Posted By: GarethCPile-o-Stone, you need to try living in Japanese homes! They're practically made of cardboard and are extremely leaky (not good or easy to make things of brick, and airtight, when they're shoogled about by earthquakes regularly). And they're heated with these things almost exclusively.

I'm not saying there aren't problems. Fashion and tastes are a major one, but if millions of Asians... Sorry, billions of Asians can do it, I think we can too.

I was interested in your post about Japan, and did a quick google to see how they balance low insulation against high energy costs.

I saw this about a Kotatsu, which is "a low, wooden table frame covered by a futon, or heavy blanket, upon which a table top sits. Underneath is a heat source, often built into the table itself."

"Most Japanese housing is not insulated to the same degree as a western domicile and do not have central heating, thus relying primarily on space heating. Heating is expensive because of the lack of insulation and the draftiness of housing. A kotatsu is a relatively inexpensive way to stay warm in the winter, as the futons trap the warm air. Families may choose to concentrate their activity in this one area of the house in order to save on energy costs. In the summer, the blanket may be removed, and the kotatsu used as a normal table."

I'm not sure Mrs Stone and the the pebbles would be overly keen on us all living in one room based around a heated table!

A different site had this to say:

"Central heating is not as widespread in Japan as it is in other developed countries. Heating an entire house or apartment uniformly is considered wasteful since all rooms are not necessarily going to be occupied at the same time, and energy prices in Japan have always been high. Heating a residence is done in a component fashion, with each room having its own discreet heating device. The rationale behind this has proved to be lucrative for Japanese utilities and home-appliance makers. With central heating, any improvements are made through maintenance and repairs, but with a component system, they are made through replacement, which can happen fairly often if technology improves over time.

But a component system can also be wasteful. Heating devices that are constantly being discarded have to be recycled, otherwise they simply end up as landfill. And component heating is not going to be any more energy efficient than central heating if a residence isn’t airtight and properly insulated."

What the little I read, it looked like Japan was also moving towards having better insulated and airtight houses to reduce overall costs. The majority use air based heating such as Air conditioners, kerosene heaters and fan heaters but agan there seems to be a move towards other heating tech:

"[ASHP Air Cnditioners] Then there are aesthetic considerations — the big white box on the wall and the even bigger fan unit outside with all its unsightly connecting tubes. They can be noisy, too. More significantly, however, they are not suitable for very cold climates since heat pumps don’t work as efficiently when the outside air falls below a certain temperature. In Hokkaido, for example, floor heating and storage heaters are more popular, and now along the Japan Sea coast, these methods are becoming more common in new homes."

Looks like having a well insulated and air tight home with storage type heating (i.e. UFH in a large slab) is the most efficient model to aim for?

Another point regarding Japan is that it pretty much sits between 30°N & 45°NThat's a good deal South of the UK. More like Spain in terms of latitude, though I'm not aware of any North Atlantic Current equivalent, so possibly slightly swings & roundabouts?

Posted By: skyewrightAnother point regarding Japan is that it pretty much sits between 30°N & 45°NThat's a good deal South of the UK. More like Spain in terms of latitude, though I'm not aware of any North Atlantic Current equivalent, so possibly slightly swings & roundabouts?

Japan's climate is dominated by warm moist winds from the Pacific Ocean in the summer and cold dry winds from Siberia in the winter. So, even at sea level, its usual for temperatures to drop below zero in the winter. The more northerly and higher altitude areas have regular snow fall.

David

Here's a question. What organisation might most likely try to produce some field data on UK air con performance for us? It shouldn't be all that difficult to do. Surely a university with green research interests, or the centre for sustainable energy, or even Which, or SOMEONE should have the resources, and interest, to monitor a few air con units over the course of a UK winter. Any ideas? I tried DECC directly a while ago, but they didn't seem interested.

If you want to fund it, for about 4 years, I am sure I can create a PhD course for it.
Only cost about £125,000 for one student.

As for weather, Madrid is 667m high, almost double that of Rough Tor on Bodmin Moor, and it gets snowy up there.
Tokyo is about 35m, lower than I am.

I think that the frosting up of ASHP has a lot to do with the initial sizing of them. If they are too small for the load required, the pass more air though the cold heat exchanger, this then freezes up the moisture.
If the ASHP is oversized, most to the time, it can cope without freezing.
It is hard to sell the idea that if you need a 6 kW heat load, you really should consider a 12 to 15 kW heater.

I can't find any good references for it to link to, but I think that the critical temperature range for ASHP frosting is around +3 to +5ºC as the relative humidity is still high enough at those temperatures that a lot of frost can form on the fins of the heat pump as the heat is extracted from the air. (I vaguely remember hearing that a heat pump will lower the temperature of air passing through it by around 7 degrees.)

