Tutorial #5 in the HydraCALC manual explains how to use HydraCALC-Sizer to automatically build a grid based on some simple inputs. The grid it builds is ready to be AutoPeaked. Aside from that, how does AutoPeaking work in HydraCALC? And what is AutoPeaking?
NFPA-13 Section 22.4.4.4 addresses gridded systems. It states that the designer must verify that the hydraulically most demanding area is being used. Further, it states that at least two immediately adjacent areas on either side along the same branch lines be calculated to prove that the one of them is that hydraulically most demanding area. Third, it states that a computer program that shows the peaking is acceptable based on a single set of calculations. This is where the term 'AutoPeaking' comes from.
In the days before AutoPeaking, (and still, sometimes), we would pick a remote area on a plan. We would then calculate it. We would then shift the remote area one head 'left' along the branch line and calculate that area see if the safety margin shrinks. If it did, we would keep going left until the safety margin stopped shrinking, or we ran into a main. If the safety margin stopped shrinking, then we knew which area was the remote area. If it never shrunk while moving left, we would shift the remote area one head to the right and check that one, and so on. The picture below illustrates this point. Please note that the terminology Left and Right mostly applies because it is an easy way to explain this concept, but Left and Right are are arbitrary and can be interchanged as long as the use is consistent along all the branch lines.
If the grid is non-typical, we still calculate additional areas manually in HydraCALC to this day.
With HydraCALC, AutoPeaking must only be used on 'typical' grids. That means the gridded branch lines:
- The spacing between each head in the remote area must be the same
- Must not have any elbows or tees between the heads in the remote area
- Must not be on arm-overs
- Must be labelled with Left and Right markers (L and R)
If these conditions are not satisfied, you will need to perform separate calculations for each remote area and print and submit them to the AHJ. You cannot use the AutoPeaking report in HydraCALC under these conditions.
Why? Concerning Condition #1: Because in a non-typical situation (heads spaced differently along branch line, for example), the number of heads that must be calculated along a single branch line may change as the remote area shifts one head at a time. Remember, the NFPA rule is that the length of the branch line to be calculated be at least 1.2 times the square root of the remote area. This calculates out to 46.5 +/- ft with a remote area size of 1500 sq. ft. In the example below, the heads are spaced 12 ft. apart, requiring the calculation of four heads per line. If the spacing were, say, 12' / 12' / 12' / 12' / 10' / 10' / 10', four heads would not be sufficient when the area was shifted 12' towards one head or the other. Thus, the shape of the remote area would change and possibly the number of heads calculated in it.
Conditions 2 and 3 are listed because the AutoPeak feature in HydraCALC requires that none of the points in between flowing heads have any fitting on them. Condition #4 allows the program to recognize the remote area points to be shifted. This will be explained later.
Example:
Each area contains the same amount of heads; spacing is 12' between heads along the branch lines.
Scenario 1: Area 1a (red area) is the first area placed and calculated. Area 1b (purple, one head or 12' 'left' of Area 1a) is then calculated and found to be less remote than Area 1a. Area 1d (green, one head or 12' 'right' of Area 1a) is then calculated and found the be less remote than Area 1a, meaning Area 1a is 'most' remote.
Scenario 2: Area 1a (red area) is the first area placed and calculated. Area 1b (purple, one head or 12' 'left' of Area 1a) is then calculated and found to be more remote than Area 1a. Area 1c (blue, one head or 12' 'left' of Area 1b) is calculated and determined to be less remote than Area 1b, making Area 1b the most remote. Area 1d (green, one head or 12' 'right' of Area 1a) is never calculated as the remote area consistently marched to the left.
There are other scenarios, but these are the two used here for illustration.
Left and Right markers
Left and Right markers act as 'bookends' which border the area to be calculated in HydraCALC. These can be typed in manually when inputting a calculation yourself. The AutoCalc process from within Hydratec for AutoCAD or Hydratec for Revit will add the appropriate left and right markers on grids that satisfy the four conditions listed above. They will also be added automatically by the HydraCALC-Sizer program, if the job is a grid and if it is transferred to HydraCALC using the Build Hydraulic Input function.
As mentioned above,Left and Right applies because it is an easy way to explain this concept and Left and Right are are arbitrary and can be interchanged as long as the use is consistent along all the branch lines.
From Tutorial #5: The L and R markers are added before the length automatically. Note in this example that L6 and R78 are used as the bookend lengths.
The common length between heads is 12 (ft). Given this situation, HydraCALC will shift the area being calculated by 12 each time. Since there is no room to take 12 away from (L)6, the process will instead calculate the first area and then march 12 feet each time to the right. After the area shifts to the right one time, the L6 will become L18 and the R78 will become R66. This will not be noticed in the input unless you choose an option to do so when you calculate it. Speaking of which, here are the Options:
The AutoPeak Grid Calculation option tells HydraCALC that you want to peak the calculation. If this is checked, the second option is available, Auto change peak lengths (L&R values). This option is the one referred to above. It will alter the L# and R# values to reflect the location of the remote area. This will make the calculation faster the next time, ans it may not have to shift the area as much. If the L and R markers are not added to the calculation, these options will not be selectable.
When you print out the final (submittal) calculations, you will be able to select the AutoPeaking Sheet for printout.
The AutoPeaking Sheet:
The List of Pipes for Area Calculated section reports where the remote area ended up after it was shifted automatically in the calculation. This is so the user can mark the remote area properly on their plan.
In the report above, the distance between reference points 2 and 3 is listed at 38.170 (feet). In this example, 2 is the branch line connection at the cross main and 3 is the first flowing head in the remote area. The other side is 30.830 ft. The fourth line, right side, from 54 to 55 is 66.830 ft due to that line having less flowing heads operating.
The next section of this report shows the demands associated with the remote area. The most remote area is the one listed as AREA CALCULATED. This area is the one referenced in the List of Pipes for Area Calculated. The Flow Required and Safety Margin are reported for this location.
The LEFT listing reports on the demands of the area if shifted one head left, at the distance seen (12.000). The one head RIGHT listing is also reported. These directions are consistent with the note above. If the remote area calculation had to ‘move’ the remote area more than one head in a given direction, you will see multiple LEFT entries, each one one head further along the grid line, until the pressure starts to drop, and the peak is found.
The Typical Distance Between Heads is reported. The Split Point Used in Area Calculated refers to the reference point name designated to the most remote head.
The H-Factor 