Who has used, is using, PHPP?

[Dreadnaught]

@Russdl and I were just discussing PHPP in a private discussion and we wondered who on BH has experience of actually using PHPP to design a house. I know @PeterStarck did his own calcs, and he was kind enough to show them to when I visited his splendid build in East Kent.

 

Who else has a PHPP model for their house, or is preparing one?

 

(For those wondering, PHPP is the Passive House Planning Package, a huge and complex spreadsheet for calculating the thermal and other characteristics of a building, produced by the Passive House Institute in Germany and available to buy for about £200. It is a requirement for a certified Passive House. More info here: https://passipedia.org/planning/calculating_energy_efficiency/phpp_-_the_passive_house_planning_package.)

Edited July 11, 2018 by Dreadnaught

[Russdl]

That's it - it's out in the open!

 

Here's my post to @Dreadnaught to add to the debate.

 

~~~~~

 

Hi Dreadnaught.

 

So as not to drift the thread too much from the 'house cooling ideas' I thought I'd message you directly. Are you doing the PHPP yourself and if so, how are you getting on? 

 

My first dealing with PHPP was with an 'expert' who was a complete clown so I bought my own copy of the PHPP and started entering the data myself  - and, if I'm honest, I've been struggling with elements of it.

 

After a while I went to see another 'expert' who agreed to review my attempt, he was definitely much much better but he'd still missed some school boy errors that I'd made, which I discovered after learning stuff from my meeting with him. Also he was going into minutiae that I hadn't for one moment considered. For example, the timber frame company we will most likely go with use nail plates to join elements of the timber frame, his modelling of this in the PHPP proved that the claimed U value was incorrect (if you factored in the amount of timber in the walls and the metal nail plates), so I've taken that on board in my PHPP but not even started on the roof construction!

 

Despite that I've managed to get my overheating down to zero using awnings on the southern elevation of our planned house, but I wonder, have I?  What else have  I missed...

 

I'd appreciate your thoughts.

 

Cheers.

 

Russ.

[Dreadnaught]

And my reply to @Russdl.

 

~~~~~

 

I was tempted to do the PHPP myself but in the end I got an expert to do the first version for me. My expert is from one of the timber frame companies. Compared to some, he's quite good value, which is why I used him. And also I liked that he does PHPP every day of the week, compared to some "experts" who don't.

 

I agree PHPP is quite intimidating and it took my a few days to get my head around it. I have done quite a lot of other modelling in the past so am comfortable with spreadsheets. From now on I think my expert and I will work together as a team as we develop the design with me spending as much time with my nose in PHPP as he does.

Edited July 11, 2018 by Dreadnaught

[MikeSharp01]

I have used it to fine tune our design - I took the BRE course and worked from there alongside our architect modeling their ideas and telling them what the PHPP outcome was. I have a working model of our build now with all the different window supplier combinations - enough to drive you mad, but it was good fun in the end, and I suspect will continue to be.

[Dreadnaught]

@MikeSharp01 do you go for certification? When you were modelling in PHPP, what were your areas of focus? Form factor, shading, window positioning, overheating, energy use?

 

Where did you come on the key parameters?

[Russdl]

Out of interest @Dreadnaught are you going for certification? I was on the fence but very happy to use PHPP to guide me. The better half was/is very keen that we get certified but after our last meeting We are now not so sure.

[Dreadnaught]

@Russdl I would love to and will do so if I can. But because of planning constraints, the form factor of my planned home will be very poor (4.6) and so we are struggling a little. Its a modern bungalow with lots of roof windows but behind a tree. 

 

It may come to the point where the compromises are just too great (or too expensive) to make it under the thresholds to get certification, in which case we will almost be there and instead I might go for the lower certification (the PHI Low Energy Building Standard). Irrespective, I will proceed in the design and build as if we are going for Classic certification, with the air tests and rigorous attention to detail as, in my opinion, that is what brings a comfortable home.

Edited July 11, 2018 by Dreadnaught

[MikeSharp01]

5 minutes ago, Dreadnaught said:

@MikeSharp01 do you go for certification? When you were modelling in PHPP, what were your areas of focus? Form factor, shading, window positioning, overheating, energy use?

 

No I didn't go for certification. The way I figured it was if I was eventually going to get the house certified I would cross all the quals bridges then or hand my design to a qualified assessor and let them do the work.

 

Not sure what you mean by the key parameters but page 1 looks like this:

 

 

Have some changes to make as  the foundation now has more concrete and less insulation in a few places and this one is based on generic windows which, when the final choice is entered, push things a bit the wrong way as well but we have a margin and the front and rear elevations now have more insulation than this model by 20mm or PIR so that will help a bit in the right direction. Overheating here looks OK but this is very optimistic and I think we will exceed this if we are not careful - putting the ASHP into cooling mode also pushes things the wrong way. PHPP is a balancing act where you trade off things all over the place to reach an optimal setup - like finding the, or a reasonable, maxima in a multidimension regression (type) exercise.

