then get away with a smaller inverter.

    In the winter it could/will freeze here but we do not plan to be here in the winter and will drain the lines before we leave.

    Thanks
  • inetdoginetdog Posts: 3,121Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?

    RV water faucets often include a switch that turns the pump on when the valve is opened. If that is not done, there will often be wall switch near the sink or shower that turns the pump on.
    A small pressure tank and pressure switch along with a one way valve at the pump (may not be necessary for some pumps) will do the job too and will remove the need to put switches at several places inside.
    SMA SB 3000, old BP panels.
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    Shurflo and Flojet brand RV water pumps incorporate a pressure switch in the pump housing. With all points of use shut off the pump runs until pressure builds to the set limit of 30 to 40 PSI. Then the pump shuts down. A well maintained pressure water system will hold that pressure for weeks on end if no water is drawn. Open a faucet; the pressure drops and the pump runs until the faucet is closed. I do have a disconnect that cuts all DC power to the small DC devices we run. That is pulled when we leave to head off any issues if a water line or something failed during an absence. There are pumps with varying pressures and varying GPM capacity.

    Only once in the space of the last 8 years I did have a small piece of something gets stuck in the pump valve system. That was last year. That caused a small bleed back and the pump would run for a second or so every 10 -15 minutes. Disassembly and cleaning cured that. No water leaked out of the system, it was just a nuisance noise that over time could have become worse. WEe run a filter immediately before the pump but I guess the screen was not fine enough. I don't like trying to suck water through a finer filater. Pumps do not like that much.

    Since our cabin is in the boonies I stock a repair kit, valves and pressure switch. The pump motors seem to have very long life. I have never replaced a pump motor in 30+ years of RV use.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    There are 115 VAC versions but why make the inverter have to run? Add to that having a few DC lights may be a good idea. In summer when we were blasted by lightning the OB inverter was one of the main casualties. The water pump and DC lights still worked and made life easier until the backup inverter wa shauled out. I waited a whole day to do that while we sorted out what had been killed and what was okay.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    and is a 24v to 12v converter recommend over a 115v pump from the inverter? I assume so because I can then get away with a smaller inverter.

    Nothing wrong with a 115 volt pump, especially if the pump is a long distance from the battery. There are all sorts of quality pumps to choose from, but I do NOT recommend the 115 volt versions of the RV pumps (shurflo, aquatec, flojet, jabsco, etc). This is because the high voltage in the AC pumps will wear out the (non-replaceable) brushes in just a few hundred hours. I learned this the expensive way. by the way, in the pumping world, these RV type pumps are usually called 'demand pumps' because they have built in pressure switches that respond to the demand. The exact same pump without the switch is called a transfer pump.

    Although I don't recommend the 115 volt demand pumps, there's nothing wrong with the 12 and 24 volt versions, either of which I recommend for your situation. By the way, after the brushes wore out in my 115 volt shurflo, I replaced it with a 12 volt jabsco which I power from 115 volts (via a 12 volt power supply located near the pump). I could have bought the 24 volt version and powered it directly from my batteries, but i did not want to run 70 ft of cable from the battery. My inverter is on all the time anyway, so I bought a 10 amp, 12 volt power supply to put near the pump, and I power the pump from battery to inverter to power supply.
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    Good to know about the reliability of these pumps. And running one of these to a propane tankless heater is pretty standard?

    This 'demand pump' will be under the cabin so 12v/24v seems best since it will be a short run of wire from my proposed 24v battery bank. So would a setup like this from Flojet be good? or am I better off making my own setup? http://www.xylemflowcontrol.com/marine-and-rv/water-pressure-systems/flojet-water-pressure-pumps/switched-pumps/2840-series-high-volume-pressure-systems.htm
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    I've never liked the idea of an accumulator tank in an RV or a part time use cabin. It is just another item that needs to be winterized. I prefer to drain rather than fill lines with RV antifreeze. If the plumbing has not been built in yet try to have pipes slope to low points where drain valves can be located. Almost all our pipes drain themselves when I get ready for winter. I have one unavoidable loop that requires an air blowout but with a preinstalled air valve that is easy enough.

