A well balanced system starts with good system design. The designer calculates the mass of water required at each terminal unit, whether heating or cooling. Balancing valves create additional resistance in each branch to direct water in the required proportion to each terminal unit.
Initial design considerations will take into account: the size of space to be conditioned, space usage, occupancy, construction materials and their thermal properties, heat losses and gains and general climatic conditions associated with the building.
Achieving optimum flow rate is essential too high a flow rate may cause noise, whilst too low a flow rate may not dislodge entrapped air. Flow velocities will generally be in the range 0.75 to 1.15m/s for pipe sizes 1/2 to 2in and 0.75 to 3m/s for sizes DM65 to DN300 with pipe pressure drop per metre length generally calculated at 140 to 260 kPa.
System equipment
The choice of equipment is a key part in achieving a well balanced system. Today’s modern fixed orifice double regulating valves combine flow measurement and regulation into one valve for ease and speed of commissioning. The ART 25 commissioning valve from Albion, for example, was specifically designed to be easy to fit and easy to use. The design of the position indicator allows it to be read from four directions which makes recording the final set position easier, even in confined spaces — unlike conventional designs where the scale only appears in a small window.
Fixed orifice regulating valves (FORV) or variable orifice regulating valves (VORV) are an option to consider and system specification will dictate which type is to be used. Fixed orifice wilt nearly always be specified in the UK, with VORV more common in continental Europe and North America.
It is generally accepted that fixed orifice will provide a more accurate flow rate, usually to a tolerance of- 5% — compared to- 10% (or greater) of design flow rate in variable orifice systems.
Metering stations
Some systems will specify metering stations to be installed separately to the regulating valve, but a combined valve and metering station benefits from having a single piece body with no joint between body and metering station. This reduces potential leak points as welt as being compact and a lower cost option than a 2-piece commissioning set. The Albion ART 2S and 250 can be installed in any orientation as long as the flow is the same direction as the flow arrow on the body of the valve.
To ensure accurate flow measurement, guidelines for the installation of the valve or metering station will specify the length of uninterrupted pipe required on either side of the valve. This is to avoid turbulence caused by other fittings within the system or change of flow direction which otherwise may be close to the valve, that could affect the accuracy of the reading.
Other considerations
Because valves are often installed in ceiling voids it is important that handwheels/levers/test points and drains point down for ease of access and commissioning.
Pipework and valves in CHW systems should be insulated and provided with effective vapour seals to minimise condensation and thus prevent damage to ceiling voids.
It is important to ensure that all air is removed from the system, as this can seriously affect commissioning results, and always remember that commissioning should only be
carried out when the system is cold.
About Albion
Established 15 years ago specifically to service independent merchants throughout the UK, Albion has grown from a supplier of a single brass ball valve to designing, sourcing and supplying over 5000 valve and pipe product lines. Albion launched its own range of commissioning valves last year, and now supplies a complete building services valve solution which offers installers significant savings without compromising on quality. The company produces a simple guide to illustrate a typical commercial heating installation and system requirements.
For a free copy, simply email Nicola Vollans: nvoltans@albiondistribution.co.uk or enter the number below on the freepost reader enquiry card inside this issue.
