ENERGY CONTROL STRATEGY CHILLED WATER SYSTEM
of hours per day, it becomes clear how savings were achieved. The issue of matching system response
to AHU loads required rigorous testing to ensure comfort conditions were always met. This was achieved through a considerable amount of analysis, enabled by the BMS system. The eventual solution, in the form of an innovative control strategy, is one that can be applied to a wide variety of applications. An example of this reapplication has been achieved in RTÉ, with a neighbouring building to the Television Centre. In late August 2009, as a direct result of
further investigations into enhancing the modulating capabilities of the CHWS, the project evolved to include the introduction of Modbus control (a communication protocol for connecting industrial electronic devices) for the chillers. This added control allowed for the control strategy design to introduce a variable return temperature set-point for the two chillers. The implementation of a variable set-
point allowed for the strategy to write a set-point between 7°C and 11°C to each chiller, dependent on the load requirements of the Television Centre AHUs. This level of control interfacing reduces the chillers; annual electrical energy consumption by approximately 25% – dependent on outdoor ambient conditions on site. The inclusion of the Modbus interfacing for the two Montair chillers required a capital investment of €3,400 (£2,716). This is the only capital investment that was required for the implementation of a modulating control strategy for the CHWS. The implementation of the project –
based on the fi ndings of the air conditioning system audit, modulating control strategy and Modbus control implementation – has led to electrical energy savings for the entire project of approximately 691,000 kWh in its fi rst year of operation, equating to around a €70,000 (£55,600) saving. This stringent scheduling and demand-led control was pivotal in the delivery of a cohesive energy strategy for the CHWS and, most importantly, required only a relatively small capital investment.
Project performance review The project is continually evolving, and the management of the new CHWS strategy – in terms of both manpower participation and energy monitoring – are the key areas that keep this project on track. Figure 1 illustrates the overall electrical energy usage on site for the measured period (2008 to 2011).
34 CIBSE Journal December 2012
Electrical energy consumption yearly comparison
1,400,000 1,350,000 1,300,000 1,250,000 1,200,000 1,150,000 1,100,000 1,050,000 1,000,000
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Dec Month Figure 1 Electrical energy usage comparison: 2008 - 2011
• Innovative control strategy allowing demand-led modulating control of a large
Project summary
• Implementation of policy changes within RTÉ to allow interdepartmental
CHWS
• Introduction of Modbus interfacing between chillers and existing BMS to
coordination, leading to schedule matching between users and their respective AHUs
• Informing the capital expenditure budget to maximise returns on investment and
• Continuous professional development of staff in relation to new control and
energy reduction reporting technologies
It is hoped that the results outlined in this paper will benefi t both building services engineers and energy managers alike, by delivering a greater understanding of the operation and design of a CHWS, and the potential energy saving measures that can be implemented for best effect. CJ
maximise the BMS control ability over the chillers internal control strategy
ACKNOWLEDGEMENTS
This researcher would like to acknowledge the contribution and assistance of Michael Chaney and Jim Carraher (RTE Property & Services) & Troy Bannon CEng MIEI PMP (RTÉ Building Services Engineer) for their time and technical support, which was invaluable to the project, Niall Leonard of Ashdown Controls, Dublin, for his technical assistance in the development of the control strategy and Colm Agnew from the School of Electrical Engineering Systems, Dublin Institute of Technology, for his time in assisting in the completion of the original dissertation for this research.
2008 2009 2010 2011
A typical air handling unit
A full version of this article will appear in the second issue of the SDAR Journal (
www.arrow.dit.ie/sdar) The SDAR Journal is the journal for Sustainable Design and applied Research in Engineering of the Built Environment. It is practically orientated with articles mainly by working engineers about building services applications. It is jointly published by CIBSE (RoI) and the Dublin Institute of Technology (DIT). The fi rst two issues are about Irish projects, but the outcomes may be of interest to all practicing engineers. The 2013 issue will include British projects if papers are forthcoming. Details about submissions are available on the website, or by contacting the editor, Dr Kevin Kelly, at
kevin.kelly@
dit.ie
www.cibsejournal.com
KWH
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