Water supply for a single family home

[lx255]

Can anyone tell me what the standard design flow rate for a single family home on a well is? Need to size the line from the well to the house. House will be 157 feet higher than the top of the well casing and approx. 250 feet of pipe length.

 

[BigInch]

Some ideas for you here,

http://www.engineeringtoolbox.com/wfsu-pipe-lines-d_1075.html

http://www.engineeringtoolbox.com/wsfu-gpm-d_1074.html

http://www.engineeringtoolbox.com/water-supply-expected-demand-formula-d_1076.html

You'll lose 70 psi just from the elevation difference. Probably a few more psi to the upstairs shower.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[bimr]

The typical house would have a daily demand of 3.5 people x 100 gallons per person per day or 350 gallons per day. The peak hour flow is approximately 1.5 to 2.0 gpm. The peak hour will vary slightly depending on the size of lot, income, yard water sprinkling, and climate. Fire sprinklers are not included.

 

[cvg]

typical service connection size for residential application is 3/4 inch or for a larger house 1 inch. Maximum flow rate for this 1 inch line is probably around 18 to 20 gallons per minute. You should try to deliver water to the house at about 40 - 60 psi. Try to keep your minimum delivery pressure above 20 psi. You may want to upsize the line to 1 1/2 inch to reduce friction loss. Your pump will be running between 90 and 130 psi. Lower flow rates will not reduce this by much.

 

[bimr]

As CVG stated, the standard in the past for water services was 3/4' service piping. In some areas, the standard is now 1 1/2" because of larger houses and fire sprinklers.

 

[lx255]

Thank you for your responses. I've decided to provide 20 gpm to the house and in order to keep my friction losses low enough, this works out to be a 1-1/2" line.

The pump is going to be on a vfd.

Thanks again.

 

[dicksewerrat]

And your well is large eough to supply 20 gpm?

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com

 

[BigInch]

How's the VFD going to work with all that static head? Is your pump way too big or something?

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[jonr12]

You should read these two discussions and understand them.

http://www.eng-tips.com/viewthread.cfm?qid=260203&page=1

http://www.eng-tips.com/viewthread.cfm?qid=262245&page=1

Otherwise you won't be happy, because the VFD will not save any energy as you have probably been promised. What would be important for me on my house supply, is a dependable system with adequate pressure tank storage. I don't think VFD's can even make use of a pressure tank.

 

[BigInch]

They won't if the tank pressure is high relative to the disch head of the pump, besides which a tank should be sized to provide flow at high demand anyway, thereby making the purpose of a vfd pretty much redundant, even if it could be made to work properly.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[cvg]

I agree, a hydropneumatic system with properly sized tank can deliver as much water as you need without the need for a vfd

 

[lx255]

Another snag to this is that we are going to supply two houses. The main house will be located near the same location as the well and a guest house will be at the top of the bluff. So my reasoning for using a vfd pump is so that I can offer a steady pressure at a varying degree of supply. There will be a PRV located in the main house. I've been around several single family home well systems where the well driller installed a vfd pump along with a small pressure tank. The pump would be able to operate at the top of the well casing at say 130 psi. I anticipate that there will be a small bladder tank at each house.

Saving money on this project is not even remotely on the radar. The foundation alone for the 1600 sf house built next door to our proposed guest house (which is owned by the same owner) cost $500k. Trams and a lot of hand work is all we can use. The garage is down below and you have to ride a tram to the house. For this guest house, there will be a total of 3 trams. Two to get to the house and one to get down to Lake Michigan. The top floor of the guest house will have a water storage tank that will feed a fire suppression system because the fire department said your pretty much on your own.

I really appreciate the input on this and am digging into the various links and ideas.

 

[bimr]

You have not said what the well depth is, so the well HP can not be determined. I would expect that the well HP is not large and the VFD will not be expensive.

I agree that saving money would not be a reason to install a VFD.

Regarding static head on start-up. If your well is deep, the well water will drain back down the well on pump shutoff. Deep well pumps have internal check valves that allow the water to drain back down. So the static pressure will not be large on start-up. You are not starting against system pressure.

The VFD is beneficial if the water level in the well will vary. With a fixed speed pump, the discharge pressure will change as the water level in the well varies.

You probably should buy a VFD with bypass. The bypass feature allows you to run the VFD at 100% capacity and will mimic the operation of a fixed speed pump.

 

[lx255]

I have a call into the well driller to begin discussions with him. He's the same one that did the other house. I intend to collaborate with him and give him the top of casing information and let his experience of well sizing take over. Typically the well is checked at the source otherwise a back siphoning would occur and/or a lot of air would be introduced into the system upon each successive startup. Just for reference, I looked up the well log for the existing well serving the other house and the screen was set at about 50 feet. The new well is going to be about 50 feet away from this location and is pretty much along the same surface contour.

 

[BigInch]

Well ... that's a different story.

**********************
"Pumping accounts for 20% of the world’s energy used by electric motors and 25-50% of the total electrical energy usage in certain industrial facilities."-DOE statistic (Note: Make that 99% for pipeline companies)

http://virtualpipeline.spaces.live.com/

 

[lx255]

BigInch,

My original question was regarding the required flow rates for a single family home but the more everyone is weighing in on this and expanding the post, I felt you all needed to be made more clear on the situation.

The pressures and such are not new to this area. The more common well depths are between 100 and 200 feet and sometimes even higher. So sustaining pressures with static heads of more than 200 feet is not uncommon. We will have a 50' deep well serving a building that is 170 feet above the top of casing. Its more in creating an adequate water distribution system that services both the main house and the guest house and providing a consistent pressure that can easily be managed. That is the reason for the VFD in this situation. Secondly, a $200 PRV sure beats putting in two separate wells.

 

[jonr12]

"They won't if the tank pressure is high relative to the disch head of the pump, besides which a tank should be sized to provide flow at high demand anyway, thereby making the purpose of a vfd pretty much redundant, even if it could be made to work properly." BigInch

My thoughts on a tank are that the VFD is holding a steady 130 PSI, so how can the tank deliver any water? I have found that even with a tank on line, a VFD pump has to start when even the slightest amount of water has been used.


"Regarding static head on start-up. If your well is deep, the well water will drain back down the well on pump shutoff. Deep well pumps have internal check valves that allow the water to drain back down. So the static pressure will not be large on start-up. You are not starting against system pressure." bimr

Starting against system pressure or a closed valve is the best way to start a pump. Starting with no head against the pump will cause upthrust on the pump and overload the motor, which is not a good thing.


"The VFD is beneficial if the water level in the well will vary. With a fixed speed pump, the discharge pressure will change as the water level in the well varies." bimr

With only a 50' setting, the water level won't vary enough to make any difference.


"You probably should buy a VFD with bypass. The bypass feature allows you to run the VFD at 100% capacity and will mimic the operation of a fixed speed pump. " bimr

I would also recommend a bypass. Especially in such a remote location. You will still need a pressure tank to run the pump on bypass. Just doesn't sound like a good application for a VFD. Of course I have just been bitten by a similar application of a VFD, so I am gun shy.