TerryE

As Jeremy says, this just isn't a real risk in a passive house. The heat imbalance is typically at most 1kW or so and for a typical slab this might need it's surface to be 2-3°C cooler than room temperature to do this. This is way above condensation temp for the RHs you find inside a passive house, thanks largely to the continued MVHR circulation.

We had a dance with our enforcement officer because our front door style wasn't to plan; they told us to put in an NMA (pointing out that the door wasn't even visible from the road) -- which we did and the planning office turned it down because "any change to the principle elevation is not non-material". So we have (i) admitted that we'd changed from our original plan and (ii) our door was not to plan. Game set and match. I suspect that its the 2m that triggered the reaction. That plus the fence looks nice and permanent. I'd be tempted to do a variant of what Peter suggested (i) don't put in an application; (ii) build a low bedding wall backfill with soil and plant the hedge. (iii) leave the posts, but remove the top 40cm of the fence or maybe and replace it with trellis. If you put in an application then you are effectively admitting that you are intending it to be a permanent structure. Stick to your point that you need some form of 2m fence because of the use of the safety issues, and keep to your line that it's just temporary. The issue will really become one of whether they think it worth the effort to execute an enforcement order for a temporary fence. If you've already got the hedge in place then its clearly not permanent . If they execute an enforcement order on removal of a 2m fence, you can immediately respond with "what 2m fence?" Don't put in the application, and just keep spinning it out. Threatening emails are cheap, but enforcement orders are costly to execute and pretty hard to enforce. Are they really going to take you to court for a fence that won''t even be visible by the time that you go to court? You could always add some "temporary" Hessian screening or plant some rapid growing clematis or honeysuckle to the trellis once the EO dogs have got bored.

As @Alphonsox says it's a BS quoted power law fit. The way I read it , the non-unity power term really reflects the convective element starting to kick in for higher delta temperatures, but in the case of a low temperature passive salve, I'd just stick with a straight proportionality. Is it 7 or is 8 or what depends on such factors as the material type (roughness, and transmissivity) -- we have a slate floor and I am sure that a dark matt slate would have a slightly higher coefficient than a light polished tile. The coefficient comes out of a linearisation of the Stefan–Boltzmann law. I used 7 rather than 8, but that's the sort of ballpark. I've only had 3 days of living in our house (rather than working in it 7 days a week for years)) so I am still getting to grips with the dynamics and will do a blog post on this, but I think that the coupling between floors is less than I'd hoped. Maybe its all of that acoustic insulation in the ceiling void, maybe its that the house hasn't reached a proper equilibrium vertically, but if our ground floor is at a comfortable 20°C ish, then the 1st floor is definitely a couple of degrees cooler. I have my office on the first floor and it's enough to notice when I am sitting working at my PC. At the moment, if the outside temp is around 0°C and the MVHR is 90% efficient, then the inflow air is at around 18°C. I am considering putting an inline heater in the MVHR in-stream to lift the air temp to say 22-24°C to counter this effect. Jeremy won't be experiencing this because of his Genvex. At @jack mentioned in and earlier related topic, the temperature differences and thermal gradients are so low, that I don't see any material evidence of convective flow between floors. The only material coupling is though the ceiling/ floor and MVHR circulation.

Yup you can do this, especially if you use btrfs, but a Kingston UV400 SSD + case costs around £50. Speed and reliability are worth more to me than a few £10s bought-in cost savings. I'd be happy with USB3 if the linux driver supported ATA pass-through. Failing that, it's OrangePi or BananaPi. These also have the benefit of supporting 2Gb RAM.

@Onoff na. Bad idea. It's cheaper to do it properly and get an SSD.

SD cards have a very primitive controller and don't support TRIM. Whatever the weakness of SSDs they are materially more reliably than SD cards if you are using them as a RW device. Whilst the RPi3 can now boot off a USB attached FS, I find it just easier to leave the /boot partition on the SD. It's almost never written to, so this is fine. If you do want to use an SD for R/W then the trick is to use a reasonably large one so that the FS utilisation is small. Also from what I gather one of the main reasons for failure of an SD isn't wear exhaustion, but rather a power fail whilst the RPi is in the middle of a write to the card. You can avoid this entirely with a small battery backup hat which can keep the RPi up for 10 mins say and does an orderly shutdown after 5min without power, so that any unwritten buffers are properly flushed to SD and written through before the FS is properly dismounted.

