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Showing content with the highest reputation on 24/03/17 in all areas

  1. 3 points
    No comment milud. actually it was a blind date set up by our friends, her first question was "what do you want to do with your life", I said retire and build my cottage in the countryside and I don't care where." I asked her what she wanted to do with her life and she replied " I want to retire to where I come from, Devon, and I just happen to own my late fathers old timber and asbestos bungalow out in the sticks down there", ( and flattering her long eyelashes said) "but I don't have the resources to do it up or anything". Kerching ? ( not a bad cook)
  2. 2 points
    Hi Ted. Welcome to the site. I wish you luck and a future MRiCS, but to be honest this won't go anywhere. My attitude to the 2020 EU nearly Zero Energy Buildings Directive as a context for UK self-build homes, is that it is not a context for UK self-build homes because we are leaving the EU in 2019. No one - whether self-builders or construction companies - will spend any time on it. And having gone through the last Zero Energy Buildings Initiative as wished on us by Mr Blair and Mr Brown, which imo was a bit of a dogs' breakfast requiring a scattergun of ideas wished on us by an out of touch Government relying far too heavily on technical gimmicks rather than quality building, I am glad that it is not coming here. The only possible bit of context I can see left is for people importing their kit homes from the EU. Is it possible for you to refocus your project on something that is actually going to happen? For your interest in energy saving there is potential in: 1 - comparing self-build standrds with corporate build. What difference and why? 2 - perhaps perceptions of why individuals feel a need to import "low energy" kit homes rather than build them here. 3 - related to 2, my suspicion is that far too much money is being spent on expensive solutions that happen to have particular country labels on them ,which is a success for Brands over knowledge. There may also be something about a related lack of clear information concerning the UK industry and what is available. 4 - Jeremy's point above about the proliferation of planning and compliance costs is an area that needs work. Could you reframe your project around barriers to achieving high energy efficiency for self-builders and corporates? One angle would be the massive increase in people and bodies who have a right to be consulted in a Planning Application over the last 2-3 decades (this is one of my hobbyhorses). 5 - Exploring the enforcement of building regs standards and declared designs in what is actually built. This is a Jeremy area of interest, but your target audience would probably need to be Building Standards Officers in Planning Authorities as the enforcer, and corporate builders, and self-builders. I think you need a rather sharper focus, and perhaps a project redefinition if it was set up before June 23rd 2016. I am sure that people here would be willing to spend a little time on advising you publicly or privately. There are also people here who could introduce you to the right industry people to interview. Hope that helps a little. Ferdinand
  3. 2 points
    Nah, just what I say when I start the day in 'clean' clothes, and then have to go back home to chuck the boots and combats back on Well, before this got to a point where we assumed anything, and then you acted upon it, I thought it best to chat briefly with the tech guys at Telford to see what can actually be extracted from a X sized buffer tank with regards to DHW uplift via an instantaneous coil of X size. Bigger of both = more and vice versa. So....after a chat and a brew....deep breath...."options" :- On the assumption that, You already will have an ashp installed and working. You already will have a buffer of whatever size installed, according to majority advice and positive feedback here ( against running a HP to Ufh directly in a 'low' energy home ). You will have a reasonably sized Pv array. I have arrived at the following :- The costs of the larger buffer tank, having it fitted with a 4.5m2 DHW uplift coil ( the minimum size that would offer any meaningful yield at low temp but also physically too big to go into any less than a 300L cylinder ), accepting a reduced max flow rate of 18litres per min, ( you may well only have 18litres per min coming in so case specific for that point ), and the additional volume of antifreeze ( plus replacment of the antifreeze every 5 years as it has a limited working life ), make the TS and coil option for DHW uplift very tight, if not plain uneconomical for your expected DHW needs. So, after more head scratching, further tea drinking and procrastinating..... The figures do stack up quite well in favour of going for a small buffer and copying @JSHarris with a plate heat exchanger, but as your expected DHW consumption and flow rates may well be double his, I'd suggest going for a pair of 30kw versions running in parallel to get a combined pipe size input & output of 22mm ( to match the UVC accordingly ). PHE example only PHE's are far better at transferring heat from a wet source than coils, especially when being used at lower temps. I've had to adjust my thinking accordingly for this case, and even so, I still think it's a worthwhile endeavour. Less long term labour of the ASHP = longer life expectancy. Far fewer defrost cycles compared to driving DHW directly from the ASHP at high temp range. Majority