This is where technical memorandum 54 comes in, it was published by CIBSE in 2013 with the aim of providing building designers and engineers with an approach to estimate the operational energy demand of a building using a DSM (Dynamic simulation model) tool; this can even be carried out at the design stage. It outlines methods on how to estimate the energy consumption of a building for each energy category (heating, cooling, auxiliary etc.) and contains guidance on including for margins of uncertainty on the estimations.
To carry out a TM54 assessment the building must be modeled in much greater detail then it would be for an L2 and EPC assessment a few examples of how are:
· The actual building occupancy for the building should be modeled and this should account for people coming in early or staying later in the evenings – what if the building has more or less occupants than the design included for? This should be accounted for within the uncertainty margin calculations.
· Electrical equipment included in the building should be assessed in detail, things like how many PCs per room, what power consumption each PC and monitor will have and will there be any additional equipment such as desk lighting should be considered.
· External lighting, Lifts and small power are to be included in the results.
· The HVAC should be modeled as closely as possible to how it will run in reality.
· The assessment should include iterations of the model to show high and low end estimates for each energy usage category.
The graph below shows an example comparison of energy consumption estimations for part L, TM54 and the actual building (which can be obtained using metering over an occupied year) , it’s clear to see that the L2 assessment is not to be used for an actual buildings energy consumption approximation.