Variable flow water systems Design, installation and commissioning guidance

In Variable flow water systems Design, installation and commissioning guidance There are significant benefits to variable speed pumping in terms of both energy cost and capital cost. The main energy savings derive from the pump law relationship which indicates that (for a system with fixed resistance) halving the flow rate would reduce the pump power to roughly one eighth its previous value. This theoretical saving is however unlikely to be achieved on an actual variable flow installation because of the following:

• Changes in the system resistance as valves close
• Reduction in the pump efficiency as the system characteristics change
• Variable speed drive losses. Capital cost saving opportunities are likely to arise from the potential diversity of load during pipe and pump sizing.

Constant flow heating and chilled water systems generally well understood by designers and commissioning specialists. The commissioning procedure involves setting up systems to achieve fixed flow rate parameters. Most of the valves used for commissioning  manually adjusted during commissioning, and three-port valves used to modulate flow rate and hence heat transfer across coils.

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Variable flow water systems Design, installation and commissioning guidance

• DEFINITIONS
• LIST OF SYMBOLS
• INTRODUCTION
• PIPEWORK SYSTEM DESIGN
• FLOW MEASUREMENT AND REGULATING DEVICES
• GUIDELINES FOR COMPONENT SELECTION AND APPLICATION
• SPECIFYING FLOW RATES AND TOLERANCES
• DESIGN CONSIDERATIONS
• EXAMPLE OF VARIABLE FLOW SYSTEM DESIGNS
• MANAGEMENT
• PIPEWORK INSTALLATION PROCEDURES
• INSTALLATION OF VARIABLE SPEED DRIVES
• INSTALLATION INSPECTIONS
• CONSTANT VOLUME COMMISSIONING PROCEDURES
• SYSTEM COMPONENTS COMMISSIONING PROCEDURES
• VARIABLE FLOW COMMISSIONING PROCEDURES
• HYDRONIC VARIABLE FLOW COMMISSIONING
• REFERENCES

There are significant differences in systems where pump speed  allowed to vary. Some of the valves used may be self-acting types responding to changes in pressure. Control of heat transfer more likely to be achieved through the use of two-port valves which need to be able to shut off against the system pressures. Inevitably, th designer and commissioning specialist must take into account part load conditions as part of commissioning and system proving.

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Variable flow water systems Design, installation and commissioning guidance

Variable flow water systems Design, installation and commissioning guidance