Will this work? (Two booster pumps for different purposes plumbed and wired in parallel)

[MarsGeo]

We bought a house 25 years ago that came with a well, 5000 gallon storage tank, and a 5hp pump to send water from the storage tank to a pressure tank and the house. (I believe the large pump is required to run the home's fire sprinklers and was required by code.) Everything worked fine until we bought a 14kw Champion Axis home standby generator for our frequent week-long power outages here in the Santa Cruz Mts. If the generator tries to start when the pressure tank is low, the startup-draw of the 5hp pump prevents the generator from starting.

I believe I found an electrical solution: Champion has a Load Management Module, that communicates via powerline and will disconnect the 5hp pump before the generator tries to start. But that will leave us without water when we're on generator power. The solution I'm asking about is:
Can I plumb a smaller pump in parallel with the big one, that will run on either generator power or PG&E. (Tentatively thinking of a 3/4hp pump for our 4-bathroom house that is ~200 ft away from the storage tank and pressure pump).

The new pump wouldn't be under load control, and would be the only pump running on generator power, and it would have its own check valve. Its pressure switch would be set to turn on at say 40 psi, whereas the big pump now turns on at 38 psi. Under normal operation (PG&E power), the big pump would only turn on if the small pump let the pressure drop lower down to 38 psi (which might never happen).

My questions are:
(1) Do you foresee any problems with this plan?
(2) If it turns out that the large pump never turns on, how often should I turn off the small pump to give the large pump a chance to work? It was 7 years old when we bought the house, so now it's 32. I'd like it to operate we ever did have a fire.

Thanks for any tips about this.

 

[Chucky_ott]

I can't answer your parallel pump question but did you contact Champion technical support for more information on the LMM?

Do the LMMs keep the power off permanently or will it periodically retry to see if the generator can handle the load? Maybe once the generator is running, it would be a non issue for the pump to start.

Maybe the solution is to have several LMMs with the priority on the pump LMM set to high and the priority on another device set to low.

Or maybe remove one or more house circuits from the generator load. I think running your water pump, especially if it is used for a sprinkler system, is priority one (along with heat and refrigeration).

Have you checked the current building code to see if the pump requirements are still the same?

Have you checked to see if newer pumps have lower startup draw?

 

[Sponsor]

 

[Reach4]

(2) If it turns out that the large pump never turns on, how often should I turn off the small pump to give the large pump a chance to work? It was 7 years old when we bought the house, so now it's 32. I'd like it to operate we ever did have a fire.

I expect each pump would have its own circuit breaker feeding the respective pressure switch.

Running the fire pump periodically makes sense to me. Maybe make that an annual test, and part of your annual procedure to check the air precharge, and whatever.

 

[Valveman]

Your plan is a good one. I would probably drop the on setting for the 5HP to 35 instead of 38, but it will work. I usually set an exercise clock to turn the pump on for a couple minutes every week.. If you just exercise the 5HP manually I would let it run a few minutes every couple weeks.

 

[MarsGeo]

I can't answer your parallel pump question but did you contact Champion technical support for more information on the LMM?

Do the LMMs keep the power off permanently or will it periodically retry to see if the generator can handle the load? Maybe once the generator is running, it would be a non issue for the pump to start.

Maybe the solution is to have several LMMs with the priority on the pump LMM set to high and the priority on another device set to low.

Or maybe remove one or more house circuits from the generator load. I think running your water pump, especially if it is used for a sprinkler system, is priority one (along with heat and refrigeration).

Have you checked the current building code to see if the pump requirements are still the same?

Have you checked to see if newer pumps have lower startup draw?

Thanks for these helpful suggestions. According to the manual, the load management module checks occasionally with the transfer switch and can re-connect a managed load. The problem is that a 5hp pump draws 15-25kw starting up, and my generator is only rated 14kw. Once I have the load management module wired, it would be easy to test if the generator can handle the startup power for a short time. I did read that some generators can handle short bursts of power that are higher than the generator rating, but the manual for mine doesn't specify this. The house won't be entirely without sprinkler protection when on generator power, because the parallel 3/4hp pump would be powered by the generator.

 

[MarsGeo]

I expect each pump would have its own circuit breaker feeding the respective pressure switch.

Running the fire pump periodically makes sense to me. Maybe make that an annual test, and part of your annual procedure to check the air precharge, and whatever.

Yes, a pressure switch and breaker for each pump.

