Dishwasher power consumption when connected to hot vs cold lines?

[Lee2]

Does anyone have detailed data comparing the two. On my Sonoff 63a I can see the dishwasher uses 0.7kWH per wash on eco mode

How would that change if i fed it from a hotwater line?

My washing machine used 0.2kwh on 30 degrees, a dishwasher seems way more energy inefficient given it only needs 10l of water and a washing machine around 50 iirc

[Scorp007]

17 hours ago, Lee2 said:

Does anyone have detailed data comparing the two. On my Sonoff 63a I can see the dishwasher uses 0.7kWH per wash on eco mode

How would that change if i fed it from a hotwater line?

My washing machine used 0.2kwh on 30 degrees, a dishwasher seems way more energy inefficient given it only needs 10l of water and a washing machine around 50 iirc

The dishwasher will be better I guess. Some 8+ litres of the hot water from the geyser will be cold and would still need heating. 

[Lee2]

21 minutes ago, Scorp007 said:

The dishwasher will be better I guess. Some 8+ litres of the hot water from the geyser will be cold and would still need heating. 

As in even if you fed it from the hot line the water in the pipes would still be cold and by the time it has pulled in 8 liters it has only just gotten warm?

i.e a waste of time?

[Bobster.]

18 hours ago, Lee2 said:

Does anyone have detailed data comparing the two. On my Sonoff 63a I can see the dishwasher uses 0.7kWH per wash on eco mode

How would that change if i fed it from a hotwater line?

My washing machine used 0.2kwh on 30 degrees, a dishwasher seems way more energy inefficient given it only needs 10l of water and a washing machine around 50 iirc

So many variables. Is the washing machiner a top loader or a front loader. Front loaders take a lot less water, thus there is less water to heat.

New appliances, last couple of years, are very efficient.

In this case your dishwasher is going to use a bit less because it won't have to do so much heating of the water. It will still do some. Or mine would. My heat pump won't go past 60 degress, the dishy wants 70. And as already pointed out, if the dishy was pulling from the hot water line, the water wouldn't be at geyser temperature anyway. 

This also would mean there's a bit more heating up to be done in the geyser which has now let some more cold water in. But surely heating 9l (or whatever) of water takes the same energy as heating 9l of water?

I run our dishwasher during the day so it gets powered by the panels. Like yours it uses less than 1 kWh of power in the eco mode (I did measure it with a Kill-A-Watt, it actually uses less than the manufacturer claims). Given that it uses that power over a 3 hour cycle (if I got for the most eco of all the modes), so this really isn't a big deal. It also uses about 9l of water, also not a big deal.  If I lie awake at night, I don't spend time pondering this point.

 

[Eugenevz]

26 minutes ago, Lee2 said:

As in even if you fed it from the hot line the water in the pipes would still be cold and by the time it has pulled in 8 liters it has only just gotten warm?

i.e a waste of time?

Not have data points, just personal experience from a few years back and the electricity bills. Dish washer alone will be more efficient as it takes less energy to warm up a smaller amount of water, regardless of how inefficient your dishwasher is. The issue with drawing water from the geyser is that the temperature will not be a guaranteed say 50C (50C is my dishwashers eco mode) as you will be hard pressed to time your dishwashing for exactly after you geyser completed heating. So what will happen in most cases is you will be drawing water from your geyser which will be heated again by the dishwasher and will result in your geyser needing to heat up sooner to replace the lost heat.

All in all better just to let the dishwasher heat it up on its own, or better yet...although for most a big no no, handwash you can save between 1kw and 2kw a day by doing so.

[Bobster.]

11 minutes ago, Eugenevz said:

All in all better just to let the dishwasher heat it up on its own, or better yet...although for most a big no no, handwash you can save between 1kw and 2kw a day by doing so.

But you will consume more water. My dishy on eco mode uses just 9l of water for a full load. You couldn't do that washing by hand.

[Eugenevz]

On 2023/10/19 at 10:53 AM, Bobster. said:

But you will consume more water. My dishy on eco mode uses just 9l of water for a full load. You couldn't do that washing by hand.

You can, recent randburg water issues proved that....well it was 10L...just not a great way of washing dishes. So yes, its one of those it depends things, i found that the more people you are in a house, the dishwasher turns out to be a better option, or if you are less people and only put it on once it is full. But for our 2 people in the house usage scenario the once a day washing dishes works out great. But all of this doesn't matter if you have your dishwasher running off solar

[Bobster.]

2 hours ago, Eugenevz said:

You can, recent randburg water issues proved that....well it was 10L...just not a great way of washing dishes. So yes, its one of those it depends things, i found that the more people you are in a house, the dishwasher turns out to be a better option, or if you are less people and only put it on once it is full. But for our 2 people in the house usage scenario the once a day washing dishes works out great. But all of this doesn't matter if you have your dishwasher running off solar

I used to look at the dishwasher as a wasteful luxury. Maybe they once were. I recall friends who had them 20 odd years ago having to rinse off the dishes before putting them in the washer - which meant that you'd already used a fair bit of time and water before you turned the thing on. I used to think that well, for only a little more effort you could have cleaned the plates and the cutlery anyway and wouldn't have to run the washer.

But with modern units you just scrape off the big bits of waste. So we just put everything in the dishwasher now (big bits scraped off) and run it's when it's full and when the sun is up. It runs nearly every day, and we always use the eco mode. So 9l per day for dishes, and I can easily run it off of solar as it's less than 0.9 kWh for the whole cycle.

The 9l is claimed, or is what the test lab in the EU found. I know that when I bought this unit I checked all the labels and they were reporting useage to 0.1 of a liter. The one we bought (Smeg) had the lowest figure, but it was close run - most of them were 9.something. Also when I ran the machine through a Kill-A-Watt it came in at less than the claimed energy use figure, so I don't think they are sucking figures out of their thumbs.

The Smeg is rated A++ on the SA system. We used to piggy back off the EU ratings, but they've shifted the goal posts and that A++ unit now gets a C over there, because they want to be able to start setting new targets for A, A+ etc.

[Paulcupine]

There's a whole school of thought on the two dishwasher system in modern kitchens now.  Dishwashers are remarkably space efficient in how much you can store in them.  It turns out it actually makes sense to give up the cupboard space.  You pack one dishwasher with dirty dishes until it's full, then run it.  You use the clean dishes from the one dishwasher and pack them directly into the other one when used.  When it's full then you run that one etc.  Some small amount of dishes still get stored in the cupboard - perhaps only the last few before you want to start packing the not quite empty dishwasher again.

[Yuri]

I have a LG 14 years old

l always wash on intensive wash using 1.29 to 1.47KWh per wash

It is doing 3 heat cycles in operation 

[Paulcupine]

On mine the three heat cycles are main wash, rinse and dry.  It does not heat water for the prewash.  The "eco" cycle uses only 0.7kWh and only heats the water to about 50C, but it runs for nearly 5 hours.  We nearly always use this cycle.