TerryE

Don't worry our stacks have yet to be "christened".

Cling film?

But has it got the non-slip (a.k.a no-skid mark) coating?

Ed, just a warning: physics is against you. Bricks are the aspect ratio they are to help minimise the distance from the centre to an outside surface to help make it easier to dry out. They often have holes running through them for the same reason. Your brick has a pretty uniform aspect so it is going to take a long time to dry out, and the inside will still be surprisingly damp when the surface looks bone dry. Bricks are often baked at low temperature for a bit or put in special drying ovens to remove the residual moisture before being fired properly. If you don't achieve this level of internal dryness, then the internal stream being generated when you attempt to fire it will probably cause it to crack up or at worst explode. Your lettering looks about 8-10mm deep, so one way of minimising all this is to make a brick that is only 25mm deep or so. As soon as it is dry enough, break it out if the mould and leave on a baking grid in a well aired place, but protected from rain etc., and since the moisture only has 12mm or so to travel to get out, then it should dry better. Once fired , there is nothing stopping you pouring in a 2:1 or even stronger mix into the mould and leaving 25mm gap at the top. Then wet the fired brick and lay it on it on top of the wet mix to bring it up to full width. No one will know the difference once it is cured and up. Any, carry on with what you are doing but just have this option as a back-pocket one.

@Construction Channel Ed, any update, or has the clay set in the barrow?

I think that the main lesson from this is to ensure that your plasters use the bloody template in the first place!

It's only Dec /Jan where this might be a problem. The figures are all modelling and estimating, but I think that we're running a tad less than 20 kWh worst case -- call that £1.40 / day or £55 per month. It we spill into having to do peak rate top-up of another couple of hours, its another £1.20p. But until I've collected live data, then I don't know. I could more into the slab, kW-wise but I'd rather not plan on this. As I implied in the preamble, the fall-back is to put in a smallish monoblock ASHP, and if I am finding that I need to do peak rate top-up for more than 30 or so days a year, then we'll cross that threshold, I think. And picking up @joe90's point the unknown is the summer cooling issue. If I can't tune the MVHR bypass mode to dump enough heat then we'll need an ASHP anyway and this heating issue is no longer a problem, as the ~4× CoP makes a big difference to the electricity bills. As to the water preheat for the DHW, that's an issue for another blog post, but my main reason here isn't saving £s as I pay for the kW either way -- at least in net heating days. It's more an issue of guaranteeing flow rates and DHW capacity. Again models take you only so far. We need real operating data, but I don't have a Tardis.

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.

Yup, the Wundatrade people have a series of excellent YouTube videos which explain how to intall their UFH manifolds and I only picked up about this by watching them.

The proper tool is only a fiver, so compared to everything else I am buying, its pissing in the wind not to.

@jack @JSHarris Thanks guys, it's nice to have this confirmed. I'll be ordering al this kit in the next 24 hrs.

High flows are the ones where you'd get pissed if they dropped in pressure / went of of mixing balance when someone turns on a shower or started running a bath: the main sinks, the baths, the showers. The low flows are what they say and flow rate isn't that important: the toilet cisterns, the hand basins, bidets, etc.

@Calvinmiddle David, I should have asked the guys when they laid the slab, but looking at the pipe it is 16 mm PexAlPex or PertAlPert, so you go for the 16mm Pert-Al-Pert adaptors on the manifold?

@JSHarris Jeremy how did you deal with the overflow (rather than the drain)? The Installation instructions state "the hose should be run downhill all of the way and terminate at the exterior of the building if possible" (as a warning pipe). My thinking is that I've now got 4 pressure relief / overflows I was think putting them all through tundishes to common waste into our stack but with a moisture / wetness detector so that I get an alarm to check them if any starts dripping.

@pocster. Seek and ye shall find. Search the forum for hep20 and you'll see some active threads on all this -- including mine.