    The use of an accumulator will reduce pump cycling and that should increase pump life, but I've had any issues with the DC motors, and only one pump issue that was related to dirt not cycling. It will also eliminate or reduce any pulsing that sometimes can occur if two or more points of use are opened simultaneously. The accumulator may even save power if the number of motor starts are reduced.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • westbranchwestbranch Posts: 5,009Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?

    you can make an accumulator (also called an air hammer) with a vertical mounted 2 - 3 foot piece of PVC a cap, a bicycle type air valve, in a hole drilled into the cap and teflon tape sealed, and a compressor.

    Mount it above the highest pipe after the pump and fill once a year. it can also be used to blow out some problem pipes. fill system in spring with water, turn on the pump to bring it up a bit and then add air till you hear a bit go down the line, have a tap open , then you know the accumulator is full of air. Top up during the use season if the pump cycles in shorter spurts...
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
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  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    So would a setup like this from Flojet be good? or am I better off making my own setup?

    Build your own. If you wish, you can use a regular residential pressure tank rather than one of those little accumulator tanks that they sell for RVs.

    btw, it is not uncommon to have two plumbing circuits in a situation like yours. You might, for example, run gravity to the kitchen sink and pressurized water everywhere else. You will need a separate hot & cold spigot at the kitchen sink... don't try to mix gravity cold with pressurized hot in a mixing faucet.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    Mountian Don, I have not put the plumping in yet so I will take your advice on installing drain valves at the low points when i do it. I assume PEX is the best choice these days.

    I will have to decide on whether I put in an accumulator tank and if I do whether I make my own of buy one. I do like the idea of not having the pump come on every time I turn the tap on.

    vtMaps, I like this idea of having two plumbing circuits for the kitchen sink. I was trying to figure out a way take advantage of the gravity fed and this seems like a good ways to do it.

    As for check valves, are they required and where are the recommended spots in the plumbing to put them?

    Thanks
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    I like PEX a lot. The tubing can withstand freezing, but not the fittings. Three types of fittings and bands to choose from; black bands that are crimped, S/S that are cinched and Uponer/Wirsbo. Uponer is used by pros a lot; some advantages, more expensive tools.

    PEX needs to be shielded from direct UV exposure.



    Not sure if there are any requirements for a check valve in a std residence. Was there a particular instance you were thinking about?
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    I was thinking about in parallel with the demand pump so that if I am out of power or the pump is switched off some water would still come through the taps by gravity feed.
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    I was thinking about in parallel with the demand pump so that if I am out of power or the pump is switched off some water would still come through the taps by gravity feed.

    OK... what I was suggesting is a separate faucet for the gravity... I think you want one faucet that defaults to gravity when the pump is not working. That can be done. You need to put a check valve in the gravity side of the parallel plumbing circuit. It needs to be a 'swing check' type of check valve.

    I removed the water saving flow restrictions in the faucets that I use for low pressure. Once you remove them, I'm not too sure they would be pleasant to use with high pressure.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    vtMaps, I did understand your separate line for gravity only. I am planning to do that for a kitchen faucet (gravity cold only). Plus have a mixer or hot only for kitchen too (pressurized). I think this was what you suggested to me. The washroom and shower with be pressurized. But was just thinking that if no power or pump fails it would be nice to at least has some water come out of the washroom faucet even if it would be cold low pressure, so that was why I thought of putting in the check valve parallel with pump.

    btw where are the water saving flow restrictions usually found? Is in the little mesh at the tip of the faucet?
  • BB.BB. Posts: 27,350Super Moderators admin
    Re: Gravity fed or pressurized system ?

    In the US, if you want a "full flow" faucet--Get a laundry basin faucet. No flow restrictions and full sized passages--Should work well with low water pressure.

    I think it was this one, or similar to it that I purchased:

    http://www.deltafaucet.com/kitchen/details/2133lf.html

    Pleasantly surprised--And 1/2 tempted to replace my "nice" low flow kitchen faucet with one.

