IES-VE User Forum

I think this has been a very useful discussion and if nothing else we've been able to revisit a part of the Notional Building rules programmed into our ApacheSim route and confirm they are still behaving properly and matching our original interpretation of the modelling guide (that will be the QA side in me).

Regarding the "interpretation" of the guide and the fact we have two DSMs behaving differently, it can happen and the framework that has been developed over the last 10 or so years allows for this quite rightly as each calculation engine will have its own nuances and there may be different ways of meeting the criteria. What you have identified here is quite blatant when we look at it in isolation and could be argued they can't both be right, in which case it has to come form the authorities most likely in a future modelling guide revision to state if one or other is not the right operation of the Notional Building. We have a good relationship with those responsible for the guide so I will ask that this can be put on the agenda and if it does get clarified and we are not doing the right thing then it's an easy enough change to make from a development perspective with the added bonus that everyone will suddenly find it easier to pass.

Personally I think when it comes to the building regulations it's good to err on the side of caution, better to encourage hard work to squeeze every bot of efficiency out of a building than allow easy passes only to then fail in reality. This might not be practical in application and I'm not working on that side of the fence where I have to deal with the pressures that manifest.

We do have one extra guide when it comes to unclear aspects of the modelling guide and that is SBEM. SBEM and often iSBEM are published and approved in advance of the Modelling Guide final drafts usually and well before any DSM will be ready and we've learned over the years to defer to SBEM behaviour in cases such as this one where we have to make some decision. I feel it keeps us right beyond doubt and makes SBEM an invaluable resource in cases such as this.

we're really not arguing your point and can see why most engineers would support your case that it should be changed but i really think for a number of years we have had this solution implemented and approved and we should stick with it unless it is a forced change in which case we'll happily update the software. I hope that is all the input on this you require from IES at this time because we are running out of ways to express this same stance.

Phil

Thanks Phil

Yes, I agree this has been discussed enough and I'm grateful that you and Terence have taken the time to respond. When these sorts of ambiguities arise, it can be very frustrating for those of us at the sharp end that we have no direct line of communication with the decision makers. This inevitably leads to us peppering you with questions because you are our only conduit and mechanism for implementing change.

Of course, if you would like to tell me who your shadowy (BRE?) contacts are I promise I'll send them my queries from now on and leave you alone

Otherwise, I'd be very interested to hear how your discussions go about the Tas/IES differences in this matter.

CP

SCare wrote:Looking at the draft version of the NCM modelling guide for Part L 2013 (page 20). It would appear that the notional building will keep the 0.9 W/l/s for zonal SFP.

So the confusion may roll on for a few more years. If anyone has a contact at BRE now would be a great time to sort this!

I don't think this is going to change. I have come to grudgingly accept that the BRE really have decided that 0.9W/(l/s) is the correct notional building system SFP for a standard mechanical supply and extract AHU. In my mind I make sense of this by assuming they are setting the figure as an aspiration or future target for fan manufacturers to aim at. Maybe they even truly believe that it should be achievable today with large enough duct work and efficient enough AHUs.

Whatever the reason, I think it's something we are just going to have to live with, at least until one of us gets a job at the BRE.

CP

I've been emailing the SBEM helpdesk at the BRE about this issue and they certainly are adamant the notional building receives the 0.9W/l/s whether you have a zonal supply fan or local/zonal supply and extract system with heat recovery.

I really struggle accepting that! Especially with the new table on the 2013 BRUKL where if you take the other approach and add the the supply to the exhaust it's not only logical and realistic but the notional building would receive figures that sit snuggly below the standard values. In my mind this is where the notional build should be in the whole ethos of part L.

Personally i would rather see realistic figures used throughout the notional building and where this doesn't achieve enough of a reduction renewables added. Perhaps fan manufacturers will get there one day but i don't think this is driving them when the non domestic compliance guide has more relaxed targets.

The BRE did say they would refer some of my comments to AECOM who validate the software and gave me the generic email for DCLG to raise my concerns with them.

The BRE did say they would refer some of my comments to AECOM who validate the software and gave me the generic email for DCLG to raise my concerns with them.

That is the right route to follow, I think occasionally people think IES are just giving an easy answer when we advise this but BRE and DCLG are responsible for administering the whole regulations framework and are the only ones who can make these decisions and add them to the standards, not IES.

There is a panel of experts from different areas who have input on this process by the way, AECOM are involved in validating DSM softwares (if they can pass the initial hurdle of dumbing down enough to match SBEM results!) but are not final authority.

Phil

Hi

I do appreciate the processes you are going through and whilst my initial frustrations are vented towards IES this is only because it is my software of choice. The open discussion on platforms, such as this, really help develop understanding. the input from IES and other users is fantastic and greatly valued.

I think clearer definitions within the NCM modelling guide would benefit us all.

I do intend to write to the DCLG and would encourage others to do so. contact detail are on the ncm website under the feedback section.

I'm not sure how open they will be to my comments and i'm not exactly sure how to approach it yet?. can you dive straight into the technical details? or will they need all the background...

I'd expect they will be familiar enough with the situation, you can reference the sections from the NCM guide and then give a brief summary of your reading of it and what is provided in the software. All you are requesting is a clarification is published which we can all get on board with.

there are very few discrepancies like this so the ones that are proving problematic I am certain will be on their radar already. Just usually requires a few voices to instigate action or at least to get it on the agenda for the next round of reviews.

Phil

Previous posters might want to have a careful look at the November 2015 release of the NCM guide

http://www.uk-ncm.org.uk/filelibrary/NC ... er2015.pdf

And in particularly at the amended wording of paras 64 and 65 (with regard to the Notional Building) and 99 (with regard to the Real Building).

My reading is that this firms up the position that there will be a BER penalty for any local balanced supply/extract system, with heat recovery, with an SFP greater than 0.9, (despite the facts that the Non-domestic Building Services Compliance Guide allows an SFP up to 1.6, and that there are no technologies available that could meet this requirement).

Or am I reading this wrong?

Wasted

Good spot Wasted.

The addition of the "& extract" in para 65 now makes it pretty clear. The 0.6 allowance for dedicated extract is a separate entity to the 0.9 allowed for the main supply and extract system.

I wonder if EDSL will be changing the way the notional building behaves in Tas now?

Hi,

Yer good spot. After 3 years of this thread, it seems to have finally been cleared up.

It looks like IES had it right all along! 0.9W/l/s is for Supply and Extract.

The big question is what will TAS do with their notional building.

A lot of contractors want the cheapest solution to meet Part L etc. As it stands TAS buildings (with mech vent) are very likely to be much cheaper!

Are there any TAS customers out there that can ask the question and post the response on here?

Thanks
Ross