IES-VE User Forum

Hi

Question : can I use TM 52 tool in IES vista pro to assess overheating compliance for a school project under the priority school building program (PSBP)?

I am aware that PSBP requirement is slightly different than the TM52 requirements ( for the first criterion ) , it requires max 40 hours of times where operative temperature exceeds upper limit of adaptive temperature by 1K or more whereas IES tm52 limits the same exceedance to 3% of the occupied hours, which can make it more difficult to comply with this criterion ( 3% of the occupied hours can be less than 40 hours , so under the PSBP , this should be looking pass but IES fails it due to exeedance of 3% , let me further clarify what I mean by the following example ;

Say , total number of days in summer day are 153 days (from May to September ) , and say only 48% of these days occupied in a school building ( by considering school holidays ) , this give us 73.4 occupied days in a summer period . school time on each day is 6.5 hours based on 9am-15.30 pm so this gives us total number of occupied hours 477.36 hours . after the calculation ; say within 16 hours of the occupied time ;operative temperature exceeded upper temperature limit 1K or more , which will be equivalent 3.3 % of the occupied hours , this will automatically fail to comply with TM52 Criterion 1 as a result of 3% exceedance , however the total exceedance is still below 40 hours requirement , so it should comply it rather than classifying as a fail. based on this , I am wondering if I can simply ignore this output of failure and assume it pass if the % of hours is found to be less than 40 hours (from the tm52 result )

Please let me know how you evaluate or assess overheating compliance with the PSBP scheme projects ( I think the method of spreadsheet analysing by exporting relevant parameters in excel appear to me as unnecessary because IES already does it for you , you just need to check criterion 1 compliance to see if it is less than 40 hours )

and can I use NCM school profile in absence of pre-determined profiles given by the client? BB101 use to refer between 9am-15.30 pm for occupancy period , is this still the same for PSBP project ? ( is it written anyway in the output specification) I assume BRE must have already considered this when they evaluate the profile, and that is why they come up with slightly extended occupancy period


Lastly ; when you run the TM52 , do you change default air speed (0.8 m/s for summer time ) if you do change it, what would be the more appropriate air speed for summer time

Your thoughts on this matter would be greatly appreciated

In its current form, I don't think the TM52 tool in vistapro can be used to assess anything other than the standard 3% under criterion 1 at this time because it is effectively a black box and does not output the detail of the calculation within the results report. As you say, 40 hours flat is not the same as 3% of occupied. No doubt, additional functionality will appear in time but, as far as I know, it's not here yet.

Until IES update the software to output a detailed breakdown of the results, I think you're stuck with manually doing it on a spreadsheet.

As for occupancy scheduling, I think that's a question for the people who wrote the PSBP criteria. I haven't looked at it yet, but you may find that condition hidden away at the back of a document somewhere if you look hard enough.

I think some of the CIBSE guides mention air speeds but, failing that, you could try to estimate yourself from the macroflo vent rates and the free areas. I personally tend to leave it on 0.8m/s, but maybe I'm lazy.

Hi,

Just to add a bit on the summer air speed.

I had a look into this and found that it actually made such a small difference it wasn't really worth worrying about.

I seem to remember it is used to calculate the operative temperature, but it only ever changed by a fraction of a degree.

Ross

Hi Complex Potential,

first of all ; thank you for the reply. it is hard to find concrete level of evidence sometimes in any guidance or supporting documents, so great to hear what you think .

I agree with you about the first criterion (3%) , which does not address PSBP requirement in the current version of IES , I think they can easily integrate this in the software rather leaving this to us to externally analyse the result , especially it can be very important when you analyse impact of single output in the model , it is just an hustle every time you need to export and analyse it outside of IES

anyway ; coming back to your response again; don't you think the result generated from the TM 52 tool for criterion 2 and 3 are still valid and the same as what is required by PSBP , Because it looks into weighted exeedance and upper threshold level(Tmax+4K) during the occupancy period, so I cannot see why we need to do further spread sheet assessment for this criterions, only the first criterion make the difference where you need to sum the exeedance of hours . all you do is to have a look TM52 result and see what % of operative temperature exceeded adaptive temperature , ) % is already in the result , you just simply evaluate what that equates in terms of number of hours then see if it is over 40 hours or not, however if you want to graphically present the operative temperature , daily mean running temp and upper temp limit for selected rooms , then you can get this information from the vista pro variable section . please let me know if I am missing something here

I don't think you're missing anything, it certainly sounds like the standard TM52 outputs give you enough to directly deal with C2 and C3, it's just C1 that's a pain, as you say.

I'm sure IES will eventually include a drop down box for switching between TM52 and PSBP and hopefully it won't be too long coming.

complex potential

Thank you for your kindly response