Lesson 13

Zones and department costs

The audit puts a price on the air of the whole plant. The plant manager wants it per department. A zone is a frame around part of the scheme whose label keeps its totals live — demand, pressure, leaks, cost a year — and the report splits the bill between the zones.

1. Go back to the plant as it is

   Open lesson12.gf9 and save it as lesson13.gf9. Choose Scenario → As is (baseline): the strip above the sheet reads BASELINE: As is. Press Audit. Zones belong to a scenario, like the elements; this lesson draws them in the baseline first.

2. Draw the compressor room

   Choose Edit → Add zone and drag a frame around COMP and FM. A right click, or a click without dragging, cancels. The zone gets a label in its upper-left corner, and the Text tab opens with it:

   Zone 1
   Zone.Q, min Zone.Pmin
   leaks Zone.Leak, Zone.Cost/yr

   Replace Zone 1 with Compressor room. An element belongs to a zone when the centre of its outline lies inside the frame: keep P1 outside. The label can be dragged anywhere inside its frame — on the screenshots the label of the compressor room sits at the bottom, under the compressor; the frame stays where it is.

   A frame that holds a source is a supply zone. It shows what it delivers, not what it consumes:

   Label shows	Expected
   Zone.Q	1960 NL/min	Qn of COMP at maximum load
   Zone.Pmin	6.5 bar	Pout of COMP
   Zone.Leak	0 NL/min	no leak drawn inside
   Zone.Cost	2172 €	the full yearly cost of its source

   The cost is the one the audit settled on in lesson 11: Annual cost calibrated. Without Audit power it would be Cs, the estimate; with an accepted machine, its Annual electricity cost. The label shows about four significant figures — 1960, 6.309, 618.4, 783.9 — and a zone without leaks drawn in it shows 0 NL/min, not a dash.

3. Draw the two lines

   Add two more zones, each around a branch and its consumer:

   Zone	Frame around	First line of the label
   Line 1	P2, B1	Line 1
   Line 2	P3, B2	Line 2

   P1, PG and T1 stay outside every zone — the main belongs to nobody, as on a real plant. Zones should not overlap; if they do, an element counts in the smallest one that covers it.

   Label shows	Line 1	Line 2	Unit
   Zone.Q	1095	618.4	NL/min
   Zone.Pmin	6.309	6.341	bar
   Zone.Leak	0	0	NL/min
   Zone.Cost	1388	783.9	€

   Check by hand: how the bill is split

   The cost of the plant, 2172 € a year, is split in proportion to the demand at maximum load: Line 1 gets 1095 / (1095 + 618.4) = 63.9 %, that is 1388 €, Line 2 36.1 %, 783.9 €. Two things are not in the split:

   • utilization. B1 runs half the time and B2 30 %: by the air they really take on average, 558 against 189 NL/min, Line 1 would pay 75 %. Zones that work different hours are not weighted differently;
   • the unidentified leaks. They are spread over the nodes of the network, not drawn as elements, so no zone owns them — and their cost goes to the lines with the rest. Zone.Leak counts only leaks drawn on the sheet: leak orifices and drains.

4. Make a label say more

   A zone label is an ordinary text block: everything of lesson 5 works in it, and Zone.Q, Zone.Cost and the others are numbers in formulas. Click the label of Line 1 and type in the Text tab:

   Line 1
   Zone.Q, min Zone.Pmin
   {=Zone.Cost / 12} a month, Zone.Share
   if Zone.Pmin < 6.2 then Pressure low at the line

   Line of the label	Shows
   3	115.6 € a month, 63.9%
   4	nothing — B1 gets 6.309 bar

   Dividing by a plain number keeps the unit, so the cost a month is still in euros. Zone.Share comes with its % sign, written without a space. Zone.Share is the share of the zone in the demand of the whole scheme, Zone.N the number of its consumers, Zone.Pmax the highest pressure inside it.

5. Give the zones to the plan

   Proposed and Leaks repaired have no zones: each scenario has its own. Select the three zone labels (click one, Ctrl+click the others), copy them with Ctrl+C, switch to Scenario → Proposed and paste with Ctrl+V. Ctrl+V puts the copies a little to the right and below the place they came from (20 points), so that a paste is never lost under its original. Move them back as a selection: Ctrl+click the three pasted labels and drag them together — a selection carries the frames with their labels, while a single label dragged on its own only moves inside its frame. Fix a side by dragging if an element ends up on the edge. In Proposed, Line 2 also holds R2. Press Audit.

   Label shows	Line 1	Line 2	Unit
   Zone.Q	1050	421.7	NL/min
   Zone.Pmin	6.009	4.006	bar
   Zone.Cost	113 a month (1356 a year)	544.6 a year	€

   Line 1 now shows Pressure low at the line: at the lower setting B1 gets 6.009 bar — just above its 6, what the plan wanted, and below the 6.2 you chose as a warning. The compressor room shows 1708 NL/min at 6.17 bar and 1900 € a year.

   Line 2 pays 239 € a year less: the regulator cut its air by a third, from 618.4 to 421.7 NL/min. Line 1 takes less air too, 1050 against 1095 NL/min, yet pays only 32 € less (113 € a month is 1356 € a year): its share has grown from 63.9 to 71.34 %. The bill is shared, so a measure on one line moves part of the cost onto the others. Judge a measure by the total of the plant, and read the zones as the split of that total.

6. Save it

   Save lesson13.gf9. The PDF report (lesson 16) has a section Compressed air cost by department: the cost of the scheme and where it comes from, a row per zone of consumers — demand, share, cost a year, leaks, lowest pressure — a row Outside the zones and a total; the compressor room follows in a table of its own.

When it does not work

Try this next

• Put a leak orifice on P3 inside Line 2 with Audit leak flow 50 NL/min and press Audit: Zone.Leak of Line 2 shows it, and Line 2 pays for it.
• Edit → Redraw zone frame with a zone label selected draws a new frame for it.

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