SteamyTea

No idea. There are a few Alt+xxx that help, but very limited. The alternative is is type up in LATEX (or your favorite editor and screen capture it.

Thanks - this is the key bit. You cannot get better than the Carnot Cycle. Everything else in Thermodynamics is a disappointment. Yes, it affects the value of k. Not sure. J.K-1.K-1 just leaves J, or energy. That seems to make sense, but not sure it is actually equal because if you break down the units for entropy, you get: kg.m2.s-2.K-1 So the amount of time you have a fixed temperature comes into play. Time always (expletive deleted)s up physics. Acceleration double so.

That is a better explanation than the real physics that goes on, and probably did not take you two hours to type.

It takes a disproportionally higher amount of energy to heat it to a higher temperature. This is down to the thermal losses being higher. If you think of a sphere of water, it has the minimum surface area possible, that is how the molecules, within a water cylinder, can be modelled, but the ones that are touching the sides of the cylinder 'change shape' to a sphere cut in half, increasing the surface area to volume ratio, and therefore the thermal losses. Keeping the temperature lower is, in effect, reducing the number of water molecules that are cut in half, this reduces the losses.

Because it is based on the Carnot Cycle. When a refrigerant gas is compressed it changes phase, from vapour to liquid (condensation) and when it is decompressed it changes back into a gas (vaporization). The heat capacity of the two phases is different. Taking water as an example (because it is also a refrigerant gas and you can test things at home), when in the liquid state it take 4.18 kJ.kg-1.K-1 to change temperature, when a gas it takes 1.86 kJ.kg-1.K-1 to change temperature. This may seem odd and you have to wonder where the extra energy goes when it is compressed, well it comes out as thermal energy. It is that thermal energy that is used to heat the building. There is a complication at the phase change temperature. At the exact temperature that water changes from vapour to liquid, or liquid to solid, energy is released, and oddly, a lot of energy. 2500 kJ.kg-1 in the case of water. It is a huge amount of energy and drives the global weather system. When a material is heated or cooled, it is not a linear process. but follow an exponential curve for both heating and cooling, with 'steps' at the phase change temperatures. Isaac Newton formulised this in the 1701. The formula for this is T = (T0-T1)e(-kt) There T is the final temperature after time, t. T0 and T1 are the initial starting temperature and the final temperature. k is the system propertied and is closely related to Ideal Gas Law and the physical restraints of the heat pump i.e. shape and surface area of the pipework. Knocking up a quick spreadsheet you get this. It is easy to see that the temperature drops very rapidly at first then tails off, taking longer and longer to cool. The reverse is the same when heating, except in reality energy is put into the compressor so I have adjusted the value of k to reflect this. Now to answer your question "Why are air-to-water heat pumps more efficient at lower water temperatures" It is down to where you are working on the chart. Knowing that the heating, or cooling, is very rapid when there is a larger temperature difference, and the compressor and air fans have to work harder to pass the fluids though the relevant heat exchangers, which are physical restraints on the system, and knowing that energy is just power multiplied by time, you can see that the same time is taken to raise, or lower, the final temperature by ever decreasing amounts. That is fairly simple, but in the real world, a heat pump is more complicated. There would be 4 temperature/time charts. Starting from outside and working inwards. 1: Outside air temperature and refrigerant temperature difference 2: Phase change within the refrigerant 3: Refrigerant to transfer fluid temperature difference 4: Transfer fluid to internal air temperature difference Throughout all those steps, there are different efficiencies, calculating them is our favourite pastime Solutions to Partial Differential Equations. Personally I prefer to call them Partial Solution to Differential Equations. It is for this very reason that collected data is used to create the CoP charts at varying temperatures and is often misleading when the underlying physics is not appreciated. There is also the problem what the Celsius temperature scale is used which highlights the phase transition in the outside air temperature and humidity changes, giving an unexplained drop in CoP between 4°C and 0°C (the frosting window) This usually shows up as a minima and is often misunderstood and thought of as a CoP of zero. Note: I used water as a refrigerant gas as you can play with this at home. You can put a litre of water in a pan, turn on the ring and monitor the time it takes to get to boiling. You can stop the experiment then and plot how long each K of temperature rise takes, giving you a heating curve. But for extra marks, you can leave it on the ring and see how long it takes for all the water to evaporate. The water will be at 373 K, but the time taken will be longer than you think. You can also do the reverse, but with kilogram of ice melting in a bucket of water, initially it will loose mass quickly, but slow as time goes on. It is because of this that the 'Ice Kings' could transfer Canadian ice to Barbados and store it in straw insulated building. It was the tail end of the chart that allowed it to stay frozen for months. In a heat pump, the cold side is between 250 and 260 K and as the ambient air gets closer to that temperature, the ability to heat the expanded gas diminishes, so the efficiency, with respect to time, is reduced. Again this is often simplified in manufacture's data to a difference in CoP between outside air temperature and delivered temperature, with a smaller difference increasing the CoP. Different refrigerant materials have different phase change temperatures, pressures and heat capacities, and what is used in Sweden for heating may not be ideal for cooling in Florida.

I just need the 'pudding'. Not a house, that is not a good way to test materials.

It must be worth getting a vacuum pump then you can check the few bit you have to connect up.

I tend to agree, and usually only manage to burn my finger when doing electronic. But I do wonder how difficult it really is.

(expletive deleted)ing hippy.

They have given some of it to Cornwall as well. Every year they come and check up in their investment.

I would have thought it would be off the shelf kit though. You can get small, relatively inexpensive, full sine wave inverters, they would work, though not safe to connect to the grid supply.

