"Care about underfloor heating? Easily install underfloor heating"
Figure 1: Network
?Definition
Psychrometric Enthalpy Diagram: A line diagram showing the relationship between air parameters.
The enthalpy-humidity diagram is like a dictionary You can search the word (other air parameters) based on the pinyin (a certain parameter).
? Some air parameters
Dry bulb temperature (°C): called temperature, it is the temperature generally measured by the temperature.
Moisture content (g/kg): The mass of water vapor in humid air that coexists with one kilogram of dry air.
Usually there is water vapor in the air, so it is humid. Humid air can be divided into dry air and water vapor.
Relative humidity: percentage of water vapor pressure and pressureof saturated water vapor in the air at the same temperature.
A cubic meter of dry air can “drink” 10 g of water. Now he only “drinks” 5 g, so the relative humidity is 50%.
Enthalpy (kj/kg): How many kilojoules of energy are contained in one kilogram of matter.
This can be simply understood as generalized internal energy, which corresponds to the amount of energy that the air contains.
Heat-moisture ratio: The ratio of the change in enthalpy (△h) to the change in moisture content (△d).
The ratio of changes in heat and moisture content.
?Contour lines
Figure 2: Mu Youcun
< p > Isothermal: The temperature on the line is the same. Its parallel lines are also isotherms.
At the same temperature, the higher the moisture content of the air, the higher the relative humidity and the valueenthalpy are high. (Non-horizontal)
Isoenthalpy lines: The enthalpy values on the lines are the same. Its parallel lines are also isenthalpy lines.
For the same enthalpy value, the air temperature increases and the moisture content decreases.
Isohumidity lines: lines with the same humidity. Its parallel lines are also equal humidity lines.
For the same moisture content, the lower the air temperature, the lower the enthalpy (energy).
Equal relative humidity lines: The relative humidity on the lines is the same. Its parallel lines are also lines of equal relative humidity.
For the same relative humidity, the higher the air temperature, the higher the enthalpy (energy).
?Small application
Dew point temperature: the temperature at which the vwater in the air turns into dew drops. The temperature at point A in Figure 2 is 35 °C, the relative humidity is 100%, the enthalpy value is 130 kj/kg, and the moisture content is 36.6 g/kg.
Figure 3: Mu Youcun
If the temperature drops to 30 ℃, the moisture content and pressure of the 'air will remain unchanged. Point A reaches the state of point B (virtual point). At this time, the relative humidity is greater than 100%, and the excess water will condense from the gas state into water droplets until the relative humidity is less than or equal to 100%.
At this point you should be able to understand the enthalpy-humidity diagram, let's try again.
?Wide application
Example: The use of air conditioners in winter and summer corresponds to changes in enthalpy - humidity diagram.
Figure 4: CVC girl
Point A: A room withouts air conditioning in normal summer, temperature: 30℃, relative humidity: 60%, moisture content: 13.6g/kg.
A → C (domestic air conditioning cooling line in summer)
The moisture content becomes smaller: people and objects inside the room "vomit" "Water vapor coming out＜Air conditioner outdoor unit exhaust
The enthalpy value decreases: the heat emitted by people and objects in the room If the room is too large or if the window is open , the top may be too big and the room will not be cool Decreased temperature: Decreased enthalpy means the air has less heat. energy and the temperature is lower Relative humidity increases: the lower the temperature, the less the air wants to “drink” water. At point A,air can “drink” 3 g of water, air contains 1.5 g of water and the relative humidity is 50%. At point B, after cooling, only 1 g can be “drunk”. The drain pipe discharges another 0.8 g, leaving 0.7 g, and the relative humidity is 70%. Because the air has a low desire to "drink" water, it is generally not too dry when the air conditioner is turned on in summer. Figure 5: HVAC girl B → D (Home air conditioner heating line in winter)
Enthalpy increase: room loss Heat < The heat added by the air conditioner
If the room is too big or if the window is open, the upper temperature can be higher than this and the room will not heat up.
Increase in temperature: the air is heated, the energy increases and the enthalpy value becomes greater.
