Jeremy Harris

I agree that there is always going to be a degree of imprecision when modelling the thermal performance of a building, just as there is when modelling the performance of anything, in any respect. However, my point about the use of the term " thermal mass" is primarily to do with both measurement, and hence the units used, and the perceived benefit, in terms of comfort of the occupants, that it may, or may not, help to provide. The most common argument for including "thermal mass" is that it will help to stabilise the internal temperature, so that any rapid step change in external temperature will not be mirrored by a similarly rapid step change in internal temperature. I believe that this is what many people, perhaps most, would understand as being the thing that "thermal mass" contributes to a building. Do we agree on this, or not? Assuming, for the moment, that we are in broad agreement with regard to perceived comfort being a key factor for wishing to have sufficient "thermal mass", then we perhaps need to get back to the original point in this thread that created the diversion. How do different construction methods contribute to internal thermal stability? The definition that SAP uses isn't particularly helpful, as it doesn't directly relate to internal thermal inertia, my guess is that BRE came up with the term as a way to very roughly model the impact of diurnal temperature changes only. The SAP expression takes no account of the heat capacity of the internal structure, and I think that most of us would be in agreement that this is a key factor in terms of stabilising internal temperature. I've both modelled the way the internal structure of our house behaves, thermally, and measured it over a period of several years now, and have a pretty good feel for the elements that contribute the most to the measured thermal time constant, or thermal inertia if that term is preferred. Our house is of all timber construction, a twin stud timber frame, clad with larch externally and with a 50mm service void and skim coated plasterboard internally. The floor is a reinforced concrete slab 100mm thick, with all the floor insulation underneath the concrete. With an internal/external temperature differential of about 10°C and no heating, either direct or incidental and no occupants, the inside of the house will initially cool at about 1°C per 24 hours. It behaves in a similar way when the temperature differential is the other way around in hot weather, but solar gain through the glazing contributes a significant amount of incidental heat gain. I can measure no heat gain through the walls or roof, the internal surfaces just do not increase in temperature to any measurable degree (absolute accuracy of measurement around +/- 0.2°C (corrected), resolution of measurement +/- 0.0625°C). From the data collected by logging the temperature on the internal and external surfaces of the house, every 6 minutes for several years, it's clear that the two internal elements that contribute the most significant temperature stabilising influence are the plasterboard walls, followed by the ground floor. The plasterboard walls have both a relatively high specific heat capacity and a fairly high thermal conductivity, so heat from inside the house can fairly quickly and easily flow in either direction. The effective heat capacity of the concrete slab is almost as powerful at helping to stabilise internal temperature, but is hampered slightly by the poorer thermal conductivity of the floor coverings, furniture etc. This shows in measurements, where the slab usually remains very slightly warmer in its centre than the internal surface of the walls. The effect is small, perhaps no more than 0.3 to 0.4°C at most, but it is consistent. One other thing of note is that the real temperature stabilisation effect of any material inside the house is limited to a fairly shallow depth. The surface layer of the ground floor, perhaps no more than the top 50mm or so, has the greatest effect, and the lowest part of the concrete slab, 100mm down, seems to have very little effect. From this I'd (very broadly) conclude that it is probably better to have relatively a thin, high heat capacity and high thermal conductivity layer of material over as large an area of the inside of the house as possible. It may well be that doubling up on the thickness of plasterboard, for example, could make a very worthwhile contribution to internal temperature stability, as well as increase sound attenuation between rooms.

I agree with @nod, looks like a simple error that's transposed those two elements. Good thing to have spotted at this stage. I'd also add that the airtight barrier might be better described as a vapour tight barrier, as it's primary purpose is control of vapour migration outwards through the structure.

I do wish that you would refrain from making ad hominem attacks in some replies. I find the references to my supposed disabilities particularly offensive. So far you have alleged that I'm autistic, have Asberger's Syndrome and have selective blindness. This is solely a debate about facts, not personalities. I fully accept that SAP misuses terminology, as do some architects and other building professionals. That does not make such misuse correct though, as no internationally recognised standards body (such as Système international (d'unités)) has either ratified or adopted this measure for "thermal mass". This definition also does not match either of the expressions given in earlier replies, given that the SAP definition of kappa includes specific heat capacity, a linear dimension and density. Unfortunately it also does what other aspects of SAP does, and simplifies the calculation of the true property it is trying to define in order to help make the SAP assessment process somewhat easier. As I think we all know, SAP is imprecise, because it both makes some assumptions that are based on standard methods of construction, and because it simplifies many of the calculations in order to make them somewhat easier, or to make it easier for an assessor to obtain, or derive, the base data.

Not at all. So far I've seen no valid units given for "thermal mass", nor have I seen any valid expression given by which it might be calculated. All I've seen given has been an expression for non-dimensional heat capacity, together with an unusual expression for heat capacity per unit area. Neither of these expressions would allow what I believe most might understand to be the effect of "thermal mass", in the context of building thermal behaviour, to be determined or measured.

