CIBSE TM52: 2013 New Overheating Criteria?!

[RossThompson87]

Hi,

In the latest version of the CIBSE journal they have announced new overheating criteria which have been released in CIBSE TM52:

http://www.cibsejournal.com/archive/201 ... omfortably

My understanding is this will (if it hasn't already) supersede the old criteria in CIBSE A 2006. A new edition of CIBSE A is also due this year.

I have now read through TM52 and am slightly concerned the IES outputs won't be sufficient to test compliance.

To calculate the operative temperature you need the air velocity within a room (see TM52 for equations). Does IES give us this?

I am also concerned that IES limits the amount of data that can be exported to Excel (in tabular form) in one go. To build a spreadsheet to test for the new crtieria hourly data is required across a number of variables. With the current set up only a handful of rooms could be tested in one go. So testing say 100 rooms would take all day.

Are IES planning a tool to calculate this for us?

Is anyone out there thinking about making their own spreadsheet?

Any other feedback on the new criteria is welcome. CIBSE have also gone to great measures to address the issues with the old system - however it is defiantly a lot more complicated than before!

Ross

[Complex Potential]

Hi Ross

A good question.

The operative temperature is essentially the same as the dry resultant temperature which is already provided as an output by IES.

However, your concern about performing the necessary calculations on the outputs is quite valid, although I imagine that a specialist function could be built into vista to automate the process. On a spreadsheet one would presumably have to add a column (or two) which calculates the hourly running mean of the external dry bulb from the basic outputs and then assesses the rest of the criteria from that point.

You are correct that without a specialist function within vista, all 8760 rows would need to be output for multiple variables for every single applicable room in your building. As it stands, there is indeed a limit on the number of rooms that can be exported in one go but this is a combination of software and hardware limitations: IES is a 32 bit program and therefore can only utilise a certain amout of your computer's available memory (2GB I think?) which means 4 or 6 GB are often going to waste.

For IES to increase the limit on large data exports they would need to find a way around this limitation which I suspect would require a massive overhaul. Therefore, I predict we will be seeing a vista function added in fairly short order.

CP

[RossThompson87]

Well if the dry resultant temperature can be taken as the operative temperature that would make things a bit simpler on a spreadsheet. I can imagine it would still need some complicated formulas to justify all three of the new criteria though!

It would be good if we could get some feedback from IES on whether they have anything in the pipeline.

Ross

[JohnLloyd]

We've been working on this in relation to the similar overheating criteria for the Priority Schools Building Programme and have now got the skeleton of a spreadsheet that automates the calculation on the basis of simple tabular output from Vista. It needs some polishing to turn it into the final product but we're nearly there.

The spreadsheet calculations are obviously different, but getting the information from IES and into the spreadsheet is no different to what we've been doing for years to do BB101 criterion 2 analysis. I don't really see it as too much of a problem.

As a side-note, some of the criterion is a little loosely defined so we are having people come up with different interpretations. Hopefully there will be some more clear guidance issued before too long...and possibly an industry standard calculation tool.

[Jules]

John,

Do you have an update of when you expect Vista to be able to output the TM52 criteria as I am being asked to provide overheating calculations in compliance with these new rules on forthcoming projects?

Thanks,
Jules.

[JohnLloyd]

Sorry Jules, I don't work for IES. by "We've been working on this" I was referring to my company.

We've now got a fully fledged spreadsheet based tool that takes the IES output and does all the TM52 calcs for you. If you know your way around Excel quite well it shouldn't really take too much effort to knock up your own.

[Jules]

Apologies John, I put 2+2 together and got the wrong answer - obviously in need of a spreadsheet.

I see the latest revision of Tas includes for the TM52 calculation so I don't see why we should be having to draw up our own spreadsheets?

Thanks for your response,

Jules.

[PCully]

Hi Jules,

By pointing out TAS have the specific criteria assessment in their software then obviously we'll need to get ours out this week...I'll make sure the dev team are on it. Any tips on how they have implemented this?

In the meantime you might want to consider looking at other ways to assess this. I always find there is a lot you can learn by really getting into these kinds of assessments so that when you do get a report from your software tool that tells you a room fails you will know what you need to do about it or what options are available to you.

I hope everyone can understand that where there is a demand for these kinds of bespoke reports or assessments from our users (for example this thread but also from our own market research) then we will do a feasibility stud and make a decision to add a new function in the software either in Vista or as a report from a Navigator for example but the software is a global tool used for many different purposes so we can't just tack on interface for every specific requirement users have, instead the challenge is to keep things as flexible as possible for the different kinds of ways people want to assess the performance of their building models. One way of doing that is to provide a very powerful DSM calculation engine (Apache) that links to different parts of the software and then allowing customisation and open access to the results files, Vista/Vistapro are great ways to interrogate the results and really quick but if the variable you need isn't there then don't give up, I'm often very impressed by some of our larger clients and the spreadsheet based systems they develop to get exactly what they want from the results files in a format they can use in their own reports, I think it's something the good companies look for when they are recruiting and it surely keeps them ahead of the curve.

Going off track a bit here, will raise with development and see if this can be added to the agenda.

Phil

[Jules]

Phil,

Apologies for using the 'T' word! Maybe you could give them a call and I'm sure they'd only be too happy to tell you how they managed to implement it and why they felt the need to keep abreast of changes in (UK) regulations. I must admit selfishness in that I'm not really concerned with global compliance. Are IES stretching themselves too thin?

It would seem that I am in the minority of users who primarily use this software in the design of buildings which are required to meet compliance almost exclusively with the now recently released TM52 and also BB101, neither of which IES natively outputs. Are these really bespoke criteria? Oh well, I will accept that I'm being unreasonable in my expectations and would be grateful if you could at least raise it with the dev team.

Right....I'll leave it at that. I'm off to flex my Excel muscles and improve my job prospects.

[Complex Potential]

By pointing out TAS have the specific criteria assessment in their software then obviously we'll need to get ours out this week...I'll make sure the dev team are on it. Any tips on how they have implemented this?