this post was submitted on 22 Nov 2023
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I have a Sanco2 heat pump water heater. The heat pump is located outside the house, with the tank in the basement (so no noise!). It is so absurdly efficient that I thought I was measuring the power draw wrong. Its expensive up front, but a big fat govt tax credit sure helped and the monthly power cost is about the same as my coffee maker.
The tank inside is 83 gallons. I can run the dishwasher, two showers, and anything else I can imagine and it handles it like a champ. The heat pump heats the water so fast that it refills it in minutes, not hours.
And since there's no element or anything in the tank, there's virtually nothing to break or fix in it. Nothing to rust, no joints to go bad. The tank is constructed solely for water in and out via pump and that's it. It looks like a military designed tank because there's no reason not to fortify it to last forever. So they did.
Between that and my induction range and heat pump AC/furnance, we turned off our natural gas connection. I love love love all of them.
Oh, you Americans with your hot-water dishwashers! ❤️
Wait, are hot water dish washers not a thing outside the US?
I think it's everywhere but in the US the water comes already hot, in Europe the dishwasher heats it up from the regular cold water.
Yeah the hot water way seems better.
It's because our dishwashers are massively more efficient and environmentally friendly.
They use very little water, which they heat up themselves to save energy
The only drawback is they take longer to clean the dishes, up to three hours
But nobody would be so selfish as to demand their dishes be done quickly over preserving our environment, would they?
Why would that save energy? It's going to be resistive heat, which at best matches the water heater. Some models in the US include a heating element, but it's more of a convenience. The vast majority are simply connected to the hot water line, since that's why it's there.
Also, let's talk numbers. From what I could Google, EU dishwashers use 1-1.5KWh/load, while US dishwashers use an average of 1.15KWh/load. Certainly there are more efficient models, but this shows that there isn't a significant difference in energy usage between them.
your energy calculations are forgetting the energy cost of the pre-heated water, it's the appliance equivalent of an offshore tax haven!
Do European homes not have hot water heaters?
They do, they're just not connected to the dishwasher so don't need to be factored into its energy usage.
Your system - Add cold water to water heater and heat (using energy). Keep at required heat until needed, could be a whole day or more (using energy). Pump hot water through cold pipes to dishwasher, losing energy. Reheat (using energy)
Our system - add cold water to device directly. Heat (using energy)
I couldn't explain it any clearer so I'll fuck off now
Your criticism is accurate in terms of thermodynamic efficiency, where we have to account for all energy entering and leaving the system.
But we are talking about economic efficiency, where we only count the energy passing through the wires. In the context of a thread on heat pump water heaters, the distinction is important: heat pumps use a small amount of electrical energy to scavenge a large amount of thermal energy from the environment. Thermodynamically, we have to count that energy; economically, that energy is "free" for the taking.
I have never heard of a "heat pump dishwasher"; the dishwasher is using a resistive heat source, and not the "free" energy from the environment.
When you understand why heat pumps are commonly 200% to 300% economically efficient (without breaking the laws of thermodynamics or becoming perpetual motion machines), you will understand why heating cold water in a dishwasher can be less efficient than heating it in a water heater.
I'm confused, our as in European dishwashers are more efficient and environmentally friendly?
But wouldn't it be even more so if the hot water that was stored and not being used was the feed instead of cold water? That was the temperature increase is minimal and a lot more efficient.
The eco wash is the best wash on my dishwasher.
It has nothing to do with energy efficiency, and everything to do with UK plumbing. A building's hot water system is presumed to be subject to environmental contamination, and not considered potable. Only the cold water supply is considered potable.
It's the same reason why they have separate taps for hot and cold water, while the US uses mixing taps almost everywhere.
No.
The reason your dishwashers use cold water is because your hot water supply is not presumed to be potable water.
EU regulations allows for gravity-fed hot water tanks in certain jurisdictions, open to atmospheric pressure, and thus possible contamination. They did this to prevent the possibility of exploding boilers.
Since the building's hot water supply is presumed unsafe, dishwashers are required to use the safe, cold water supply to generate their own safe, hot water.
US regulations do not allow hot water to be held at atmospheric pressure. We use T&P valves to limit boiler pressures and prevent explosions. Our hot water is not exposed to environmental contaminants, and is presumed potable.
