Jeremy Harris

I'll just chuck a few facts and views in for fun. The very best plants can convert around 7% to 9% of the energy from the sun into usable energy, as biomass, oil etc, per unit ground area. Most struggle to get better than about 5%. A poor solar farm might convert 15% of the energy from the sun over that area into electricity, a good solar farm might convert 18% to 20%. The price of solar panels and the associated kit is now cheap enough that there are no subsidies needed for commercial solar farms, and they still generate electricity at a lower price than many other forms of power generation. As a final point, solar farms can still grow some plants around them, and even graze sheep on the land, so all told solar farms are still very much a positive in terms of the productivity of the land. Whether people like the look of them is another point. Personally, I'd rather see a field of solar panels than a field of oil seed rape, but that may be because I hate the smell of oil seed rape..............

Ours is in a room next to a bedroom - can't hear a thing, in normal background ventilation mode these things are near enough silent. You can just hear it if you put your ear to the casing, but that's about it. The noise does increase slightly in boost mode, but it's unlikely that the thing would be in boost mode when anyone's sleeping. I was overly concerned about noise, so opted to line the inside walls of the service area with acoustic foam, the "egg box" stuff. I really needn't have bothered, as it turned out the noise was a lot less that I expected.

Might be worth seeing if there is a difference in humidity with height above ground. I have a feeling that there will be at certain times, for example when wet ground starts to warm up from the sun early in the morning and the moisture evaporates off. Whether this is significant around the intake to an ASHP as to make a measurable performance different I doubt, personally, but it may do. I think there are other good reasons for adding a rain shield to one, anyway, so will add it to the list of things I must get around to one day..............

There's some evidence that keeping rain off the unit does help a fair bit, from what I've read. As long as the air flow isn't restricted, anything that helps to keep the area around the unit dry has to help a bit. It probably also helps prevent external corrosion a bit, too. Although designed to be sat outside, there are signs on mine of minor corrosion around some of the fasteners, presumably where the underlying galvanised coating has been scratched. It it were under cover then spraying a bit of grease or similar around the fasteners might well be more effective at limiting future corrosion.

But these are hardwood sleepers, so I'm guessing they are very similar to the oak ones we used as a retaining wall. They don't smell at all, because they aren't treated, and, AFAIK, creosote/tar etc just doesn't penetrate hardwoods well, which is why they don't bother to treat them. We bought new oak sleepers, rather than reclaimed ones, but only because around our way the new ones were both easier to get hold of and around the same price as the reclaimed ones.

My guess is that it will run at the same sort of pressure as a normal. The typical pressure for mine is around 125 to 150 bar with a 0.015 nozzle, and but with something thicker than un-thinned emulsion and a 0.021 nozzle the pressure might have to be closer to the upper limit for the pump, which is around 200 bar IIRC. In general, airless sprayers operate at or above pressure washer type pressures; they are pretty powerful bits of kit.

Wait until Openreach or the DNO come along and replace an old pole with a new one near him! They smeech of creosote for at least a year or so. We have two that were put in around 3 years ago, and even now they smell on a hot day.

The sort of professional machine needed to run a nozzle of that size with a decent spray pattern is going to be around £600 to £800 to buy, and as the nozzles wear (and my guess is that this stuff will wear the nozzles faster than smoother paints) the hire cost might be a bit more than few quid a day. I bought my machine second hand from a local chap, who hadn't used it at all, for a couple of hundred and it was a real bargain, but it's only got a relatively small motor and pump, which is fine for spraying emulsion with around a 10" wide spray pattern, but it would probably struggle to deliver that sort of spray pattern width with a bigger nozzle, I think. There's also a fair bit of clean up time with an airless sprayer - it takes a lot longer to prepare and mix the paint and clean out the spray pump, hose and gun, than it does to do the actual painting I found. It is very quick though, and makes painting in awkward areas a bit easier.

