Jeremy Harris

Unsurprisingly, Sir Henry Tizard featured prominently in a few places where I've worked. I lost count of the number of labs and facilities named after him.

As @Russell griffiths says, I think we need a bit more info. Can you try and see where the inspection chambers are, relative to that pipe you've uncovered? There should be inspection chambers wherever a drain connects to that one, so in line with that run. Tracing back where these are will give you a better idea of what you're dealing with. It's debatable as to whether this has anything to do with the water company, it could be just one of your own drains, or it may even not be a foul drain at all, but a rainwater drain leading to a soakaway.

Doesn't work well without some careful management of air flow rates. There are some exhaust air heat pumps that are smart enough to ensure that the house isn't over-ventilated when heating the cylinder, like the Genvex units, then there are some fixed speed Chinese made units that will massively over-ventilate the house in order to pump enough heat into the tank.

Yes, that's what an MVHR unit does (Mechanical Ventilation with Heat Recovery). Ours is pretty typical, and recovers around 85% of the heat that would other wise be wasted from ventilation. Bonuses are that the consistent ventilation rate ensure nice fresh air in the house all the time, and there's a pollen filter on the intake, so the house stays pollen free.

It very much depends where you are going to site the ASHP. Ours sits around the back of the house, a foot or so away from the wall, and I just ran the pipes through the wall, so no need to put them in the slab. Out of interest, had you thought about reversing the order and putting the UFH pipes in the slab? We did this and it works well. From the bottom up we have compacted type 3, grit blinding, 200mm of EPS insulation, DPM, 100mm of EPS insulation, 100mm concrete slab, with steel fabric set in the centre and the UFH pipes cable tied to the steel before the pour. we also have 200mm of peripheral insulation around the slab to reduce the edge heat loss.

10mm should be fine for a run to a sink. I've noticed that French plumbing often seems to use much smaller pipe than we do, around 10mm or so seems normal for basin and sink pipes, and they seem to work OK. The pipe that runs from our boiling water unit up to the tap is really small, around 5mm bore, yet that works just fine (in fact we've had to turn the flow rate on it down a bit). The same goes for the flexis that feed mixer taps, they only seem to have a bore that's around 6mm or so, yet work just fine. I have a feeling that we tend to use large pipes just because historically houses had low pressure hot and cold systems, fed from a tank in the loft.

But then there's the old Greek proverb: "It is a wise man who plants a tree, knowing that he will never sit under its shade". Not sure I'm wise, but I have planted 12 trees here now.

We get FiT on the generation, plus 50% deemed export at 5.38p/kWh.

Same here. I'd guess that we're exporting to the grid for a fair bit of the time. Right now my car is fully charged, the hot water system is fully charged, the washing is done and the house is sat exporting about 4.5 kW to the grid (for which we get paid a bit less than the peak rate import cost).

The bit I struggled with was making the model sufficiently dynamic that it would reasonably accurately deal with significant room-by-room variations in incidental heat gain. At the time I was looking at including incidental heat gain in the model, and some aspects were reasonably easy (solar gain moving around the house through the day) but other aspects (variations in heat gain from cooking, or using the vacuum cleaner) were more difficult. In the end I remembered that I'd set out to make a simple model, really for just comparing different construction materials, and opted to stick to the whole house, ignoring incidental gain altogether, on the basis that all that mattered really was getting a fairly accurate worst case heat loss. One interesting point is that the standing charge distorts the comparison of running cost by fuel type a fair bit. I still think I need to try and work out a split for the electricity standing charge, as that charge would exist irrespective of the heating fuel chosen.

By extrapolation from the air permeability test data for any house built in the last few years (where this has been a requirement in Part L1a), or from the MVHR setting and efficiency if the house has MVHR. For example our house has a low air permeability (the air test was 0.49 ACH @ 50 Pa) and I run the MVHR at 0.43 ACH, and the MVHR has an efficiency of about 85%.

The challenge I found when trying to do a room by room analysis was determining the ΔT, U value and relative ventilation heat loss between adjacent rooms. Just dealing with the outer thermal envelope, to determine the whole house heat loss, made life easier, and seemed to be more representative with regard to the way homes are often used and heated. I could have used degree days, but opted to use the Met Office average climate data for our location instead. As it happens that significantly over-estimates our true heat loss, as, being down at the bottom of a valley, with the house partially set back into a cutting in the hillside, so sheltered from the wind, means that we have a local microclimate that is around 1°C to 2°C warmer then the Met Office data.

The figures that @SteamyTea has given look spot on to me. There are a lot of myths circulating about stuff like heat capacity in particular. There are also lots of really poor heating installations around, that operate at well below their optimum efficiency.