 

[MarsGeo]

Your plan is a good one. I would probably drop the on setting for the 5HP to 35 instead of 38, but it will work. I usually set an exercise clock to turn the pump on for a couple minutes every week.. If you just exercise the 5HP manually I would let it run a few minutes every couple weeks.

Thanks for your suggestions.

 

[MarsGeo]

Phase 1 is complete. The Champion load management module is installed and tested; the module disconnects the 5hp pump whenever the generator turns on.

I'm posting this update hoping that someone can offer advice on what pump to get for everyday use (and then the 5hp pump will be relegated to standby use for the indoor fire sprinklers and turning on if the pressure drops to ~35 psi).

My estimated water demand is 10 gpm, from the existing 5000 gallon storage tank to an "85 gallon" pressure tank located about 8 ft away. Currently, the pressure switch is set to 40/60 psi, and this provides satisfactory pressure in the house. So I need a pump that can supply 10 gpm at 40/60 psi.

I'm tentatively thinking of a 10 gpm, 1/2 hp, 230v, 3 wire submersible pump like a Goulds 10GS05412CL (~$800 with controller) or Franklin 10FA05S4 (~$1400 with controller). I like the idea of a submersible pump because the plumbing will be simpler for the existing piping, pump protected from our rainy climate, pump cooled in water. Does anyone have an opinion of these 2 pumps or other pump suggestions? My wife reminds me that I'm 74 and won't want to replace a pump in 5-10 years, even if it's only in a tank and not down a well. Would a csv help in this situation or alter the pump selection? Thanks for any advice.

 

[Valveman]

Between the two pumps you posted I prefer the Goulds as it has a floating stack design as opposed to Franklins floating stage. 2 wire is fine but you will need the regular control box with the 3 wire model. However, for 150 bucks you can get a 1HP Hallmark. The 33 GPM design works great with cisterns when using a CSV, as the CSV will make it work down to as little as 1 GPM regardless of its size. I am also not sure the name brand pumps will last any longer these days. Eliminate the cycling and even cheap pumps will last a long time. I know of one of these at least that is over 9 years so far.

A CSV always helps. The CSV would give much stronger constant pressure. Pressure in the house is much stronger at 50 PSI constant as compared to an average 50 PSI as the pump cycles on and off between 40 and 60. The CSV eliminates water hammer and makes pumps, check valves, pressure switches, control boxes, and everything last longer. Although the CSV will work with any size tank, the pressure in the house will be much worse with an 86 gallon tank than a small tank. The CSV cannot make the pressure strong and constant until the pump starts. Pressure in the house will be decreasing from 60 all the way down to 40 as the 20 gallons in an 86 gallon tank is used up. Only then will the CSV be able to supply enough pressure that soap is no longer necessary. Lol!

 

[MarsGeo]

Valveman, thanks for these additional details. I get it that reducing the pump discharge reduces the current through the motor, but I've been wondering how pumping efficiency varies. If the water discharge decreases proportionately more than the current through the motor, then the pumped water becomes more expensive.

I found another thread of yours (https://www.plumbingforums.com/threads/cycle-stop-valve-csv-and-shroud-question.26030/) that discusses this, using perhaps hypothetical numbers suggesting that without a csv, a pump might use ~1100 watt-minutes to pump ~11 gallons (~100 watt-minutes per gallon), whereas with the csv that pump might use 800 watt-minutes to pump one gallon (~800 watt-minutes per gallon). For the 100-200 gallons we use each day, this corresponds to an additional 70,000 watt-minutes (roughly 1-2 kWh per day, at an additional cost of $0.50 to $1.00 per day).

I'd like to follow your advice from that other thread: "To be efficient with a CSV or a VFD, the flow rate being used must still be close to BEP or the pumps best efficiency point". So if our typical instantaneous demand for the two residents in our household is only two fixtures (perhaps 3-4 gpm), but peak demand might be perhaps 10 gpm, what is the sweet spot for a pump so that the BEP is low enough to be efficient with a csv at 3-4 gpm, but high enough to be able to handle peak demand (10 gpm)? For example, the Goulds GS series I was looking at has pumps with best efficiency at 5, 7, or 10 gpm. Would I be best off with one with BEP of 5 gpm and a recommended range of 1.2-7.5 gpm, or a BEP of 7 gpm (recommended range of 1.5-10 gpm), or BEP of 10 (recommended range of 3-16 gpm)?

Thanks.

