The research of this paper provides a useful insight into the many barriers leading to building services overdesign, within the context of NHS hospitals. The issue of overdesign in building services is a systemic problem, whereby numerous contributing factors manifest into an issue that inevitably leads to poor system performance and excess costs. A key factor leading to oversizing is the excessive and uncoordinated application of design margins across the various stages of a building services project. Poor communication between project stakeholders is another significant barrier that inhibits the distribution of information between design groups; unknown requirements, system redundancy and poor system specifications further add to the problem. There are many complex interrelationships associated with the building service design process in hospitals, with external stakeholders adding to the complexity. This points to the importance of effective communication between stakeholders and clear contractual terms between NHS Trusts and external private sector organisations. Many of the barriers identified within this paper are by no means limited to building service systems but also impact on a range of other engineering disciplines.

Energy consumed in buildings is a main contributor to CO2 emissions, there is therefore a need to improve the energy performance of buildings, particularly commercial buildings whereby building service systems are often substantially over-designed due to the application of excess margins during the design process.

The cooling system of an NHS Hospital was studied and modelled in order to identify if the system was overdesigned, and to quantify the oversizing impact on the system operational and embodied carbon footprints. Looking at the operational energy use and environmental performance of the current system as well as an alternative optimised system through appropriate modelling and calculation, the case study results indicate significant environmental impacts are caused by the oversizing of cooling system.

The study also established that it is currently more difficult to obtain an estimate of the embodied carbon footprint of building service systems. It is therefore the responsibility of the machine builders to provide information and data relating to the embodied carbon of their products, which in the longer term, this is likely to become a standard industry requirement.

The capacity of building services in many hospitals exceeds the requirements by significant amounts. Oversizing of building services has a direct impact on building efficiency and operational costs, ultimately impacting upon patient care, by diverting much needed funding. A key factor leading to the oversizing is the excessive and uncoordinated application of design margins across various project stages. Based on a hospital case study, this paper analyses the reasons for the overdesign of a replacement cooling system and raises the importance of managing margins activity to avoid overdesign.