After a day of work, when you come home in the evening, you can hide in the bathroom and wash off your tiredness, which is a very pleasant thing for contemporary migrant workers.
But reality always backfires.
You feel that the water temperature of the shower is a bit high, and you turn the handle slightly, but you are inexplicably poured cold water on your head;
Your parents are washing vegetables in the kitchen, and as soon as the kitchen faucet is turned on, the temperature of the shower water rises sharply, and you almost scream like a pig
The leisure mood of taking a bath is completely destroyed, and you can't help but shout loudly**, why is the temperature of the bath water always hot and cold?
In fact, the sudden change in the temperature of the water heater is often inseparable from your own operation.
Generally speaking, the water heater valves used in the bathroom at home are all mixed water valves. The mixing valve has three openings, which are connected to the hot water outlet, the cold water inlet, and the water outlet. When we open the valve, the cold and hot water can be mixed at our own adjusted mixing temperature to become the bath water that is sprayed in the shower at a moderate temperature [1].
The red and blue outlet pipe is the standard configuration of every household water heater.
When we turned the valve to adjust the water temperature in the bath, the old water in the water valve pipe had not yet been used up. It is only when the old water in the pipes is drained and the regulated water flow is injected that the temperature of the bath water really changes [2].
There was a delay [2]. And we often think that we are turning the valve at too small an angle, so we continue to twist the valve and put in more hot or cold water. When the old water in the pipes is drained and the new water arrives, it will naturally be scalded or frozen.
Another reason that can make you feel like a sudden change in the water temperature of your water heater may be related to your own psychological factors.
Psychophysicist Stevens argues that there is not a simple linear relationship between the intensity of external stimuli and the intensity of human sensations [3].
When adjusting the temperature of the faucet, even if the angle of rotation of the faucet handle is intentionally controlled, the user's perceived feedback on the water temperature does not change in the same amount as the water temperature increases or decreases [4].
In general, when the human arm is subjected to thermal stimuli that exceed the critical temperature171 , our mental perception of this heat is significantly higher than the temperature of the actual stimulating arm [3]. The temperature of the bath water is generally between 35-40, and when the water temperature is suddenly turned up in the shower, the "hot" you feel is just the psychological feeling you feel when you face the temperature stimulation.
When you are shocked, the intensity of your sensations also grows much faster than the physical intensity of the shock.
If the bath water becomes too cold or too hot when you adjust the valve yourself, you can still be a little mentally prepared. But if your mother suddenly turns on the kitchen faucet, you are standing under the shower, and you suffer a real "unwarranted disaster".
In order to save costs and facilitate maintenance, the water supply system in residential areas mainly adopts the control method of one frequency converter to control multiple pumps. When one of the users turns the faucet on and off, the water system redistributes its own flow, affecting the change in water pressure [5].
If you are using cold water in your kitchen, the water pressure of the cold water outlet of the mixing valve will drop accordingly under the condition that the municipal water supply pressure remains unchanged, the cold water flow will decrease, and the temperature of the mixed water will rise suddenly, making you scream when you are taking a bath.
The academic community has long noticed this defect of the old mixing valve, and has developed a thermostatic mixing valve, which has been widely used in various electric heating products.
The thermostatic mixing valve contains a temperature sensor, which can monitor the water temperature at the outlet in real time, and feed this monitoring signal back to the valve controller, which adjusts the water flow so that the water flow is always maintained at a constant temperature [6].
Thermostatic mixing valves are not only used in water heaters, but also in household faucets.
However, if you want to adjust the amount of water and the water temperature at the same time, you need to rotate two valves separately after installing a thermostatic mixing valve, which is very inconvenient to use for public faucets or showers, so it is difficult to popularize.
Since manual adjustment is so troublesome, is it possible to switch to an electric water heater with self-regulating temperature once and for all?The answer is that even so, you still can't escape the fate of being burned or frozen.
This type of electric water heater generally uses a temperature controller to regulate the water temperature. A temperature controller is an electronic component that can adjust its heating power to maintain the water temperature at a user-adjusted temperature by adjusting its heating power [7].
However, the temperature controller itself has a reaction delay, which makes it impossible to adjust the power according to the amount of water in the first place[8], and it is often too late for the warm water to meet your expectations until you have been scalded or frozen.
Instantaneous electric water heaters may be affected by water pressure, delay, etc., and it is difficult to fully meet the constant temperature needs of users.
For social animals, bathing is a rare moment to decompress, which can not only cleanse the skin, but also relieve mental stress [9]. However, according to an industry research report, in 2022, more than 30% of consumers believe that hot and cold water temperature is the main problem of water heaters today[10].
Hopefully, one day, you will be able to take a hot bath without being burdened by the hot and cold water temperatures.
Written by Xia Chunhua
Article**: The answer is as follows.