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Review of changes to TM22 energy assessment toolApril 2012

Making sense of energy use has got a bit easier with a major revamp of CIBSE's TM22 energy assessment tool. Peter Tse explains the changes.

The energy analysis tool TM22 has long provided a systematic framework for undertaking an energy survey, and reporting and benchmarking the results. CIBSE's latest version of the spreadsheet tool now allows a building's energy use to be calculated in greater detail, with more scope for using submeter data and different benchmarks.

Technical Memorandum 22: Energy Assessment and Reporting Methodology, to give it its original name, is an excellent aid for operational feedback, and makes energy analysis simple, unambiguous and robust. It has undergone significant development by the CIBSE since its last release in 2006, with the latest reincarnation partially driven by the Technology Strategy Board's (TSB) £8 million programme for building performance evaluations of domestic and non-domestic buildings.


Screen shot of the TM22 energy assessment spreadsheet showing the navigation bars (click image to zoom)
Although the 2011 version of TM22 is a beta edition for those working on the TSB programme, public release is scheduled for later in 2012. To support the TSB programme, your author has been engaged as an evaluator since May 2010, and has had an opportunity to use the tool and assess its strengths.

So what are some of the major changes over the old versions of TM22? The first item to note is the building types now align with the 237 options for a Display Energy Certificate (DEC) from CIBSE TM46: Energy Benchmarking. This is a significant development, as initially the tool was developed just for offices. It was expanded later to include hotels, mixed use industrial buildings and high street banks and agencies.

As many non-domestic buildings seldom have one particular function, the new TM22 allows up to five different building functions to be modelled. This provides a mixed-use building benchmark that is also area-weighted.

The energy benchmarks in TM22 now cover all types of non-domestic building. Users can choose one of three reference benchmarks: those from a Display Energy Certificate (DEC), from CIBSE TM46: Energy Benchmarks, or benchmarks specified by the user.

The DEC benchmarks for electricity and heating are building-specific, accounting for location, degree days, typical hours of use and any mixed use. If a DEC is not available benchmarks from CIBSE TM46 can be used. However these are median benchmarks that need to be modified to suit the study building. User-specified benchmark data can be derived from a property portfolio of energy studies.

A simple assessment is confined to one worksheet, which gathers basic information for the building including floor area, energy use, input and output energy of CHP or renewables, separables and metered data. This is all that is required to benchmark the energy consumption and carbon dioxide emissions, with and without separables. Furthermore, it begins to provide an understanding of the building's energy efficiency, as the contribution of renewable sources is included in the section on building energy use.

Provision of CHP or renewables can certainly offset energy use, but can potentially mask the true building efficiency or energy use. For example, a large photovoltaic array that provides all the electricity in a building won't mean its electricity systems are efficient. TM22 looks at the building energy use to gauge efficiency, which is the sum of delivered energy plus on-site renewables. This is consistent with information found on DECs, with renewables charted as a negative value for total carbon dioxide emissions.


Electrical sub-meter data is used in TM22 to reconcile against known loads and run-times (click image to zoom)
The next stage is a detailed analysis, which involves capturing information from electrical sub-metering and any gas sub-meters, such as for catering kitchens. A reasonable starting point is to gather a list of all sub-meters and records of energy use. Twelve months is a common period of appraisal, but analysis can be adjusted for any period. The best approach is to start at a basic level and build up the picture with more detail as one becomes confident in the method and the accuracy of data.

All energy consumption is assigned against 20 end-use categories. Fifteen of these are pre-defined and five are user specified, including the six official DEC separable energy uses. There is a maximum of 30 items that can be assigned to each of the 20 categories, and each item is referenced to the appropriate sub-meter.

The latest version of TM22 allows for 50 sub-meters. Where a building has more than 50 sub-meters the user will have to aggregate loads of a similar nature. A certain degree of judgement is required, especially if the aggregated load turns out to be a significant fraction of the total.

TM22 allows the user to account for energy in three distinct periods; core hours based on occupied period, out of hours (normally weekday nights) and weekends. This can provide a valuable insight into the building's energy consumption during occupied and non-occupied hours, helping to identify base load consumption and wastage.

Fifteen operational profiles for equipment use can be defined, which allows the on and off times to be set for equipment, and provides total annual running hours. Some profiles are prefilled but able to be edited, while the remainder are totally user-defined.

Seasonal use is considered within each profile, with a proportion of the year assigned to each seasonal period, winter, summer and spring/autumn. For example, buildings in colder climates may spend a greater proportion of the year running in winter conditions, with significant heating and lighting demands and minimal cooling.

As with its previous versions, the TM22 model requires a value for intensity of equipment use. For example, equipment may only be used 80 per cent of that time. The load factor is another requirement, which is the difference between the rating of the equipment and the actual power use. For instance a pump can be rated at 1 kW, but where it is supplied by a variable speed drive it may consume 500 W, thus providing a load factor of 0.5.

Once this level of detail is complete, TM22 will sort the data and complete reconciliation of the energy use against each of the sub-meters, and total energy use recorded by the utility meters. If half-hourly or quarter-hourly data is imported, the model can compare the amount of energy it thinks is being consumed at different times of the day with actual energy consumption being recorded.


TM22 will automatically generate a graphical breakdown of the building’s energy use by kilowatt hours and carbon dioxide emissions per annum (click image to zoom)
Half-hourly data only becomes important when trying to understand an energy consumption profile where wastage or sub-optimal running needs to be identified. At the early stages, half hourly data is not as critical as submitter totals. When undertaking a building survey it's not unusual to find sub-meters that are incorrectly calibrated or not even functioning.

In a new building this is a defect that needs to be rectified under warranty. If failings in meters are not resolved, there is an option to assign energy use to a 'no meter' option. Inevitably this adds a level of ambiguity to the results and should be considered only as a last resort.

Detailed analysis can deliver a breakdown for the 20 categories of electrical end use. This is presented as both electrical demand and equivalent electrical carbon emissions. When this information is integrated with heating loads, TM22 can provide whole building fossil fuel (equivalent) carbon emissions.

An additional feature allows the user to calculate savings for any improvement measures, by changing ratings or the use of equipment. For example, a pump might be replaced by a more efficient item which draws less power. The results are graphically represented in end use breakdown charts showing comparative before and after totals. This worksheet can be used in a variety of ways, including review of in-use performance before and after a refurbishment or comparison of design predictions with actual measured values.

The latest edition of TM22 has the potential to be a powerful tool of analysis, providing a common reference point for designers and operators alike throughout a project. It is a useful aid for aligning expectations and providing a check mechanism for regulatory tools like SBEM and similar. Designers can use the tool with the client at briefing stage of a project to discuss a building's likely load profile, and use that information to set realistic (but also stretching) performance targets.

After handover, facilities managers can use it to identify poorly performing systems and wasteful practices. For energy assessors there are clear ties to labelling and energy assessments for owners, operators and designers. Owners can benchmark their study buildings against typical benchmarks or estate derived benchmarks.

Peter Tse MEng, CEng, MCIBSE is a senior design consultant with BSRIA. This article is based on material provided by Robert Cohen of Verco, developers of the latest edition of TM22.  A major revision to the TM22 Beta version will be available from the end of April 2012, and will be released to researchers on TSB-funded building performance evaluation (BPE) projects. If you are involved on a BPE project and wish to know more about training for the TM22 update and its availability, contact robert.cohen@vercoglobal.com.

BSRIA provides independent building performance evaluation services including energy surveys using TM22. For more information contact Sustainable Buildings Group at BSRIA:

T: 01344 465600
E: energy@bsria.co.uk

 

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