Cit). This is surprising because of the emphasis that KS8 places on engineering designers to ensure a proper foundation for the design process through comprehensive analysis of the brief.
A detailed analysis of this document is contained in Section 3.2.6. From that analysis the following evidence is pertinent to the engineering design process. There is a clear requirement for engineering designers to:
a) Gather design information, such as occupancy hours, activity and density of occupancy (p10).
c) Analyse the impacts of occupancy and activity in order to assess internal heat gains (p32)
d) Analyse internal design conditions for the assessment of intermittent operation, internal loads comprising small power and lighting (p19)
e) Perform a load diversity analysis to establish peak demand (p30) f) Understand the impacts of oversizing heating systems (p36)
MB In the practice guide – CIBSE Guide F and the Knowledge Base Series – both refer to the Energy Efficient Brief.
(MB the reads out to PB the Energy Efficient Brief requirements from KS8)
PB Not to my knowledge do we use these guides – but we do write energy efficient briefs for our projects. In some projects such as WWF they come out as a specific project requirement. But generally these come out in the Stage D brief.
PB Concerning occupancy analysis as listed - No we do not do that.
MB It seems to me with the new occupancy data we create the opportunity to design the systems from first principles – or we could use the ‘black-box’ approach where we use formulaic principles to calculate the loads. Alternatively I could use a mixture of both formulaic and data, which is a kind of ‘grey box’ approach.
PB But remember buildings have always been designed assuming an empty building as explained earlier – icy cold with no heating in it. I would guess that in most hospitals you go to the heating plant will be over-sized by a factor of three or four times, because it is just the way that the Institute recommends that you size heating
Formulaic – ‘rules of thumb’ guidance.
systems. It is mad – but that is how it is done.
When we come up against other consultants – we find that our way of doing it is very unusual.
MB My challenge is that on the Brighton project we showed a massive difference for the basis of design. Yet there view was the impact on the sizing of the engineering systems was not going to be significant. In terms of cooling loads they said that from our experience the hospital cooling load will be about 70kW/m2. I argued that if we wished to optimise the design how can we do so with such a ‘top-down analysis’, with such a formulaic approach. Surely what we should be doing is coming at the design from a ‘bottom-up analysis?’ Surely we should optimise each department – manage concurrent peak demand and size the systems accordingly? Does this make sense to you?
PB Sure – of course it does! In a current project the other engineers wish to size cooling load on 150kW/m2 and we believe it should be around 55kW/m2 – I ask them where this figure comes from? It comes from an ‘accountants’ approach to engineering – which comes from adding all the numbers up and see what they come to – versus an engineering method.
What you are advocating is logical – it is clearly the right way to do the engineering. The problem is that many engineers are totally risk averse…they take the absolute worst – case and size the systems accordingly. So if the client goes way at Christmas and turns the heating off – when they return to work and switch on the boiler it has to be big enough to cope with that demand – that is clearly ridiculous – but it is the way that many engineers
Example of the benefit of using building engineering physics compared to an ‘accountants approach’ to engineering.
think.
MB Can we move onto my analysis concerning gaps in our knowledge? How strongly would you agree or disagree with the following statements?
Gap in our knowledge - 1
: Lack of comprehensive In-Use data, means that engineering designers have poor empirical evidence on which to base engineering decisions. Specifically the gap in our knowledge concerns the potentially critical importance that building occupancy datasets have on building engineering physics and in particular the impact of building occupancy on accurate energy performance and the forecast analysis of In-use.PB I would strongly agree with that. The corollary to this though is that engineering design standards take precedent over an occupancy driven design analysis. There are standard ways of designing without having to analyse occupancy.
Cross ref-13
MB I accept this point, and what arises are the big assumptions concerning occupancy and In-use.
Gap in our knowledge - 2
: Models of engineering analysis can be considered to be imperfect. Models are rarely tested with In-Use data (most often because it is not systematically collected), and consequently the science fails to mature. The lack of testing against reality means that model errors are likely to be repeated from one project to the next. Specifically a gap in our knowledge concerns lack of knowledge concerning what data could be available from In-Use such that it could be used to inform engineering model design and to validate forecasts of energy use.PB Yes it is an appreciable gap. There are two other issues that go with this. Firstly, that clients are usually unwilling to pay for post-occupancy review. Secondly, a liability one – people often do not wish to know that the building is not performing because it raises question of liability – who is at fault for the under-performance? Then you start to get a ‘witch-hunt’ as top why? This is what BREAM outstanding requires – a back-check of your design.
