SimonD

If those are known quantities, then yes, change the dT. The standards just ask for default values, so an MCS design requires the use of the default Design Outdoor Temp as the difference with suspended floors. There are some aspects where deviation is okay for MCS designs but you have to be prepared to justify them if asked.

That's actually what I do when I have a space like a hall or landing and when I have rooms with large open plan openings, so I create a non-existent door - as long your room dTs match, and set to 0 then it doesn't impact the fabric losses. It also shouldn't affect the ventilation losses because the exposed envelope is set and the calculation uses that. It's a bit prescriptive on the ventilation, so there isn't anything immediately available to make adjustments to this ventilation factor. There are still some questions about how BS EN 12831:2017 treat ventilation and the CIBSE guide uses a bit of SAP in there. I'm going to have a think about this one. It's really the way it's calculating infiltration leakage which is giving you the high figure, but you've got to be a bit careful how you interpret the Ventilation - Emitter Sizing. This calculation isn't saying that you are going to use this amount of energy at a given time, which is your Fabric loss and Ventilation - Generator Sizing. The Ventilation - Emitter sizing, although provided as a total, should really be looked at in relation to individual rooms because it's essentially calculating the effect of high winds on each room based on the exposed area. So at any given time the rooms won't be losing all heat to the outside, but transferring to other rooms within the building. But high infiltration will increase the heat load within the room subject to high infiltration and so the standards are encouraging us to install slightly larger radiators and thus improve efficiency. Does this make sense?

No worries. Thank you!

Here you go. This is a lot better. Not quite there yet, but about 1/2 of what you were seeing, but as you can see the calculated fabric losses of 4.22kW are much closer to yours, but this is at -4.6 which is the conservative MCS post code lookup: In the rooms editor, there is a column labelled Design dt (C). When you add a new element, it default to the Design dT of room temp - outdoor design temp. Then next to it is another column for ref dT which is the default delta T between room temp and Typical Outdoor temp. For all internal elements this needs to be set to the difference between internal rooms, or 0 if there is none. I've just gone and updated all your internal settings to this, which has made the difference. I may have incorrectly amended some of your insulated ceiling which may be external? I've then gone and change the outdoor design temp from -4.6 to -2.5 and as you can see, the fabric loss is now down to 3.84kW and generator sizing is 5.26kW: The total emitter sizing is quite large compared to what you're experiencing with your low flow temps etc. which means I need to dig into the calculations to make sure I haven't got something wrong in there, but I suspect that because of the way it has been implemented, there's been a cautious approach taken by CIBSE in how they've implemented the new method. It wouldn't surprise me and is actually a good thing as it's better to upsize rads for worst case scenarion and reap the benefits of lower flow temps over the long term. But I will need to check. I'd also recommend you go over your element inputs just to check the assignment of U-values from your U-value library and some didn't quite match. Hope that helps?

14.83kW emitter sizing load? That seems massive. Something doesn't seem right there. Do want to show some of the room inputs? Or PM me screenshots?

No, not stupid at all, just something you need to get your head round for heat loss calcs. In the 2 story: - Ground floor gets 1 x Ground Floor (Slab) or (Suspended) + Ceiling - 1st Floor get 1 x Floor + Ceiling You're not really double counting because if both rooms have the same design internal temp, the Design dT is set to zero on both the ceiling of ground floor and floor of 1st floor so there are no losses between them. If there is a difference in internal temp, you just need to keep in mind that the Design dT becomes either + or - the difference. So if one room is 21C and the other 18C, it's +/-3 either way on floor & ceiling. You'll not know this now because the standard U-values aren't in the global database yet, but one thing to keep in mind is that the floor always has a lower U-value than the Ceiling for the same buildup - The CIBSE standard for plasterboard, joists, floorboards, with 100mm insulation is 0.32 I think. The same buildup as a floor is 0.25. Hope that clarifies it?

Clearly, I've never measured them properly to begin with 🙄 My assumption was that as with timber products which is what I'm more used to working with, or pipes, you get what's specified. And maybe it explains why I had to get rid of the plasterer I was using? I was just told that gaps above 3mm must be prefilled, nothing about leaving a gap when boarding but he and another did most of the boarding so far. Oh dear!

I've just plaster boarded up a ceiling and while doing so realised that plasterboard sheets seem to have shrunk? First I thought it was either me or my tape measure and then I twigged the sheets are all actual 2395mm and not 2400 long - my mistake was not taking this missing 5mm into account when I cut short ends of the plasterboard. So rather than waste a load of sheets, I now have some very annoying gaps in my ceiling. Main question is: what should I fill these gaps with? Drywall join filler or some expanding foam? My sense is drywall filler is more sensible. The other thing I also realised is that all my sheets are 3mm less than 1200mm some along both the walls and ceilings the screws get closer and close the batten/stud edge. Is this sheet dimension new or have I just been blind to it before?

Windows or Linux machine? I'll test on my windows 11 machine to see if I can replicate. And put it in the bug list for further investigation.

32.6/66.2 (although you can just use room internal measurements) = 0.492

Hmm interesting. The card you should be seeing looks like this: I wonder whether you have the older version of the app from before I sorted the radiator saving issue locally. Can you close your browser and/or do a hard refresh? On both my browsers - Chromium and Firefox, decimal entry in the form I have is fine from keyboard. and I have the add & select button rather than add to database. Would be interesting to see what you get following full refresh. Ah, no sorry! You're in the Radiator Library editor on the multi project beta! So the card is correct. Inputs on both my browsers work fine for decimals on water content. What browser are you using?

Yes, of course, share the numbers.

Best thing to do with odd shaped rooms, it just calculate the P/A ratio yourself and enter it into the calculator. In the Floor Dimensions and Exposure Card, select Manual P/A, then measure the length of the exposed perimeter of the room and divide by the total floor area - then you can just add the p/a ratio into the Enter P/A Ratio Directly - this is specifically designed for complex shapes. You can the ignore all the other dimension inputs in that card. Hope that makes sense?

Because this is an implementation of the CIBSE reduced method, these are really the only choices for this particular version. However, when I get the full BS EN 12831:2017 method tested and run, there will be full freedom for proper and complete fabric inputs for the calcs. The CIBSE method covers pretty much 90% of projects we see, which is why I went for the quicker win to begin with. The tool will still give you a pretty good result right now as fundamentally this gives you a conservative result as that's what all the methods tend to do. However, to get around this now, you can select the tab to the right of SAP Estimate and select the Measured/Tested air permeability and then add your SAP design figures, that completely gets around the problem and is the better approach right now.

It is, and applied well and in the right place, it produces an extremely good finish. I've been in many houses where it looks stunning. A lot of the other paints like the trade ones are developed I think to go on easily and hide a multitude of sins.