Increase in moisture content: asAs the temperature increases, the air has a greater desire to "drink" water and continues to absorb moisture from the air.
Relative humidity decreases: continuously "drinking" water in the air still cannot satisfy the desire to "drink" water which increases significantly as the temperature increases, and the air is still "thirsty".
The numerical example can be seen as the process going from B to A. Because the air is constantly "drinking" water, it will be very dry when the air conditioner is turned on in winter. You can put a basin of water in the room and let the air "drink" the evaporated water in the basin. instead of water on our skin
There should be an advertisement here: "Why do we need underfloor heating when we have air conditioning. ?" 》^_^
?Extended knowledge points
?Wet bulb temperature
Compared to the temperatureerasure of the dry bulb. Simply put, the wet bulb temperature is the lowest temperature that the current environment can reach simply by evaporating water.
Figure 6: Baidu Encyclopedia
?Enthalpy formula
< p > An important state parameter that characterizes the energy of a material system in thermodynamics. The thermodynamic energy of the system is added to the photovoltaic energy.
H=U+PV
H represents enthalpy, U represents internal energy, P represents pressure and V represents the volume.
?Absolute humidity
Under standard conditions, the mass of water vapor contained in each cubic meter of humid air, which is the density of water vapor, the unit is g/m?.
? Sensible heat and latent heat
Figure 7: Network
< p> Sensible heat: The heat required to increase or decrease the temperature of 'Aobject without chemical change or phase change is called sensible heat.
The heat absorbed when water at 50°C is transformed into water at 90°C is sensible heat.
Latent heat: refers to the heat absorbed or released by a substance when it passes from one phase to another under isothermal and isobaric conditions.
100℃ of water becomes 100℃The heat absorbed by the water vapor is latent heat.
? Pay attention to the small dots
Figure 8: Network
1. The empty saturated line is the relative humidity line equal with 100% relative humidity. Features: Dry bulb temperature, wet bulb temperature and dew point temperature are equal.
2. The temperature line of the isothermal bulb is basically parallel to the equal enthalpy temperature line, so in engineering, the enthalpy lineequal is approximately used in place of the equal wet bulb temperature line.
3. The constant moisture content line is the constant dew point temperature line. Because the definition of dew point temperature indicates that the state point has the same moisture content, the dew point temperature is the same.
?How to find dry bulb temperature, wet bulb temperature and dew point temperature on enthalpic psychrometric chart
Figure 9：Network
?How each function of the air conditioning unit is reflected in the enthalpy-humidity diagram (Figure: Network)
Questions additional^_^< /p>
Known conditions:
1. Suppose that an air state point A be known. The dry temperature at point A is. 20°C and the relative humidity is 60%.
2. When the air absorbs heat frome Q=10000KJ/h and a humidity of W=2kg/h. The air therefore changes and becomes state point B.
3. The enthalpy value after change is 59 kJ/kg.
Figure 10: CVC girl
Parallel line solution:
< p > 1. Find the initial air point A on the enthalpy-humidity diagram
2. Heat-humidity ratio ε=Q÷W = 10000Kj/h÷2Kg/ h=5000, and Draw a line L through point A parallel to the line with a humidity/heat ratio of 5000.
3. Find the isenthalpy line with a enthalpy value of 59kJ/kg The intersection with line L is point B.
Key points: The heat-humidity ratio line must be the line connecting the initial state point A of the air to state point B after air treatment.
END
Further reading:
100 questions on new underfloor heating (Collector's Edition)
Whatdegree should the underfloor heating be adjusted?
How much does it cost per month to turn on underfloor heating 24 hours a day?
With a constant temperature of 20°C and monthly heating costs of 300 yuan for 300 square meters, can you believe it!
Water flow is directly related to water pressure and water resistance. The faucet is nothing more than providing water resistance.
Blocking the faucet with the hand actually increases the water resistance, but the mechanical structure of the hand cannot guarantee that this resistance is smooth and precise, so the water cannot not flow drop by drop.