Your hot water setup might be costing you hundreds
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- Опубликовано: 6 фев 2025
- Some math:
3kW of electrical power means that the electrical resistance is going to draw 3000 Joules from the outlet every second and add 3000 Joules of heat to the water every second.
Increasing the temperature of 1 liter of water by 1 degree Celsius requires 4185 Joules, so if the faucet is running at 1L/min, the temperature will be increased by 43 degrees Celsius over the temperature that it entered the faucet at (3000J/s*60s/4185J), and if it's running at 2L/min, by 21.5 degrees Celsius
Unlike with showers, the exact temperature of hot water at sinks doesn't usually matter much, users are happy with anything with a "warm" feeling, which is anywhere between 30C and 42-ishC
If your tap water is coming from river capture like mine does, the temperature is going to vary wildly between summer and winter. For me, it peaks at 25C in summer, drops below 18C in late October, bottoms at around 1C in the coldest weeks and climbs above 18C sometime in April. 18C, as I've discovered experimentally, is most people's threshold for "too cold" if they aren't trying to economize, so in practice, people in my household just use cold water for almost everything when it's above 18C and hot water for everything when it's below 18C.
The electricity use of the faucet doesn't vary with the input temperature, it's either 0 when it's off or 3kW when it's on. The heat production doesn't vary either, so if you want to adjust the water temperature, you have to adjust the flow itself. If the input temperature is 1C, a water flow of 2L/min is going to yield water at about 22C, which isn't really warm, so if I want it at 35C, I'm gonna have to turn it down to about 1.2L/min. As I said in the video, you develop the muscle memory to do this very quickly and it all works a lot better than I expected.
So because the energy consumption varies only with operating time, despite the input water temperature varying wildly between October and April, the daily electricity consumption doesn't, according to actual measurements, because the number of minutes that the hot water is on each day is remarkably consistent. Hence my "200 "winter days" per year" estimate.
Again, much of this would not hold if you were using this device for showers, and if you look at similar devices that are actually designed for showers, usually called "power showers", they typically have more precise power control, with a 9kW power shower often being constructed of three 3kW heating elements that you can turn on and off individually, along with a precise flow dial, allowing you to set a precise and consistent temperature for the entire duration of your shower.
Finally, isn't the $160 per year value a bit high? Well, kind of. Remember that I live in Europe and we have a bit of an energy crisis, so saving a small amount of energy translates into saving a large amount of money. Probably cut that down to around $80/yr in normal times.
Thanks Michael a simple but important step. Well presented 👍
Giveth the affect on indoor air quality, I refuse to live anywhere that even has natural gas piped into it. Which, thankfully, most places where I live don't. This is a great innovation!
Very, very interesting. I wonder if this also exist for showers. That would be a game changer for sure, my dad currently use an electric heater but the only three places that really need hot water is the shower, bathroom sink and kitchen sink.
They certainly do exist- it is common for a long time London suburbs. For showers, not for sinks though:)
They do exist.
They exist. They are much more popular than gas heaters in Latin America, because of how cheap they are, and don't need the infrastructure of hot water pipes. They are quite good, I even had a gas heater in another house and ended preferring the electric one. the only problem they have is that they can work regardless of the quality of the electrical network of the house, wich is usually very bad. So they dim lights arround the house when they are used, and aren't as safe as they should, but that's not their fault, that's the network's fault
Makes sense, I anyway already put as much as possible in the dishwasher and frequently use boiled water from the water kettle,
so I barely use the hot water tap in the kitchen.
This is perfect for that little bit of hot water I sometimes use in the kitchen.
Thanks!
Good video, will investigate the electric tap options at my local hardware store.
Sounds neat! I wonder if they're available for North American 120v/15 amp outlets?
Does your grid support more than 1.5kW per appliance? If not it will probably work poorly.
I have one ,but the electric installation can't handle the 3 kWh .
Also,in winter ,water heat enough only at the expense of loosing pressure, which is not good for shower
3:00
couldn't you have a big one and a small one? in series?
also looked it up, ofc there are less hideous ways to have at source heating.
Nice videos btw
Do they make small ones? It's an interesting idea
Thanks for the kind words!
Love the idea. I have some long runs that would truly benefit in the dry western US. What is the make and model?
I can't tell you a brand, as they seem to be selling them under different brands in every country, although they're obviously all made in the same factory. Just check your local stores, or maybe online stores
What a joke, my tankless gas boiler Junkers zwb-24-de is 24kW but it can modulate into minimum od 3kW, thats what heats my water even though I have 16kWp of solar because I dont have room yet for hot water tank