PMV index depend on 6 factors: velocity, humidity, air temperature, mean radiant temperature, clothing insulation and metabolic rate. The first four can be found easily by, for example, using CFD. My doubt is how to fix the last two if I want to represent the iso-PMV lines.
Do I simply suppose a constant metabolic rate and clothing in the whole domain?
If I wanted to find thermal comfort of someone in a room, I would just do the average of PMV single point values in the space occupied by that person?
PMV algorithm:
PMV=(0,303e-2,1M)·((M-W)-H-R-Ec-Cres-Eres)
Where:
M: metabolic rate. INPUT
W: mechanical power. INPUT
H: heat exchange by convection. H=f(fcl, hc, Tcl, Ta)
R: heat exchange by radiation. R=f(fcl, Tcl, Tr)
Ec: heat exchange by sweating of the skin. Ec=f(M, W, HR)
Cres: dry respiration heat loss. Cres=f(M, Ta)
Eres: latent respiration heat loss. Eres=f(M, HR)
In which everything is INPUT except fcl, hc and Tcl. First two can be found directly using empirical equations and Tcl through an iterative process. This iterative is based on assuming Qcond_skin-clo=Qconv_clo-air+ Qrad.
I have the following two questions:
- Does it make sense to plot iso-PMV lines? By looking the algorithm it seems to me a whole body sensation instead of a single point property.
- How to find PMV value using numerical methods like CFD? Running a CFD code we get velocity, temperatures and humidity for single control volumes. So the only way to insert them in PMV algorithm is by doing an average of this properties surrounding the body, right?
I would appreciate any help or document in which these topics are explained in more detail.
Thanks in advance.
PMV (predicted mean vote) , as the name suggests is an index applicable to groups of occupants and should not be applied to individuals. This is the first consideration to keep in mind.
Iso PMV lines/surfaces may make sense if you are talking at the room scale - to figure out if there are pockets where occupants would be more uncomfortable than in the room in general
And again, even though physically, you can think of the model as being based upon heat balance of the whole body, yet, the conversion from heat load to PMV value makes the index inapplicable to individuals.
To the second question, it is indeed true that averaging environmental properties is the way out. However, if you are witnessing unexpected stratification or non-uniformity in the environment, it is suitable to consult the relevant standards and not depend solely on interpreting PMV values
First of all, thanks for your reply.
So then PMV can’t be calculated for one single person? I understand that if I wanted to do a field study it wouldn’t make sense to query only one person, but when we are talking about simulations it doesn’t seem a problem to me. PMV value is a direct result from an algorithm, so the number of people in which is applied shouldn’t affect. Notice that I am only talking about simulations.
In fact, by simulating you would only get an idea of global thermal comfort and how it is distributed over the room. Probably it goes against the concept of PMV but it’s a useful tool to have a global vision.
- The heat balance portion of PMV model is objective so you can apply that for a single person. However, the translation of a heat load on body to the PMV index is based on a statistical model which depends on average responses. So, you cannot evaluate the PMV value for a single or even 2-3 persons
- For the simulations, as I mentioned before, it makes sense to evaluate PMV for global conditions over different zones of the space you are modelling. However, since PMV is a steady state model, to ensure you do not have issues like stratification, radiant asymmetry, local draft, temperature change rates with time etc., causing discomfort, you will need to consult ASHRAE Standard 55 , or something equivalent, to make sure the conditions are within the recommended bounds
You can simulate iso-pmv lines by HoneyBee(grasshopper plugin) and also the Designbuilder CFD.
I think, you can use this website: http://comfort.cbe.berkeley.edu/
this website based on ASHRAE-55 and EN-15251
- Badges
- Science topic
- Similar topics
- Social Psychology
- Attitude