January 7, 2014
In the majority of commercial buildings the building operator or energy manager is not provided with the tools to fully understand and manage the performance of heating and cooling systems at a meaningful level throughout the life of the asset. However, many people are reluctant to acknowledge this uncomfortable truth – in fact, it is the elephant in the room!
The trick in overcoming these constraints with a view to optimising building performance and complying with Government Soft Landings (GSL) is to find a way to ‘eat the elephant’. And the obvious way is to first divide it into smaller, more manageable portions.
To fully meet the requirements of GSL, design strategies need to enable:
Clearly these criteria present a number of challenges. For example, at the design stage of a speculative building the owner or developer knows about the whole elephant but usually won’t know how it will be divided up. Consequently the heating and cooling systems will need to incorporate sub-metering so that tenants or departments can be billed accordingly. Choosing the most appropriate level of sub-metering is clearly critical, but it can also be tricky.
One option is to meter each system centrally but this only provides a coarse overview of system performance without the granular visualisation needed to fully understand performance at zone level. Nor does it facilitate billing in multi-tenanted buildings.
At the other extreme is metering at each terminal unit (fan coil, chilled beam etc.) but this will greatly increase capital and installation costs and generate unnecessarily high volumes of data.
Another option is to put meters on each floor, which will certainly provide a higher level of visualisation but won’t be much help for billing on floors shared by several tenants/departments.
When the limitations of these three options are taken into account it is clear that the ideal solution is to meter the terminal units in zones, with each zone being served by a commissioning module connected to a number of terminal units. In this way the ‘elephant’ is divided into manageable portions of data for the purposes of understanding system performance and improving energy efficiency.
The saying ‘you can’t manage what you can’t measure’ is just as relevant to building services performance as it is to business performance. In fact, the Chartered Institution of Building Services Engineers (CIBSE) advises that the first stage in improving energy efficiency is to understand how energy is being used through effective metering. Clearly metering on its own will not improve efficiency but it will provide the measurements that enable effective management, assuming the appropriate parameters are measured.
In the case of heating or cooling systems the temperature differential (Delta T) between the flow and return temperatures of the heating and chilled water systems is critical to the efficiency of such systems. For example, in heating systems a high Delta T provides the low return water temperatures that condensing boilers, combined heat and power and heat pumps require to operate at maximum efficiency. Similarly, a low Delta T in a chilled water system can reduce chiller operating capacity so that more chillers run at part-load and less than optimum efficiency.
Maintaining optimum efficiency is therefore dependent on being able to measure and understand key performance parameters such as Delta T. It is equally important to understand how such parameters are impacted by changes to the building or its usage. Changes made to the thermal performance of the building envelope, or a change in staffing densities, will both impact the Delta T so it’s important to be able to easily adjust the systems and re-align them to each zone’s requirements.
When all of these factors are taken into account it is clear that commissioning modules with integral electronic flow measurement and energy data logging capabilities will meet all of the criteria outlined above.
The commissioning modules themselves provide a centralised ‘header’ for fan coil and chilled beam systems, acting as a distribution hub for a group of terminal units. In the event that a floor layout is reconfigured it is very easy to ‘move’ a terminal unit to a new zone – simply by connecting it to a different commissioning module.
Each module incorporates all of the valves required for commissioning, including 2-port actuated control valves and a differential pressure control valve (DPCV), the latter ensuring that each module is independent. A bonus of this arrangement is that zones can be installed gradually, in-line with project schedule requirements, without affecting other zones. It also makes it easier to reconfigure individual zones.
Commissioning modules can also be fitted with an electronic flow measurement device that enables continuous monitoring of flow rates, recorded and accessed through the building management system. Such devices will also continuously monitor the Delta T across all terminal units to ensure efficient operation and support maintenance of the system. Furthermore, they are equipped with data loggers to allow energy metering within each zone of terminal units.
With this arrangement the building operator or energy manager then has very easy access to real-time performance data about the heating and cooling systems on a zone-by-zone basis. This enables them to identify any areas that are not performing efficiently and implement appropriate remedial measures, while underpinning accurate billing of tenants or departments for their energy consumption.
From a facilities management point of view it also provides reassurance that set-point temperatures and comfort conditions are being maintained within each space, even when some of the occupants may think otherwise.
It is it is very rare that anything positive is achieved by ignoring the elephant in the room. It makes a lot more sense to acknowledge its presence and get to grips with how best to tackle it.
*Elio Galluzzi is Product Manager for Commissioning Modules at SAV Systems.