Sunday, November 19, 2017

How’s your HVAC?

As most readers probably know, the HVAC of the title refers to Heating, Ventilation and Air Conditioning. And what does it have to do with modeling? I am simply thinking of the roofs of model buildings. Even before World War II, it was commonplace to have fan housings and other equipment atop buildings, but with increased use of more extensive ventilation schemes, not to mention air conditioning, these rooftop facilities increased in size and, often, in number. Most layouts provide us with quite an excellent view of the roofs of our model buildings, so we do need to be conscious of what ought to be there. This post is about deciding what and how to fix the glaring absence of HVAC on most of my roofs.
     A simple addition that is suitable for many industrial buildings is one or more ventilators. There are a variety of these in the prototype, and a corresponding variety in model form. An example from my layout is the shipping building for my lemon packing house, the Coastal Citrus Association. Located near the Pacific shore, the climate is usually mild and air conditioning would not be needed. Instead, ventilators can do the whole job. As shown below, I added a cylindrical fan-driven ventilator at left, and a traditional “wind turbine” at right. This may be enough for this industry.

Note the field boxes of lemons in the open doorway.
     But what most people envision for rooftop HVAC would be cabinets or enclosures of more significant size, usually containing motor-driven equipment for air filtration, air circulation, and air conditioning. For example, shown below is an image from the internet, showing a typical rooftop unit in the foreground.

Note also that there are a number of other units in the background, typical of many modern roofs. All visibly exhibit some of the typical characteristics: air intake opening, fans on the top surface, grilles on one or more sides, and painted a light gray or beige color. Some of these are doubtless manufactured packages, but custom units are common too.
     There are several ways to model such units. Obviously a simple styrene box can be the basis, and addition of fans, grilles and intakes is fairly simple. One source of good fans is diesel locomotive shells, but you don’t have to cut up a shell; Athearn sells a set of good-looking fans, their part ATH11692, which are 48-inch pan-top fans, with multiple sets of fans in the package. Of course, if you start by cutting up a shell, you also get grilles. Let me illustrate.
     I happened upon a cut-up shell for sale cheap at a hobby shop, and bought it, pretty much an impulse purchase, thinking of possible HVAC projects. I’m only vaguely familiar with more modern diesels, but this looks to me like it may have been an SD39 at one time (apparently a dynamic brake section was cut out). But the parentage doesn’t matter: this is just raw material for HVAC cnclosures!

There are two fans at left, grilles on the sides, and another grille toward the cab, under the air filter box. These can be easily cut apart and added to a plain styrene box, but more simply, can even stand on their own. I simply used a razor saw and cut oversize, then used a file to clean up the parts. With the cab cut off, all three salvaged segments at bottom, and other removed parts in the middle, here is the state of things at this point.

Shown below are the rear two fan sections, plus the air filtration box and grille from right behind the cab, cut apart and prepared for making into HVAC enclosures:

These are already a large enough size to be the foundation for an HVAC box of modest size. I simply close the open ends with pieces of 0.010-inch styrene sheet.

The resulting unit can be further detailed, as I will do presently.
     I will return to this project with some other HVAC enclosures, as well as the ones cut from the diesel shell above, along with detailing of them, in a future post.
Tony Thompson


  1. Don't forget the Walthers rooftop detail sets.

  2. Good point, and thank you for mentioning it. I had intended to identify this excellent set in the second post on this topic, but here it is now: Walthers no. 933-3733. It's not expensive and has quite a range of pieces, including an enclosure much like the prototype photo I showed in this post.
    Tony Thompson