    Modern fixtures can have flow restrictions in several areas--An add-on at the house plumbing connection, or in the head (may even need to drill out an orifice). But many have such small passages, that even with flow restrictions/aerators removed, they probably will not move much water at low pressure.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    btw where are the water saving flow restrictions usually found? Is in the little mesh at the tip of the faucet?

    As Bill mentioned, there are several different designs. The restrictions I removed on my several faucets were the ones out at the tip.
    BB. wrote: »
    But many have such small passages, that even with flow restrictions/aerators removed, they probably will not move much water at low pressure.

    To meet federal guidelines, residential faucets must conform to certain flow standards... they try to deliver a fairly uniform max flow rate, no matter what your house pressure is. The way they do this is by carefully designing the flow paths to induce turbulence at a certain low pressure (maybe about 8-10 psi?). The water flow follows ohms law (increasing the pressure increases the flow) until turbulence is achieved. At that point the flow does not increase much at all as pressure is increased.

    I have found that I get a very adequate flow through my kitchen and bathroom faucets with about 5 psi. My showerhead is a garden hose sprinkler head and we can get about 3 gpm through it with only 4 psi (showerhead is higher than faucets, so less psi).

    The OP has lower pressure than I do, and I expect that if he uses regular faucets (with tip restrictor removed) he will have disappointing results. Bill mentioned the solution:
    BB. wrote: »
    In the US, if you want a "full flow" faucet--Get a laundry basin faucet.

    Also, most bathtub faucets are 'full flow' without turbulence restrictions. Many can be adapted to the kitchen sink. Also, restaurant sink faucets are available in various flow rates... I recall seeing faucets rated to 5 gpm.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • treefrogtreefrog Posts: 7Registered Users
    Re: Gravity fed or pressurized system ?

    Bill, thanks for the tip.

    vtMaps, when I wrote that I will have about 6 psi that was calculated to the height of the shower head. So its seems I would have slightly more than you. And as I wrote in the first post I would prefer to just have gravity for everything. Its just I cannot figure our a way to get hot water without upping the psi so that it work with a tankless heater. So how do you heat your hot water line in your system?

    After you gave me the tip of having two circuits I found this cold only faucet ( http://www.blancocanada.com/frames/BlancoStart.htm#/pages/DC-St-Produc00-Kit0-Compac0-FLORA_.htm ) that I thought would work well but if it does restrict flow too much and those restrictions cannot be removed I will need to look elsewhere. Though Bill's and yours tip on laundry and bathtub faucets is good I don't really want to have two faucets on the kitchen sink each with their own hot and cold knob. Not sure it would fit plus it would probably be confusing. Attached photo of my sink, we have removed the hot water knob since we have no hot water. We did remove the screen at the tip years ago and flow is quite good. But we would like to now add a hot water system and finally have a washroom sink faucet and shower.

    Attachment not found.

    I know that in the UK low pressure faucets are readily available since it is quite common to have a cold water tank in ones attic. The faucets they advertise work with pressures as low as 0.1 bar (1.5 psi)!! and look really nice too. http://www.islandbathrooms.co.uk/sub-category/low-pressure-taps

    thanks again for all the advice.
  • Mountain DonMountain Don Posts: 493Solar Expert ✭✭✭
    Re: Gravity fed or pressurized system ?

    How much hot water do you need? And is a tankless the only choice? Are there any official inspections / approvals involved by government agencies?

    I ask as when we built our cabin I pondered how to make water heat for everyday use from kitchen to showers. It was a given that propane would supply the heat and maybe someday I would supplement that with a solar heater.

    I went with an RV water heater; 6 gallon size with pilot light. There are also some with electronic ignition. The heater mounts through the exterior wall and is under a kitchen cabinet. I have extra insulation around it. For our normal use, once the water is up to the set temperature )low on the thermostat) I turn the burner to pilot only. The heater set like that provides all the hot water we need for normal use. If more than one of us wants a shower I switch the burner back on.