So ironically the higher temperatures in the UK may be a negative when comparing against the Malmö performance data,

Posted By: Chris P Baconthe critical temperature range for ASHP frosting is around +3 to +5ºC

I wonder if there's any connection to the maximum density of water at 4°C?

I put this on Navitron after an article there showed that grid carbon intensity has fallen by over a quarter from figures used in my OP:

Reduced coal and increased renewables, by my calculations, have cut UK electricity carbon intensity, including distribution, from 0.52 kgCO2e/kWh in 2013 to 0.40 by 2015. Those figures are annual averages , so current intensity (esp. given recent coal power station closures) might be lower (Earth.org.uk says it's currently about 350, so less than 400 even with distribution).

In 2013 a heat pump had to achieve an SPF of 2.3 to emit less than a high efficiency natural gas boiler. UK ASHPs manage SPFs of 2.6 on average, so in 2013 they emitted just 11% less carbon than a gas boiler. Given their expense, it was probably worth sticking to gas if possible.

By 2015, the necessary SPF was just 1.8, and ASHPs were delivering 31% less carbon than a good gas boiler – not bad! A high performing ASHP with a 3.0 SPF delivers 40% less carbon.

i.e., even 'average' heat pumps now deliver decent C02 savings, which will increase as the grid continues to green. Better options for those inclined to reduce their domestic emissions.

The fly in the ointment is that the economics haven’t improved. You still need an SPF of 3.0 (in fact I reckon 3.2)to have a lower running cost than gas (and that might worsen). And installation costs still make ASHPs unattractive for retrofits.

Shame, if costs came down a chunk, these would be a good way of cutting domestic emissions.

Posted By: ringiWhat’s the marginal grid carbon intensity in winter?

This is the key question. I think it's safe to assume it's somewhere between that of gas and that of coal though moving towards gas.

There are very few days in the UK when current renewables could provide 100% of the current demand. Therefore renewable don't have much effect on the marginal grid carbon intensity.

Ah, I see what you mean. I do think it's interesting that, if you took all the gas currently burnt directly for heating and hot water, and instead used it to produce electricity driving averagely performing heat pumps, you could produce the same amount of heat and hot water with (probably at least) 30% lower carbon emissions. Unfortunately the capital cost, in terms of building extra power stations and retrofitting heat pumps, render the idea less interesting.

Interesting... But I can't get my head around how that works... Modern boilers are about 80-85% efficient. I can see how generating electricity using gas locally at, sat, 35% efficiency might lead to a net emissions benefit overall, but surely it must be small? I can't see how it would be half. My head hurts. Is the half compared to marginal, dirty centralised generation?

Posted By: ringiBut you must have a good use of the heat, and a way to store the heat until needed.

The best way to think of CHP is as a heat plant that also generates some electricity. So you run it to generate the heat that you want and only when you want the heat. The electricity is a bonus that can reduce your own usage and/or be fed back into the grid. If you want electricity at a time when you don't want heat, then you buy it from efficient generators on the grid.

I wrote: "According to http://www.ukconversionfactorscarbonsmart.co.uk/ the factor for 2015 is 0.46219 kg CO2e/kWh"

But looking at https://www.ecotricity.co.uk/our-green-energy/energy-independence/uk-grid-live it says that the current number is .375 but also flags it as a red traffic light, which I presume means it is high.

But 0.375 < 0.462 so I'm confused! Help!

Posted By: djh

Posted By: ringiBut you must have a good use of the heat, and a way to store the heat until needed.

The best way to think of CHP is as a heat plant that also generates some electricity. So you run it to generate the heat that you want and only when you want the heat. The electricity is a bonus that can reduce your own usage and/or be fed back into the grid. If you want electricity at a time when you don't want heat, then you buy it from efficient generators on the grid.

You do have the DWH tank that does not need fully heated until bedtime showers, so can be heated based on the evening usage of electricity.

Ceres Power claims to have a small fuel cell that can achieve 50% net electrical efficiency, if this becomes a usable system, then the heat can be considered the bonus, with the fuel cell sized so the electrical output can be used in the home for most of the day. (Let the grid cope with peak usage, as the export payments are so low, so not worth sizing a system that will expert much.)

As soon as electrical storage comes down in price, the fuel cell can be sized to provide most of the electrical needs of the house (and maybe car). (As fuel cells can track electrical demand in near real time, if the capital cost of having a larger fuel cell is not great, then electrical storage is not needed.)

Then it gets interesting, as you have about 10kwh of “free” heat each day, but that is not much more then what a lot of households needs to heat the DHW.....

It all depends on when small CHP become cheap enough to be mass market and what the service costs are.