A recent project undertaken by Health Facilities Scotland (HFS), IES Consulting and Mabbett & Associates has highlighted the importance of implementing accurate data for energy and thermal comfort design modelling from the early stages, and throughout, the building development process.
HFS, part of NHS National Services Scotland, commissioned the study after it became apparent that a number of new NHS healthcare buildings were falling short of their energy and comfort design predictions once in operation. In particular, they wanted to understand and address the issues concerning space overheating causing uncomfortable conditions for occupants and elevated cold water temperatures increasing water safety risks.
It is important to note that these issues arose despite the building design and staged modelling having demonstrated compliance with local government building regulations. So, what went wrong?
The main problem here lies with the lack of specific and accurate building data available (or used) at the design stage.
Currently, building compliance is tested against the UK government sourced National Calculation Method (NCM) data, which is also widely used for design calculations in the absence of intended operational data. However, it is widely understood NCM data is intended to be used for comparison only, not an absolute calculation, and therefore the results of any UK compliance calculation can never be regarded as a true prediction of operational energy use, nor thermal comfort conditions.
The NCM data unfortunately only takes into consideration heat gains attributed to occupied spaces including loads for people, lighting and equipment, meaning important gains from hot pipework and electrical cables in adjacent voids can be omitted from the calculations entirely. Furthermore, differences in the time schedules results in heat gains within the operational buildings that contrast significantly to NCM-based predictions at different times throughout the day or year.
IES Consulting first created separate baseline models using the NCM data to represent a typical healthcare centre and hospital ward (since each building type has different operational requirements). IES then modelled the same buildings using "improved" data gathered and provided by Mabbett & Associates from representative existing buildings, to create the Corrected Base Case (CBC) models. The CBC models provide a more accurate reflection of the operational health centre and hospital buildings, by drawing from the experience of true to life data of similar developments.
The discrepancy between the NCM and CBC data proved to be significant in many areas. In the case of hospital bedrooms, for example, the CBC demonstrated that the real world energy consumption - and associated heat gain - within the space was as much as six times higher than the NCM data assumed. The overheating risk was found to be greater when using the improved CBC data, with results showing more than 1,000 hours of predicted overheating per year compared to 0 hours when using the NCM. Now, while the NCM may produce more favourable results at the modelling stage, the comparison here proves that the unsatisfactory operational performance of the buildings is more or less inevitable and could have been predicted from the start of design.
Current 2015 building regulations in Scotland now incorporate more stringent requirements for insulation and improved airtightness when compared with previous versions. It is therefore paramount that designers maintain an awareness of the impact these changes have on space heating requirements, which will be greatly reduced when compared to older buildings. The chance of overheating, even in cooler months, becomes more of a risk. Designers must take into account the way occupants will interact with the space during cooler months. For example, an occupant not used to high insulation standards in their place of work or home may find it unintuitive to open windows when outside temperatures are low, an issue which should be addressed during the design phase.