Building Perimeter Heat Gains?

[kryanl]

Hello all,

I've been assigned to begin performing HVAC calculations for various buildings/rooms for my company. As an intro to the work, I was given a stack of old calcs previous engineers have done. I understand everything, except when it comes to head loads through the perimeter of a building floor. I can not see any consistency between differerent engineers' calculations, when they add a heat gain into the building from either the floor or the linear footage of perimeter. For example, let's say there's a 10' x 22' x 18'H building, sitting all alone out in a field. One method used would be equivalent to 220 sq.ft. * deltaT * Ufloor. Another was 20ft*Uperimeter*CLTD + 44ft*Uperimeter*CLTD. Sometimes, the floor wasn't considered, or a strange combination of the two above examples was used. There isn't even a particular method a single engineer stuck with. I checked through ASHRAE Fundamentals, and was very surprised to see in their Cooling Load calculation disscussion, they never even addressed floors or perimeters! Do I not need to concern myself with this? (And, if I do, might someone be able to explain how exactly you get the U-value of a perimeter, that I also was not able to follow.) Thanks so much!

 

[IRstuff]

You haven't described, and there's not enough room for that probably, the individual buildings.

Different foundations, flooring insulation, and different surrounding soil/earth environments could account for different approaches to the thermal losses.

I would suggest that you review the calculations on the assumption that not all of the buildings are constructed the same. This would be a perfect opportunity for a road trip or at least an inspection trip to some representative buildings to see if there are any differences that required different calculation groundrules.

For your legacy, you might want to start with an all encompassing equation with both area and perimeter calculations and annotate what your assumptions and conditions were for the next guy in your shoes.

TTFN

 

[caluna]

How interesting! You must be in a very warm climate, or one with lots of solar gain to warm up the top few feet of ground. I never even thought of including the gain thru ground as input to the cooling load (but then I am quite far north)..and have never seen that gain included in ASHRAE or Carrier or any of the other calculation methods.