Yes, I reckon it'd do the job, but a high pressure airless sprayer to effectively apply isn't a cheap bit of kit, even the cheap'ish one I bought. Not sure a cheap one would handle the relatively big nozzle needed, either. Mine's OK on a 0.015 nozzle, but might not deliver enough pressure to drive a 0.021 nozzle well.

Looks like a replacement for a cheap and quick traditional high cement ratio parge coat to me. At a guess, I'd say a parge coat would be cheaper and quicker, and not need the expense of the spray kit.

I agree with @Triassic, ignore him, after pointing out that these are HARDWOOD sleepers, so have not, and cannot realistically, have ever been treated with creosote or tar. We have oak sleepers as part of a low retaining wall and there's no detectable smell from them at all.

What's the worse and best that can happen if you decide the DIY things? Worst case, you end up calling in a plumber to sort things out, and in all probability you will have got much of the hard work done by then, so the job will likely be easier from the plumber's point of view (who will look at stuff like running lots of pipes etc as being the "hard" work, and won't be fazed by the joints etc). Best case is that you will gain a fair bit of knowledge and skill, save a fair bit of money, get the satisfaction of having done the job yourself, gained confidence in tackling other jobs and you have the back up of some people here who've either been up the same learning curve or are already professionals in that trade.

Yes, but it would be a lot of faffing about - if you've read the very lengthy discussions on this then things might be clearer. I'd need to go in and start lifting wires from the wiring box and reconfigure things. The valve that shuts off the UFH loops from the ASHP would need to be forced to close when the ASHP was operating (you can't just disconnect the UFH circulation pump, as the built in ASHP circulating pump will still cause flow through the UFH system), and I'd need to rewire the valve to the buffer tank to hold that open when the UFH valve was closed (not a normal operating condition). It would be perfectly possible to do, but I've already spent the best part of a year fine tuning things and I'm reluctant to start taking it apart again just to try and gain a bit of information that would be of no practical value to me. I know, after a couple of years of operation, that just keeping the flow temperature at 40 deg C means the ASHP never defrosts. Our system works an absolute treat like this, with a high COP (higher than the spec sheet says by at least 10 to 20%), so I'm content to just leave it alone. We have no electricity bill at all, in effect, and the house is all-electric, so all the initial experiments I did a couple of years ago when trying to both understand how the heat pump actually worked (rather than what the manual said - the two were quite different!) and fine tune the settings needed to get good control over a house with a high thermal time constant and low overall heat losses (which turned out to be relatively easy, but I chose to take an overly complex route to reach that conclusion) have been worthwhile, but may or may not be relevant to a house in a different area, of a different size, shape and orientation, with different thermal characteristics and occupants with a different lifestyle.

I've never been able to quantitatively measure the total heat energy going in to the defrost cycle, only the time it takes and the electrical power drawn. All I can see is that the fan and compressor both ramp up to maximum electrical power over the first 30 seconds to 1 minute of the defrost cycle, after the heat pump has shut down and the 4 way valve operated, then the compressor shuts off and the fan carries on running at near full speed for a minute or two until the end of the cycle. It then shuts down, operates the 4 way valve again and ramps back up in heating mode over the next thirty seconds to a minute.

What I also found (there's loads elsewhere here about it) is that increasing the flow temperature from even a massively over-sized ASHP makes it defrost a lot. There's no gradual transition that I could find. Running at 40 deg C flow means it never defrosts, running at anything over 45 deg C means it defrosts at least twice an hour, sometimes three times an hour, when the outside air temperature gets to around 4 to 6 deg C and the humidity is high (typical English winter day!). Each defrost cycle lasts about 10 minutes, and seems to work the heat pump hard, presumably to get as much heat from the house into the evaporator as quickly as possible. The result is that lost energy from the house during the defrost cycle is often a lot greater than energy gained during the normal operating cycle for the same time period, as the ASHP doesn't seem to modulate down in defrost mode. It was quite a shock the first time I saw a defrost cycle, and saw the 70 litre buffer tank temperature plummeting down to well below room temperature as heat was being drawn from it!

