Water Metering

[Tom]

The standard water meter in the area I'm looking at is 1" which does 50 Gall/min max. To calculate my max water loading I took the total water per wash for each machine and divided by 3 to account for the wash and rinse cycles then multiplied out all the machines assuming they all were started at the same time --- this still gives me a huge number which would not even be serviced by a 2" meter which handles up to 180 Gallons/Min ($$).

Do you really try and design to have full service at peak loading or accept that on that rare occasion it will just take a little longer to fill the machines? I'd really like to get away with a 1-1/2" meter if all possible. Thanks for your help.

[Anonymous]

I think there is a problem with your math. First the flow from a 2" line is much more than double that of a 1". You must look at the crossectional area. A 1" pipe is 1/2" radius, squared times Pie gives you the cross section. A 2" is 1 squared times Pie. So, the 2" has 4 times the cross section not to mention less pressure drop.

You can run a laundromat with hundreds of machines on a 1/2" line if you want to. All you need to do is install a storage tank with a pump. You fill the tank when usage is low, and draw from the tank when the supply line cannot keep up with demand. Your trade-off is the capital cost of installing a larger line, versus the cost for a tank and pump plus the operating cost of the pump.

[Tom]

I got those flow numbers from the water company for those meters. Maybe it's the meters themselves that somehow govern the flow that's not a linear function with the pipe size?

[Andy]

You must also take time into account.

What were your assumptions regarding the minimum fill time?

If you assumed instantaneous fill then you need to adjust this.

If you have 20 machines that demand 50/3 gallons at the same time then:
20*50/3=333.33gallons

At 50gpm you will fill these machines in 6.67 minutes:
333.33g/50gpm=6.67

[Tom]

Thanks for the reply. I understand the calculations, what I'm wondering is how many minutes to fill in busy conditions would most folks think is the worst you can expect? If all 20 of the machines I'm planning to have fill at the same time and I allow 1.5 minutes to fill that has 2" meter maxxed out. To have a 2" meter installed is $33K plus a higher monthly fee.

Do people generally feel that 3 minutes to fill machines (in total peak conditions) is too long or OK? If so I can get by with a 1-1/2" meter which is much less expensive both initially and ongoing. Thanks again for all your input.

[Anonymous]

You should probably be fine with the inch and one-half. You claimed that it takes three fills, in actuality most front loaders divide the water into 5 fills - prewash, wash 3 rinses - thus your actual simultaneous use will be lower than you calculate. How much of the time do you really think every single machine will be running at once? Further, they will never all get started at the same time nor be drawing full water at the same time. I think you can live if a machine takes an extra 90 seconds under peak peak demand time, which is maybe 3% of the time.

Just make sure you install hoses that are a minimum of 5/8" inner diameter to the larger machines - it makes a big difference. I have 3/4" hoses going to my big machines.

[Tom]

Thanks Kirby

[Andy]

I don't think a three or so minute wait is out of line to wait for a fill.

[Anonymous]

You might not, but your customers probably will. Remember if there are fire fills to a wash then that three minutes is really 15 minutes. I think the manufacturers are assuming something like 5-8 minutes (you'll need to check that) so, you are talking about what may be 7-10 minutes longer for a wash than your competitors - that could be a problem.

[Lar Hylobates]

I have played with these numbers in the past. I am lucky enough to have a 2.5" main line if you can believe that so pressure is not a problem.

As far as I am concerned each machine needs a minimum flow out of the end of the hose of at least 5 gpm to be efficiently run, more is better. Most of mine pan out to be 6-8 gpm and my store runs pretty well overall.