Where to put pressure tank in off grid home.
I am building an off grid home on a site with an existing well. I am building the house about 200′ from where the well is. The well was drilled around 1970 and has a well-x pressure tank from the same era. I don’t think it was ever used, and I believe it is functional.
I have a separate solar system for the well house, and decided to add a 700 gallon cistern. I have a Grundfos SQ Flex Submersible pump that will fill the cistern, and a pressure pump that will draw from the cistern, and supply water to the house and 3 faucets on the water line between the well and house. I have ordered a new 32 gallon Well-X Trol pressure tank (I don’t really trust a 52 year old pressure tank no matter how gently used).
So with that long introduction; where should I put the new pressure tank? I have read that it should go into the house, but to do that I would need to either put the pressure pump in the house or run the control wires from the house to the pump. The other issue with the pressure tank in the house is the faucets will not have pressure if I put a one way valve at the house.
It seems like there are reasons to have the tank in the house, but what are the alternatives.
If I put the pressure tank in the well house, the faucets will have pressure and no issue with control wires. So that seems like the best solution, but it also means running the faucets will bleed pressure off of the house when the outdoor faucets are running.
I could try to use the old pressure tank and the new together. Which would mean running control wires from the house, and connecting the pump to both pressure switches. I think the reality is that if the pressure pump can’t keep up then having to pressure tanks will not help.
I have been rambling I know but it seems like I am missing something.
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If you have a well house I'm assuming you have a shallow well pump. Typically what you have is a check valve between the well and the pump so that the pump doesn't lose its prime. Then the pressure tank and the pressure switch are on the output of the pump. You want the pressure switch to be close to the pump, because on a long run there will be pressure drop when flow is high and you want the switch to reflect what the pump is actually seeing. But it doesn't matter where the tank is, it will function the same anywhere on the supply line.
Usually the biggest concern is keeping the plumbing from freezing. The pressure tank is the biggest component and inside the house is the easiest place to keep it warm. If your pump house is well-made (or you don't get freezing weather) the pressure tank could go there as well. I don't see any point to two pressure tanks, if you don't trust the old one get rid of it.
I have had three situations. One was off grid where the jet pump and pressure tank were both in a shed next to the house and the pick up from the lake was 100 feet away. This was a summer house so we didn't have to worry about freezing because we drained the system when we left. Worked fine.
Currently, another home has a shallow well in the basement with a jet pump and pressure tank. Works fine and never freezes. Another other house has a very deep well and submersible pump at 350 feet that runs underground to my detached, heated garage and the pressure tank. This then feeds the water to the garage and upstairs apartment, PLUS, we have a 1 1/2" (?) plastic water line underground that runs 60-70 feet to the main house.
The only time we ever have pressure issues with multiple faucets/showers going in the last situation is when the inline sediment filter needs to be changed. This system is 45 years old, with the tank and pump only being changed once each.
I would put the pressure tank in the house. This will give you more consistent flow rates in the house, and will be less of an issue with freezing, since presumably the house is better heated/insulated that the pump house. You can leave the pressure switch at the pump house, but test this setup -- if the pipe is too long for the flow rate required, you could potentially have some "bouncing" with the pump cycling off, then cycling on for a short period after pressures stabilize. You want to avoid short cycling. If the pipe between the main house and the pump house is sized appropriately, this shouldn't be an issue. The pressure at the pump house will read slightly higher than that in the main house while the pump is operating, with the difference being from "head loss" (pressure drop) in the pipe which is a function of flow rate. After the pump shuts off and the flow stops, pressures will stabilize and the pressure will read the same at both ends of that long pipe.
I wouldn't trust the old pressure tank, either, but for an additional reason besides just age: The old tank probably doesn't have a membrane/bladder in it, which means it will tend to gradually loose it's air charge, and when it does, it won't work as a well pressure tank anymore and you'll risk short cycling your pump. Since you probably won't be in the pump house all that often, you might not notice the tank needs to be recharged with air. Too much short cycling of a well pump will kill the pump.