 

[Reach4]

A lower HP pump, especially a 3-wire or Grundfos SQ pump, will be easier for a generator to power.

If you are using 180 gallons per day, the pump will not be running long.

Using a cheap 1 hp pump with a CSV, rather than a 1/2 hp pump, will take more power, but will help your cash flow and save space that a bigger pressure tank would take.

 

[MarsGeo]

A lower HP pump, especially a 3-wire or Grundfos SQ pump, will be easier for a generator to power.

If you are using 180 gallons per day, the pump will not be running long.

Using a cheap 1 hp pump with a CSV, rather than a 1/2 hp pump, will take more power, but will help your cash flow and save space that a bigger pressure tank would take.

Reach4, your post gets to the crux of it. How much more power will the 1 hp pump with CSV use? (I already have the 85 gallon pressure tank, so I'm not concerned with that cost.) Using the numbers in Valveman's post (linked above), a 12 gpm pump delivering water at 1 gpm uses 8 times the electric energy (in kWh) of that pump with CSV pumping at a rate of 1 gpm. At our California rate of $0.53/kwh the additional power would cost ~$300 per year.

My design target is to find a 7 or 10 gpm pump (1/2 hp?) that with a CSV would have both adequate performance from 3-10 gpm and meet Valveman's suggestion to stay close to the pump's BEP. I don't know if that is possible, because I don't have the data for how fast efficiency drops as the flow decreases from the BEP.

 

[Valveman]

Valveman, thanks for these additional details. I get it that reducing the pump discharge reduces the current through the motor, but I've been wondering how pumping efficiency varies. If the water discharge decreases proportionately more than the current through the motor, then the pumped water becomes more expensive.

I found another thread of yours (https://www.plumbingforums.com/threads/cycle-stop-valve-csv-and-shroud-question.26030/) that discusses this, using perhaps hypothetical numbers suggesting that without a csv, a pump might use ~1100 watt-minutes to pump ~11 gallons (~100 watt-minutes per gallon), whereas with the csv that pump might use 800 watt-minutes to pump one gallon (~800 watt-minutes per gallon). For the 100-200 gallons we use each day, this corresponds to an additional 70,000 watt-minutes (roughly 1-2 kWh per day, at an additional cost of $0.50 to $1.00 per day).

I'd like to follow your advice from that other thread: "To be efficient with a CSV or a VFD, the flow rate being used must still be close to BEP or the pumps best efficiency point". So if our typical instantaneous demand for the two residents in our household is only two fixtures (perhaps 3-4 gpm), but peak demand might be perhaps 10 gpm, what is the sweet spot for a pump so that the BEP is low enough to be efficient with a csv at 3-4 gpm, but high enough to be able to handle peak demand (10 gpm)? For example, the Goulds GS series I was looking at has pumps with best efficiency at 5, 7, or 10 gpm. Would I be best off with one with BEP of 5 gpm and a recommended range of 1.2-7.5 gpm, or a BEP of 7 gpm (recommended range of 1.5-10 gpm), or BEP of 10 (recommended range of 3-16 gpm)?

Thanks.

Efficiency would matter if you were irrigating or had a heat pump. But only using 100-200 gallons per day, the extra power needed for the 1HP on a CSV will be more like a dollar a month, not a day. Like was said, a 1/2HP Grundfos SQ or SP would be more efficient at low flow, but I doubt it would ever pay for itself.

The real problem is paying 53 cents a kw. Here it is still 10-12 cents. I do not understand why CA is paying such high rates when they are getting so much cheap power from the coal plants in Mexico? We sell US coal to Mexico for cheap. They make dirty power and sell it back to CA for 53 cents. OMG! Highest price paid for dirty power in a state that thinks it is being green? OK, I will get off my soap box now.

 

[MarsGeo]

OK, thanks for your replies.

 

[MarsGeo]

Hi Valveman, I'm still wondering if I understand the CSV correctly. If the only water use is a single shower at 1.5 gpm, does a CSV then provide whatever restriction is required so that the pump only outputs 1.5 gpm? Or does the pump discharge also depend in some way on pressure in the pressure tank? And for the Goulds GS series, the only viable choice for a range of 1.5 to 10gpm is the 7GS05. Is this correct? And at the low range, the pump would use something in the range of 4-6 times the electricity per gallon as near the BEP (to avoid having to consider local electric rates)?