of the DHW getting produced at the better CoP rate, ( DHW will be your biggest energy requirement as its needed year round eg also when you have little or no Pv gain ). Smaller buffer tank ( circa 100 litres ) with less loss, size, and reduced antifreeze required. ( thanks @Alphonsox for the example costs, makes it a game changer tbh ). So, to summarise, I'm still thinking of DHW uplift from the ASHP via a buffer, but a smaller buffer and PHE's instead of the coil. That will require a pump and flow switch, ( any PHE will need one ). Still relatively straightforward tbh, and may just provoke me into getting off my arse and looking for a decent plumbing schematic software so I can translate this babble into a working drawing for a / your plumber to follow. Thats the chat I've just had. These cylinders have very low heat transfer rates at low temp, so that type of cylinder would need to be VERY hot in order to do what is suggested in that image . It would also need to be KEPT very hot to do it too .
  4. 1 point
    I just wanted to include a brief post explaining from a self-builder perspective why we have decided not to use an Unvented Cylinder (UVC), Thermal Store (TS) or combi-boiler for our domestic hot water (DHW) in our new build. Instead we are using 2 × SunAmp PV heat batteries heated by E7 tariff. So why? We decided that we don't need gas to be installed avoiding the Gas connection charges, per day supply charge and the maintenance costs on gas appliances. Big saving here. We don't have the room for a TS and we've heard too many horror stories about the problems of heat losses in a passive-house class new-build like ours, so no TS. We didn't want to get into all of the regulatory crap around installing and annual maintenance contracts for an UVC. So strike this one as well. So what is the alternative? The SunAmp is a thermal battery with an in-built heat exchanger (a bit like a combi boiler) which can store ~5kWh of heat for delivery in water typically at 50-65°C. Here is a simplified schematic of the store. (Note that I've left off all of the essential safety features such as the expansion vessel pressure relief and overflows to simplify this down to the functional essentials.) The guts of the device are a couple of Phase Change Material (PCM) cells which act as the thermal store. It in essence it works in one of two modes: Discharge Heating, where the CW supply flows through the two PCM cells and is heated to between 55-65°C and then blended with a CW mix in a TMV down to a preset output temperature. Recharge. When fed with an external electricity supply (typically PV or E7 off-peak tariff power), water is circulated internally through the cells and a 2.8kW heater to bring them up to an internally preset maximum temperature. So the SunAmps can only be charged by electricity, and there is no alternative form of heat supply. The form-factor is very small – two SunAmps side-by-side take up (d × w × h) 530 × 600 × 740 mm. The rectangular packaging also facilitates the use of internal vacuum pack insulation panels so the total standing heat loss is ~ 1kWh / day which is a lot less than a typical TS. The exact choice of PCM is specific to SunAmp, but the linked Wikipedia article lists the common ones with a phase change at around this 55-65°C range. However in terms of the physics of how this all works, it is easier to describe another common PCM that we are all familiar with and which has its phase change at 0°C: water. There are three material properties that you need to consider when looking at how a PCM works: the specific heats of the solid and liquid phases, that is how much heat you need to supply to heat 1 kg of water by 1°C and the latent heat of fusion that is how much you need to convert 1 kg of water at 0°C to ice at 0°C. I could give you the figures but a good way to think about is that you need the same amount of heat: To heat ice at -158°C to ice at 0°C To melt ice at 0°C to water at 0°C To heat water at 0°C to water at 80°C. OK these ratios and the fusion temperature differ for different PCMs (as well other properties which reflect the long term stability of the using it in cells, etc.), but that is all the proprietary stuff (discussed in the detailed below from Andrew Bissell). Even so, the bottom line is simple: the systemic heat losses are far less than alternative solutions, and Weight-for weight you can store roughly four times as much heat in a SunAmp PV store as a conventional DHW cylinder. As to why we have chosen the 2 × SunAmp PV approach, there were 2 main drivers for us: 5kWh isn't enough to meet our typical daily use, and 10kWh is so we will be able to charge our stores overnight at E7 rate and only need daytime top-up in exceptional circumstances. The pressure drop across the store in Bar is roughly 0.0142×f1.81 where f is the flow rate in ltr/min, and if you crank the numbers one store doesn't give us enough flow rate. Even so if we look at our planned use (I'll go into the figures in a later blog post), our household of 3 people has had an average use of 280 ltr/day averaged over the last 6 years. Most of this is hot water -- say 80% or at an average lift of 25°C, this amounts to 5,500kgK = 6.4kWh/day or 7.4 kWh/day allowing for heat loses. This will cost us £194 p.a. at my current electricity tariff for my household's DHW. Will I really realise the payback from additionally investing in gas or ASHP based DHW systems? I think not. PS. Slightly amended wording to reflect the earlier comment of Andrew Bissell quoted below.
