I have a question regarding the CBE comfort tool and the input for operative temperature . I have measured data for globe temperature in a room . Can I use that data as the operative temperature value in the CBE tool ? My understanding is that both metrics are similar but I am not sure they are interchangeable . Is that technically appropriate ?
Operative temperature and globe temperature are two different parameters and cannot be used interchangeably. The globe temperature is a measured variable that is used to estimate the mean radiant temperature. The mean radiant temperature and the air temperature can then be combined to calculate the operative temperature. The equations to derive the operative temperature are quite simple, however, to further simplify the calculation of the mean radiant temperature, we have included the Globe Temperature tool in the CBE thermal comfort tool.
Please follow these steps to calculate the mean radiant temperature:
In the ASHRAE-55 page please select the psychrometric (air-temperature) chart from the drop-down menu above the chart.
Click on Globe temp and enter all the required variables. If you did not measure air velocity and the air in the space was still you may assume that the air speed was equal to 0.1 m/s or less.
Click on set mean radiant temperature.
You can now calculate the operative temperature for occupants engaged in near sedentary physical activity (with metabolic rates between 1.0 met and 1.3 met), not in direct sunlight, and not exposed to air velocities greater than 0.10 m/s (20 fpm) with the simplified equation provided in the Operative temperature - Wikipedia page
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I am a beginner on modelica. I wanted to transpose a model found on a paper (on internet) to a modelica model.
Here is the paper :
Insulated Cable Temperature Calculation and Numerical Simulation
I am stuck in rewritting the fomulas. Second derivative on a variable different of time --> i don't know how to do.
Another way I was thinking is to use the Thermal/HeatTransfer library. But here too, I don't know how to put the blocks togethers... I think this is due to a big lack in thermodynamic knowledge from my side.
--> I don't know what block to use to simulate the conductor and the insulation layer.
Maybe this is something too difficult ?
If someone has an idea on how to start, it will be a pleasure to read you :)
I tried to use the Thermal library :
Using heat transfert lib.
I have a current source and a resistance.
The resistance will change depending on the temperature involved by the current in the resistance.
I use 0.004 as alpha for the relationship R=R20*(1+alpha(T-Tamb)).
Let's say I have a 1 meter copper conductor with a crossSection of S=16mm² = 15.10^-6m²
then the initial resistance is R = rho.L/S ≃ 1.07mΩ at 20°C
Following this example of cable : Bayka 16mm²
To get 70°C at the surface of the conductor, then the max current for a single 16mm² wire cable is 107A in air, and 160A in earth.
I took, in my example, random value of thermal conductance and capacity to get an approximative temperature near the one given in the table (~70°C).
Is this model is the good one for an insulated cable ? (no considering values)
Or I forgot something? Maybe I am wrong in the position of the blocks ?
What do you think ?
Looks reasonable to me, might be easier to use the same component for heat conduction (heat resistor or heat conductance, not both) in order to be able to compare the two values. The mathematical formulas for radial heat conduction can be found here e.g. https://web2.clarkson.edu/projects/subramanian/ch330/notes/Conduction%20in%20the%20Cylindrical%20Geometry.pdf
Here what I am doing is that using the weather data as input parameter, if the global radiation is higher than 100 W/m^2 open the valve. First solar heat will be released to the hot water tank, and then the heat will be given to the Boundry_pT via heat exchanger. I want to see, how the temperature of Boundry_pt changes resp. time.
I also want to use water as Medium in the internal heat exchanger. For that I edited the text box in Medium in the heat exchanger, as Buildings_Media_Water. Is it correct? Otherweise how can I choose water as a medium in the internal heat exchanger?
It seems that you have two separate fluid-circuits, and you only have one expansion tank (the "exp" component - sorry if I don't have the right terminology).
That means that the flow becomes over-determined in the 2nd circuit - and the pressure under-determined. There are a number of ways of handling it - including adding an expansion tank.
I have accelerometer readings of three axis X, Y and z, will be getting data in a frequency of (62 records per second). Could you please suggest me how can I calculate the displacement.
Data in hand:
Accelerometer readings with respect to time.
Do I need to calculate the displacement using time domain data or need to convert into frequency domain. Which one will give a accurate results?
You can double integrate the acceleration vector over time to obtain the displacement. In theory this is a perfectly sensible solution.
But in practice, there will always be a component of g (acceleration due to gravity) acting on at least one of the axes all the time. Let's say you subtract the g component from your xyz vectors. The problem is that any slight error in readings (even off by a small order of magnitude) when double integration will lead to the error adding up over time rendering the displacement wildly inaccurate.
According to the integrated values, you will most likely see even an idle object fly off into space. You'll need an additional sensor to tell you the orientation - like a gyroscope, and have some point of reference (the Wiimote does this with an IR sensor).
This is primarily a time domain problem, but you could have a frequency domain stage where some amount of filtering is done to remove measurement error or process error.
tl;dr Positional tracking with acceleration sensors alone is a hard problem.
I'm using the program Dymola in this case. As you can see in the figure, we have our temperature goal (refTemp) and we are comparing this temperature with a temperature in the system(KvvTemp). Our goal is to differentiate these temperatures, then multiplying the difference with a small number so our value will become between 0-1 before entering the intergrator. Now to my question, how is it possible for the integrator's output to be the temperature we want to send in to the system (y1)? Is there any explanation on how it is possible to set the temperature that will enter the system(y1) through the intergrator?
I want to calculate the current passing in the wall socket using iphone.I am using CMMotionmanagerFramework and i got X,Y,Z values with that values i can calculate the magnetic field across the surroundings by using those values i want to calculate the voltage level of the wall socket. Please provide me the answer.
The magnetic field strength gives you the electric field strength in volts per meter, related to the velocity of the electrons. The velocity of the electrons is known as the drift velocity, and is related to the current. The electric field strength depends on the charge density in the wire, which should be a constant you can find for the wire you're using, and the distance from the detector to the wire.
So your magnetic field strength depends on a bunch of constants related to the physical arrangement of your problem and the current in the wire. You can derive that using your iPhone's magnetometer, knowledge of its accuracy and some maths. The voltage drop (potential difference) across the outlet is related to the current by the reactance, because you're probably looking at an Alternating Current system so inductances and capacitances play a role, in addition to the resistance.
However you probably don't need to calculate the potential difference, because the electrical utility company will tell you what it is.