Artificial Demand

Artificial demand is unnecessary air consumption caused by operating the system at higher pressure than required. It's one of the main sources of energy waste in compressed air systems.

The Problem

Pressure-Flow Relationship

In unregulated uses, flow increases proportionally with pressure:

Flow (CFM)
    │
 15 ┤                              ●
    │                         ●
 13 ┤                    ●
    │               ●
 11 ┤          ●
    │     ●
  9 ┤●
    │
    └────┴────┴────┴────┴────┴────── Pressure (psi)
        75   90   100  110  120  130

Concrete example:

Pressure	Flow (1/8" orifice)	Increase
90 psi	10 CFM	Base
100 psi	11.7 CFM	+17%
115 psi	13.3 CFM	+33%
130 psi	15 CFM	+50%

Economic Impact

Every 2 PSI increase = ~1% more energy

500 HP system operating at:
  90 psi: Base cost
  100 psi: +5% cost ($15,000/year)
  110 psi: +10% cost ($30,000/year)

Unregulated Uses

Common Examples

Use	Description	Problem
Open blowing	Fixed cleaning nozzles	Consumes more at higher P
Leaks	System orifices	Flow proportional to P
Ejectors	Venturi vacuum	Inefficient at high pressure
Open valves	No regulator	No flow control

Identification

                    Regulated vs. unregulated use:

    REGULATED                     UNREGULATED

    Line 100 psi                  Line 100 psi
         │                             │
    ┌────┴────┐                        │
    │Regulator│                        │
    │ 80 psi  │                        │
    └────┬────┘                        │
         │                             │
    Tool                          Blowing
    Consumes 10 CFM               Consumes 15 CFM
    (always the same)             (increases with pressure)

Calculating Artificial Demand

Formula

For flow through an orifice:

$$\frac{Q_2}{Q_1} = \sqrt{\frac{P_2}{P_1}}$$

Where:

• $Q$ = Flow
• $P$ = Absolute pressure

Example:

• $P_1 = 100$ psia
• $P_2 = 115$ psia
• $Q_1 = 100$ CFM

$$Q_2 = 100 \times \sqrt{\frac{115}{100}} = 107 \text{ CFM}$$

Artificial demand = 7 CFM (7%)

Reference Table

Operating Pressure	Target Pressure	Artificial Demand
115 psi	100 psi	7%
130 psi	100 psi	13%
145 psi	100 psi	20%
115 psi	90 psi	15%

Solutions

1. Reduce System Pressure

Before:                        After:

System at 115 psi              System at 100 psi
     │                              │
     ├── Equipment A (needs 90)     ├── Equipment A (regulator 90)
     ├── Equipment B (needs 100)    ├── Equipment B (OK)
     ├── Blowing (unregulated)      ├── Blowing (uses less)
     └── Leaks (15%)                └── Leaks (13%)

Consumption: 1,000 CFM         Consumption: 870 CFM
                               Savings: 13%

2. Point-of-Use Regulators

Add regulators to all uses:

Main line 100 psi
         │
    ┌────┴────────────────────────┐
    │         │         │         │
┌───┴───┐ ┌───┴───┐ ┌───┴───┐ ┌───┴───┐
│Reg 80 │ │Reg 90 │ │Reg 60 │ │Reg 95 │
└───┬───┘ └───┬───┘ └───┬───┘ └───┬───┘
    │         │         │         │
 Cylind.    Tools     Blowing   Motor

Each piece of equipment receives only required pressure

3. Flow/Pressure Controller

A flow controller (demand expander) stabilizes pressure:

┌─────────────────────────────────────────────────────────┐
│                                                          │
│   Compressors    Tank        Flow         Distribution  │
│   (generate    (stores      Controller    network       │
│    115-130)    high P)     (regulates)   (100 psi)     │
│       │            │            │             │         │
│       ▼            ▼            ▼             ▼         │
│   ═══════════════════════════════════════════════════  │
│       ▲            ▲            ▲             ▲         │
│    Variable   115-130       Stable        Stable       │
│    pressure    psi         100 psi       100 psi       │
│                                                          │
└─────────────────────────────────────────────────────────┘

Benefits:

• Stable plant pressure
• Lower artificial demand
• Less compressor cycling
• "Useful storage" in tank

4. Eliminate Inappropriate Uses

See section Inappropriate Uses.

Artificial Demand Audit

Procedure

1. Measure current system pressure
2. Identify all unregulated uses
3. Determine minimum pressure required by each use
4. Calculate target system pressure
5. Estimate savings

Worksheet

Use	Regulated?	Current Pressure	Required Pressure
Line A - Cylinders	Yes (90 psi)	90 psi	90 psi
Line B - Tools	No	115 psi	95 psi
Line C - Blowing	No	115 psi	60 psi
Line D - Paint	Yes (60 psi)	60 psi	60 psi
Leaks (15%)	No	115 psi	N/A

Target system pressure: 100 psi (maximum required + 5 psi margin)

Potential savings: Reducing from 115 to 100 psi = ~7% of consumption

Case Study

Typical Plant

Initial situation:

• System pressure: 123 psi
• Consumption: 1,500 CFM
• Power: 300 kW
• Annual cost: $240,000

Analysis:

• Maximum required pressure: 100 psi
• Estimated artificial demand: 15%
• Unregulated uses: 40% of total

Actions:

1. Add regulators at critical points
2. Reduce system pressure to 105 psi
3. Repair major leaks

Results:

• New pressure: 105 psi
• New consumption: 1,275 CFM (-15%)
• New power: 255 kW
• Annual savings: $36,000

Rule of Thumb

For every 2 PSI you can reduce system pressure, you'll save approximately 1% in energy costs. A typical system can be reduced 10-20 PSI, achieving 5-10% savings.