Save electricity and money by using gas heated hot water

[Deleted User]

Typically, the capped cost of 1kWh of electrical energy is £0.27 and set to rise further. Similarly, the cost of 1kWh of gas energy is £0.08 and also set to rise. Gas combi boilers heat hot water at about 84% efficiency whereas more up market boilers with an in-flue heat recovery system produce hot water at about 94% efficiency.

Appliances like dish washers and washing machines use cold water that must be heated electrically to the desired temperature. In this respect these heaters are an essential part of the machine. It is possible to change the role of these heaters from essential to include supplemental use.

Appliances come with an energy label  derived from complex criteria one of which is that the temperature of the incoming cold water is 15 degrees Celsius. In reality especially in cold weather the incoming temperature of water is 4 degrees Celsius. The efficiency of out of warranty or used appliances can be improved by using gas heated hot water at a temperature at or below 58 degrees Celsius.

Some physics: a Swiss based web site with equations has an energy calculator that determines the kWh required to raise water from one temperature to another. The energy required to raise 30L water from 4 degrees to 60 degrees Celsius at 100% (electrical heating) efficiency is 1.95kWh. For gas at 94% efficiency, it is 2.08 kWh.

 The costs are £0.27 x 1.95kWh = £0.53 for electricity and for gas £0.08 x 2.08kWh = £0.17 some 3 times cheaper saving £0.36 per wash.

Real world tests have shown that the temperature within the machine when the hot fill cuts off is around 40 degrees Celsius. The energy required to raise 30L water from 40 degrees to 60 degrees Celsius at 100% (electrical heating) is 0.7kWh (£0.19). For gas at 94% efficiency, it is 0.74kWh (£0.06). For a 40 degree wash no electrical water heating is required but for a 60 degree wash supplemental electrical heating is required.

The above assumes hot water is instantly available and a means of washing machine hot filling only for the first wash cycle with cold fill rinses for the rest of the cycle. Dishwashers just use hot fill, requiring some supplemental electrical heating depending on the cycle chosen.

A big question concerns the EU Energy Label system, is it another diesel-gate where testing is controlled to obtain the rating. Should they be using a cold-water temperature of 4 degrees Celsius to determine the energy label rating?

pochase

I have just checked and my cold water is 11.9 degree Celsius, this is much nearer to 15 degree than the 4 degree that you claim.
 
Where do you get your 4 degrees from, just checked and here they claim between 10 and 20 degree between winter and summer.

k_man

Most dishwashers and washing machines now only have cold feed.

As such, watering cans aside, gas heated water fill is not an option.

Also, when comparing gas heated water to direct electrical heated, the extra heat loses due to pipes from tank/boiler to tap, need to be considered.

victor2

k_man said:

Most dishwashers and washing machines now only have cold feed.

As such, watering cans aside, gas heated water fill is not an option.

Also, when comparing gas heated water to direct electrical heated, the extra heat loses due to pipes from tank/boiler to tap, need to be considered.

To add to that, most dishwashers also start by pumping out any water in there at the start of the wash, so the hot water you've just put in from your watering can will go down the drain and be replaced by cold.

pochase

Interesting article about hot fill washing machine here

https://www.whitegoodshelp.co.uk/is-hot-and-cold-fill-washer-more-economical/

It seems also that modern hot fill washing machines only will use the hot water for "very hot wash cycles". Makes sense as otherwise you might end up with 50 to 60 degree hot water for your 40 degree cycle and have ruined cloth.

FreeBear

pochase said:

I have just checked and my cold water is 11.9 degree Celsius, this is much nearer to 15 degree than the 4 degree that you claim.
 
Where do you get your 4 degrees from, just checked and here they claim between 10 and 20 degree between winter and summer.

From a Freedom of Information request directed at Severn Trent, they responded with a neat little graph...

https://www.whatdotheyknow.com/request/mains_water_temperature_and_heat

A seasonal variation of between 6°C to 18°C.

Gerry1

FreeBear said:

pochase said:

I have just checked and my cold water is 11.9 degree Celsius, this is much nearer to 15 degree than the 4 degree that you claim.
 
Where do you get your 4 degrees from, just checked and here they claim between 10 and 20 degree between winter and summer.

From a Freedom of Information request directed at Severn Trent, they responded with a neat little graph...

https://www.whatdotheyknow.com/request/mains_water_temperature_and_heat

A seasonal variation of between 6°C to 18°C.

Apart from a short blip in Feb 2015, 8°C to 18°C at the consumer tap seems more realistic.

QrizB

[Deleted User] said:

The efficiency of out of warranty or used appliances can be improved by using gas heated hot water at a temperature at or below 58 degrees Celsius.

This entire post needs to be tagged <citation required>.

It's full of unsubstantiated statements, assumptions and generalisations.

Also, I don't think I've seen a hot-fill washing machine in a decade or more.

Gerry1

I doubt that any worthwhile savings can be made by manually filling a washing machine with hot water.

It's probably programmed to start by pumping out any water in the drum, and modern machines use very little water except in the unlikely event that it's a top loader.  On mine the water level is so low that the door can be opened during the washing cycle, e.g. to add another item.

Effician

QrizB said:

Also, I don't think I've seen a hot-fill washing machine in a decade or more.

You can still buy them ,https://www.ebac.com/washing-machines/hot-fill-explained/

k_man

QrizB said:

[Deleted User] said:

The efficiency of out of warranty or used appliances can be improved by using gas heated hot water at a temperature at or below 58 degrees Celsius.

This entire post needs to be tagged <citation required>.

It's full of unsubstantiated statements, assumptions and generalisations.

Also, I don't think I've seen a hot-fill washing machine in a decade or more.

To be fair, the OP did state:
.... out of warranty or used appliances....