Commissioning of Pipework: Design Considerations(v. 20/95 Application Guides S.)

Proportional balancing of water flow rates is established UK practice for heating and cooling applications. The requirements for proportional balancing are defined in CIBSE Comissioning Code W:1994 Water Distribution Systems. This report explains the procedures to comply with this code. The original CIBSE and BSRIA guidance on proportional balancing was derived from a basic understanding of the relationship between flow rate and heat transfer. A combination of theory and practical experience was used to develop recommendations which have generally proved successful over the years. Implementing the guidance has not been without its problems. One of the biggest obstacles to water balancing is the presence of system air, dirt and debris causing blockages at regulating valves, control devices and terminal units. These problems resulted in the production of "BSRIA Application Guide 8/91" "Pre-Commission Cleaning of Water Systems". This explained the basic methods by which water systems are probably the most stringent in Europe. In the light of these developments, it became apparent that there was a need to review established procedures with the following objectives: to establish what are the main priorities for commissioning of water systems; and to determine the most cost-effective way of achieving those priorities. This "Application Guide" is the result of this research. The advice provided is directed to design engineers and commissioning specialists, and complements previous BSRIA guides. It is hoped that this clarification of commissioning priorities should help to offset many of the technical disputes which arise over the acceptability of system operating conditions.

Table of Contents:
Part 1 Heat transfer across heating and cooling coils: how does water flow rate affect heat transfer across coils? - heating coils, cooling oils; how do coil manufacturers select design water flow rates?; how do changes in coil heat transfer affect space conditions? - space temperatures; space humidity levels. Part 2 Flow measurement: what range of water flow rates are measurable using orifice-type flow-measurement devices?; how accurate are water flow measurements? Part 3 Flow measurement tolerances; how are water flow measurement tolerances calculated? - minimum tolerances, maximum tolerances. Part 4 Witnessing: are flow measurements which lie outside the specified tolerance range ever acceptable?; what happens is sub-branch flows don't add up to branch flows?; why do flow measurements fluctuate in some systems?; why do flow measurements fluctuate in some systems?; will changes in water temperature affect flow balance? Part 5 Selection of design flow rates: how are heating/cooling coil flow rates calculated?; why are low flow rates in pipes (IE<0.1 L/S) such a problem? - the origins of air in systems; how can problems associated with low flow velocities be avoided? - operation of series pipe arrangements, single-point measurements; what criteria should be used to determine maximum permissible flow rates?; is it possible to design totally self-balancing systems? - pre-set regulating valves, fixed orifices, self-balancing "ladder" arrangement, self-balancing reverse return systems, mixed-ladder and reverse-return arrangements; is there an alternative to regulating valves? - constant flow regulators; is there an alternative to waterside terminal control devices? - waterside control of fan coil units, airside control of fan coil units. Appendices: prediction of coil performance; dynamic thermal model for building cooling; calculating for fixed orifices.