Gap in our knowledge - 3
: The CIBSE Energy Efficient Brief fails to communicate the importance of In-Use. Specifically it fails to translate In-Use requirements in to building engineering physics in terms of ‘appropriate values’ for mathematical model based on fundamental principles’. Specifically a gap in our knowledge concerns lack of knowledge as to the content of an informed Energy Efficient Brief and specifically the means by which In-Use requirements need to be analysed to inform that brief.PB Yes agreed - the WWF brief may point to some of this – but I am not sure as to how much occupancy featured in that brief, because I am not sure that we prioritised the briefing in the way that you might have done.
Cross ref: Agreed Gap in Knowledge -3
MB It seems to me that the Energy Efficient Brief is the way that we could bring all of this together.
PB Yes sure, this makes sense.
Statement: Returning to the theory of building science as it relates to energy use in buildings it is clearly sophisticated. Yet the theory is inconsistently applied, and
much of the implementation is based on poor quality data, poor assumptions, and poor validation In-use.
PB Yes we are definitely agreed on this. Cross ref: Agreed Inconsistent
application of theory – poor quality data.
The factors that drive performance, and indeed which are critical to that performance, are becoming increasingly understood. Yet post-occupancy studies (the author prefers to use then Term: In-Use) clearly demonstrate the failings in the planning, design and engineering process for buildings to achieve anything like the aspiration of energy performance that client and the project team would hope to aspire to.
PB Yes we are agreed on this. There is also a lack of expertise in the client and people are reluctant to step up to take responsibility. There can also be changes in the client organisation over the period of the project and new members can also be reluctant to take responsibility during a period of such change.
Cross ref: Agreed concerning factors impacting poor performance.
Cross ref: Barrier to improvement: clients not willing take responsibility for energy efficient briefing.
Statement: From the literature review it is also clear that a common issue that
impacts both practice and research in the field of forecasting and designing for optimised energy In-use, is the lack of In-Use data in the public domain. To characterise the response in practice to this would be that it relies substantially on standard guidance (such as CIBSE design guides) and formulaic principles. Some of these principles are even enshrined in the recent standard: EN1521, designed to support the Energy Performance in Buildings Directive (Op Cit). Nevertheless this clearly positions what can be considered ‘best practice’ despite the obvious deficiencies. It appears to be common in practice to make numerous assumptions concerning the factors that drive engineering design and consequential energy consumption. The need is clear: an effective form of communication of In-Use requirements aligned with engineering design strategy.
PB Yes – the main danger in a big hospital – There is a reluctance in industry to ‘hang ourselves’ on what the software tells us…so there needs to be a sense check on ‘what my gut tells me.’ If your only sanity check is to go back and look at CIBSE ‘rules of thumb’, you cannot because you will be finding that your results will be telling you a 1/3 or a ¼ of what the ‘rules of thumb’ were telling you.
The industry still does not trust the software enough – would engineering designers, control specialists risk their careers on a piece of software? I met one of Germany’s leading green design specialists – he has been really frustrated by the control engineers who are incapable of designing the control system to respond to their reductive design strategies…it was not that the analysis was wrong – but that the controls were not doing what they were supposed to do. So the client goes back to the designer and accuses them of incorrect design. It then took six months of un-paid work to prove
Cross ref: Risk of reliance on software.
Cross ref: Danger of inadequate commissioning.
that it was the control design that was wrong and not the basis of the design.
MB It is partially why I feel that having users take responsibility for control would help to remove some of the complexity of the control system design.
PB Yes this makes sense – but I go back to my earlier point – if I have designed around standard guidance then if the design is wrong I am less likely to be sued. If I work outside the guidance, then I am more likely to be sued if something goes wrong. This is the real fear in the industry, which holds us back from improving. So if your occupancy studies are to be the basis of design, and the client would prefer to use these rather than basing the design on standard ‘rules of thumb’ – then Professor Bacon will you take responsibility for the results?
Cross ref: Risk of working outside standard industry guidance.
MB Patrick thank you so much for your time and insights – really appreciated.