  5. 1 point
    I have been doing the design validation of my plumbing solution partly so I am comfortable that it is feasible and partly to write this up so that others have a model of how to approach this task. The last time that I did anything like this was with my current house where everything apart from taps for drinking water was fed off a (non-potable) header tank in the roof space and the central heating system was a classic 2-pipe (with branches) radiator system fed from a gas boiler. Even though our new house is a generation away in technology: passive-class, airtight to better than 0.6 ACH, low-temperature UFH in slab, pressurised water system using a Hep2O manifold / radial configuration, I still approached the design by refreshing my understanding of pipe dynamics, etc. using such reference works as this excellent intro into pipework calculations: John Heartfield, Water Flowing in Pipes I – The Theory and useful site like the Pipe Pressure Drop Online Calculator. The first is worth a scan if you want to get a handle on some of the sizing issues. However, the figure above shows the pressure losses for the major system components in my Domestic Water System. Note that the pipework losses represent about 1% of the total pressure drop and this value is lost in the noise compared to some of the uncertainties on the larger ticket items. So it really is a waste of time worrying about the pipe losses in a pressurised radial system so long as your follow the following guidelines; this is not where you need to focus your design attention. Configure your pipe layout as a radial system. Try to avoid putting multiple appliances on a single pipe, except where there are strong practical reasons for doing do. For example, our dishwasher is adjacent to our kitchen sink and is a cold fill unit T'ed off the cold to the sink. Plumb all cold and high-flow hot radial piping in 15mm Consider plumbing low-flow hot runs in 10mm, though there is a lot of simplification and little to be lost in going up to 15mm if these runs are short. If at all practical co-locate your manifolds, DHW storage, HW heating, and other directly related equipment in a single service area. This will keep all shared pipe runs short, and associated heat looses small. Properly lag all hot piping up to and including the manifolds. Lag the cold piping as well to avoid condensation. Whilst the pressure drop on common pipework is relative small, it is well worth while plumbing this in 22mm at a minimum. Pipe noise is still a risk so where practical use swept bends rather than tight elbows, and keep track of worst case flow velocities. Keep these under 1 m/s where at all practical and under no circumstances allow them to go above 2 m/s. User full bore valves and fittings where practical to avoid unnecessary flow restrictions. It is worth finding out the the pressure drop vs flow data on all of your system components. You'll typically get these as a set of log-log plots or power curves on linear axes. They are almost invariably approximated by power curve fit and therefore all of the form a.fb where f is the flow rate and a and b are pipe / device-specific constants. So in the case of my calculations, I used the following constants to compute the PD in kPa as a function of flow rate in m/s: Name a b Int Dia 15mm HEP2O 0.00300 1.743 0.013 15mm copper 0.00243 1.742 0.0134 22mm copper 0.00038 1.728 0.0202 25mm MDPE 0.00035 1.748 0.021 28mm copper 0.00011 1.718 0.0262 SunAmp 1.42000 1.810 n/a Softener 0.27600 1.740 n/a PRV 0.04400 2.000 n/a TMV 0.10000 2.000 n/a I then created a test scenario that I wanted to make sure that my system could cope with. IMO, at a minimum this should include two high-flow devices at full open setting running in parallel, but for our design I used what I considered a worst case morning scenario and that was one shower @ 10 l/min and 42°C, one shower @ 8 l/min and 42°C, and the kitchen sink @ 8 l/min 48°C. Note that if you crank the numbers using Dec/Jan water supply temperatures, this comes out at an equivalent instantaneous heat demand of 67 kW, and given that combi-boilers top out at 40 kWhr, this is well over 50% more that the largest combi- boiler could deliver. It's then just a case of doing the