Number of Cycles, Large Tank verses CSV

[Cary Austin]

The number of times a pump cycles on and off per day will be the same with the Pside-Kick kit and 4.5 gallon size tank as it would be with an 86 gallon size tank and no CSV. The difference is the CSV system will make the pump cycle a few times for things like toilets and hand washing, but will keep the pump running continuously for longer uses like showers and garden hoses. While the big pressure tank system will let you flush a few toilets without the pump coming on, but will cause the pump to cycle repeatedly when using water for longer terms like showers and garden hoses. But the number of cycles per day will be about the same with both systems for in-home use alone.   The CSV will allow the pump to cycle for a few random toilet flushes, which is not detrimental to the life of the pump.  But the CSV will keep the pump running continuously during long-term uses of water as with showers and garden hoses, as that is more important to the life of the pump. 

When you are using water for longer terms like a shower, the large tank will deliver varying pressure as the pump cycles from 40 to 60 PSI then drains from 60 to 40 PSI. So part of the time you are in the shower you will have 60 PSI and part of the time you will only have 40 PSI.   And for longer-term uses of water like hoses or irrigation, the larger the pressure tank the fewer times the pump will cycle.  But the pump will still be continually cycling on and off, which will shorten the life of the pump and system.

With the CSV and small tank, you will have a strong constant 50 PSI all the time, even if you are in the shower for a month. And a steady 50 PSI delivers much stronger shower pressure than when the pump cycles between 40 and 60 over and over, as when no CSV is used.

Most people already have 500-1500 gallons of water stored in a supply tank or get water from a well where there are millions of acre feet of water at their disposal. An 86 gallon pressure tank only holds 23 gallons of water.  What good is storing another 23 gallons when you already have so much water available?  23 gallons would not even be enough for a shower. The ONLY reason for a large pressure tank is to limit the pump cycling. And when you have a Cycle Stop Valve to do that for you, a large tank is no longer needed. The Pside-Kick kit is less expensive, takes up less space, is easier to install and service if needed, and delivers stronger shower and sprinkler pressure than a large pressure tank. The big plus with the CSV is that it will adjust to any flow rate for any length of time.  With a CSV there is virtually no flow rate you can use that will cause destructive cycling of pump, even if water is being used 24/7 and 365.

[moxiemoney]

I guess I don't understand: if the number of times the pump cycles is the same, why would the CSV be easier on your pump than the 86 gallon tank? Unless there's a difference on how the pump turns on and off with the CSV, seems to me that unless you will use long term watering (sprinklers, long showers, etc..) frequently enough so that the number of pump cycles is higher for the 86 gal. tank vs. the CSV system, then there is no benefit. Am I missing something?

[Cary Austin]

The number of cycles per day for a CSV and small tank compared to no CSV and a large tank are the same when the water is used only for the house.  The main benefit is that the CSV will make water used in the house come at a constant 50 PSI, instead of going from 40 to 60 and 60 to 40 over and over again.  Constant pressure makes for much better pressure in the shower, washing machines fill faster, and keeps instant water heaters from going on and off as they do when the pressure is varying from high to low continually.

And yes the CSV is beneficial to the pump and system when it does start or stop.  The CSV gives the pump a mechanical soft start and soft stop.  With a CSV the pump can start at 1 GPM, which reduces the starting amp load on the motor.  The CSV also  keeps the check valve from flying open, and eliminates the pressure surge or water hammer that is normal to a non-CSV system. Then when the pump shuts off the CSV has already reduced the flow to 1 GPM, so the check valve does not slam and cause water hammer.

Not to mention the space and heat savings of the smaller tank with a CSV verses the larger tank.  Not only does the smaller tank take up much less space, but you don't have 23 gallons of cool water coming into the house several times per day, which soaks up heat from the house and waste energy.

Also with the CSV and small tank the water coming into the house is fresh from the well and hasn't been sitting in a rubber bladder getting warm for several hours.

The point is that even when water is only used for the house, there is no benefit to the larger tank.  And anytime water is used for extended periods of time like filling a pool, irrigation systems, or just using a garden hose, there are considerably more benefits for using a CSV. 

[Wolpy]

Interesting!

[mxtoomes]

hi - hope everyone at CSV is safe and healthy.

you mentioned "The CSV gives the pump a mechanical soft start and soft stop.  With a CSV the pump can start at 1 GPM, which reduces the starting amp load on the motor."

would you explain how this occurs?  it seems like the pressure switch in the youtube video "Pressure Tank with Cycle Stop Valve Installation Sharpie Drawing" is a basic on/off switch, and therefore would not regulated amperage.

thanks

[Cary Austin]

You don't have to regulate amperage for a standard full speed pump.  The amperage will naturally self regulate on any pump as the flow of water is reduced.  it is not the 40/60 pressure switch that causes the amperage to decrease but rather the restriction of flow from the CSV.  Reducing the flow with a simple valve of any kind will reduce the amp draw of the motor almost exactly as much as varying the pump speed.  This is just a natural phenomenon of any pump and people who sell VFD's just don't understand how pumps work.  Actually I think many do understand and are just letting the wool stay pulled over your eyes so they can sell you and expensive and short lived VFD.