AFAIK the discharge mode is essentially passive, so you can get H/W even if the power is out. But as to charge mode, have you got a standby generator for your current gas central heating system? If not, then you are in exactly the same situation today. I have two SunAmps in parallel so both have to fail to lose H/W. And then I have a Propane 2-ring gas hob in my kitchen so tea and coffee are still available. And the power would have to be off for more than 3 days before the house starts to feel a little cool. 5hWh / 2.8kW = just under 2 hrs if you've exhausted the store totally. In practice squeezing the last 0.1kWh of heat out of the device probably isn't worth it so the trick is to size your system so you rarely run out, but all of this is exactly the same as if you had a conventional UVC.

No, and in fact MDPE is approved for any use where it could be exposed to direct sunlight. Just search the forum for Hep2O and there's loads of background material.

Neil,as per Mr Punter, but it is also important to keep the rise and going exactly the same all of the way up the stair, and this includes turns, top and bottom stair. So you need to allow for your floor coverings at the top and bottom. The bottom tread rise is slightly less critical. The reason is that your brain is very good at placing your feet, but if the rise and going aren't exactly the same then it becomes quite easy to trip or stumble and this is very dangerous on a stair. So if you do need a turn in your stair then you will find it more comfortable if this is an evenly swept turn, though having this type of design costs more. A 45° split on the turn is the worst.

We do have a few hidden joins -- some of the runs travel vertically down the walls but need to come out at 90° to the wall (e.g. for the shower fittings) so these have elbows just behind the plasterboard. Other than that, none. If there is a leak at one of these, then at least it's just a matter of cutting a hole in the board fixing and repairing. But you want to buy a load of Hep2O end-stops, and then you can at least pressure test before boarding out -- if you don't want to take the risk.

As well as the ease of fitting, cost and significant risk of leeks, the Hep2O / manifold approach (or equiv from other vendors) is a lot easier to balance and has significantly less heat losses. If it's not too late in your design process, then centralise you heating / DHW tank / thermal store, manifolds, etc. in a single service area. That way your copper runs are only a few metres long at most and the hot works can be properly lagged to minimise thermal loses. You will still end up dumping heat from the hot radial runs, but this can be minimised if you split your hots into low-flow and high-flow and plum the low flow hots in 10mm.

All commissioned and working IMO, the main design issue with this is that we have standard 2×2 induction hob, a 120mm separator bar in the worktop and then the 2×1 gas hob. This makes for quite a wide worktop footprint: you need roughly a 98cm gap in your top cupboards above the hobs (where the extractor fits.)

My logic is this: the SAPV is a thermal store that enable you to charge it with E7 or PV electricity at times when electricity is cheap, and because f its low heat loses, you can then discharge it into heating your DHW when you need it. It is optimised for heat delivery in the 40-60°C range. In an MBC house with a passive slab (or other equivalent vendor offerings) you already have equivalent thermal store but one that is optimised for storing heat at 20-25°C and that is the slab. I had to get my head around using it this way, which was the reason behind my topic Modelling the "Chunk" Heating of a Passive Slab, but my current plain is to use a small electric water heater to pump a chunk of heat into the slab each night when I am in net heating days.

I don't know. I suspect that it's not, but it one of those things that will bite you badly if you don't and something goes wrong. Will you be insured? Will you be criminally liable?

Typo. It's amazingly -158°C. The entropy of a crystalline structure is a lot lower than the liquid phase which is why converting from one to t'other soaks so much heat. And this is also why the specific heat of ice is a pretty much half that of water. This effect is also why steam is so dangerous. If it condenses into water on your skin it chucks a lot of heat and causes serious scalding. If you run out of heat, then you run out of heat. It's store not a generator. But there's nothing to stop you topping it up during the day if you need to and one of the standard uses is to dump your excess PV into it during the day. My quote wasn't cheap John, this one is a bit off-topic but l will answer this. In essence a UVC is classified as a potentially dangerous appliance, which is not surprising really since if one burst at 3 bar and blasted a few hundred litres of scalding water around your house, then people could get seriously hurt. This is covered in Part G paras 3.17 to 3.21. Installation of a UVC is notifiable and must be installed and certified by a qualified installer. Your B Insp won't sign off your completion certificate without this if you have a UVC.

Yup the main difference is the max flow rates. I don't understand why they plumb up the cells in series rather than parallel.