temperature blend and flow-rate calculations and cranking the numbers in a spreadsheet. On my first pass through, it was very clear that attempting to satisfy this short of flow rate through a single SunAmp was just beyond its rate capacity, but luckily we had already two configured in parallel. Even so, the parallelled SunAmps account for ~ 0.55 bar pressure drop, along with the DHW TMV. The water softener accounts for 0.8 bar and the Honeywell pressure regulator 0.3 bar. The difference in pressure drop on the 3 pipe runs (all being ~1% of the total) is negligible, but since the total is ~2.25 bar and the actual head is 3 bar, we have ample headroom to sustain this scenario. (Actually one of the showers is on the second floor, so in this case we lose nearly another half bar getting the water up there.) If the net figures are negative then we aren't going to achieve this flow rate and we will be system limited. But they are all positive, so we are OK, and this means that the taps or the various flow restrictors are going to have to do their work to limit the flow. So what could I do if I wasn't achieving the desired flow rates? Basically the answer either to revise my expectation downward (after all my current house design can just about deliver half of this); to increase unit capacity by upgrading in some how (e.g. in my case doubling up on the SunAmps), or to think out of the box. The biggest single hit here is the water softener, and in fact I introduced this fairly late in the design process when I realised that having one is pretty much essential with my level of water hardness, but that's life, I guess.
  6. 1 point
    Finally got watertight after much fighting with Velfac doors, wrestled with insulation, polythene, underfloor heating, shuttering for liquid screed, access for 3x concrete trucks. Anyway the pumped screed was finally completed today and this has always been a major milestone in my mind. It also happened to coincide with the day the scaffold came down which has put today up there with the best days of the build so far for me. Sitting back with a brew now enjoying the moment after having quite a few low times feeling rock bottom over the past 10 weeks! Such is the emotional rollercoaster of self build. Big Travis delivery coming first thing tomorrow with all the CLS so I can start on studwork and materials for cousin to start external rendering on Monday. Externally the place should look finished within a couple of weeks, internally a slightly different story. Ive always seen this journey as split in to thirds - first third was admin, raising funds completing the purchase tendering for builder etc, lots of work with little achievement, second third was all the work I put out to my builder (watertight shell), final third now is me finishing the build and turning it in to a home. 4-6 month push now starting tomorrow morning, on the home straight! P.S big credit to @jamiehamy for posting me some samples of the Cedral light oak cladding, it firmed our decision to go for it and we are really pleased. He wouldn't take any payment or gift of thanks so here's a public thank you at least!
  7. 1 point
    You've got to ask the price every time at builders merchants, other wise you get ripped off!
  8. 1 point
    I think it does for a lot of Chinese stuff, far more of it just ignores the safety regulations then most people realise. Years ago I had a friend who had a business making custom bicycles and he imported almost all his components from either China or Taiwan. He went to Shenzhen in China to meet some suppliers, and sent me some photos of his trip. He spent half a day in one of the massive emporiums there, and one of the photos was of a stall that only sold stickers with things like fake CE marks, Windows and Apple logos, etc. I remember him telling me that it was very difficult for a small business to get manufacturers in China to adhere to any sort of standards, as they always want to try and reduce the cost by cutting corners. He gave up with getting components from China in the end, having experienced non-existent adherence to specifications, and now buys only from Taiwan, where it seem that manufacturers understand the need to stick to an agreed specification.
