Internal mass for a warehouse

asked 2016-06-06 09:37:30 -0500

Jim Dirkes
3424 ●25 ●15

Dear forum, I don't normally pay much attention to internal mass, but am modeling a warehouse which is relatively full of tall steel racking and products. These seem to represent a LOT of internal mass and should not be ignored. I have made an estimate of total internal surface area (which appears to be in excess of 2 million square feet for a 100,000 sq.ft. warehouse), but am now thinking in more detail about the properties of the internal mass.

Racking is steel and has high surface / mass ratio
The products which are stored on the racks are unknown, but almost certainly will be a composite of steel, aluminum, plastic. wood, etc. These products will be inside packages (e.g., boxes) that reduce overall surface area of the product, so surface / mass ratio is probably lower than the racking.

Have some of you done research on this topic? Have you made reasoned assumptions? studied the impact and found it to be too small to worry about?

Thanks for your insights.

answered 2016-06-07 08:21:42 -0500

JasonGlazer

6540 ●20 ●12 http://www.gard.com/

In my opinion the internal mass needs to be considered in a warehouse since it will represent a strong dampening factor to temperature changes. So the approach of calculating the surface area and mass (or representative construction and materials) makes sense to do.

Unfortunately, I think warehouses and the internal mass that is represented inside are also pushing another assumption that is used in building energy simulation which is the "well stirred zone" if circulation fans are not used. The idea that the temperature is uniform throughout a zone when zones are the size of warehouse zones is probably not very accurate. You may have experienced how some aisles in a warehouse can seem much colder than others. Given that, not all the surface is really actively interacting at the same temperature so perhaps some of surface area of the internal mass should be adjusted downward.

I am not aware of any specific reports that have investigated this. One of the few places that I know that describe modeling assumptions for warehouse internal mass is PNNL-17056 "Technical Support Document: The Development of the Advanced Energy Design Guide for Small Warehouse and Self-Storage Buildings" by Liu, et al. (See section 7.3.4). It shows some calculations for internal mass but not much other discussion on the topic.

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Thanks very much, Jason. Everything you say makes excellent sense to me. I'll take a look at the PNNL document to see what additional light it sheds. I may do some sensitivity analysis with different amounts of mass and surface area, just to see how big an impact it makes on overall performance.