My concern is that nothing has changed with the ethos behind software design. Back when I first got a PC, around 40 years ago, software was released with bugs and there was an expectation that consumers would do all the final debugging, with the suppliers releasing patches to address all the faults that were found. Nothing has changed at all. If you buy the very latest generation of most operating systems there will be bugs found by consumers within the first few days or weeks, and it will be consumers that have most of the burden of having to update their machines to work as they are supposed to. I think it's cultural, there just doesn't seem to be any real interest in making sure that software is free from bugs before it's released. This is unlike other products, like cars, where if they all had to be fixed to get rid of inherent faults within the first few days or weeks people would just stop buying that make of car. What's really annoying, is that I know it doesn't have to be like this at all. The helicopter programme I ran for a few years involved a machine that was fly-by-wire, with a great deal of software controlling everything from the instrument displays, through the main flight control systems, to the engine management systems, as well as all the weapon and sensor related code. There were no bugs in that when that aircraft first flew, none at all. The code had been written in a robust language, using formal methods, had been complied with accredited compilers that we knew would always produce the same machine code for any given source code, and the machine code had been checked via a full static code walk through before we even started functional testing on hardware.

I've proved it's not - if I just keep the flow temperature at no more than 40 deg C then the ASHP never defrosts at all. Boosting from the 40 deg C in the buffer to 50 deg C or so for hot water uses very little energy, especially as most of the time that comes from a Sunamp PV, and if the Sunamp PV isn't charged, the variable power input instant water heater (a Stiebel Eltron DHC-E) will add just enough extra heating to bring the pre-heated water up to a usable level for DHW. Our ASHP is oversized simply because a 7kW one came along at a bargain price. Our house heating requirement when it's -10 deg C outside is only about 1600 W, so the heat pump never has to work very hard. Accreted Ice isn't involved, as the design of the heat pump is such that it defrosts before ice builds up.

Bear in mind that all the COP data almost certainly ignores the energy loss in defrosting. That's certainly the case for the data I've seen, where the COP has been quoted at a figure for a certain temperature differential, but when you estimate and add on the actual heat energy pulled back out of the house during defrost (which has to be replaced when the heat pump starts running in heating mode again) you find that the real world COP can be around half the quoted figure.

The water company guys still just use a listening rod to find leaks. I watched them doing it back in the summer, trying to find a persistent leak that's been breaking up the surface of a lane near us. It looked to me like a bit of steel bar around 10mm in diameter, with a rubber cup on the top that they placed on their ear, like a stethoscope. It seemed to work, as after ten minutes or so of the bloke walking along, stopping every foot of so and placing the rod on the ground and listening, he marked where to dig and sure enough, they found the broken pipe right away, about 3ft down. I've just done a quick web search and come up with this: http://vernonmorris.co.uk/shop/category/leak-detection/listening-sticks

It varies a great deal with load. There are times when the evaporator on ours is barely cool, and other times when it's well below zero. In general, if our ASHP is running at it's normal pretty low load, and the air temperature is above about 5 or 6 deg C, then the evaporator barely reaches 0 deg C. Push the load up, by asking it to deliver water at a higher temperature, and the evaporator cools down pretty dramatically, even with the fan speed having increased to try and shove the maximum amount of air through it. From what I've observed, the first thing to change when the load changes on the ASHP is the fan speed. The internal logic and timing seems set to speed up the fan first, to establish a higher air mass flow and get the evaporator as close to ambient as it can. It then very gently ramps up the compressor speed, so cooling the evaporator. Somewhere in the settings I think there is a way of displaying the effective evaporator temperature from one of the internal sensors, I may have a go and see if I can get a better feel for how cold it gets. The lower temperature limit for the evaporator is set by two things, the static pressure inside the evaporator and the saturation pressure of the refrigerant. Some refrigerants have a pretty low saturation pressure at low temperatures. like CO2, for example. This means a CO2 filled ASHP will still function with the evaporator down well below -30 deg C. The more typical zeotropic mixes that are used in most modern units (typically R410A, which is a 50/50 mix of difluoromethane and pentafluoroethane) have saturation pressures that are zero at around -40 deg C, so, depending on the pressure in the evaporator circuit, they may work down to about -25 deg C or so.