 

Source (https://www.ncss.com/software/ncss/upgrade/)

 

 

[Dreadnaught]

From the numbers, that looks like a very nice balanced build, @MikeSharp01. What is the form factor? I am guessing close to 2.5.

 

I fully agree with your point about PHPP being a balancing act and all the better for it, in my opinion.

 

On certification, beware that you require a lot of photos of the build and other docs, which you may have, as referred to in Warm's design checklst: http://www.peterwarm.co.uk/?dl_id=35.

 

 

[Russdl]

18 minutes ago, Dreadnaught said:

rigorous attention to detail as, in my opinion, that is what brings a comfortable home.

 

I think you've hit the nail on the head there.

 

9 minutes ago, MikeSharp01 said:

Not sure what you mean by the key parameters but page 1 looks like this:

 

The thing is Mike, mine looked like that (without any shading) but I'd made a mistake in the data, which wasn't spotted by my second PHPP expert (and his credentials put him right up there - expert that is), and when I corrected my error it was 10% 'frequency of overheating'.

 

I'd always planned on shading for the SE and SW elevations because I reckoned it would need that by just 'eyeballing' it. After fixing my error and putting the shading back in I'm down to 0% overheating.

 

I think.

 

That's what my PHPP says at the moment anyway.

 

 

 

[Dreadnaught]

@Russdl what are your further thoughts about certification, why was your other-half keen? And what is your house like?

Edited July 11, 2018 by Dreadnaught

[Russdl]

Still on the fence, but falling towards 'not' (if permitted, we all know the rules) 

 

I've loved and loathed messing with the PHPP in equal measure. My geo-located Sketchup model has probably guided me more than the PHPP as you can produce the sun/shadows for any time of the year/day and it really reinforces that gut feeling.

 

It's around 190m2 and may look something like this.

[Russdl]

12 minutes ago, Dreadnaught said:

why was your other-half keen?

 

In case we had to get shot of it before we popped our clogs is the main reason. Or maybe lack of faith in me getting it right ?

 

Probably the latter.

 

Probably justified, time will tell.

[MikeSharp01]

8 hours ago, Dreadnaught said:

From the numbers, that looks like a very nice balanced build, @MikeSharp01. What is the form factor? I am guessing close to 2.5.

I can't recall the form factor but we did play with the shape a bit to optimise it. Will look it up when I get home. 

 

Also agree that the challenge with the overheating tends to sit on a knife edge and I do worry that I may have got a number wrong somewhere. We do have the option of shutters on the south facing glazing and if needs be we will install them if, in the end PHPP says we need them or, down the line, sweaty experiance says we do!

[Jeremy Harris]

I used PHPP in the early stages of our design.  Useful for confirming what I already thought in many areas, but like all models I found that it's only as good as the data that's available.  In our case PHPP over-estimated the heating demand and underestimated the overheating risk.  I spent a bit of time working out why this was, and concluded that it was the climate/weather data that was in error.  Our house is cut back into a South facing hillside at the bottom of a valley, and PHPP cannot accurately account for the impact this has on the local air temperature and wind speeds.  Measurements taken locally and compared to the data set used by PHPP showed marked differences, in general the area immediately around our house seems to be 1 to 3 deg C warmer than expected, all year around.  Wind speeds are also way lower all year than expected from the climate/weather data, so accelerated convective cooling from the outer skin is significantly lower, which alters the effective wall, roof, glazing (and floor, if suspended) U values.  This accounts for the majority of the errors between the model output and our real world findings.

 

Interestingly, in terms of just heating requirement, the very crude and simple spreadsheet I wrote years ago, that was intended only for comparing where the cost/benefit trade offs might best be made at the design stage, turned out to be very close to the PHPP output (and equally in error in terms of overestimating heating demand).

 

Models like PHPP are certainly very useful, but I would urge extreme caution in taking their output as anything other than rough design guidance.  As our house has shown, models like this (and there is also a very good free Canadian model worth looking at) fall over, often quite badly, when the external conditions are not as they predict from the data sets they rely upon.  We did not anticipate any overheating, yet in practice this was quite a problem, and one that caused some significant changes to the build.  Luckily, during our ground works I had a hint that there may be a local problem, as when the guys had dug out for the retaining wall it was very noticeable that the local temperature, in the North East corner in particular, was very high.  This caused me to change the MVHR choice to one with an integral air-to-air heat pump, to add around 1.5 kW of comfort cooling.  What I didn't anticipate was that 1.5 kW of comfort cooling wasn't going to be anywhere near enough.  According to PHPP it should have been, but in practice it wasn't.

[Gone West]

17 minutes ago, JSHarris said:

I spent a bit of time working out why this was, and concluded that it was the climate/weather data that was in error.

That is exactly what I found. I started playing around with PHPP in 2009 and found climate data had a significant effect on the results. I used climate data from Meteonorm, Manston, SE England and also Vlissingen to compare results. I also found the limited wind screening aspects and therefore micro climate effects modelled crudely. I think this is why modelling decrement delay is so difficult and why it is so important in your situation and not in mine. I don't have the latest version of PHPP, mine being updated in 2010, so maybe things have changed since then.