  9. 1 point
    The electrician that has installed/signed off your installation should have made sure that not only was there a proper earthing scheme fitted, but that it had been tested and was compliant with the regs. AFAIK, being off-grid doesn't exempt anyone from the regs - if the system is above 50V AC then it is an LV installation and the regs apply as they would for a grid connected system. For a generator or inverter powered 230 VAC system the requirements are that a local protective earth should be provided, in the same way as would be the case for a grid supply with no protective earth. The 230 VAC connection from the inverter should be connected via a suitably rated fused double pole isolator to the consumer unit, with the protective earth being provided by a TT system. This means fitting an earth rod, testing Ze to make sure it's within spec (no greater than 0.8 ohms normally) and using that as the protective earth for the installation. The consumer unit, or other distribution point, must have a double pole RCD or RCBO. The inverter you have looks to me as if it's a Chinese made unit, as it's marked 220V, yet it carries an EU CE mark, which is odd as the EU supply voltage standard is 230 VAC, not 220 VAC. Fake CE marking is extremely common, so common that I suspect there are more fake marks around than genuine ones. That doesn't mean the unit is inherently unsafe, although as it has a metal case and makes no mention of earthing one has to be just a bit suspicious. The case should be earthed, but it would be wise to check that the output is really isolated from the case before doing this. An electrician could test this in a few minutes, easily enough. Finally, there is usually an insurance requirement that any temporary LV supply (and LV is anything over 50 VAC and under 1000 VAC) should be installed, tested and signed off by a competent person. Even if an insurer doesn't require this, then it still important that it be done, particularly if a third party, like a contractor, is working on the house. Failure to have a properly installed and tested LV electrical installation, even a portable site system, could make you personally liable in the event of an accident. Edited to add: Looking more closely at the photos of that inverter, I can't see any shutters on the outlet. Well worth checking this, as a properly approved BS1363 outlet must have an earth-pin operated pair of shutters that close off the line and neutral sockets. If it's as I think, without shutters, then the CE mark will definitely be fake and it would be advisable to do some testing to make sure that it has adequate internal insulation and isolation between both the DC input terminals and the output terminals, and between the output terminals and the case. For use as a temporary, perhaps portable, supply then I'd suggest that the minimum requirement should be a decent earth rod and connecting conductor connected to the inverter earth, together with a plug-in RCD to provide protection to any user. Edited again to add: The seller gives a valid GB VAT number, but this traces to this flat: Member State GB VAT Number GB 243079218 Date when request received 2017/03/24 10:54:40 Name JUNFENG CAO Address FLAT 93, ADDY HOUSE ROTHERHITHE NEW ROAD LONDON SE16 2PD
  10. 1 point
    I've now got 15 cheap Chinese ones. I'll buy some from Darnell and compare them in my test rig. I've been buying the waterproof ones - partly because the probe packaging with lead is far more robust. The cooling cup of water is a good way to check.
  11. 1 point
    The local planning process?
  12. 1 point
    If anyone is interested, then I can post design and assembly details, esp8266 code or links to it, etc.
  13. 1 point
    They look pretty good and amazing for the price. I use various 3D drawing packages and Photoshop every day as an architect but couldn't compete with that price. Even if you get some poor student in college learning the program you won't beat that price. Great value.
  14. 1 point
  15. 1 point
  16. 1 point
    Brief (and belated) update. After much deliberation, we've finally ordered a staircase. Had several quotes in the £5.5k to £6.5k range for oak stairs similar to the one I linked to in the first post, but decided we'd really like something more contemporary (even if it meant spending a bit more). Ours will be styled as per the one in the image below, albeit with a double winder. Lead time is 8 to 9 weeks but will hopefully be worth the wait
  17. 1 point
    Well I designed our build over 20 years ago ( in my head) and it was not until I met my wife ( who had a plot with an old knackered bungalow on it) that I had somewhere to build, we just turned it round 90' luckily my wife liked the design, we both love cottages and it's the Devon countryside. What's not to like!
