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EV-based road transportation is not viable
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tom66:

--- Quote from: tszaboo on February 21, 2023, 03:57:36 pm ---
--- Quote from: tom66 on February 21, 2023, 03:48:28 pm ---Good diagram.  But, does it account for the difficulty in insulating UK homes to support heat pumps?  Having embarked upon the process of insulating our 1930's detached home, it is definitely not a trivial process usually requiring bespoke techniques for each property.

--- End quote ---
Heat is heat. There is no difference for heat pump heat or heat from a boiler or gas.

--- End quote ---

Not really.  Heatpumps have the highest COP when running at lower power outputs.  The ideal heatpump runs all day (when you're awake) at low power outputs, relatively low delta-T at the radiators.  Typical flow and return of 55C and 35C not uncommon, well below that of used for boilers.  If you have insufficient insulation, you need a very large heat pump, which becomes uneconomical.
nctnico:

--- Quote from: Ice-Tea on February 21, 2023, 06:36:29 pm ---So, uhm, that's your argument then? You disregard any data that doesn't fit your narrative and call all those that run with it idiots?  :o

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There is no narrative and there is no argument. Just the fact that heatpumps are not economic to run when it is cold. This is obviously clear from looking at specifications from actual heatpumps. There is no need for yet another fantasy number that is invented to compare heatpumps because it says nothing about the suitability of heatpump for a less insulated home.
tom66:

--- Quote from: nctnico on February 21, 2023, 06:42:58 pm ---
--- Quote from: tszaboo on February 21, 2023, 06:26:09 pm ---Typical winter with this climate, the deltaT is 20-30, entirely possible to provide this even with air source heatpump.

--- End quote ---
It is not about the temperature delta, but the absolute temperature operating range of a heatpump! And at some point the outside unit will ice up preventing extracting heat from the environment. The graph you posted is way too optimistic. A heatpump simply does not work well in a climate that has close to or sub-zero temperatures.

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Below zero most ASHPs cycle and turn the outside radiator into a heating element by extracting a bit of heat from the interior to melt ice.  This typically happens for 1 minute every 15-20 minutes.   I guess some may also use an electric heating element now and then.  For multi split units only one of the units does this, the others shut off entirely.

From someone who I know who owns a cheaper TCL unit (Chinese air conditioner) the bigger problem is the firmware doesn't detect the icing condition soon enough, so efficiency falls off because air flow through the rad drops.  The better units have ice sensors, but the cheaper units just wait until the system doesn't seem to be performing as well as is expected. 

I also wonder if anyone has considered periodically spraying an antifreeze onto the fins, though you'd probably go through a lot of glycol you might be able to recycle it a few times.
Ice-Tea:

--- Quote from: nctnico on February 21, 2023, 07:00:26 pm ---
--- Quote from: Ice-Tea on February 21, 2023, 06:36:29 pm ---So, uhm, that's your argument then? You disregard any data that doesn't fit your narrative and call all those that run with it idiots?  :o

--- End quote ---
There is no narrative and there is no argument. Just the fact that heatpumps are not economic to run when it is cold. This is obviously clear from looking at specifications from actual heatpumps. There is no need for yet another fantasy number that is invented to compare heatpumps because it says nothing about the suitability of heatpump for a less insulated home.

--- End quote ---

But.... it does. Nobody is arguing that the efficiency of a heatpump goes down when temperature does. That's why you have the SCOP value. It tells you what your seasonal efficiency will be. And it does say something about suitability for less isolated houses as you typically have this value for 35C and 55C feed temperatures. And if 55C doesn't suffise: get crackin' on isolating your barn, please.
PlainName:

--- Quote ---The better units have ice sensors, but the cheaper units just wait until the system doesn't seem to be performing as well as is expected.
--- End quote ---

Not sure what mine is but probably classed as a cheap unit - when turned on, if the desired temperature is the same as the actual temperature it can get into a permanent defrosting cycle (fix is to just turn up the desired temperature until it recovers, then put it back). When it is cold outside, like below freezing, I do notice it goes into the defrost cycle now and then, but it never actually fails to keep the place warm. Worst case is it feels like it's idling (which, I suppose it is if it's just recirculating air) but it doesn't last long enough to make any difference.
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