I'm not in any way upset. It is simply a matter of using units consistently, within a well-defined framework, so that any calculation that uses them is repeatable, when undertaken by different people at different times. Consistency of units is important, which is why mankind has put so much effort into creating very specific definitions for them. Heat capacity can be defined in four ways, and four ways only: Non-dimensional heat capacity is energy per unit temperature, J/K Volumetric heat capacity is energy per unit temperature for a specified volume of material Mass heat capacity is energy per unit temperature for a specified mass of material Molar heat capacity is energy per unit temperature for a specified molar quantity

So far I still haven't seen a valid expression for "thermal mass" given in this thread. Expressions that I believe were intended to be those for heat capacity have been given, and an expression for heat energy per unit area have been given, but that is all. That latter seems not to be very useful unless the specific or volumetric heat capacity for the material used for that defined area is also included, together with its thermal conductivity.

Heat capacity can be expressed either as a non-dimensional term, as heat energy, J/K, or as a dimensional term that includes either mass or volume, J⋅g−1⋅K−1 or J⋅cm−3⋅K−1 Heat capacity multiplied by mass is just the mass heat capacity, and is not "thermal mass" These units are well-defined, and in common use, and the expressions in the quote above are incorrect.

OK, I'm going to be very specific here, and ask again for the specific units of "thermal mass", as a property, as I cannot see anywhere in this thread where any valid units have been given. As mentioned earlier, you gave two sets of expressions when asked this before, one I think was meant to be a unit for non-specific heat capacity per unit area, " For a thermal element, it's Kj/m2K ". Correct me if I'm mistaken, but I believe that what was probably meant here was kJ/m²·K, kilojoules per m² · K. This is a measure of heat energy per unit area. There are no units of time, thermal conductivity, mass or volume expressed here, so how can that relate to either "thermal mass" or thermal inertia? I think we are in agreement that time is a key element, in that what is trying to be described is the rate of change of temperature with respect to time, inside the house. The other expression given earlier was non-dimensional heat capacity " For a building as a whole (albeit this needs to be treated with caution, as an entire building does not respond as one homogeneous and uniform element), it's simply Kj/K ". Again I'm going to translate this into what I think was meant, which was kJ/K (kilojoules per kelvin). If I've mistakenly interpreted this then please correct me. This basic expression for heat capacity is not tied to any units of mass or volume, so cannot be used as it stands to determine how a building will respond to changes in temperature. As before, it doesn't have any measure of thermal conductivity, mass, volume or time, either. If we wish to try to define, and model, how a building will behave, in terms that I believe most people would find useful, we need to include time, as the key factor for comfort (which is really what we are trying to predict or measure) is how quickly the inside of a building responds to a change in temperature. If someone chooses to give valid units for the generally used term "thermal mass", such that all the key parameters that define it are clearly expressed, then I'd accept it. It does seem very clear that what many interpret as being the meaning of this term is the rate of change of temperature inside the house in response to either a step change in external temperature of a step change in heat input to the inside of the building, which can be determined easily from the thermal inertia.

I'd try it as it is, then see if more suction is needed. The commercial systems just use a small fan, like a computer cooling fan, to extract air from the cistern and blow it through either the foul drain or an activated carbon filter: http://www.toiletfriend.com/2012/03/18/how-does-the-toilet-odour-removal-system-work/

Not sure I'd ever voluntarily connect anything to the Evil Empire, either. It's becoming increasingly clear that Google is at least as evil as Facebook, Microsoft et al, in terms of abuse of personal data.

We lost a massive amount (as in about 40% of what we'd paid) for a house sold in 1992, that we'd bought 5 years earlier. We had no choice, I was posted to Scotland, from Cornwall, so it was move or resign, at a time when jobs were scarce.

It was pretty dire having to pay that much interest. The real killer was that the interest rate rose to that sort of level pretty quickly, so people were getting into real difficulties with repayments. There were a fair few cases of people just walking away and handing their keys to the lenders.

You need to have the seat down and the space over the seat partially closed off, as it would be if sat on it. This causes the very gentle updraft through the flush holes and pipe to draw most of the air from the closed off area in the pan. Getting up too quickly after an event tends to make the system work less effectively. Sitting with a good book, or perhaps a copy of Viz, will give time for the system to flush away the air space in the pan fairly well.

Yes, pretty much all of them have a sensitivity adjustment and turning this down will both reduce the range at which people trigger the light and increase the size of warm thing needed to trigger it. GCNs shouldn't trigger one, as they are cold blooded. The mammals hunting them (presumably with the appropriate licence to hunt a protected species) might trigger the sensor, though.

Looks good though, be interesting to see how well it works. Probably needs a good dietary challenge...