It would be great to do some practical experiments on different rendering materials and techniques. Round round off my working life a treat as I started off in a company that made material testing machines.

Maker Why used coffee grounds may be doing your plants more harm than good We are often told to add used coffee grounds to garden soil to perk up plants. But the science doesn’t support this, says James Wong 14 June 2023 By James Wong DGLimages/Alamy WANDERING around an achingly cool San Francisco coffee shop a few years ago, I was fascinated to see huge, open-topped barrels filled with used coffee grounds and a sign saying they were free for customers to scoop into recycled bags and take home to perk up their plants. I realised that we had reached peak hipster. Indeed, the claim that coffee waste dramatically boosts plant growth has been a staple of organic gardening books since at least the 1970s, and seems to be seeing a modern renaissance. Proponents everywhere wax lyrical about how the spent grounds are not only rich in nitrogen – a key plant nutrient – but can help lower the pH of garden soils for species whose roots require acidic conditions, like blueberries. It all sounds like such a brilliant idea: upcycling industrial waste into free, organic fertiliser. It is just a shame that in reality it is probably doing the exact opposite. Let me explain… Coffee grounds, even after brewing, are still a rich source of caffeine. This compound seems to be produced by coffee bushes – at least in part – as a herbicide to suppress the growth of smaller competing plants. The phenomenon is called allelopathy and is a strategy loads of plants have evolved to help reduce the competition for light, space, water and nutrients around them. Leaching out of the grounds, the highly soluble caffeine percolates through the soil and has been repeatedly shown to severely stunt the growth of small, neighbouring plants’ roots and slash the rate of seed germination, even at relatively tiny concentrations. Not exactly what the plantfluencers of social media promise. The weirdest thing about how often this tip is recommended is that we have known about the allelopathic potential of caffeine in coffee plants for decades. The first paper I could find on this was from 1980, and its conclusions have been echoed by study after study. So effective is caffeine at suppressing plant growth, it has been investigated as a potential novel herbicide for agricultural use, both in the form of direct application of coffee grounds on farms in Brazil and even tea leaves (which also contain caffeine) on plantations in Vietnam. This effect is so pronounced that over years of intensive cultivation, the accumulated caffeine in the soil of long-established coffee farms can reach levels where it doesn’t just hamper the growth of small weed seedlings, but even the mature coffee bushes. Studies have been conducted to see if underplanting coffee with more resistant herbs, like sage and oregano, could help reduce the caffeine contamination in the soil by drawing the compound up through their roots, while providing farmers with an extra crop to harvest. I wonder if the world is ready for caffeinated herbs. But that’s another matter. James Wong is a botanist and science writer, with a particular interest in food crops, conservation and the environment. Trained at the Royal Botanic Gardens, Kew, he shares his tiny London flat with more than 500 houseplants. You can follow him on Twitter and Instagram @botanygeek For other projects visit newscientist.com/maker.

I wonder if failed render is often a consequence of poor preparation. It is easy to make a job fail, some workers seem to take pride in it to prove a point. When I used to test bonding of dissimilar materials, I tried to include some known faults, the idea being that not every surface will be perfectly prepped. That little ply to plastic test I did for @joe90 is an example. I should have sanded and cleaned both surfaces, but I just wiped the mildew off with my fingers and held the ply sample in place for 5 minutes.

Anymore than utility scale storage which will be cheaper?

Do you mean that expanded metal sheet stuff that is nailed to the walls?

Jeremy is not about anymore, but there are a few others that have recently fitted them. Have a hunt around and you should find it. Try a google site search, it is much better than the forum search facility.

Well I have ordered a new SIM from Smarty (3), should be here next week, shall see how it goes at £16/month.

Do any blame themselves?

Purely from a science perspective it is not conclusive at all. Find 1001 walls that have the same starting conditions and see what the results are. Then calculate the confidence interval. Yes, I am not sure how it affects everything. I get the impression it is used to keep the dust and grit in place until the first coat is on. @nod, do you know?

Some parts of our economy will be though. As we are more interested in building, we may forget about financial or legal services. The definition of 'two consecutive quarters' can be an issue, as can converting output to cash values. Say I make a widget by hand and it takes me an hour, I charge £40/hour. Now I get a machine and I make 50 of the same widgets an hour, still charge £40/hour. My widget is now £0.80 instead of £40, but I now sell them for £30. If I can only sell 30 widgets a week (price of saves has dropped from £1200 to £900), have I gone into recession as I am now selling less then I can produce?

Yes, I think the problem with all renders, and then secondary coatings is really the problem, and that is before the real issues of what is causing the vapours to permutate though the walls is addressed. Do people who are about to lime render still coat a wall with PVA? Or a similar adhesive. How much difference to compressive and tensile strength does the type of sand or 'grit' make? What about thermal expansion, are there much differences for the same amount of sand in the mixes? A wall in the sun can get quite hot, even if the air temperature is not excessive.

Here we go again. Breathability. It is taken on trust that lime based renders breath, and cement based renders don't. Can anyone evidence this, I have been looking for years, the data is scarce to say the least. What you need is a number in SI which is kg.m.m-2.d-1, that is the unit for vapour permeability. Unfortunately most people in the industry do not stick to the SI system (why I have no idea as for most there is only 4 units to remember) Thankfully there is this table to help people out. I have found this, which is about rammed earth, but it does mention lime. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8123846/ Trouble is, it does not specify what the concrete mix type was, or the lime mix type. But it does show how the testing is done.

There are a number of ways it could be done.