How Not to Build Hotel Rooms

When I was at that work conference in Chicago, I came to the conclusion that this conference--despite being a big HVAC show--often puts us up in hotels with the crappiest building characteristics. For instance, they held the convention in Hawaii, and the hotel closed down shortly afterwards due to mold complaints.

At this Chicago hotel, it was friggin' cold out (5 F during my walk down Michigan Avenue), and the frost that was all over our hotel room window gave a great little building physics demonstration. So I thought I'd share the geekery.

Peering out the window, I noticed that there was a fair amount of frost built up at the bottom of the window.


And when you pulled the curtains back, you could see this lovely distribution of frost/condensation patterns.


This is demonstrating two things. First, windows are coldest at the bottom--at this cool surface, the interior air falls as it cools (as it becomes more dense), and gives up heat, forming a "film" at the interior window surface. This is natural convection in action. By the bottom, that air is pretty cold--it has given up its heat, so the bottom of the window is the coldest/frostiest here. You can see the gradient from bottom to top, going from thick frost, to partially melting ice, to condensation/sweat.

Incidentally, when people complain about drafts at windows, it's both air leakage (moving parts + seal = air leak), but it's also that there's that sheet of cold air coming off the window--there are actually formulas to calculate what the velocity of that flow will be.

Second, you can see exactly where the curtains were partially open overnight. The curtains function as insulation--both reducing heat loss from the interior, but also making that glass surface colder. At that opening, less insulation=warmer surface=less frost/condensation. Neat, eh?

Of course, being the geek that I am, I had the infrared camera with me. The temperatures are exactly what you'd expect--the coldest spots are the parts with the worst frosting/condensation. Some of the coldest spots on the frame were 26 F (yep, below 32 F = frost formation).


But when you close the curtains, the surface temperatures (i.e., the surface that your body "sees" when it is radiating heat away) is much better--close to room temperature, with cold spots at the bottom, where the air is flowing out (as per that natural convection described above).


One bit of trivia--some folks have done studies, and there are cases where curtains increase the overall heat loss at the windows. "Really?"--you might ask. Although the surface you see is warmer, the convective air movement has enough flow that it's acting as a natural buoyancy-based heat exchanger, flowing enough between the curtain and the window.

Anyway, check out the window frame--totally covered with frost.


Note that the windows in this hotel room are single-glazed, aluminum frame window. Is it just me, or is that about the same as a storm window? NEWS FLASH: DO NOT USE STORMS AS YOUR SOLE WINDOWS IN CHICAGO. DUH.

As if you needed any reinforcement that this is a bad idea, check out the placard next to the thermostat.



It reads:

There are many seasons that you may not be able to achieve a comfortable room temperature without the assistance of the hotel staff.

Please do not hesitate to call 'At Your Service' by dialing 'O'

We look forward to assisting you any way we can.

Oy. The dumbness is painful. Of course, some value-engineering wonk back in the day must have thought this was a good idea. Ah well.