 

[Valveman]

Doing a little quick math on a 1/2HP pump, if all your usage is at 1.5 GPM for 200 gallons a day the electric bill will go from 0.2KWH to 0.8KWH a day. That is worst case scenario with all usage at 1.5 GPM. Usages closer to BEP will cost less. Even at those rates and worst case scenario that would only be about 30 cents a day or $9 a month difference.

Yes, the CSV adds enough restriction to keep the pump running continuously as long as you are using more than 1.5 GPM. The 1 GPM minimum built into the CSV is designed to keep 2HP and smaller motors cool. Doesn't have to be a 7GS05 as any pump up to 2HP and 25 GPM will work fine down to 1.5 GPM. As soon as the tank is empty the water comes directly from the pump, bypassing the tank, and the tank has nothing to with the pressure. The pump discharge is entirely controlled by the amount of water being used at any given time.

Using a little larger tank with a CSV is always recommended when there are many small uses of water, like when there is a leak that can't be found. Even then only a 20 gallon pressure tank is needed to make a big difference in number of cycles as well as energy use.

 

[MarsGeo]

Thanks again.

 

[MarsGeo]

Just to see if I understand pump efficiency, I tried to reproduce your calculations, and I found a confusing result. Maybe you can tell me what I did wrong.

I can't find efficiency numbers anywhere for the Goulds 10GS05 with pump end, but I did find the numbers for the Grundfos 10SQ05-160 (at https://supremewatersales.com/10sq05-160-96160140.html), so I used that as a trial.

At BEP, the pump produces ~10 gpm, with P2 of 0.85hp and eta of 0.48. The equation I found online says that P1 = P2/eta. Inserting the values from Grundfos gives P1 = 0.85hp/0.48 = 1.8 hp, which is approximately 1.3 kW. At these efficient conditions, the pump takes 15 minutes to pump our daily requirement of 150 gallons and uses 0.32 kWh. Is this somewhat lower than the 0.2kWh you calculated, because I used a daily consumption of 150 instead of 200 gallons, and perhaps because the Grundfos is more efficient?

Our $0.53 per kWh is for peak hours. At off-peak the cost per kwh is "only" $0.37. Averaging the two rates, we can say $0.45 per kWh. For our daily use of 150 gallons, this corresponds to $0.14 per day.

Then I went through the same calculations for pumping (with a CSV) at lower discharge of 2 gpm, at which P2 = 0.6 hp, and eta = 0.2. In this case, the equation relating P1, P2, and eta yields the result that the pump uses 3 hp, or 2.2kW, to pump at 2 gpm. This seems counter to your results that pumping with CSV uses less power, so I wonder if I made a mistake somewhere.

 

[Valveman]

The blue line in the HP curve is what the pump does. It uses 0.85HP at 10 GPM, but only 0.6 at 2 GPM. The CSV causes it to use less power at lower flow, but the pump will need to run longer to produce the same total amount. With a small tank, if all uses are only 2 GPM, the pump will run 75 minutes. 75 minutes at 0.6HP is 3.5 times as much as 15 minutes at 0.85HP. Worst case 0.32kwh compared to 1.12kwh. Using a 20 gallon tank with the CSV will cut the low flow run time in half, making it 0.56kwh compared to 0.32kwh.

This is exactly the same thing that happens with the VFD or variable speed pumps. But everybody still claims VFD's save energy because they see the power or amps drop when the RPM is reduced. But it drops the same without reducing the pumps RPM by just using a Cycle Stop Valve. So, again, any pump is most efficient when running close to its BEP no matter how it is controlled. The only way to make a pump run close to BEP all the time is by using a pressure tank only. However, there are so many problems caused by letting the pump cycle on and off all the time that using a little more energy to keep the pump from cycling itself to death is well worth it. Cycle Stop Valves don't just stop the pump from cycling itself to death but also delivers strong constant pressure to the house, which is hard to quantify in worth.

 

[Bannerman]

Another consideration is startup current.

Without a CSV, there will be a significantly greater number of pump starts. Although each startup current draw will be momentarily, each startup will typically consume approx. 6X the operating current the pump will consume while pumping a its maximum delivery flow rate. When a pump is forced to cycle repeatedly within a short time period, the additional startup current will cause greater heat development within the pump's electric motor.

While a CSV will result in the pump operating continuously for almost the entire time water is consumed, there will typically be only one pump start cycle so there will be less startup power consumption and heat development, and the long run time will provide continuous cooling flow over the motor, especially when a flow inducer sleave is utilized.