Could hot fill appliances make a come back?

Ectophile

grumbler said:

1L of water is about 6m of 15mm pipe.
Full cycle takes about 50L. Washing with hot water takes less, but much more than 1L.

When I run the hot tap in the kitchen, it takes about 3 litres of water before it even starts to run warm.  It's enough that it's worthwhile catching that water in a water carrier to re-use.  My washing machine is next to the kitchen sink, so would also need to run through the same amount of water.

The total water used in a wash cycle isn't very relevant.  Modern machines only use hot water for the main wash cycle.  Rinses are all done with cold water.

grumbler

Ectophile said:

grumbler said:

1L of water is about 6m of 15mm pipe.
Full cycle takes about 50L. Washing with hot water takes less, but much more than 1L.

When I run the hot tap in the kitchen, it takes about 3 litres of water before it even starts to run warm.

Well, houses aren't all the same. That's why I disagreed with the sweeping statement " The inefficiency of using hot+cold fill appliances (whether using stored or combi-heated water) is well documented." 

Also, those with combi boilers who are very keen on saving energy can run a 10mm plastic pipe from the boiler to their WM and DW. This more than halves the volume. BTW, a kitchen tap doesn't need a big flow of hot water either (unlike a bath or a shower).

The total water used in a wash cycle isn't very relevant.  Modern machines only use hot water for the main wash cycle.  Rinses are all done with cold water.

That's why I said : "Washing with hot water takes less, but much more than 1L."

Section62

grumbler said:

Well documented that heating with electricity is more efficient? I don't think so. The boiler or the HW cylinder can be just few meters away.

Direct heating of water is close to 100% efficient.  That is well documented.  Heating only the water required is also well documented.

Leaving hot water in pipes to cool down, whilst having to heat the previously hot water which went cold, is well documented as a less efficient approach than directly heating the required volume of water within the appliance.

The money saving mantra is "only heat what you need".  Except in circumstances where timeshifting the heating and consumption to make use of cheap/free energy may save money.

Hence my comment about "Hot fill enables the use of stored hot water heated by solar or off-peak electricity..." (and not gas) because at the present time there are no (AFAIK) 'off peak' gas tariffs and it doesn't appear probable there will be.  If there were, I'd be happy to edit my post to include 'gas'.

grumbler said:

Well, switching to a two-rate tariff only for washing and dishwashing makes little sense for many people as you pay more during the day.

^Sweeping statement?  In reality, whether an off-peak tariff makes sense depends on many factors around the total amount of energy used, and the ability to timeshift.  There are lots of myths about how E7 only makes sense if you have storage heaters, but that isn't necessarily true.

Perhaps more importantly - given the OP is looking into the future - it is probable that multi-rate tariffs will become (virtually) compulsory for all.  One day people will need to get used to the idea of paying more for electricity used at times of peak demand, and less in times of excess generation.  In which case, appliances with hot-fill capability may make economic sense, even if they are less efficient.

grumbler said:

Well, houses aren't all the same. That's why I disagreed with the sweeping statement " The inefficiency of using hot+cold fill appliances (whether using stored or combi-heated water) is well documented."

The statement is true though.  You can't get more efficient than 100%. Having the water storage or combi boiler closer to the appliance will reduce its inefficiency, but it cannot be more efficient than having a heating element in the appliance directly heating the (small) volume of water the appliance is using.

There is perhaps some confusion here between "efficiency" and "economics". If you need to run a washing machine during the day then based on current SVR rates, a gas combi boiler right next to a hot fill washing machine may be the cheapest overall way of doing the washing, but not the most efficient.

grumbler said:

Also, those with combi boilers who are very keen on saving energy can run a 10mm plastic pipe from the boiler to their WM and DW. This more than halves the volume. BTW, a kitchen tap doesn't need a big flow of hot water either (unlike a bath or a shower).

Again, this will reduce the inefficiency of the external-heating method, but it still won't equal the efficiency of directly heating the water inside the washing machine/dishwasher.

FFHillbilly

Section62 said:

grumbler said:

Well documented that heating with electricity is more efficient? I don't think so. The boiler or the HW cylinder can be just few meters away.

Direct heating of water is close to 100% efficient.  That is well documented.  Heating only the water required is also well documented.

You can't get more efficient than 100%.

you can get more efficient than 100%, heatpumps can acheive average effifiencies of 3-400%.

also it's not all about the efficiency, cost of the fuel comes into it.
heating water with resistive electric element (100% efficient, 35p/kwhr) would equal 35p to put 1kw of energy into a body of water
heating a cylinder of hot water with gas could be around 80% efficient, and gas costs 10p/kwhr. so as an example if you put in 3kw of heat, you loose 20% and you still have 2.4kw of energy in the water and it only cost 30p. so thats more energy for less money compared to resistive electric heating

so in the near future when heatpumps take off, why would you want to use resistive electric heating thats only 100% efficient when theres a cylinder of water available thats 300% efficient?

Section62

FFHillbilly said:

also it's not all about the efficiency, cost of the fuel comes into it.
heating water with resistive electric element (100% efficient, 35p/kwhr) would equal 35p to put 1kw of energy into a body of water
heating a cylinder of hot water with gas could be around 80% efficient, and gas costs 10p/kwhr. so as an example if you put in 3kw of heat, you loose 20% and you still have 2.4kw of energy in the water and it only cost 30p. so thats more energy for less money compared to resistive electric heating

Which I addressed in my previous posts.

Your calculation also only holds true if you are paying 35p /kWh for electricity.  As I pointed out, some people are paying 11p (+VAT) /kWh or less.  If a unit of electicity costs 11p and close to 100% of that goes into making the water hotter, why would you pay 10p/kWh for gas and throw 20% of that away in losses?

The issue for this thread is that storage of hot water heated when energy costs are at (daily) lows is likely to be cheaper in the future than instantaneously heated water (by gas or electicity), and if that is the case then appliances with hot fill capability look better than they have in the last few years.

FFHillbilly said:

so in the near future when heatpumps take off, why would you want to use resistive electric heating thats only 100% efficient when theres a cylinder of water available thats 300% efficient?

Who has said anybody wouldn't?

As I said "Hot fill enables the use of stored hot water..."

With hindsight I regret not including all the other possible sources of heat (including nuclear fusion perhaps?) rather than keeping it simple and mentioning some of those already commonly used, namely "...heated by solar or off-peak electricity".

diystarter7

Hi OP

Another excellent thread by a top flight, good poster

When I read the title, I thought surely not.

However, reading you post and a few others, IMO it will come back and is but not like the old days

Thank you again for a puka thead

anon_ymous

diystarter7 said:

Hi OP

Another excellent thread by a top flight, good poster

When I read the title, I thought surely not.

However, reading you post and a few others, IMO it will come back and is but not like the old days

Thank you again for a puka thead

I've got an update for you. I accidentally found this on AO

https://ao.com/product/bden38560chpa-beko-heat-pump-standard-dishwasher-black-101466-23.aspx

So it seems hot water fills may not make a comeback given they've basically put the heat pump at the "source" instead of having that water transported via said heat pump. This is probably better than filling a washing machine (or in this case a dishwasher), with hot water from a heat pump that might be a few metres away. That's kinda cool