I had a Part P chit for the external wiring and the small CU and Henley and isolator switch that was installed when we had our meter installed. The SSE chap didn't ask to see anything, though, so I may as well not have bothered.............

Sounds like my experience. I've completely rewired two houses, and partially rewired three others, excluding any work on the new house. It was all dead easy. The first rewire was a new build that a friend was doing, and when it came time to get the meter installed I'd just left the tails sitting ready on the board (this pre-dates having meter boxes) for SWEB to connect up. Their chap just turned up, installed the cable, company fuse and meter and connected the tails. He never asked to see any bit of paper at all. The second one was similar, except it turned out his son was an apprentice with SWEB and was one of my students, so we had a chat about that. Again, no paperwork, just reconnect the supply that had been relocated during the rebuild of the farmhouse and that was that. The partial rewires never involved anyone else. I tested the installation (as I'd done with the previous two), but no one asked for any bits of paper. With our current old house I've been taking out additional wiring I've added over the years, and putting things back exactly as they were before we well it, as I just don't want the hassle of having to explain away why I have a garage with a dozen extra outlets, a separate CU with an RCD etc, so it's back to how it was, a light switch and a single double gang socket (with all my tools temporarily running on extension leads and a plug-in RCD..............). The last thing I'll remove is my car charge point, as that was home installed from an existing outside power socket, which will get replaced as it was.

I did a bit on domestic earthing systems here some time ago: http://www.mayfly.eu/2017/01/domestic-electrical-installation-earthing-and-circuit-protection-part-1/ and here: http://www.mayfly.eu/2017/02/domestic-electrical-installation-earthing-and-circuit-protection-part-2/

Ours certainly runs air through the evaporator when the compressor is turned off, albeit fairly slowly, with the fan speed modulated right down. Presumably that's to try to keep the evaporator as close to the ambient air temperature as possible, which would reduce the risk of icing for as long as the outside temperature is above zero. Under those conditions, damp air would warm up the evaporator towards ambient more quickly, because of it's greater heat capacity. The local humidity thing is really more about trying to prevent the area around the ASHP from being wetter than elsewhere. Although they are designed to be left uncovered, having rain running down the evaporator will make it ice up more quickly, I'm sure, than if it was kept sheltered from the rain.

"Turn off and wait" would work well when the air temperature is well above zero, the house has a long thermal time constant and you have enough stored water to meet the hot water demand for the next hour or two. The snag is it wouldn't work at all if the temperature was below zero, and would take a long time to work if the temperature was only just above zero. I can't say for sure, but all the tests I've done on ours suggest that icing is most likely when the air temperature is just above zero and the conditions are damp, a combination that is common here, as after a warmer day, as the air cools during the evening it tends to become saturated with water vapour, which then looks to condense out on any cooler surface, hence the dew and frost we see. I think positioning an ASHP so that the rear face (where the evaporator is) faces the sun, particularly later in the day, might help. Anything that warms that area up, even by a small amount, would make a difference, and even in the very coldest weather solar radiation can be pretty powerful (a look at how the ice and frost on the side of a car facing the sun melts pretty quickly in the morning shows that). I remember reading a thread ages ago, not sure whether it was on ebuild or somewhere else, where someone proposed fitting a ASHP inside a south facing conservatory, fitted with ventilation grilles to allow air in, sort of built in to the wall, with the exhaust facing outwards. The idea was that it would be able to draw in slightly warmer air, even in winter, when the conservatory wasn't being used, which would make it less prone to icing. Anything you can do to lower the humidity around the unit would help, too. I keep meaning to add a small overhanging roof over ours, to both stop it getting wet in the rain (which must raise the local humidity a bit) and also to slightly reduce the radiative heat loss, by shielding the unit and the ground around it from the cold night sky. The idea is that the water vapour in the air would condense out on colder surfaces nearby first, as the lose heat to the very cold night sky, so the air reaching the ASHP would already be just a little bitdrier.