Max Day Demand Peak Hourly Flow

[SamPete]

Standard AWWA curve has a peak hourly flow factor of ~1.8 at average day demand. This however would not be the case at max day demand and should be a good bit lower, but AWWA does not have a standard diurnal curve for max day demand.

If I knew my residential demands were as follows:
ADD = 300 GPD = .21 GPM avg
MDD = 600 GPD = .42 GPM avg

and I know my Max Instaneous Demand is 0.5 GPM per residence

Could I then assume my Peak Hour Demand during MDD would be 0.5/0.42 = 1.2

If so, could I then derieve a new diurnal curve by multiplying each hourly factor by (1.2/1.8)

Thanks in advance

 

[hydrae]

SamPete
Do you have access to actual demand data? if not, do you know the age of the houses? I have found the follow rules of thumb, Newer and more expensive houses will have automatic irrigation equipment which will turn on at 3 or 4 am giving a PHD of up to 2.5 to 3.0. Older houses will consume peak hour at 6 pm to 9 pm of about 2.0 to 2.5, Houses that do not support green lawns will use the ADD no mater what the weather, when all are mixed I have found a 1.7 to 1.8 of peak day about right. These are peak hour on the peak day, if these demands can not be met, the system will respond by lowering the pressure, if the pressure drops too much you start getting complaints.
The max instantaneous demand of 0.5 gpm is only valid with large numbers of connections.
Your asssumption of a peak hour during MDD of 1.2 would only be valid if strict conservation measures are enforced. Possible, but not pleasant to implement.
The best is when you can use actual demand data, the flow charts at the sources and level charts at the storage, crunch those numbers in a spreadsheet and get the specific diurnal curve to the system.
Hydrae

 

[SamPete]

Unfortunately the Utility does not have access to such data to where I could do mass balance and calculate the diurnal patterns for them. So I have to use my assumptions. The only thing I have is ADD. Im assuming a 2.0 factor for Max Day.

My assumption is that Max Day Demand is usually a holiday weekend and water usage doesnt have the peaks and valleys as a regular work week as people wake up at different times and shower, use the rest room, etc at all hours of the day and continue further into the evening hours and therefore an approximate flat plateau line of a 1.2 Multiplier from about 7AM to 10PM. This sorta mocks the standard curve of an 8-5 business (a flat plateau) since people are at home all day like when people are at work all day.


This should work in my model, otherwise I am forced to use a 3.6 peak hour ADD multiplier during Peak Hour of Max Day Demand, which is too conservative and skewing my results and future designs.

 

[hydrae]

SamPete
Do you have weekly or monthy meter readings on the source? How about the power bill for the well pump? that would help get an average MDD
Hydrae

 

[SamPete]

I have high month and low month billing records in addition to historical max plant production. Unfortunately during max day they supplement with wells that have no flow meters and they do not know the capacity, so Im stuck working with a base of ADD and going from there.

They are installing a new scada system as we speak with their new plant upgrade and should be able to give me much more accurate data to compile a diurnal curve for peak day. In addition they will abandon all wells once the upgrade is complete.

My main concern is that I am over designing future projects due to such high head loss using a 1.75 Peak Hour during max day demand, which equates to 3.5 x ADD, which I know is not true and is more like 2.4 x ADD. So when demand gets to 4 MGD ADD, my Max Instaneous Demand should be about 9.6 MGD as opposed to 14 MGD if I used standard diurnal curves during MDD.

 

[hydrae]

SamPete

As for the wells, have you got hp and static water level? or even amps and volts or power bill

At 4 mg ADD I would expect this is not all residential but a peak flow of 14 MGD I would not call unreasonable. is this growth infill or subburb expansion? if infill you will be taking large lawns and converting them to houses which the 9 MGD is a valid target, if expansion the 14 MGD is a valid target. In either case a cost comparision for using smaller pipes with distribution storage should be done.

Another idea, are the wells located where they can augment the peak flow issue? if so conversion to ASR may help you out.

I worked with a water utility that installed 24" pipes 35 years ago when their ADD was 1 to 2 mgd, that investment is paying off big time now with an ADD of 7, MDD of 12, and PHD of 18.