This is yet another RPi thread. Some of you might be interested. I was originally intending to use 2 RPis for my HA, but on reflection I have decided that one of the two is hardly doing anything and it actually makes life simpler to collapse all of the functions down onto one RPi. I had considered moving to a more powerful SBC (such as the one discussed in this companion thread) but in the end I decided to stay with an RPi for now. This will host a MQTT broker, a MYSQL (InnoDB) database, a limited lighttp webservice and a Node RED instance, all on a minimal headless server -- that is no desktop and only SSH access for login and file transfer. I want to keep battery backup (mainly for orderly shutdown on power outage) and some reliable mass storage device and this really means SSD if I am going to be battery backup friendly So I really want to cover two topics here: using DietPi to provision my server, and some issues around SSD performance. DietPi. This makes building the Pi a doddle. You download and image onto an SD card a smallish (<100Mb unpacked) provisioning file system and if you want a headless install there is a single config file, /boot/dietpi.txt, that you need to edit to select your Wifi credentials, some passwords and software that you want to install. Plug it into the RPi, turn it on and come back 15 mins later and you can SSH into the build server. There is a simple terminal-based menu system for doing further configuration S/W installation, etc and also maintenance functions such as move the root partition onto a USB-based device, e.g. memory stick, HDD or SSD. and so configuring the SSD is a couple of click operation. Once you've done this, you still have /boot on the SD card, but the OS and user directories run off the SSD (in my case). All very good. SSD performance. Because of the underlying page-base nand storage technology, this does have some significant performance and lifetime issues if not actively addressed by the OS and the filesystems on the SSD. The RPi uses a Linux family OS, and both the OS kernel and the main FS used on the RRi (Ext4) are SSD aware, and the OS includes a TRIM function to enable the SSD controller to align its garbage collection to the use of the file system. Without this, the performance of the SSD can significantly degrade over time as unused clusters my contain garbage and the whole page need erasing and rewriting to do a write. (This is a good article explaining how TRIM works) The gotcha that I've found is that the TRIM command is a native ATA one, and Linux does support this for directly attached SATA disks. However, it is not in the standard USB FS interface, so the USB-to-SATA chip needs to support ATA pass-through, and the Linux kernel driver for these USB chips don't yet support this. So the nice features which prevent SSD performance degradation effectively don't work with RPi's USB attached SSDs. Bugger.

IMO, we can get a bit too paranoid about this. If you pack something loose around the pipe insulation such as wool insulation or even rockwool, then the difference in local U value will be fairly small. OK, you might lose the few W along the pipe, but it's also leaking waste heat so it will probably be a wash. The odd few W here and there isn't going to matter, so long as there isn't a material thermal break which is causing a cold spot near the condensing temperature. In this case if you insulate the pipework and any gaps around the pipework, then I doubt that you would be able to detect any difference in surface temperature with an IR thermometer.

We are in the process of carrying stuff into the new house (which is next door to our old one) because we are vacating the old one next week. I thought that the temperature in the new house was dropping a bit and I put it down to the fact that we were constantly opening doors to walk furniture and other contents in. So in the end I checked and the slab had definitely dropped a couple of degrees in temperature. What was going on? It was then that I realised that I have made a boo-boo and the heating hadn't been on for over 2 days!! Well insulated houses stay warm for a long time without being heated.

I have never had any such probs with compression fittings for normal house plumbing. The pastes work well, but I have found that they tend to set hard, so can be problematic if you every need to break the joint. And Peter, your installation counts as a piece of artwork!

Sounds to me like you've got a plan ?

If you've seen my posts on my plumbing then you will see that this is pretty much my heating system. 7 hrs of Willis heater on E7 keeps my house to temperature.

AFAIK, something like this falls under the scope of your planing permission. Read the NoD. It will normally include a clause like: The development shall not be carried out otherwise than in complete accordance with the approved plans Drawing Nos: ... received on the DD Mon YYYY, unless a non-material amendment is approved by the Local Planning Authority under the Town and Country Planning (Development Management Procedure) Order 2010. Reason : To clarify the permission and for the avoidance of doubt Unless the Velux literally can't be seen by your neighbours, I suspect that the LA will treat this as a Minor-Material Amendment rather than a NMA.

