Dreadnaught

Except for evaporative cooling, for example by drying clothes indoors. Such incidental evaporative cooling is modelled in PHPP. More generally, humidity is worth considering when considering comfort and energy. One thing I am evaluating is having an enthalpy heat exchanger in my MVHR.

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

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.

In this earlier video on his plastering, he mentions that the interior plastering is more like a two layer render, for a nice texture, and being really good for the airtightness. He wanted to avoid dead flat surface and sought a slight "rub" to the texture. A scrubbed sponge finish with different textures on the walls and ceilings. He seems to have been experimenting. I suspect he's regretting it now.

@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.

@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?

Blimey, I did not know this could happen to plastering, and from Mr Charles Luxton himself. What was the cause? How can this be avoided?

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.

Send a message to a mod, such as @JSHarris or @Nickfromwales. They will turn on the functionality for you.

@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.)

Another idea, could those who welcome visits add it to their signatures or "about me" sections? Would that help? I have visited four BH members so far, from whom I have learnt a huge amount. I am immensely grateful for their generosity and hope to return it to the community when I am in a position to do so.

Yes, I agree. I have come across two recent examples of well-inslulated recently finished builds that are overheating. One was modelled in PHPP and one was not. Some don't take overheating seriously enough at design stage. The 10% of annual hours over 25ºC that is part of the passive-house standard is, in my and many other people's views, far too high. I would like to see a limit of 5% or even 2%. For me, passive house is foremost about making a lovely comfortable home. Time over 25º, let alone any time near to 30º, needs to be considered and minimised. Working through PHPP for me has been a revelation. As the saying goes, "all models are wrong, but some are useful". I have found PHPP to be immensely useful in making me think about the things that are important. I had read about PHPP extensively before modelling my own house. Even so it has exceeded my expectations.

Agree. For example, in my design when I swapped from a hot water tank to a Sunamp, with its much lower heating losses, that change alone reduced my modelled annual over-heating rate by two full percentage points. Agree. For me that will be a simple and comparatively low-cost split air conditioner in the large double-height living room. I might also go for a second indoor unit in the master bedroom too (you can have up to 5 indoor units as I understand), not sure yet. I might try and build the indoor unit(s) into the ceiling as I have void where they could fit. I think it could look quite good.

Here is a blog post on overheating that might be of interest for those designing an highly insulated house: https://elrondburrell.com/blog/passivhaus-overheating-design/. I am adopting its lessons in my design.

For a passive house, overheating in summer is generally the greater risk than an inadequacy of heating in winter. Best practice: first step is to design-it-out to the extent possible (<2% ideally), then consider other solutions, including active cooling. I recommend The Passivhaus Handbook by Janet Cotterell if anyone's interested. Chapter 7 & 11 discuss overheating at length.

Fair challenge. Its not about elimination of all overheating in all circumstances. Zero % overheating is unrealistic, as you say. I am referring to optimisation at the time of design. PHPP presents an average % of hours overheating per year, defined as a temperature over 25ºC. The standard for certification requires a modelled figure of 10% or less. Most aim for below 5% and I prefer below 2%. Architectural design optimisation of overheating is effective for this, as I am finding. Oh and I plan to have the option of an air conditioner, should it prove required.

Ah, the bat to eat the flies and moths, clever tactic. I like it.

True. Evening and night tends to be worse: moths, mozzies and worse.

Oh, and if you are playing with the summer overheating % in PHPP, as I am at the moment, there is a new advanced shading sheet available from Peter Warm. Warm said we are the first to be using it in the UK. It enables better modelling for transparent shading objects, such as trees. Useful for me because I have whopping horse chestnut slap bang between my new build and the southerly sun and about half a meter from my boundary.

Purge is good but I hate flies (and moths at night). Any purge windows I have will need fly screens. As Jae Cottrell once told me, fly screens also help marginally with shading.

Oh yes, on summer bypass, some MVHR models have "simulated" bypass. The Paul Climos 200, which I rather fancied, has this. As far as I can tell, this means it shuts down extract. It does not actually have a physical bypass of the heat exchanger. I assume the heat exchanger assumes you will open a window for the extract, which makes some sense. I am not sure how this can be called "simulated" but that's another matter. As I don't want to open windows if I can avoid it, this means I will be choosing another MVHR model.

Some observations. Designing out cooling is quite easy and effective. I am doing it now with PHPP for my build. As mine is a modern house, I have more freedom to play with window sizes and architectural features, such as overhangs. Floor to ceiling glass is to be avoided and I am doing so in my build. The glass below knee height offers little extra light but much extra heating gain. Building regs require an openable window in every habitable room for purge ventilation. I wish it didn't, I don't want them in my modern house as it it does not have any conventional windows, just large frameless roof lights and architectural glass. Problematic. Purge ventilation is sometimes defined as 4 air changes per hour (ACH). Most MVHR work at about 0.4 ACH. Trying to achieve it with an MVHR will lead to hugely over specifying the MVHR and require much bigger ducting. I know, I tried. The MVHR I needed was 271 kg! Using water UFH for cooling delivers that cooling in a sub-optimal place, the floor. Sub optimal for convection. And if not carefully controlled can cause condensation. I decided against it. In the end, I plan to put in a conduit for a split air conditioner in case I need it in my Passive House. Because split air conditioner are highly common they are very very cheap in comparison (about £800 tops) and finding someone to install or service it will be easy I imagine. I will try the house for a year and install an air conditioner if I need one. Its easy to over engineer the solution and get carried away. I am aiming for a very simple, as simple as I can make it and for it to be cheap, and maintenance free.

Oh, and if cooling is needed, first it shouldn't be much as it should be designed out at PHPP stage, but if it is needed then just install an £800 air-to-air split unit air-conditioner. (I will put in place a conduit and wiring for one just in case.)

For a passive house, isn't the simplest and lowest maintenance the following… E7/E10. No gas, no PV* Sunamp for DHW electric UFH cables embedded throughout the slab (not just bathroom) for space heating Big difference is no wet UFH. What's wrong with this? * I have huge tree blocking the sun.

@PeterStarck, why do you say "in a PH larger than 130m2"? Wow, Peter, you have really got me thinking! I am thinking whether I really need wet UFH. How about simple electric UFH instead across the whole house as you also reminded me of something @TerryE said a while ago. Until your comment my plan was wet UFH and SunAmp eDual with E7/E10. But @TerryE's reasoning, which I have just remembered, is (to invent a quote) "don't store heat energy in a Sunamp and later transfer it into the slab. For a Passive House, where the diurnal temperature fluctuation is minor so the time of day of heating doesn't matter much, just put the heat straight into the slab according to the E7/E10 timetable, the slab will release the heat gradually in to your home." Thus, if I went with electric UFH then this would make my system even simpler. Just E7/E10, a SunAmp for DHW, and electric UFH for space heating. Simple as can be. Like you, I like simple. (However, with no wet UFH I would lose the chance to add an ASHP later if my heating demand turned out to be higher than I expected.) (Mine will be 117m2 TFA Passive House*. I can't have PV because its behind a huge tree . I am currently at the stage of PHPP modelling.) * hopefully certified, am working on it.