  18. 1 point
    There shouldn't be any capacitors on the AC side of the inverter, but with no protective earth (!) the earth conductor won't be doing anything useful. With a DC to AC inverter (or generator) you must provide a protective earth with an earth rod or other connection to a known to be good protective earth conductor, to make the installation safe. The installation should be wired in a similar way to a TT mains supply system, with a tested and known to be OK earth rod providing the protective earth at the supply end, in this case the inverter AC output side. In theory a floating supply "could" be safe, as long as there is no possibility whatsoever of an incidental connection, or leakage path, that could mean that the inverter AC output terminals are referenced to local earth. Frankly I would NEVER want to go near a non-earthed installation like this, though. I know people often completely ignore the instructions to provide a protective earth when running generators - that does not make it safe. (The above photo is a joke, before someone makes any comment about it........................)
  19. 1 point
    Shouldn't we touch on the waterproof "exterior" and the more general (and cheaper) everyday versions of PVA? Big difference in price. I know back when I temporarily dust proofed my concrete floor in the bathroom I used dilute SBR bonding agent on advice here rather than PVA. This on the basis that when tiling later there's a risk of water getting under the tiles and affecting normal PVA. It was cheaper using SBR than buying exterior PVA. I do know some on here have dust proofed say their new garage floors with dilute PVA. I've certainly glued T&G chipboard flooring together with it. I'll often use it when doing noggins before I screw them in. Doing it throughout boxing in in my bathroom. I've used it btw when the kids have run out of "craft glue" and topped the bottle up. Made many a paper mache'd balloon head when they were younger!
  20. 1 point
    We have a passive-class house where the net heating requirement to keep the house warm in the coldest winter months is approximately 1kW. The only heating system for doing this an underfloor heating (UFH) system base on 3 ~100m UFH loops buried in our passive slab. That's it; no upper floor systems; no towel rails; nothing. The reason for this is that our timber framed house is super insulated and air tight so there is very little temperature variation throughout the house, but that's all been covered in earlier posts. What I want to do in this post is to provide a simple explanation of how I am going to heat my house and how this works so that John (@joe90) and other forum members understand my approach. This basic heating strategy was first evangelised by Jeremy Harris (@JSHarris), but variants have been adopted by other forum members and their consistent experience is that it works and works effectively for this class of passive house. However, what I am doing is a slight variation on Jeremy's approach: I am using the slab itself as my main heat store, so no buffer tank. I will be heating it by circulating warm water through the UFH loops and this water will be heated by a simple small inline 3kW electrical heater element. The heating charge will normally be done as a "chunk" once per day during the E7 cheap rate period to take advantage of low tariff rates. However, I am also including in the design provision for the later addition of an ASHP, should the heating data collected over the first year show that there is a 10-year payback in doing this. As I said, Jeremy's approach has been well documented by him in his blog and by others. He has recently described that his system settles down into a repeating pattern over the colder winter months winter where his heating comes on for a few hours once a day in the early morning, and the heat in the slab is topped up during this period. This is broadly what I call "chunk heating": unlike a traditional house central heating system which is turning on and off pretty continually, the heat losses in our type of house are so small and the house has such a high thermal inertia that you can heat the it practically with a single daily top-up to the slab; this heat then "trickle feeds" into the house over the day. Yes, there is a slight residual ripple on the temperature in the house, but this is less than a 1°C undulation over the entire day and so this isn't really perceptible to the occupants. I am adopting this same approach, but shifting my heating period earlier so that it ends at the same time as the E7 low rate tariff ends. The main difference in my implementation is that I am heating the slab directly without a buffer tank. I wanted to get my head around this before committing to this decision, so I modelled this in some detail and covered all of this physics and modelling stuff in