Starting a pump against a closed or almost closed valve as with a CSV also gives a mechanical soft start because of the same natural function of a centrifugal impeller as described.  When starting against a closed valve the amplitude and duration of the starting current is greatly reduced.

[Don]

Hello - thanks for all the good info on this forum!  I get that a small tank is all you need for the house, but I'm wondering if a large low-pressure tank might work well for a geothermal HP? I'm building a new home and just drilled the well - 175 GPM with a 20' static head. My two-stage geo needs between 4.5 and 8 GPM (at just a couple of psi), and I'm estimating the house at 14 GPM (2.5 baths, DW, front-load washer, just the two of us).  I'm thinking about putting in a 1/2 HP 25 GPM submersible to fill a large unpressurized tank to supply the geo, and a 1/2 HP booster with a CSV to supply the house at 50 psi. 

My thinking is that when the house isn't using water, the well pump will fill the large tank, running at its pressure/flow efficiency sweet spot.  When the geo comes on, it gravity feeds from the large tank.  If someone opens a tap, the booster kicks on.  If the well pump is currently filling the big tank, it just reduces the flow into the big tank to meet the house demand.  If the well pump is off, it comes on with the booster, again running at its sweet spot, since whatever excess the house doesn't need goes into the big tank.

I think the big tank needs to be big enough to supply the geo for at least one complete heating/cooling cycle, and should only call for water when it's empty.  That would minimize cycling while supplying the geo.  And, any time the house calls for water when the big tank is less than full, the well pump would run at peak efficiency even if it's just supplying one sink in the house, because it's filling the large tank with the excess.  If the geo empties the big tank, the well would kick on and refill it, again running at optimum efficiency.  The only time the well pump isn't running at peak efficiency is when the geo tank is full and the house calls for water, at which point the CSV throttles the flow, reducing the power consumption of the well pump (although at a significantly reduced efficiency).

Am I thinking clearly?  Not pretending to be any kind of expert, but trained as an electrical engineer and like to learn new things.  Having a lot of fun designing this system for our new house.  Thanks.

[Cary Austin]

Hi Don
I don't think you can run the Geo system at 2 PSI.  Most geo systems need about 20 PSI to overcome the friction loss in the heat exchanger coil.   Have you looked at how we do a two pump system for a Geo?  You don't need a storage tank because you have millions of gallons stored in the well.  You don't need a very large pressure tank because the CSV will keep the pump from cycling.

A small pump in the well working with a 10/30 pressure switch and a CSV set to 20 PSI can supply the geo by itself.  The low pressure well pump can also supply water to a small booster pump as well.  The booster pump has its own pressure tank and pressure switch working at 40/60 with the CSV set for 50 PSI.  In this way the well pump feeds the geo, and when the house needs water the well pump and the booster pump run at the same time.

[Don]

Hi Cary,

Thanks for the quick response!  I'm putting in a Tetco TY-036, two-stage, 3 tons.  The spec sheet gives the pressure drop across the heat exchanger as 1.0 psi at 4.5 GPM and 2.8 psi at 9 GPM.  I'm in PA, with 50F ground water.  The COP increases by about 10% for the higher flow rate, so I'd rather err on the side of higher flow.  I was thinking that a plastic tank, couple hundred gallons maybe, mounted on a platform, would give me at least 2-3 psi.  Maybe that's not enough?  20 psi seems like overkill, but it probably would be a simpler setup.

Don

[Cary Austin]

Add in the pipe, elbows, and other fittings going in and out, plus the electric valve itself has quite a bit of friction loss.  You can always turn the pressure down if needed, but people usually want to turn up the pressure, not down.  Also not much difference in pumping energy cost between filling a tank at say 10 PSI and going straight to the Geo at 20 PSI.

[Don]

Friction losses noted - I hadn't taken that into account, and at the flow rates the HVAC needs, they would be significant.  I did think about doing a two pump system, but that requires that I run a high-flow submersible at low flow a lot of the time, and the efficiency drops off a lot at lower flows.  I still like the idea of an unpressured storage tank for the HVAC.

I'm thinking of putting a small high-flow, low-pressure DC pump at the outlet of the tank, together with a Hall-effect flowmeter to do closed-control of the flow through the heat pump.  If I do that, then maybe I could get away with just one well pump that would be able to supply the house at 50 psi and send the excess to the tank. 

Can you put two CSVs in parallel?  One 50 psi for the house and another one for the tank?  I'm thinking that if the one for the tank was set just a notch above 50, then it would open any time the pump was capable of producing more water than the house required and send the excess to the tank, and close if the demand was high enough that the house pressure fell below 50.  Am I thinking clearly?  Thanks for your patience in answering my questions.

[Cary Austin]

Won't do any good to have two CSV's.  Water will take the path of least resistance anyway.  What I normally do to fill a storage tank but not starve the house for water is use an electric solenoid valve with pressure sustain to fill the storage tank. Setting the pressure sustain at 40 to 45 PSI means only the excess above what the house needs goes to storage.

If you get the right high flow low pressure submersible like a Grundfos, the amps at low flow drop considerably and it is fairly efficient for the heat pump.

If I am right about the 20 PSI needed, a storage tank would need to be 46' tall.  Using a booster pump to draw from the storage tank and produce 20 PSI to the heat pump probably won't be much different than just running a high flow low pressure well pump. Especially because the water is being pumped twice.