Bill
Why the cistern? Seems a little complicated unless your well has a very low recovery rate or you have a big demand like extensive irrigation or livestock watering. If your well has adequate recovery/gpm it already acts as your cistern, so to speak, and your grundfos should do everything you need depending on the depth of the submersible and the amount of head.
That is a fair question, and ultimately it was a judgement call. I went back and forth on that decision, and hopefully it was an unnecessary expense.
The main reason is that the well casing has split at the point where it joins the well screen at 120 feet. At that point the casing bows in about 2 inches. The well was drilled down to 160 feet, and it is artisan so that static water level comes up to about 90 feet. I have tried unsuccessfully to find a driller to repair the well casing, they are all backed up on drilling new wells, so it's not worth it. On the advice of a driller, I set the pump right above the split. At that location with the pump producing 6 gallons a minute It will start surging after about 90 minutes. That is still a lot of water (540 Gallons), so I could probably get by. My fear is that because of the compromised casing the well will fill up with a significant loss of production. In that event, with a cistern we can get by with reduced output, or in the worst case by hauling water while waiting to get a new well, or repairing the existing one. Maybe it is a belt with suspenders, but I decided it was worth the 1500 and extra labor to add a modest sized cistern.
At this point it is a done deal so I might as well use it.
OK, here's what I'm thinking:
Put the pump at the base of the cistern. Put the pressure switch right by the output of the pump. Take all of your outdoor lines off of the line between the pump and the house. Put the pressure tank in the house.
Put a check valve on the input to the pump.
Thanks DC.
I am not sure I understand what you are suggesting, so if I have it wrong please forgive me.
As I understand it your design is the same as if the pressure tank is co-located with the pump in the well house the only difference is the distance to the tank. If that is true, what would be the advantage of putting the tank in the house?
Yeah, it doesn't really matter for system performance where the pressure tank is, as long as there isn't a valve between it and the pump. I like to put it in the house because it will last longer in a conditioned environment, pump houses tend to be damp. But it's not a big difference.
Thanks all for your responses. It has helped me process through the options a bit better than I had before.
The pit in the well house is underground and has insulation. I will likely need to improve the insulation, because the LiFePO battery which powers the submersible pump must be kept above 30 degrees for efficiency of charging and operation. Despite it being viable to put the pressure pump and tank in the well house pit, I have decided to put the pressure tank, and the pressure pump for the house in the basement of the house. I think this configuration will give the house the most consistent pressure which is where it matters most. I will put a check valve at the point where the water enters the house to isolate that circuit. The well house and cistern are at a slightly higher elevation so I think the jet pump will be able to draw from the cistern without a problem.
So ignoring the house for a moment the issue remaining is how to provide water to the rest of the system. For that I think, at least to start, I will make use of the old tank. In the most common scenario when you turn on one of the hydrants it will be to supply 10's of gallons at least. In that case the pump will be coming on anyway so as long as the old system triggers the pump to come on it will be doing its job. I don't think short cycling will be much of an issue. To supply the water to the outdoor circuit I will need to put a check valve upstream of the tie in point, because I intend to draw the water to the house directly from the cistern. I think I need a separate intake for the external circuit pump. I have not quite figured that out yet.
So the question remaining is if the 1" supply line will be sufficient with both pumps running in series. The supply line pipe is HDPE, so pressure will not be a problem. I am sure there is a calculation for the volume of water the pipe will support for the pump size, but that will take some more research.
What's difficult is that you haven't given us enough background as to why you're doing what you're doing. I don't see why you need two pumps or a cistern. I don't see why you want to separate the outdoor supply from the house. More background on your thinking would be helpful.
I do want to comment on one aspect of your design, which is that the pressure tank and the pressure switch don't have to be at the same point. It's possible to put the pressure switch in the well house and the pressure tank in the house-house. The only requirement is that both be on the same side of the check valve.