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Room tempearture calculation

Room tempearture calculation

Room tempearture calculation

(OP)
Does anybody know how to simulate the room temperature rise, without any air conditioning system, and given room heat gain from people, lights, equipment, fenestration and initial room temperature. I need to find out at what would be the room final temperature and how long it will take to reach this temperature.

RE: Room tempearture calculation

Heat in = Heat out + Heat stored

All you need know is the specific heat and mass of everything in the room and the building, and their starting temperatures.

Chop it up into what ever time slice suits your needs.

Eventually you will reach a steady-state condition where the the heat stored term goes to zero.  That temperature can be estimated by:

Tinside = (Heat in/UA)+ Toutside

Assuming of course that the outside temperature is kind enough to stay constant.

RE: Room tempearture calculation

As a civil I rarely need to use heat transfer but I'll take a stab anyway ...:)

Heat generated = heat transfered + sensible heat to objects & air in room/walls
(probably can neglect sensible heat unless there is a lot of mass in room/walls and the time aspect is critical)

-probably are standards for heat generation by people at rest
-lights, use energy output/wattage
-fenestrations (do you mean windows) - just include them with walls etc. in the heat transfer calcs.
-if you weren't looking at time, then would solve for inside temperature at which heat transfer rate = heat input.  But to determine time, will need to do a time step analysis.

RE: Room tempearture calculation

I saw somewhere once that the average sized person gives off 600 BTU/hr when relatively inactive, more naturally if active.  But I can't remember where I saw it and can't substantiate it.

The lights and appliances and equipment is easy because they all have ratings and their heat goes directly into the room.  Heat transfer through walls and windows, well you are getting into an area that is involved and has lots of variables.

rmw

RE: Room tempearture calculation

Try a thermo humidigraph for a couple of weeks when all systems are go and consult with management as to when the worse conditions happen

RE: Room tempearture calculation

Human basal metabolic rate (BMR) was given in my physiology class as 70 kcal/hr, which is roughly consistent with http://en.wikipedia.org/wiki/Basal_metabolism.  The 600 BTU/hr works out to be about 140 kcal/hr, which would be about double the BMR

TTFN



RE: Room tempearture calculation

Maybe that figure I quoted was for people who had just made a mad dash to get to the meeting.

rmw

RE: Room tempearture calculation

Well, 2xBMR might be considered a reasonable upper-end for determination of heat load:http://instruct1.cit.cornell.edu/Courses/ns421/BMR.html
The examples show "studying" at 1.7xBMR for a 1.75 lb person, making 2xBMR a reasonable design point.

TTFN



RE: Room tempearture calculation

IRstuff
Wow, that's a small person! :>)

RE: Room tempearture calculation

oops..175, although, premature babies less than 1 lb have successfully survived.

TTFN



RE: Room tempearture calculation

Funny-I had to go back and look for what you were talking about.  I hadn't seen it.  I do remember the 600 being given as a design point for something and have always remembered it.

rmw

RE: Room tempearture calculation

no, just studying his beer

TTFN



RE: Room tempearture calculation

biott number?

Take the "V" out of HVAC and you are left with a HAC(k) job.

RE: Room tempearture calculation

Radiant sunlight is a major player in this type of calc.  I've ised the sol-air temp to estimate this before, but not on a temporal basis - mine just assumed instantaneous gain/loss.

My scenario was a partition wall in front of a glass curtain wall which sealed it off.  We got concerned that excessive heat build up btw the window and the wall was going to pop the windows down onto the street!  We ended up putting a damper into the wall.

RE: Room tempearture calculation

Try the ASHRAE standards

Regards

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