Hello All,
I have to calculate the PMV for a zone and I did the analysis already in eQUEST. I need the mean radiant temperature though to perform this calc. I am pretty sure that MRT is not an output variable so I'm guessing I need to calculate the wall temperatures and do it myself. Has anyone tried to do this before? I didn't find anything in the archives or in the DOE22 manual. Thanks.
John Grando LEED AP
John,
I'm guessing you wouldn't be doing this analysis on a project unless you were concerned about thermal comfort issues from skin related stimuli.
So if you had a PMV of +4 in one zone and -4 in another would you say that on average everyone in your building is comfortable?
Calculating MRT in a lumped node simulation program is kind of like that - an average MRT for a zone is often misleading. For example - a room with a large west window in the summer time will have a much higher MRT for someone sitting next to the window than for someone sitting near an interior wall on the other side - especially if there is direct sunlight in the room. Similarly - in winter - proximity to a north window might result in a much lower MRT than for someone sitting near the core.
Bottom line - you pick the tool that's appropriate to the analysis. You really want a full-field solution tool (like a CFD program or a thermal software like RADtherm) to perform comfort analyses like this.
Vikram Sami, LEED AP
I read John's question as asking: can you get the MRT for each surface? - perhaps I misread it. I would assume, though, that if you could get it for each surface, than you could calculate the PMV of each zone. Your end result would show that zone A had -4 and B had +4 and they wouldn't be averaged together. This approach would understand and provide results that back up Vikram's point that a space near a fa?ade will experience different MRT than a core zone. Is that not possible in eQUEST?
Regards,
Alex Krickx
The surface property is really a surface temperature (not MRT). MRT is not really a surface property of a single surface - its the average of radiant fluxes acting on a point in space. The point is the fluxes are a result of the view factors (solid angles) of the surfaces from that point - which is precisely why you cannot have a single MRT for a zone.
Vikram Sami, LEED AP
Vikram,
Thanks for correcting me - I mixed up the terminology. I guess the point I was trying to make was, although MRT will vary throughout the zone at each point in space - is it unfair to take a representative point (say, at the center of each zone) and calculate the MRT at that point? In a perimeter zone during summer the MRT would be hotter closer to the window, and cooler closer to the core, so taking a central point would seem reasonable. What seems difficult to me would be to take the surface temperatures (which I am now assuming from your response we CAN retrieve from eQUEST), calculate the solid angles and figure out to automate the process for every zone...
I take your point that this is an average for the zone. My gut says as long as you're not averaging across a whole floorplate that this methodology would be sound. I don't mean to be contrary, I'm just interested in learning what the software is capable of.
Regards,
Alex Krickx
Actually - I don't know of a way to get surface temps out of eQUEST - I don't think there is an option in the hourly reports.
I could be wrong though.
Vikram Sami, LEED AP
I haven't found one yet but I did find the variable "unweighted heat transfer from wall to space". I just used the current zone temp and q = u*a*dt to find the wall temp. What do you think about that?
John Grando LEED AP