Taking control of commissioning
Centralising the commissioning function for a number of terminal units using commissioning modules reduces installation time by at least 20% and more than halves commissioning time.
The commissioning of piped services inevitably faces time and budget constraints. Peter Rees considers how these challenges can be addressed.For more than 85% of the heating season, the months when a building’s occupants are likely to complain that they are too cold, the average thermal plant load is lower than 50% of its full capacity. Likewise, in the warmer months of the year when demands on the cooling system are at their highest, 75% of the time sees the load operating at below 50% of its capacity. This means that full loads are only designed to be used for minimum periods of time in the course of a year and are on the whole under-utilised. Of course, at either end of the year, the load is affected by internal and external influences. For example people generate their own heat, while lighting and computer equipment contributes to the internal temperature of the building. Externally the weather is the largest influencing factor, and sunlight also plays its part in affecting the heat gains inside a building. Variable flow
With the expected fluctuations in temperature, the building-services engineer is compelled to ensure that the internal working environment is maintained at a comfortable and sustainable level. A variable-flow system is well suited to the mentioned load variations, and its introduction provides savings in reduced pump energy consumption and compatibility between production and distribution flows. When installing a differential-pressure controller, the system designer can control pressure across the system, measure flow rates and balance the system. Otherwise, by specifying a differential pressure and an appropriate control valve, the engineer can also ensure savings in installation time and space. Where there is no authority over the system the engineer will incur the cost associated with discomfort of staff — generated by the reactive process of manually altering the room’s control settings according to the temperature requirements. When the flow fluctuates the pump will not operate at its optimum level, and the energy used will be greater than if the system is properly commissioned. For example, if a room is even as much as 1 K too warm in heating mode, the cost can be as much as 12 to 18% greater. Likewise if the temperature is just 1 K too low in cooling mode, the additional cost incurred can be up to 6 to 11%. Reducing costs
Commissioning the system correctly is effectively the most cost-effective action to take. However, commissioning a system to ensure each control valve has the correct authority and the flow works in the correct way can be a time-consuming and costly job in itself. Another problem affecting incorrectly balanced systems is that of noise — something which will receive a large volume of complaints in a commercial office environment. When a building is well balanced there is less likely to be intrusive noise from the system. Primarily the largest challenge is locating the valves in the first place. This can be particularly time-consuming when valves are located in rooms with restricted access or in hospitals and schools where access can only be gained at specific time. Where several terminal units need to be balanced it could be that the best solution for designing a new system is to locate them all in one place. Specifying integrated commissioning modules offers time (and therefore cost) savings of at least 20% for installation and over 50% for commissioning. The maintenance time of hydronic systems is also significantly reduced. These savings are delivered through the reduced time spent installing and then commissioning via a single unit that comprises several valves. Of course, because all the valves are accessible, engineers can schedule commissioning with far more certainty, reducing the pressure of handover deadlines and decreasing the potential for bottlenecks. Maintenance can also be more flexibly scheduled as there is no need to disturb occupants. Forces
With prefabrication, flexibility and efficiency the overriding criteria for today’s busy construction agenda, meeting time and budget requirements are predominant forces that a centralised commissioning system can help to overcome. By partnering with a valve supplier that can help with and support the design of a new hydronic system with technical expertise, proven experience and online specification backup, the engineer can meet increasingly demanding targets using cost-effective solutions. Peter Rees is technical director with Tour & Andersson.