OFFICES

Office buildings are not big water users - at least not on a per occupant basis.

Generally we put them in the category of timed uses because arrival, mid-morning break, lunch, mid-afternoon break and quitting time are events that occur at predictable times and these are the plumbing peak demand times.

Since we know when these peak demand events will occur and what the maximum potential use might be it is a simple matter to design a Well Manager® system to supply the need.

The peak demand flow rate can be calculated by surveying the installed plumbing fixtures and then using the tables published in most plumbing codes to determine the maximum expected flow rate. A delivery pump with the required capabilities can then be chosen.

The total amount of water that might be used at each peak demand period would be the number of occupants multiplied by the consumption rate of the fixtures they might use.

The duration of the peak demand event is the time allowed for the activity. Morning and afternoon break might be ten minutes while lunch may be ½ to 1 hour.

The amount of storage would be governed by the well yield and the amount of water that can be collected between peak demand events.

For the sake of example: Let's assume 65 people each using a 1.6 gallon per flush toilet and a .5gpm lavatory faucet, getting a one cup drink on the way back to their desk.

Using the assumed figures we come up with a peak demand need of 144.63 gallons occurring at 8:00AM, 10:00 AM, 12:00 PM, 2:30 PM and 4:30PM. What would the required storage be if the well yield is 2 gallons per minute but we wanted to be cautious and use only 50% of the yield in the system design?

The following Excel Spreadsheet shows water use and the amount remaining in storage throughout the day if we collect water three times per hour. For safety sake it has been decided to set the system up to use no more than 1 gallon per minute of the well yield. This means well yield would have to fall below 1 gpm before our plumbing system would be affected at all.

Download the above spreadsheet here.  The spreadsheet will automatically calculate all figures in the blue cells. You enter the figures in the yellow cells only. You can try different storage, collection and usage arrangements to see how each affects stored water volume. If stored water runs out or gets too low you can alter the storage arrangement until you get a situation you feel comfortable with.

As you can see the stored water level never gets below 125 gallons if we collect 50% of the well yield (1 gallon per minute) three times per hour and have 330 gallons of storage.

Well Yield for the hour = 60 minutes x 1 gpm = 60 gallons
Collecting 3 times per hr. (every 20 minutes) 60 ÷ 3 = 20 gallons per collection

If you ran the same scenario with a 220 gallon tank you would find that storage drops to 15 gallons at 4:30 PM. This was a little too close for comfort so we tried 330 gallons. Two 165 gallon tanks piped together will provide 330 gallons of storage and still allow us to work with 31" diameter tanks. If access were a problem, two 160 gallon 28" diameter tanks would provide 320 gallons of storage which, according to our spreadsheet, would still be adequate.

We have entered the "gallons used" in a single cell at all times except lunch. When people arrive for work, leave and at coffee breaks the use happens over a short period of time but at lunch, where there is more time, water use is likely to be spread throughout the period. But, if usage at lunch was entered in one cell, storage would still be adequate.

This design shows that it is possible to support 65 office workers using 50% of the yield of a 2 gallon per minute well. It also shows that one cannot expect to waste water with such an arrangement.

When working with low yield wells, plumbing must be kept in good operating condition. If a flushometer were to become stuck open or a tank toilet were to be allowed to run, water could be exhausted from storage. The beauty of a Well Manager® is that these occurrences cannot pump the well down. This system is only collecting 50% of the well yield so; even though the tanks are empty the well is still nearly full.

To restart the system, someone would need to fix or turn off the flushometer or toilet and then use the HOA switch (Hand - Off - Auto) on the Well Manager® panel to pump enough water from the well into storage to get the system back on and then set the switch back to automatic.

A Well Manager® is a water saving device since it will not let you use more water than it is set to collect plus the amount in storage. Even a burst pipe can't pump the well down!