    If you get sufficient flow from a faucet or shower fixture from gravity flow this water heater should also work with gravity. I might choose to use 3/4 PEX instead of 1/2 to reduce internal line loses, and a minimum number of fittings. We do use a 12 volt RV water pump.

    Using an RV heater will not pass residential plumbing codes though.

    Just a thought. Some of my reasons for not going tankless include; draining some on demand tankless heaters can be a task when winterizing. Sometimes they don't like low flow rates, let alone low pressure. They need vent piping if mounted inside and can freeze in cold weather when mounted outside. When dealing with quite cold incoming water some do not have a very high temperature gain.
    Northern NM, 624 watts PV, The Kid CC, GC-2 batteries @ 24 VDC, Outback VFX3524M
  • vtmapsvtmaps Posts: 3,738Solar Expert ✭✭✭✭
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    vtMaps, when I wrote that I will have about 6 psi that was calculated to the height of the shower head. So its seems I would have slightly more than you. And as I wrote in the first post I would prefer to just have gravity for everything.
    OK... I misread your post... I thought you had 6 ft of head. You should do just fine with gravity pressure.
    treefrog wrote: »
    Its just I cannot figure our a way to get hot water without upping the psi so that it work with a tankless heater. So how do you heat your hot water line in your system?

    I have fairly hard water so I never considered tankless. I use a 50 gal propane direct vent water heater. It has side taps, and is located above my woodstove... I hope this winter to hook up a coil in the woodstove to the side taps and make hot water (in winter) from the woodstove. Looking further into the future, I hope to hook up a heat pump water heater for use in summer. Anytime the woodstove or heat pump does not produce enough, the propane will seamlessly kick in.

    I think there are tankless heaters that are rated to work with 6 psi... not sure how well they work. It will also be difficult to find a washing machine and a dishwasher that work on 6 psi. Speed Queen still makes an old fashioned agitator type washer with mechanical controls that will work well with low pressure. I'm not sure there are any modern dishwashers that will work with low pressure.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • GrinninGrinnin Posts: 39Solar Expert
    Re: Gravity fed or pressurized system ?
    treefrog wrote: »
    I was hoping this would be enough to run through I tankless hot water heater so that we would not need to have a pressurized system (to save money, electricity and to just eliminate one more piece of equipment that could fail). I found a tankless heater than will activate with 8 psi made by Marey
    The tankless heaters I've seen from Marey require 110V to work, even the gas-fired heaters. So when you use hot water you need the inverter anyway. The amount of current required for a simple pressure pump would be a small addition. Perhaps Marey makes heaters with DC controls that I don't know about. There ARE gas water heaters that don't require electricity and I've repaired and adjusted and cursed one at the orchard where I occasionally work (Bosch). The little in-plumbing turbine that generates electricity for the control electronics really requires more water pressure than the specs say.

    Beware reading specs -- the number may represent where the device fails even in a well-controlled development lab, let alone the variable environment where it's installed.

    My own water system is 1500 gallons of rainwater in the ground with a 12V ShurFlo. I don't pay attention to the amperage of the pump but the UV element on the filter uses more current than the pump.
  • wiliamjakewiliamjake Posts: 1Registered Users
    edited February 15 #24
    dear have you seen some of the [stuff... -BB moderator] they are passing off as faucets lately?
    the price hasn't come down but the no-lead laws have forced the manufacturers to switch from good quality heavy brass to plastic [stuff]..

  • mike95490mike95490 Posts: 7,611Solar Expert ✭✭✭✭
    I'd go with the simple elevated tank and slightly oversize pipe (like 1" pipe instead of 1/2", much lower flow resistance).  If the water is insufficient to trigger the heater, then install a RV booster pump only for the hot water system.
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  • EstragonEstragon Posts: 2,219Registered Users ✭✭✭✭
    With the thread being over 3yrs old, let's hope OP has it figured out by now :smile:
    Off-grid.  
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  • BB.BB. Posts: 27,350Super Moderators admin
    He is probably he is probably out of Pakistan. Giving him a chance.

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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