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CIBSE GUIDANCE TM54


Document L2A (ADL2A) and monitored energy use after five years of operation. Using the case study building in TM54, the graph compares the original Building Regulations Part L model, the estimates based on the TM54 methodology and the actual energy use of the case study building. The stack bars show that the calculations based on TM54 provide a much closer estimate of actual energy use than the model used to demonstrate compliance with ADL2A. So why the big difference? The main


reason for the discrepancy between the left and right bars is that the ADL2A calculation uses standard inputs for variables such as the hours of operation, and excludes energy uses such as small power, external lighting, lifts and so on. This makes complete sense when you are demonstrating compliance with regulations, as you have to remove many of the input variables to allow comparison between different buildings and you can only include the fixed building services (that is, heating, cooling, ventilation and lighting). However, it is clear from this graph


that ADL2A calculations should not be used as a prediction of operational energy performance, and when they are, they are contributing to the ‘design/performance gap’.


How TM54 works The methodology in TM54 (figure 2) is built on some key principles to ensure that it aligns with other CIBSE guidance and


thinking: l The principles and approach published in TM22: Energy assessment and reporting methodology are adopted to ensure that the energy end-uses are assessed and reported l Energy-use calculations are taken from


Acquire information about the building and prospective use


Step 1 Establish floor areas


Calculations outside a DSM


Step 3: Lighting


Step 4: Lifts and escalators


Step 5: Small power Step 6:


Catering Step 7:


Server rooms Step 8:


Other equipment Step 9:


Domestic hot water Step 12:


Humidification and dehumidifaction


The Chartered Institution of Building Services Engineers 222 Balham High Road, London SW12 9BS +44 (0)20 8675 5211 www.cibse.org


Calculations within the DSM


ISBN 978-1-906846-38-1 Step 11: 9 781906 846381


Space heating, cooling, fans and pumps


TM54 is available on the Knowledge Portal at www.cibseknowledgeportal.co.uk


Step 2


Establish operating hours and occupancy factors


Inputs into DSM Step 10: Internal heat gains TM54: 2013


Evaluating operational energy use at the design stage


Step 13: Estimating management factors Using the results


Step 14: Running scenarios


Step 15: Sensitivity analysis


Step 17: Presenting the results


Figure 2: Methodology for evaluating operational energy use at the design stage


Step 16: Review against


benchmarks


Design-stage energy models based on the National Calculation Methodology (NCM) templates provide an excellent way to compare different design options and to demonstrate compliance with Building Regulations


www.cibsejournal.com


September 2013 CIBSE Journal 35


Evaluating operational energy use at the design stage


TM54


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