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Wage Slave wrote:I think Gramps has a big tank as well - Perhaps that would be a good idea and it would certainly save me the weekly trip to the petrol station as well as allowing for buying when the price is a bit more attractive. How many litres? 400 or so? No-one around here has one though so don't want to start the neighbours gossiping.
As for calculations I think kerosene for my main room (18 tatami) costs about 20 Yen an hour to run at the current price. The problem is I don't have an accurate(ish) figure for how much power the air conditioner actually uses to do the same job. I know how much it can consume running full tilt but not how much it does consume to keep 18 degrees or so, if that makes sense. If anyone can find anything in Japanese that gives even rough estimates or example comparisons ....
Russell wrote:Wage Slave wrote:I think Gramps has a big tank as well - Perhaps that would be a good idea and it would certainly save me the weekly trip to the petrol station as well as allowing for buying when the price is a bit more attractive. How many litres? 400 or so? No-one around here has one though so don't want to start the neighbours gossiping.
As for calculations I think kerosene for my main room (18 tatami) costs about 20 Yen an hour to run at the current price. The problem is I don't have an accurate(ish) figure for how much power the air conditioner actually uses to do the same job. I know how much it can consume running full tilt but not how much it does consume to keep 18 degrees or so, if that makes sense. If anyone can find anything in Japanese that gives even rough estimates or example comparisons ....
Use of electricity by your aircon depends on the size of the room, isolation, etc.
If your aircon runs on 100 V, then you can buy an electricity meter. Tells you exactly how much electricity you use.
I bought one at Don Quichotte.
Big is relative, even more so in JapanWage Slave wrote:I think Gramps has a big tank as well
Wage Slave wrote:As the article points out though, the replacement cost of the machine is much higher - and that needs to be considered.
Russell wrote:Wage Slave wrote:As the article points out though, the replacement cost of the machine is much higher - and that needs to be considered.
But you can use in the aircon in the summer for cooling, so this is a non-argument, unless you live in a place that is already cool in the summer.
Wage Slave wrote:Russell wrote:Wage Slave wrote:As the article points out though, the replacement cost of the machine is much higher - and that needs to be considered.
But you can use in the aircon in the summer for cooling, so this is a non-argument, unless you live in a place that is already cool in the summer.
True, but if it is used for heating as well as cooling it will last half as many years before needing replacement. The heating wear and tear can be done with a kerosene heater which costs at least 160,000 Yen less to replace for 18 tatemi.
Yokohammer wrote:Wage Slave wrote:Russell wrote:Wage Slave wrote:As the article points out though, the replacement cost of the machine is much higher - and that needs to be considered.
But you can use in the aircon in the summer for cooling, so this is a non-argument, unless you live in a place that is already cool in the summer.
True, but if it is used for heating as well as cooling it will last half as many years before needing replacement. The heating wear and tear can be done with a kerosene heater which costs at least 160,000 Yen less to replace for 18 tatemi.
Thinking about it, you know I don't think I've seen an air conditioner actually fail completely in the last 20 years or so. The built-in system we had at the house in Yokohama ran for the entire almost-20-years we were there (although it was stupid expensive to run), and the el-cheapo Corona unit that the previous owner of our current house installed in 1998 is still running just fine ... although I've had to beef up the laughably bad installation job he did. So that's been running for 16 years. I'm not sure it's even worth worrying about the longevity of these things any more. The only real issue is that an aircon from, say, 15 to 20 years ago is likely to be a lot less efficient than a new one.
wagyl wrote:I think you are really only going to be able to answer this for yourself by buying that meter and doing practical tests.
Wage Slave wrote: airconditioners have the benefit that they can extract some useful heat from the environment via the radiator/fan in the compressor unit if it is at least 5 outside.
wagyl wrote:Wage Slave wrote: airconditioners have the benefit that they can extract some useful heat from the environment via the radiator/fan in the compressor unit if it is at least 5 outside.
Well that rules that option out for me! (I was aware of the fact that the heat pump operation would fail through the ambient temperature being cooler than the range of the heat transfer medium anyway)
wagyl wrote:If the operating temperature of the refrigerant in the heat pump is greater than the ambient temperature, it is not going to be able to extract heat from the ambient. Unless by "the compressor will have to do all the work" you mean the only remaining source of heat is the heat waste from the electric motor doing the pumping and maybe operating the fan, in which case you will be seeing no efficiencies over those of an electric bar radiator. Albeit one placed outside your house in the garden. When the fan isn't iced up, that is.
wagyl wrote:Lowest minimum recorded is about −20, and we get a -15 almost every year. I have an indoor temperature display on my fan heater which goes down to 6 degrees and for three or four months it is rare that I wake up and it displays anything other than L, meaning below 6 degrees. As I say, the kitchen is demonstrably below freezing for much of the winter, and occasionally the toilet bowl will have a crust that the blood-temperature new additions I introduced to it just won't budge.
In other words, I'm not looking to install a heat pump based on ambient air temperature.
Wage Slave wrote:So reading a bit more especially here, it would appear that the best strategy is to use aircons earlier and later in the season, switching to burning kerosene for the coldest months.
Apparently at 8.3 degrees or above an air source heat pump is working at 100% of its potential efficiency and is pretty efficient indeed. Below that it falls reaching 60% at 0 degrees. So, it would seem my rule of thumb of about 5 degrees to switch over is probably about right. So, for now, I'm going to use aircons and just monitor their consumption with the main meter to make sure I'm not making a mistake.
wagyl wrote:The same goes for Eco-cute hot water systems which are similarly no more than ambient air source heat pumps, running in the night time during the coldest part of the day.
Russell wrote:wagyl wrote:The same goes for Eco-cute hot water systems which are similarly no more than ambient air source heat pumps, running in the night time during the coldest part of the day.
So, what you are saying is that they should be run at daytime during the colder months?
jingai wrote:To answer the original question, I modified a US-specific calculator for Japan using the best (if somewhat limited) info I could get about the efficiency of various options here. I'm trying to find a home for the article I wrote that goes along with it, but if you'd like the calculator to tweak with your assumptions, send me a private message. The short answer is that at least in the Sendai area and south, a decent aircon should be cheaper to run than a kerosene heater but at a much steeper upfront cost (though with benefits like no CO, fuel deliveries, fires, or dumping large amounts of moisture into the air.) The trickier part of the calcuation is adjusting the aircon performance based on climate. I have decent info on this for the US but have found no similar info for Japan and the industry uses Tokyo's climate as a reference, so my attempt to solve this is basically playing match the climate between locations in the US and Japan using weather station average annual heating degree days.
I think even in the heart of winter a decent aircon should work fine until night, and you could switch to kerosene as backup if needed for supplemental heat. The Wikipedia article mentioned doesn't seem to distinguish between (central) air source heat pumps from far superior ductless minisplits, and its info about cold weather performance cites a Canadian study on commercial units from 2002! Much has changed since then (heck, even since 2009.) Modern Mitsubishi and Fujitsu units ought to perform (COP > 2) down to -15 C or so. They do in the US. 5C should not be a challenge for any modern unit.
The aircon I bought also gives daily readouts of the electricity it uses (I couldn't find a basic external meter that works with 200V so this is a nice feature.) I plan to do a follow-up after this winter showing real world usage in coastal Tohoku vs a comparison of electricity used per heating degree day. If everything I think turns out to be wrong I will post that too!
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