Margins Leading to Over-Capacity

Abstract

This paper categorises and describes the design stages, stakeholders and decision processes of an overcapacity boiler upgrade that came about from the excessive use of design margins. Using a hospital case study, the reason behind the overcapacity and excessive margins is explored using semi-structured interviews, document analysis and process modelling. Design margins arise from a lack of systemic thinking during the design and installation phases. It is likely that margins are added as a matter of habit with no real thought to their applicability, calling into question the design process.

Understanding the Embedded Carbon Challenges of Building Service Systems

“…This indicates financial losses of over £156k per annum, given the gas unit cost year 2014/15. Over the boilers' 20 years lifetime, this generates a total loss of over £3M and a Carbon Dioxide emissions equivalent (abbreviated CO2-eq) of 992 tonnes (Jones et al, 2018); CO2-eq is a metric measure used to compare the emissions from various greenhouse gases on the basis of their global-warming potential (GWP), by converting amounts of other gases to the equivalent amount of carbon dioxide with the same global warming potential. Building service systems are designed to continue to operate in the event of system failure, this sustained resilience is achieved through the implementation of redundancy design principles (International Atomic Energy Agency, 1986).…”

Managing Margins: Overdesign in Hospital Building Services

“…One of the reasons for overdesign is the large range of margin values that are quoted within building services design guides, with very little published support on their definitive use, leaving design engineers to decide how to apply the margins, based on their previous experience (Jones et al, 2018). The little guidance that has been published tends to be through the promotion of better design consistency and standards (Race, 2007), however, it would seem from a number of building service engineering case studies (Crozier, 2000;Jones and Eckert, 2016) and the authors professional practice of 30 years working within the building services industry, that this guidance is largely being ignored and that the practice of applying excessive margins continues to be accepted.…”

“…Overdesign of critical building service systems increases purchasing and running costs, as well as carbon emissions. Building on previous research undertaken by the authors, this paper looks at design margins and the apparent overcapacity of building services within hospitals (Jones and Eckert, 2016, 2017, 2018, 2019. Through an in-depth hospital case study, this paper analyses the overdesign of a new replacement chilled water system within a large National Health Service (NHS) teaching hospital, and the circumstances that led to this, in particular the lack of systematic management of current and future requirements.…”

“…Other contributing factors to oversizing include a lack of communication and transparency across the various project stakeholder groups, including NHS Trusts, private finance providers and building contractors/installers, and the reliance on 'rule of thumb' assumptions and imperfect building data to define initial project specifications (Bownass, 2001;Bacon, 2014). Energy Performance Contracting provides a private sector 'funding mechanism' branded a private finance initiative (PFI) for hospitals to procure large infrastructure systems such as new boilers, chillers (for the generation of cold water) or combined heat and power (CHP) systems (Jones et al, 2018). A number of commercial organisations operate Energy Performance Contracts (EPC's) offering capital finance for building services infrastructure and associated guaranteed energy savings compared to the old systems they replace (Lee et al, 2015).…”

Design margins in industrial practice

“…The literature on margins is extensive and reflects that the concepts of margins are studied for particular stages of the design process, for specific domains of products as well as on margins of different types for areas such as performance (Gale 1975;Tan, Otto & Wood 2016), assurance (Hockberger 1976), safety (Möller & Hansson 2008;Iorga, Desrochers & Smeesters 2012), mitigating effects of changes (Tilstra et al 2015;Cansler et al 2016) uncertainty (Thunnissen 2005), excess from standard or platform components (Martin & Ishii 2002, Eckert et al 2019. Example domains include ships (Gale 1975;Hockberger 1976), space systems (Thunnissen 2004), buildings (Jones, Eckert & Gericke 2018), aerospace (Guenov et al 2018, Eckert et al 2019, nuclear facilities (Youngblood 2010) and automotive (Lebjioui 2018). Margin research has tended to concentrate on the conceptual stages, especially for large and complex products such as ships, space systems, aerospace and buildings (Thunnissen 2004(Thunnissen , 2005, although margin concepts such as factors of safety are discussed for the detail design of machine components by Juvinal & Marshek (1991) in their classic textbook and manufacturing tolerances, which responds to uncertainties throughout product development (Morse et al 2018).…”