For a weekend diurnal I have found 1.2 at 10 am, rising to 1.7 at 7 pm then back to .5 at midnight

Hydrae

 

[SamPete]

The wells have been 'flagged' by the department as an undesirable water source. Otherwise, I would allocate some of the wells to future developments or to supplement peak demands.

The problem with this system is its distant location from the 'action' as it is over 20 miles away from some projected developments. We are planning a 8 million dollar loop to this hot spot, but due to the small size of the utility, paying for right now is not feasible. It is a very inefficient system to say the least as it was combined 10 years ago and has 3 pressure zones that vary up to 120 feet. Very challenging to tweak everything.

 

[BobPE]

SamPete:

You are using these numbers for planning, and you should really consider the planning window you are in. I typically use a 20 year window. The peaking factors allow you to predict operation in this window. When you consider these peaking factors in the short term, they very rarely make sense, but that is not the point of their use. We design the longer life components from these numbers, the pipes, tanks, etc. Pumps, and more variable sensitive equipment is typically designed for a shorter window because of operational concerns. This is why you often see blank pump locations designed in pumps statiions for future pumps.

There are no standard diurnal curves, these are all system specific, and don't let anyone tell you different. This is why the previous posters were so interested in your historical demand data. And they are right, this is very important as to how you move forward in an efficient way. The design you make today, you will have to live with for a long time. The demands you are stating are no small demand. You should have a water engineer on board to help you in the planning and calculation of the peaks. Often time this phase is overlooked, and the consequences haunt system operation for a long time.

A 1.2 peak hour scares me, I feel it is too low....I usually see peak hours 3 to 4x ave day for residential depending on irrigation. (These referenced peak hours have irrigation for residential and commercial.) If you have industrial, then this may all be for not....and you will have to look at what the industries do to your system.. I referenced a water engineer earlier in my post, you can see how involved this gets, and how important the decisions are from the process....the price of a little bit of planning is offset hundreds of times over from the efficiencies you get in operation....

Let us know how you make out....

BobPE

 

[SamPete]

"A 1.2 peak hour scares me, I feel it is too low....I usually see peak hours 3 to 4x ave day for residential depending on irrigation."

This was my original point, that was I doubt during a Max Day Demand that the peak would be 3x to 4x MDD. Maybe for an individual residence but not a system as a whole. When you run water-cad or H20Map or whatever program you use, and if you want a extended period simulation, you need a system diurnal curve, ideally for both ADD and MDD, and unfortunately due to the technology at this certain plant we can not calculate such so I am forced to rely on AWWA standard, but that is just for ADD and not MDD. I have tried mass balance with the little data that is available but the results were skewed due to the long intervals of recordings and unknowns like the wells. There is not much within the budget to calculate this. I will know more after the scada is installed though.

Remember this is a peak hour factor during max day demand not during average day demand, where it is around 1.8.

What I'm getting at is during a Max Day Event (~roughly 2xADD), where the average consumption rate for that day (whole system) is greater than the Peak Hour Rate (1.8xADD) for an Average Day Demand, Im am doubting that the system experiences a 1.8 Peak Hour Factor during a Maximum Day Demand, since Maximum Instaneous Demand for the System is equivalent to (2.4xADD) and a peak hour during max day would be (3.6xADD) which is obviously greater than the MID.

They district does have a 25 year master plan, but you know you can throw those out the window after the first year, as the original plan following historical and county projections, projected a 3% growth rate, but last month we were notified by the district of a 2500-lot subdivision/golf-course is starting construction during the year. This development alone would be 50% of their current demand. All the while I have 3 developers on hold waiting for approval of their water plans for their neighborhoods, which is approximately another 400 lots in the next year.

I'm designing a moving target, so to speak.

 

[hydrae]

SamPete
Golf course, 2500 lot subdivision around the golf course. These homes fit the newer and more expensive criteria. Both the golf course and the new homes are going to be irrigating from 4 to 6 am. Those peaking factors are on the low side unless long term conservation measures (such as drought resistant plants) are intergrated into the plan.

As for funding, does the system charge a system development charge or 'buy in' connection fee? Invoking or raising such a fee will help with both with funding the improvements needed for such expansion and slow down the rate of expansion so you can meet the demands. Consult legal advice on how to start or increase such fees, they can be tricky.

Hydrae