[Jeremy Harris]

Thanks, @PeterStarck, it's nice to have confirmation that you found the model as sensitive to local climate data as I did. 

 

The main problem I had was not having any reasonably accurate data for the local conditions before we started building the house.  I certainly didn't anticipate the fairly large reductions in wind speed experienced in our "hole in the valley", nor the higher overall temperatures.

 

Building the house has itself changed the conditions very locally to a marked degree.  Our neighbour has a vegetable plot immediately to the East of our house, and keeps telling me how grateful she is for the improvement in growing conditions building our house has created.  She tried growing raspberries, starting last year, never having had much success in the past.  She's had a superb crop, some of which I finished off this morning on my breakfast!

[Russdl]

We're planning to use the same timber frame as @JSHarris (and many others) and if I enter the wall construction into PHPP with a U value of 0.12 I get this:

 

 

 

If I then add the % of timber frame (6.4%) and nail plates (0.016%) in the wall (as explained to me by a PHPP expert) it changes the U value a fair amount and pretty much everything else on the verification page:

 

 

 

The difference between those 2 verification screen shots is purely down to the 6.4% timber frame in the wall construction and the 0.016% of metal nail plates, I find it quite amazing the changes that produces and, as I said earlier, I've not even started on modelling the roof construction into it's component parts.

 

Has anyone else modelled a timber frame wall construction in such fine detail?

 

Is this going over the top or a useful exercise?

 

[Jeremy Harris]

I modelled our cellulose filled twin wall from first principles and ended up with an overall U value of 0.121974 W/m².  That included allowing for the joining studs and nail plates, plus the service void air gap, plasterboard, outer board, cladding etc.

[joe90]

I have not used PHPP at all, I just applied it’s principles (good orientation, high levels of insulation and airtightness) to a design that we love. We are yet to see what our energy consumption is but it will be way lower than one built to current building regs. Already people have commented on how warm the house felt (in winter before any heating was switched on) and how cool (during this exceptional hot weather). We have a wood burner for winter days and MVHR for good air even in winter. What’s not to like ?

[Russdl]

8 minutes ago, JSHarris said:

I modelled our cellulose filled twin wall from first principles and ended up with an overall U value of 0.121974 W/m². 

 

Wow! ? I should have guessed!

 

I'm just scratching the surface, clearly!

[Dudda]

I bought PHPP and have used it quiet a bit but never went as far as getting a house certified. I've also never took any course but read the manual a few times in detail. The person in our office who took the course a number of years ago hasn't a clue and never uses it.They wouldn't claim to be able to use it either.

 

PHPP is a lot of work and it takes a lot of time to input everything. It's really interesting to see little things you modify change the final results. I've also downloaded Therm and modeled the thermal bridges at floor and wall junctions, eaves, etc and incorporated them. The more time and effort you put in the more accurate the output.

 

I always model the timber supports or nail plates wherever they are. It makes a massive difference always. This screenshot is off the sun tunnells from the rooflights to the ceiling.

Edited July 12, 2018 by Dudda

[Russdl]

34 minutes ago, JSHarris said:

overall U value of 0.121974 W/m². 

 

@JSHarris I've no doubt that is accurate, and much different to the figure I've achieved in my PHPP. Can you see any glaring errors in the data I've put in to my spread sheet that has resulted in my U value of 0.137?

 

 

 

 

 

[Jeremy Harris]

Our build up uses different materials, but I allowed for the exact number of noggin/nailplates between each of the two timber frames, the 89 x 38mm timber frame elements and the number of them in total, the OSB outer skin, the Durelis inner skin/VCL, the 45mm service void, 12.5mm plasterboard, 3mm plaster skim and externally the 50mm x 25mm cladding battens, air gap and the larch cladding.

 

I then worked out the average U value for the whole area of the external walls.  Things to watch out for are the exact number of noggins/nailplates per unit area and the fact that the nailplates have a lot of voids (more voids than metal) so cannot be modelled as if they were solid plates.  Somewhere I have an AutoCad drawing of a nailplate that I used to work out the effective CSA, as it's a fair bit less than the apparent CSA.

[Bitpipe]

We had already designed our house and received PP before discovering e-build and the world of passive standard builds.

 

While trying to settle on a build method (we were considering ICF as we have a basement) we contracted a low energy specialist consultant / PM who did a PHPP and full cost analysis of ICF vs concrete basement with timber frame. We went TF.

 

Consultant was a bit of money for old rope but in retrospect we were buying some confidence that we could actually afford to build the house and manage ti ourselves (he wanted 10% of build cost) and the cost plan was very comprehensive (we came in about 15-20% under his estimate) and was a great help.

 

Can't say the PHPP really changed anything though but it did give us reassurance that the existing design would perform well and our space heating requirements would be low with overheating a manageable issue.

 

Also came in handy when applying for an Ecology mortgage as their requirement at that time was passive standard!