AIVC Technical Reports

Recommendations on Specific Fan Power and Fan System Efficiency Doawnload the full document 2 MB

P.G. Schild,   M. Mysen
AIVC Technical Note 65, 2009, 42 pp, Code TN 65

Energy use for fan operation can be significantly reduced by a 3-flanked approach:

(1) The first step is prudent sizing of ventilation rates by minimizing the demand (e.g. low-emission building materials, passive cooling design), and by utilizing efficient air distribution. The latter reduces unnecessary over-ventilation by use of airtight ductwork, careful choice of room airflow principles (i.e. minimizing short-circuiting), and controls for demand-control of flow rate.

(2) Perhaps the most important measure is to minimise flow resistance, and hence fan pressure. This is achieved by aerodynamic design of fan inlets/outlets and ductwork layout (including optimal location of plant rooms and duct risers, to reduce duct length), liberal sizing of components in the duct system, and increasing AHU cabinet size, but without oversizing the fan system.

(3) Optimize efficiency of the fan system, including the fan, drive, motor, and variable speed drive (i.e. minimize total ‘wire-to-air’ losses). Oversizing must be avoided, since fan efficiency can decrease significantly if the combination of airflow and pressure rise is not near the combinations giving peak efficiency. Motor and drive efficiencies can also decrease rapidly at low loads. Thus, oversizing and load diversity are key factors affecting system efficiency.

These three measures are far more important than any exploitation of natural driving forces, in climates where heating or cooling is needed. This guide focuses on points (2) & (3).
Besides reducing energy use, energy-efficient systems are generally less noisy than inefficient systems.

To achieve these potential savings, building developers/owners must dictate and verify fan power performance specifications. All countries should have building regulations set limits on fan power, and establish inspection/auditing schemes that include spot checks of fan power. Furthermore, there is a need for simpler calculation tools for calculating duct system pressure loss and specific fan power in buildings, and easy commissioning guidelines.

Contents

1 SUMMARY 1
2 SPECIFIC FAN POWER – DEFINITIONS AND REQUIREMENTS 2
2.1 THE SIGNIFICANCE AND CONSEQUENCE OF FAN ENERGY CONSUMPTION 2
2.2 DEFINITION AND CALCULATION OF SFP 3
2.2.1 Overall definition 3
2.2.2 Relation to pressure drop and system efficiency 3
2.2.3 SFP with variable flow rates 4
2.2.4 SFP for different system scales 6
2.3 MEASUREMENT OF SFP 8
2.3.1 Acceptance tests 8
2.3.2 Accurate measurement of fan power 9
2.3.3 Measurement of flow rate 9
2.4 EXAMPLES OF SFP IN BUILDING CODES 10
2.5 RECOMMENDED ‘GOOD-PRACTICE’ SFP 11
3 FAN SYSTEM EFFICIENCY – DEFINITIONS AND RECOMMENDATIONS 12
3.1 DEFINITION AND TYPICAL VALUES 12
3.2 COMPONENTS OF FAN SYSTEM EFFICIENCY 13
3.2.1 Fans – Aerodynamic efficiency 13
3.2.2 Motors and Motor efficiency 18
3.2.3 Power transmission 20
3.3 SUMMARY OF RECOMMENDATIONS FOR FAN SYSTEM EFFICIENCY 20
4 FAN INLET & OUTLET – AERODYNAMIC INEFFICIENCIES 21
4.1 GENERAL 21
4.2 RECOMMENDATIONS FOR FAN INLETS 21
4.3 RECOMMENDATIONS FOR FAN OUTLETS 22
5 VENTILATION SYSTEM COMPONENTS – PRESSURE LOSS 23
5.1 TOTAL SYSTEM PRESSURE DROP – RULES OF THUMB 23
5.2 FILTERS 23
5.2.1 Filter types and their aerodynamic properties 23
5.2.2 Recommendations for air filters 24
5.3 OTHER AHU COMPONENTS — HEATING/COOLING COILS AND HEAT EXCHANGERS 24
5.3.1 Types and their aerodynamic properties 24
5.3.2 Recommendations 25
5.4 AIR TRANSPORT & DISTRIBUTION SYSTEM (DUCTWORK) 25
5.4.1 Distribution systems and their aerodynamic properties 25
5.4.2 Principles of efficient duct system design 27
5.5 EXHAUST OUTLETS (INCL. ROOF STACKS) 27
5.5.1 Outlets and their aerodynamic properties 27
5.5.2 Recommendations for outlets 27
5.6 SILENCERS (ATTENUATORS) 27
5.6.1 Silencer types and their performance 27
5.6.2 Recommendations for silencers 28
6 PLACEMENT OF RESPONSIBILITY 29
7 REFERENCES 30
INDEX 32

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