It may well be that the tractor lights are higher up than a car, and as they are a source of moving heat the PIR senses them and switches on. One fix might be to try and turn the sensitivity down on the PIR, so it only responds to the movement of nearby heat sources. Unfortunately a microwave Doppler sensor won't get around this problem, as I have one set up part way down our drive as a trigger to start the CCTV recording, and whilst that's generally a great deal more reliable than the built-in motion detection in the cameras, it will get triggered by a large truck driving along the adjacent lane (not something that happens very often, though)

We have lots around the house, for much the reasons you've outline, @AnonymousBosch. The one in the utility room above the back door is brilliant, as the lights come on when you walk in with arms loaded with shopping, washing etc. There are two types, passive infra red (PIR) and microwave Doppler (sometimes called radar). Initially I had a PIR one by the back door (one of these: https://www.tlc-direct.co.uk/Products/TLPIRFL.html but we had problems with it false triggering from shadows through the window in the back door, so I replaced it with one of these Doppler ones: https://www.danlers.co.uk/microwave-presence-detection-switches/mwcefl-ceiling-flush-mounted Elsewhere we have the PIR switches and they mainly work OK, with just a very occasional false trigger. I fitted them in the WC, various cupboards, our under eaves loft space, the services room and our walk-in wardrobe. The advantages of PIR are that it mainly responds to changes in warmth, so reliably detects people and animals. The disadvantage is that they also detect warm air movement, so, for example, our walk-in wardrobe light will often come on when the bathroom door is opened, as the rush of warmer air coming in under the door to the wardrobe is detected. The advantages of the microwave Doppler switches is that they only sense movement of solid objects, so they aren't triggered by warm air movement or shadows. The snag is that they can sense through walls and doors, so movement outside a room, close to a wall or door, may be detected and turn the light on

I have a couple of refillable water filter cartridges that are identical to the one in that link, minus the phosphate balls. I use mine to hold silica gel, as an air dryer on our ozone system. The empty cartridges are cheap and easy to refill, so I keep one in use and another in a sealed plastic bag ready to swap over (I rejuvenate the silica gel granules by gently baking them in the oven). The cartidges I have are like these: https://www.ebay.co.uk/itm/10-Refillable-Water-Filter-Cartridge-Refill-with-DI-Resin-Carbon-Polyphosphate/302974549259?epid=1448362502&hash=item468ab0bd0b:g:GXEAAOSw~RVaGEds They fit a standard water filter housing.

Pretty much, yes. Our boiling water tap came with a phosphate dosing unit, that was just a replaceable cartridge filter that contained phosphate balls. Probably worth an experiment to see if just sticking some of these balls inside a clear water filter housing would work. Might be an idea to plumb a ball valve bypass around it, so that the flow rate over the balls could be adjusted, as it might work better, or use less phosphate, if the flow over the balls is adjusted to be just enough to stop limescale sticking to stuff.

This is right at the very heart of my issue with the term "thermal mass", the absence of any meaningful units to describe it. It seems very clear that heat capacity (in any form, molar, volumetric or specific) is just not "thermal mass". If those proponents of this term wish it to fit within an international accepted measurement system then they need to be clear as to what the term really means. If it means thermal inertia, as applied to the rate of change of temperature inside a building with respect to the rate of change of temperature outside the building, then that's fine, but it then needs to be defined in units that enable it to be measured. This would then enable one building to be compared to another in a meaningful way, or enable those designing buildings to optimise those designs so as to achieve a target value for this aspect of a building's performance, by calculating the impact of particular material choices in the structure of the building.

Yes, sorry, the extra 0 was a typo...

I'd stick the elbow out so that the pipe is near the centreline of the duct and then add maybe 100 to 1500 of pipe in the elbow, to create a longer length that will help smooth the flow along the outside of the bit of pipe and also improve the suction at the open end a bit.

I agree! I always just stick a tea bag in a mug and fill it from the boiling water tap, then add milk later.

Another thing to thank Newton for... Reminds me of the argument I had years ago with my wife, over whether tea was hotter or cooler if the milk went in first. I conducted an experiment (as you do) to prove it one way or the the other. I ended up being right, tea does indeed end up hotter after a defined period of time if the milk goes in first. The reason is that, because the milk near-instantly cools the incoming hot tea, the rate of heat loss from that point onwards is slower, so after a defined period of time that cup of tea ends up slightly warmer than the one where the tea went in first, heating the cup to a slightly higher temperature, and so increasing the initial rate of heat loss.

Exactly what I did. When interest rates were very high, I got used to paying a lot each month. As they reduced (from the ~14% or so they had been), I just maintained the same monthly payment, as I'd got used to it. Knocked around 8 to 10 years off the repayment period for a 25 year mortgage and left me mortgage free long before I took early retirement.