One of the key challenges facing building services engineers is how to ensure that heating and cooling systems are designed in a way that enables building owners to operate these assets efficiently throughout their life. Indeed, this is a fundamental requirement of the Government Soft Landings (GSL) policy, and facilitating soft landings is set to evolve from a ‘desirable’ criterion to an absolute requirement.
GSL is already mandated for central government construction projects by 2016 and, given the benefits this concept delivers, it is likely to be demanded by many other public and private sector projects in the near future.
The idea of soft landings makes perfect sense. It recognises that buildings change over time, so that the building services may need to change as well. The reality, though, has been that many heating and cooling systems have continued to operate with their original settings irrespective of changes in building usage or whether the settings have ‘drifted’ since the system was commissioned.
Very often this occurs because nobody really knows how the systems are performing. Usually, performance data at individual zone level isn’t readily available – and without that information how can problems or issues be identified or resolved? Ultimately, building operators are looking for smarter management of hydronic systems throughout their lifecycle, so what they need is an easy way to visualise what is happening in those systems.
For example, the temperature differential (ΔT) between flow and return temperatures for both heating and cooling systems is critical to the efficiency of the system. In heating systems a high ΔT delivers the lower return temperatures that condensing boilers, CHP and heat pumps require to operate at maximum efficiency. Similarly, a low ΔT in a chilled water system can reduce chiller operating capacity, so that more chillers run at part-load and less than optimum efficiency.
As already noted, delivering soft landings requires systems that enable building operators to understand the operation of their systems and monitor their performance. Clearly the ΔT will be measured at system level by the building management system (BMS) monitoring blended temperatures across all of the heating or cooling plant. However, this overview doesn’t provide the more granular visualisation that will enable problems to be pinpointed. For instance, issues with just some fan coil zones will impact the overall ΔT, even when other zones are operating perfectly. Therefore, making adjustments to the entire system could upset the balance of zones that didn’t require any fine-tuning.
The answer to improved visibility is to provide more extensive sub-metering. However, the cost of fitting measurement devices to each individual terminal unit would be prohibitive for the majority of projects. A more sensible approach is to introduce sub-metering at a level that provides sufficient visualisation detail of system performance without breaking the bank.
Commissioning modules with integral measurement
The obvious answer is to make use of commissioning modules – a highly effective and proven engineered solution – and to exploit the latest monitoring technologies to integrate flow measurement and data logging within each module. Recent technological advances have made this both possible and financially viable.
Commissioning modules provide a centralised ‘header’ for fan coil and chilled beam systems, acting as a distribution hub for a group/zone of terminal units, sited in a convenient, easily accessible location. Typically, the modules are pre-fabricated and tested under factory conditions before delivery to site.
Now, it is possible to equip each of these ‘centralised distribution hubs’ with an electronic flow measuring device and data logger. Each device will continuously monitor the ΔT across all of the terminal units connected to that commissioning module. Linked to the building management system, these devices therefore provide real-time visualisation of the performance of each zone, so that it then becomes easy to identify localised issues that are impacting on overall system performance.
Crucially, each module incorporates all of the valves required for commissioning, including 2-port actuated control valves and a differential pressure control valve to ensure that all 2-port control valves operate with excellent authority. This means that when an issue is identified, that zone can be easily re-configured from the central module, rather than needing to access each terminal unit in the ceiling void.
Just as importantly, this approach makes the introduction of sub-metering financially viable as the number of measurement devices is limited to the number of zones, rather than the number of terminal units. Furthermore, use of commissioning modules has been shown to introduce significant time and cost savings on commissioning. A BSRIA study has shown that commissioning modules save 28% of installation time, 43% of the time required to flush horizontal mains pipework, 23% of time spent flushing fan coil unit circuits and 44% on commissioning time – compared to traditional systems with commissioning valves on individual terminal units.
It’s also worth mentioning that use of a data logger within each commissioning module to monitor energy consumption provides Automatic Monitoring and Targeting (aM&T) in line with CIBSE TM39
. It also helps to achieve an improved energy rating under the Building Regulations Part L. Furthermore, this information can also be used for billing of tenants or departments, adding more value for the end client.