my Boffin's corner thread. This modelling has persuaded me that the mechanisms and dynamics of heating are pretty simple, and so in this post I want to cut out all of the equations and stuff (with one exception) and focus on describing what happens in plain terms. First, I am using a small 3 kW electric element to heat the water circulating in the UFH loops (the same type is used as a hot tank immersion heating element). Just like an electric shower this heats the water stream a step in temperature. Sorry I am a boffin, so I will call this temperature change ∆T. (BTW, the triangle is just the Greek letter D and is short for difference; blame Isaac Newton for that one.) Just like an electric shower, double the power and ∆T doubles; double the flow rate and ∆T halves, and if I do the sums for a typical flow throw my UFH loops, and for a 3 kW heater then ∆T works out at about 1.6°C for my system -- a lot less than a typical gas-boiler fed UFH installation, but my heater is puny in comparison. So if I start pumping 3kW of heat into my slab, then the system settles down after about 10mins and the heat output is pretty much the same along the entire 3 × 100m runs of UFH pipe, pipe work, that is each 1m of pipe dumps about 10W of heat into the concrete. This lifts the temperature of the concrete, and at the same time cools the water in the pipe pretty steadily along its length so it comes out at 1.6°C cooler than it went in. But cooler or hotter than what? The heat flows radially away from the UFH pipe creating a thermal gradient. [Boffin bit warning, and the only one] this gradient is pretty close to what is known as the steady state radial solution to the 1-D heat equation, which has a formula Tr = Tp - A.log(r/rp). where T is the temperature and r is the distance from the pipe centre, with the p subscript relating to the pipe/concrete interface. The A term is a function of the amount of heat flow. The main thing to note here is the general shape of this gradient: the temperature of the water ends up roughly 4-5°C hotter than the slab average for this sort of 10W/m value, and the temperature in the concrete falls away rapidly as you moving away from the pipe towards the average slab temperature. Since the volume of concrete goes as r2, the actual proportion of the concrete more than 1°C hotter than slab average temperature is small. So the overall effect of the heating is to slowly lift the average slab temperature. There is also a general heat gradient along the water in the pipe but once you get more than a few cm from the pipe centre the concrete is all within 1°C or so of the slab average. There are also local hot regions around the UFH pipes up to 5°C or so hotter than the overall average slab temperature. However, this is factors less than you will get with a conventional UFH system. A key difference of Jeremy's approach is that the water continues to recirculate after the heating is turned off, and now the water flow acts to redistribute the heat rapidly along the pipe levelling the previous 1.6°C gradient; at the same time (without the heat being pumped from the UFH pipe) this central warmer region rapidly flattens out as the heat flows outward, and within an hour or so hardly any heat variation remains and the entire slab is within ½°C of the slab average temperature. A good analogy here is pouring water into a bucket: the surface level steadily rises as you pour it in and the surface itself is a bit churned up by the act of pouring, but as soon as you stop pouring, it rapidly levels out to flat surface. OK in a real slab this is also complicated by the deep elements (the unheated ring beams in my slab are over a third of the total volume) and the heat does flow into these largely thanks to the high thermal conductivity of the rebar. But overall, the slab is acting as a heat battery soaking up the power that you pump in. The trick is not to put a somewhat arbitrary limit of the maximum input water temperature (say 25°C) as this will limit the amount of power that you can apply. This heat gets quickly spread uniformly throughout the slab. By the end of the heating period, the slab is 2°C (or whatever) warmer than the room temperature, and is starting to transfer heat into the room fabric at ~15W/m² whilst itself slowly cooling. This is more than the external heat losses in the house, so this heat both warms the air and the rest of the wall fabric. This creates a very slow rise and fall in the room temperature over the course of the day -- of roughly 1°C. But so long as you put in enough heat each night, the overall house temperature remains stable. So how much is "enough" heat? In my case I use a very simple strategy. I am using the UFH circulation temperature at midnight as my test. If it is less than the previous night, then I add a bit more heat than last nigh and v.v. Simple really.
