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Re: Modern computer modelling

Dave,

I too have my doubts about the modelling here. The only comment I'd make though is that carriers are enjoying a moment.

Chinese send their carrier on manoeuvres

Indians building their own aircraft carrier

So clearly there are people out there who see plenty of value in a carrier, and they aren't going anywhere soon.

Re: Modern computer modelling

Another strange feature of modern computer modelling is its very lax attitude towards modelling work actually being valid. Here's an example I noticed from a couple of months ago where modelling of buildings for energy efficiency is reported as not necessarily bearing much relation to reality:

energy efficiency modelling

Extract from the article:

"The difference between how much energy a building is predicted to use and how much it uses in reality has been known in the industry for decades, and is dubbed the ‘performance gap.’ But architects and engineers have traditionally blamed the problem on faulty construction, or unexpected use after completion - such as owners leaving too many lights on.

However David Coley, Professor of Low Carbon Design at the University of Bath, said the real problem stemmed from the practice of building modelling, which is not ‘fit for purpose.’

“It’s a serious scandal,” he said. “It affects all new buildings as well as the refurbishment of older ones.

“When one school in Plymouth was rebuilt, the energy bills for a month ended up costing the same as for an entire year in the old 1950s building.

“The problem is nobody checks that the building is performing as promised. There is very little regulation. They can't be sued. It’s like a surgeon not being bothered about whether their patient lived or died.

“The impact of the inaccuracies of building modelling professionals has severe financial and environmental implications for both the government’s global warming targets as well as building owners who are purchasing homes and other buildings that are sold to be energy efficient but in reality are not.”"


I think the origin of this requirement to model buildings for evaluation of energy efficiency came from the "Energy Performance Certificate" idea that was introduced in some UK legislation about ten years ago, and going further back than that, it comes from some EU directive (and further back than that it will have been the result of lobbying by "Big Green"). This Wikipedia article describes the Energy Performance Certificate idea:

Energy Performance Certificate

I would argue that there is not much point in trying to model the buildings if this work cannot really be done properly. The legislation should not have been introduced until there was sufficient confidence that energy efficiency of buildings could be modelled satisfactorily.

This Energy Performance Certificate idea may have contributed to the recent Grenfell tower block fire event in London. The new cladding (or "siding" as I believe it is called in other countries) for the tower block was probably introduced mainly for cosmetic purposes to help maintain high local property prices. But the Energy Performance Certificate legislation is likely to encourage somebody to think it might be a very good idea to incorporate insulating material into the cladding construction, which unfortunately increased the fire risk for the building. There is a possibility that the Grenfell tower block was in reality not that much more energy efficient than it was before the cladding was installed, even if it got a much improved rating on its Energy Performance Certificate, as the modelling activity is a bit suspect.

Re: Modern computer modelling

I think modeling has a place. It can help me recognize where efficiencies may be gained by pointing out things that might be problems. Can and may aren't will.

I suspect that some folks think that the mays and mights are as good as "will".

I am forced to camp from time to time. I have a sleeping bag rated to 20F. It is rare that I zip it up. Normally it just lays on top of me.

A tent with few vents will keep you ever so much warmer than a building with open walls.

A building with open walls will keep you ever so much cooler than a tent with no vents.

Those are the same statements. In summer, the bottom is better. In winter the top is better. This may sound so obvious as to be foolish to even talk about. I suspect that many of these folks have never integrated this information though.

A piece of 1 mil plastic will turn that frigid Adirondack into a toasty oasis (toasty is relative), but it is the difference between getting completely mummified in my sleeping bag or just lying under it.

Windows are tradeoffs. Security vs light. Vs airflow. Vs. egress. Vs. Comfort. Eventually you get to very marginal returns. If your energy bill is $800/month, there is lots of room to make improvements. If the energy bill is $200, things get a little more uncertain. $100? We now might want to look at things that will use more energy to make our lives a little easier.

Re: Modern computer modelling

In my previous post about modelling buildings for energy efficiency, I effectively made the claim that back in the old days of mainframe computers, people were much more concerned about whether modelling work was valid. I can give some evidence for that claim from my own personal experience.

In the first two years of my working life, at the end of the 1970s, I worked on noise and vibration reduction for nuclear submarines using various computer models. The models we used were taken from methods given in mechanical engineering textbooks, and we used some finite element analysis programs, STRUDL and later on PAFEC, and also a program devised by Imperial College called COUPLE which combined analysis with test data. Whenever we compared our computer models with test data, the comparison was not very impressive. Basically we plodded on doing this work, which was funded by various MoD research establishments to get some sort of onsite analysis capability into a shipyard, and it had no influence on the design of any submarine. The computer models were not regarded as being "ready for primetime". About ten years later I happened to meet somebody who was currently working in the section that did this noise and vibration reduction analysis work, and I discovered that all our computer models from the end of the 1970s had just been thrown away.

But that strikes me as the correct attitude to computer modelling work. If it isn't valid, you can still potentially fund it to some extent, but you shouldn't really make any use of it. There seemed to be a more sceptical attitude towards computer modelling work in the days of mainframe computers. When desktop computers took over, they were portrayed as representing the future of office work, and the attitude to things like computer modelling became less sceptical.