Ha ha ha that's about 50 years out of date bud 😂
It may be 50 years out of date now. It wasn't 50 years out of date when dishwashers became common and the standards were established.
It depends. Spraying your dishes with water that is prone to legionella doesn’t seem super safe to me. But even assuming that, I have dishwasher programs than run at 70C, which is above what my hot water tank produces.
Besides, isn’t there a heating element in a US dishwasher regardless? Otherwise, it feels like it has got to continually add more hot water to keep the temperature up…
That is the real reason why UK / EU dishwashers use the cold water supply. They don't consider a building's hot water supply to be potable water. Their hot water was once held in atmospheric pressure, gravity-fed tanks, exposed to environmental contamination. Brits treated central hot water as unclean. This is also why they often used separate taps for hot and cold water. If they need clean, hot water, they heat cold water at the point of use.
The US never allowed atmospheric pressure hot water tanks. Our hot water is not exposed to environmental contaminants, and is presumed potable.
As a Dane living in the U.K., I agree. I’d never seen an atmospheric pressure water system growing up but coming here, that seemed the norm. Now, 20 years after, the norm in U.K. new installation is high pressure water systems (so called “system boilers”) so it is changing slowly. But in the U.K. they have an almost mortal fear for high pressure systems, thinking they’ll explode at any moment.
I believe it's mostly due to not having always hot water hookups available where laundry would be or not consistently having hot water always available. (as in on demand, from a large boiler that wouldn't impact the remain of the hot water uses)
Yes in many places, hot water is produced on demand in smaller residences. This means your dishwasher relying on hot water would kill your shower.
I know this seems odd probably to Americans … but many houses in the U.K. doesn’t have the space for a hot water tank.
I'm intrigued- does that mean the UK uses "tankless" water heaters, at least in smaller residences? Are they underspecced that they can't handle a shower at the same time as a (typically) 3.5 gallon dishwasher?
Speaking for The Netherlands here, but I believe our situation is very similar to the UK in this regard. A lot of houses are equipped with a gas-powered tankless heater which supplies both central heating and hot water. These come in various sizes and output capacities, so you can install one which comfortably suits your needs. Using hot water for multiple things at once shouldn't be an issue if you have the right heater installed.
Same in the U.K. Although my experience is that you’ll have to have a gas boiler with some buffer (40L say) to not experience a pressure drop of hot water when somebody else washes their hands. It doesn’t matter how often I’ve heard a plumber say “you won’t feel the pressure drop with this bad boy installed”; you always feel it.
In the UK your dishwasher is typically connected only to the cold water intake, so that's not a problem unless you have multiple showers in your house... that said, water heaters are often limited to either heating or hot water (not both at the same time), but that's not an issue in practice since you're not going to be using the hot water for long periods of time.
That seems way less efficient and more prone to issue than just having a central appliance that’s responsible for making hot water.
It is, but the dishwasher has to have a water heater in it. It has to heat water to a temp that you shouldn't keep you got water tank at and heats throughout the cycle.
Your clothes washer (generally) also has a built in water heater.
My tank is 60° and my washing machine is 40° and dishwasher is 70° at a maximum. A lot more efficient to have a hot water feed to these that have them increase the temperature 30-50°.
In most places in Europe, hot water that’s been stored is treated with some suspicion. Besides, having a heating element is probably the least error prone thing you could make.
That probably means that the hot water tank needs to be larger though. Guess it depends on the heating source though
Do they not have mixing valves where you are?
Genuinely for the longest time you'd only ever see mixer taps at a kitchen sink, they were not allowed anywhere else for fear of stagnant hot water contamination.
They really help conserve water compared to hand-washing. Important with the many relatively dry arid places in the south and west of the US.
Oh yeah, I’m with you that dishwashers conserve water. I was making a playful remark that in Europe, the dishwasher takes cold water and heats it up itself, not arguing for or against dishwashers as a concept.
Awesome. I so wanted the Sanco2 but the price put it out of reach, and we don't use enough hot water toake the payback remotely reasonable. For anyone else reading, it's an R744 (CO2) refrigerant system that's massively better for the environment than HFCs (and HFOs) as well.
I've never heard of this brand before but I love that the heat pump is on the outside of the house.
They forgot the best part. That model uses CO2 (it's in the name), instead of older HFC (or very ancient CFC) based refrigerants.