Doing copper plumbing is a skill which takes some practice to acquire. So my suggestions are: Don't bother, and If you really want to then do it at the bench and Use compression fittings to joint your work to the stubs coming out of the wall. The videos say that you don't need PFTE tape, but when I do this I find maybe 20% weep, so my suggestion is at least 4 turns of PTFE covering the olive and you just won't get weeps. Less hassle. Or Use the Peglar Tectite range if you want some smart looking joins. They are a bit pricey, but they are the dog's bollocks, and wont leak. Just make sure that your copper pipe is clean. You can use Hep2O fittings to connect Hep2O to copper. If you use Hep2O then ready the Wavin guide at least a couple of times and never forget to put the inserts in. A decent pipe cutter is essential. Use a ratcheting cutter for the Hep2O -- it's just easier. If you need manifold work, just use the Hep2O plastic range. The lifetime isn't as good as the brass ones, but you should have sold the house long before there is an issue. Also remember to check that you copper pipework isn't being used for earth continuity anywhere in your house, because if it is then you need to add 10mm straps copper to copper to preserve continuity or get your electrician to do it properly. Also remember all of the bollocks about controlled activities v.v. BC when it comes to selling your house.

@Nickfromwales, Nick, I think that your approach / design template will fit many architectural layouts where there are clusters of HW services physically remote from the boiler / DHW tank. it will provide responsive HW without significant delay, and without any material running cost. So long as it is implemented as you describe. My concern is that few plumbers are at your level of sophistication. Proper insulation is essential. The asymmetric 22 / 10 loop plus trickle flow HRC pump will help. Activity based priming will help, but you could consider on of the new Doppler radar sensors in lieu of PIR. That being said, our setup where there is about 1m of pipe between the SunAmp and a heavily lagged HW manifold is a lot simpler. The first person in the morning has an extra 30 sec of so delay as the manifold warms and that's it.

Just thinking off the top of my head if we are talking about 1W/m ish and are happy to have, say, a 3°C drop along run. Again picking numbers out the air say 10m, then this would be radiating roughly 30W and 10m of pipe has 10*pi*9.8^2l or just over 3kg of water in it, so the flow rate needed to achieve this would be tiny.

The data sheet quotes 0.034 W/(m ∙ K) for the 25mm insulation so for a hot return circulate at ambient + 30 °C and a 15m pipe run this would work out at roughly ⅓ kWh per day.

Nick, normally I would do, but we are aiming to move into the new house in 5 days time +/- and we have 3 "kids", 2 spouses and 1 grandson staying for Christmas! So every room has to be commissioned and things are a tad hectic here. ? Since we are only working in the new house and only run the hot occasionally, I have noticed that heating up the hot manifold does add a good 30sec lag to the flow coming hot at the tap, but the manifold box is pretty lagged so it then only loses a few degrees an hour. But I put 2 hours of heat, E7, into one SunAmp every couple of days and that keeps the hot available.

Clive, you daft bugger. We use one in our house every night 1-7am, but we are on E7. Mind you, the washing machine is now in the new house and we (or to be honest Jan, so far) just hang our clothes on a multiline indoor dryer which is in the service room in the warm loft and the MVHR extract takes care of the moisture. But my daughter just uses a couple of airing racks either side of a dehumidifier and she gets her clothes dried fast with no humidity problems.

Dave, is there no way that you could convert this to dead space, e.g. shuttering around the skirt of the caravan and maybe banking soil up to floor level or whatever. Can you get some old fashioned bales? You could create a skirt from them.

Get yourself a small dehumidifier and a cheap timer switch.

How about http://excelcalculations.blogspot.co.uk/2012/12/heat-loss-from-insulated-pipe.html.

My immediate thought is to use 10mm runs for all of the low flow runs -- the hand basins and toilets, and only use 15 for the baths and showers, and keep the manifolds central. Route the 15s first, then the 10s and it doesn't really matter that much if you have to take a slightly roundabout route for the 10s because they have a third of the cross section of the 15s, so even if the run is twice long, there is still less dead water in the pipe runs. The alternative is as @Nickfromwales says and to use an HRC, but in this case you will get heat losses because of the standing water at 43 °C or whatever in the main 22mm even if insulated as it will be radiating 24hrs a day. One to do the sums on, I think. I defer totally to Nick on matters plumbing, but it's the potential heat losses that I would check.

@Ferdinand, I wasn't being sarcastic. My point was that dehumidifiers (as in this case) take X kWh to condense out humidity into water and in doing so release 3X kWh of heat into the environment -- plus the X kHr which also ends up as waste heat, so 1X in and 4X out.

40l = 40 × 2200 kJ = 24 kWh latent heat released for 8.4 kWh electricity so a CoP of ~ 4:1 -- pretty good, eh?