So it's a cost comparison tool, not a heat loss calculation tool, is that right? I can see the benefit of that, as long as the same heating requirement is used for all fuel types. I just had a look at the running cost of a high efficiency biomass system to add to the above. Using the current price of wood pellets here, and a typical efficiency figure for a state of the art pellet burning boiler, then the annual running cost using the same heating requirement case as before, would be £131.46, so mid-way between the running cost for an ASHP at peak rate and mains gas.

Often these organisations start out with good intentions, then run out of things to do, so start making up new rules so that they can stay in business. I'm inclined to think that the IET is heading this way now, as the last few revisions to BS7671 haven't addressed any real problems, they've just added cost and given people an excuse to rip out perfectly serviceable stuff and replace it. They seem to have become a self-licking lollipop, where they feel they have to make changes just to ensure they keep drawing in fees. A good example would be the change in the 17th Amd. 3 requiring metal (non-flammable) consumer units. The problem (a small fire risk) that they were attempting to address had little to do with the flammability of the CU case, it was caused by the combination of manufacturers skimping on screw terminal design and people not tightening terminal screws properly. Once upon a time it was normal to have two screws on every connection in a CU, made of solid brass, an arrangement that ensured a good connection. Now we have nasty terminals, often incorporating plated steel screws etc, that will loosen their hold on a wire with the slightest bit of movement. Had the IET addressed that core problem there would have been no need to switch away from plastic enclosures, and we'd not see the (more dangerous) problem of wires being run through sharp-edged holes in metal enclosures without proper anti-chafe protection. I suspect the reason we didn't was that industry didn't want to have to make better terminals, they wanted to be able to charge more money for metal enclosures.

Just a slightly wacky thought, but I wonder if it would be possible to set up a dead vertical scaffold pole in the centre, firmly set down into the ground so it can't move, and then have a 10m long arm that pivots from that to provide a reference to help keep the blocks following the curve? Some sort of adjustable stand might be needed to hold the arm at the right level for each course, but I doubt it'd take more time to set something like this up than it would to set up a line several times on a conventional build.

I think it really goes back to the first use of foam for below ground insulation, maybe 50 or 60 years ago, when EPS was cheap and very easy to make in any given size, as all it took was some polystyrene beads, a container and some steam. It's why we see so much custom moulded EPS packaging, it's cheap and easy to make in pretty much any size or shape needed. It seems that EPS has been used underground for decades because it was cheap and it was found not to degrade when wet. There are basements in places like Germany that were externally insulated with EPS in the 1970's that are still performing now as they did back then. If I had to guess, then I'd say that the preference for EPS over PUR/PIR for underground use may well have as much to do with the general reticence of the building industry to change from using something that's known to work OK as anything else. Cost may be a factor as well, as often it may be cheaper to just allow for 30% or so greater insulation thickness than pay a premium for using PUR/PIR.

Not sure about that. This article, for example, seems to show that XPS absorbs a fair bit more water than EPS: http://www.epsindustry.org/sites/default/files/Below_Grade_105_33116.pdf and that this below ground water absorption degrades the thermal properties a fair bit. This article suggests that PIR absorbs much less water than XPS, it looks to be similar to EPS, I think: http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_08ab/0901b803808ab35e.pdf?filepath=styrofoam/p This article suggests that water absorption has little effect on the thermal properties of PUR/PIR: http://www.react-ite.eu/uploads/tx_mddownloadbox/PP02_Thermal_insulation_materials_-_PP02_20130715.pdf Overall, it looks like EPS and PUR/PIR are broadly similar, with regard to the impact of water absorption on thermal resistance. EPS has a longer track record of having been used underground and submerged in water for decades, so is know to stand up well. XPS would probably be every bit as long lasting as EPS, as chemically it's the same stuff. There doesn't seem to be a lot of easy to find evidence on the longevity of PUR/PIR when used underground, but that doesn't mean that it may not be fine.

One key thing is to look carefully at the effect that getting wet has on any foam. For example, the thermal resistance of EPS is virtually unaffected by water absorption (it reduces by about 6% when wet), whereas the thermal resistance of XPS decreases a fair bit more (it reduces by about 45% or so when wet). I don't have the figures to hand for PIR or PUR foam, as I was only interested in seeing how EPS performed. The key thing seems to be to design the placement of the foam such that it isn't permanently sat in water, so that if the foam does get wet it can drain and dry out. XPS and PU foams seem to take much longer to dry out after getting wet than EPS. I believe that this may be because the interstitial spaces between the blown bubbles of EPS are inherently more porous than the very fine channels created when XPS is extruded. There's been a fair bit of testing done on various types of EPS, in order to establish how it performs long term when used underground, plus there's a few decades worth of practical knowledge gained from using the stuff to insulate basements for many years. Other products don't yet seem to have this level of collected knowledge, so it's hard to know how well they may perform in the longer term.