  21. 1 point
    As I've previously discussed we have an MBC Passive Slab and Timber-frame, but unlike most builds, our house also has a very traditional stone cottage-style exterior because the new build sits between our current farmhouse, which dates back over 400 years and a cottage which dates back approaching 200 years, so our planners required that we use the same local quarried stone. So a topic that often comes up is "how do we do the window / door treatment on a timber-framed house with an exterior stone / brick / blockwork skin?" In this blog entry I want to describe how we approached and addressed these issues on our build. Whilst I make no claims about our approach being the only or the best one, Jan and I do believe that this has worked well for us; we are pleased with how it has all turned out and we don't think that we would do it differently if we were doing this all again. So if you are in a similar situation to us, please consider this as one possible approach. There are a number of issues that we considered in designing our detailing: Decoupling the inner and outer skins. In order to achieve thermal isolation of the inner passive slab, MBC also lays a separate outer ring beam for blockwork, brick and stone skinned houses. The inner slab carries the Larson trusses of the MB twinwall frame, and the outer ring beam carries the stone skin. The inner frame is CLS; the outer stone and mortar, and these two have different expansion characteristics so you should anticipate up to 5mm, say, differential movement between the inner and outer skins. So we decided that we should not use the window and door furniture to couple these. Closing the gap. Even so, we still have the issue of the 50mm nominal air gap between the inner and outer skins and how we close this for weather protection and cosmetics. Our solution to thee two points is to move the front of the windows some 45mm forward of the outer surface of the frame. The stonework then sits immediately in front of this,overlapping the window frame by some 30-40mm. Fixing the windows and doors. We have Internorm KF200 Aluclad PVC windows and I agreed a fitting profile with both MBC and ecoHaus SW who supplied the windows. This comprised a box section (something like marine ply would do here) that framed each window opening at the top and sides as follows. there was a 10mm filling gap for fixing the windows there was a 15mm filling gap at the top ditto the windows had to sit hard at the bottom, but I inserted a 44 × 38 tanalised carrier to lift the base above the internal frame base. This was to give adequate clearance to fit the internal cills. Protecting the windows during the build. EcoHaus SW fitted the windows on day 8 of the the frame erection, so by day 9 we had a completely weather-tight and lockable house. The windows had to be in place before erecting the stone skin, and so needed protection from the stone erection process. The solution that we agreed with the ecoHaus technical manager was very simple and extremely effective and one that I would suggest to anyone else doing this. We simply covered the windows in heavy grade clear building polythene, and this served a dual purpose: It provided total protection against the muck and dust of stone erection. You need a slip surface between the aluminium cladding and the stone skin. (Cf. the first point) The PVC does this. Once the stone skin was complete we simply cut around the PVC on the mortar line. All that is then needed to achieve a total weather seal is to run a thin bead of sealer at the join. Minimising any bridging impact. The windows have fire-break socks around them which acts both as insulation and a gap closer. The doors require special treatment. Here prior to slab pour, we had the MBC team cut out 50mm deep slots at the door openings and we placed extra shuttering in to extend these out by some 40mm in front of the outer frame line. These were rebarred and when the slab was poured, these became a 50mm deep concrete tongue that extends out to the front face of the door opening. The doors then sit on a 30mm upstand on these tongues. The upstand acts as a thermal break, but to minimise any bridging through the tongue itself, we used FoamGlass structural bricks to isolate the tongue from the outer cill and the stone skin. If you do the 2D thermal calcs (or at least I did), the thermal capacity of the stone face overlapping the face of the windows materially mitigates the extremes of the temperature variation, and whilst there is a little uplift in the Psi-factors for the window, in absolute terms this equates to adding an extra ½m2 of glass to the house overall, and not enough to cause condensation risks Maximising internal light. Our old farmhouse has thick stone walls with window reveals and these work well. So we decided to ask MBC to do a similar treatment in our new build. In short not only do they work, they work brilliantly. They let in perhaps 10-15% more light than deep squared frames and they help open out the rooms. They are an extremely attractive feature and both Jan and I would recommend them to anyone considering using a twinwall frame. Here is a picture of the slab during the pour. Note the trays for the kitchen French windows and the back door. Here are a couple diagram extracts showing the window treatment and detailing: and some photos of the wall in construction showing the set forward windows and the finished effect (less the porch that still has to go in.). and an internal shot of the kitchen window detail showing the angled reveals:
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