Enjoying the savings benefits of integration
An integrated approach to building and energy controls can help reduce energy usage within a building, which in turn can effectively deliver savings to the bottom line for the organisation. Daniel Kittow of ABEC explores the benefits of a joined-up approach to energy management and what it can bring to an organisation.
For clients to understand how the Building Energy Management System (BEMS) operates efficiently, an understanding of how the individual items of plant operate, how they are integrated and where the interfaces are (if they exist at all) is required. The ongoing support of a specialist BEMS specialist can ensure all the elements are covered for optimum building performance and energy efficiency.
Control is the most important part of the four disciplines of an HVAC building system that also includes heating, ventilation and air conditioning. However, the parts that are not controlled by the BEMS, for example a toilet extractor fan, running independently without timed or occupancy control, pose a threat to efficiency.
Such a fan may be small, but everything that runs outside of the control system will contribute to a higher energy cost, so such elements need to be addressed. For example, a 1 kW motor operating for 60 h per week, instead of 24/7 (168 h) results in a saving of £11 per week, or £572 per annum, on electricity costs alone. Recognising their significance and connecting these small systems to the integral BEMS will result in an achievable payback for the client in a year or less.
As with all systems, clashes can occur where separate control regimes exist, which is likely to lead to easily preventable energy waste.
For example, in some instances air-handling units and radiators could be controlled by the BEMS, whereas the air-conditioning system has a local control set point that can be manually switched on and off at a wall-mounted controller. Therefore the same air that has already been heated is now being cooled.
Connecting the air conditioning to the BEMS will add an element of time control into the system; the implementation of an outdoor air-temperature sensor will reduce energy use according to seasonal and climatic changes and increase integration for a more controlled system.
It is optimal for the BEMS system to control the whole plant. In a typical building, most of the items have a dedicated BEMS controller or outstation. For integration it is important that the relevant information flows between the outstation and the plant to ensure their effective operation.
An approach that starts with the smaller components provides the best view for integrating controls effectively. The operational times, set points and dead-bands should be checked to ensure they are behaving as expected.
With such a vast system, how the unit is integrated into the building needs to be considered. If the set point for the unit is too high, or pumps and boilers are set at a different time control then the unit will waste energy trying to satisfy unachievable set points. An assessment of the fan-coil unit will determine if the units can be integrated to satisfy the heating and cooling modes.
When one floor has been completed, there is the possibility for the model to be extrapolated across the whole building for the other floors and systems. For such an intensive process, the modular approach allows a break before work on the next system; therefore for the building engineer or energy manager it doesn’t mean intensive work will distract from other responsibilities.
After the completion of all floors and systems, the final stage considers what the boilers, chillers and associated pumps do and how they are controlled. Modification of the existing control strategies in the name of ‘value engineering’ can result in a system that appears to function, but is not truly integrated. A Soft Landings approach should be implemented to ensure a fully optimsed BEMS from handover. If optimisation is considered in the early stages of a project, then post-handover the BEMS should be efficient.
As the BMS controls and monitors large-energy consuming systems, for the building performance to be at an optimum level the integrated system needs to achieve energy savings for cost-effective operation. The client benefits from a cheaper and more efficient way of utilising materials and labour with a flexible system that is easy to manage.
An energy survey is a useful way of addressing where the weaknesses occur in the building system and identifying how to improve them through the integration of building systems. ABEC regularly identifies average savings of 28% over the annual energy bill from an energy survey, so the cost of the survey can effectively pay back in less than 12 months after the alterations to integrate the building controls.
Daniel Kittow is managing director of ABEC