Years ago I discovered the hard way that closed cell PU foam absorbed water. A friend wanted some water skis that looked like giant bare feet for a water carnival event on Stithians reservoir. We made them using ply, covered with shaped PU foam. They looked OK and worked fine when testing them (not easy to ski on, mind). Unfortunately they got progressively heavier as the, supposedly closed cell, PU foam absorbed water. Drying them out before the event took ages.

I'm aware of two methods that have been tried, blown-in EPS beads and poured in Leca (fired clay beads). I believe that Leca may be approved for use under a suspended floor, at least a beam and block one where there isn't really any risk of mould growth.

Out of interest, why would a heat loss spreadsheet care about the heat source? I can see that the heating source would be of use in a running cost comparison, as costs vary a great deal, per kWh of heat delivered, between different fuel types, but can't see how the heat source can have any bearing on heat loss/heating requirement (as heat loss = heating requirement for any given set of conditions). I recently did a running cost comparison, for a typical year for our underfloor heating with different fuels and came up with these figures, which may be of interest (costs include standing charge/LPG tank rental, etc) : LPG fired boiler running UFH = £336.49 Peak rate electric boiler running UFH = £329.05 Oil fired boiler running UFH = £218.91 Off peak (E7) electric boiler running UFH = £206.43 Mains gas boiler running UFH = £143.76 ASHP at peak peak rate running UFH = £102.87 ASHP at off-peak (E7) rate running UFH = £89.25 Arguably the standing charge for all the electric heating options should be reduced in proportion to the ratio between heating electricity use and non-heating electricity use, as that standing charge will apply irrespective of the heating system used. I didn't bother to make that adjustment, but it would tend to reduce the cost of the electric heating options by around £40 p.a. or so if I was to do this.

For whatever reason, it seems that the AECB has gradually closed down to "outsiders" over the past few years. Years ago it had a thriving forum, with a great deal of useful discussion. Then came the "passive house/burning stuff" rift, and things seemed to gradually get more closed off. I was friendly with a couple of fairly prominent AECB local members, and my take on what happened is that the AECB chose to become more like a closed shop for consultants. It's certainly now dominated by those who run consultancy-type businesses, which isn't in itself a bad thing, but it does mean that the AECB is of little value to ordinary self-builders. This definitely wasn't the case 8 or 10 years ago, when I was pretty active on their forum. Passive House Plus (not Passivhaus - that's a registered trademark of the PHI I believe) is a pretty good magazine. I used to subscribe back when it was only available in Ireland, then took out a subscription for the UK version, and it does give a pretty good overview of passive house projects. Unless it's changed recently, though, the magazine tends not to give the sort of detail that many self-builders might want to see. It's still good for getting an idea as to what's possible, though, and for checking out new products aimed at energy efficient building.

No, it's not tectonic movement as such, but the slow rebound from having the mass of ice removed from the end of the last ice age. In effect, Scotland is "floating" up very slowly, relative to the South of England.

Years ago I wrote this heat loss model: Heat loss calculator - Master.xls which has been shown to work fairly well. Quite a few here have used it over the years and found that it gives a reasonably accurate estimate of heat loss. The two main flaws in it are that it takes no account of thermal bridging losses (unless these are included in the overall fabric U value figures, which would be normal design stage practice) and it also takes no account of incidental thermal gain (gain from occupants, appliances, solar gain etc). For sizing a heating system it seems fine though, as it gives a worst case heating requirement. FWIW, our heating system normally works at around 5W/m² on average. In extremely cold weather (-10°C OAT), with no occupants in the house and no incidental thermal gain the heating could get as high as about 22 W/m², but we've never seen it get that high. At 22 W/m² the floor surface temperature would be about 296.45 K, so the peak radiated wavelength from it would be roughly 9.78µ. At 5 W/m² the floor surface temperature would be about 294.75 K, so the peak radiated wavelength from it would be roughly 9.83µ Overall efficiency for this maximum heating condition (excluding the COP of the heat pump, and only considering thermal efficiency) would be 92.3%. Electrical power efficiency for this maximum heating condition, (electrical power input versus useful heat output to the rooms in the house), would be 249.2% I look forward to seeing your data in due course, @Clive Osborne, as it would be interesting to model your heating system performance alongside the above wet underfloor heating system and compare the relative efficiency between the two different heating methods, and compare the peak wavelength radiated from each, perhaps.