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When designing a building, the final product may be just a few sheets of paper with lines on them.  Put that way it doesn’t sound too impressive (or that difficult), but since design work is a lot more than just a few lines let’s take a moment to look at how those lines got on the paper.

Most design professionals use some sort of Computer Aided Design, or CAD, program.  At it’s most basic level, the program would be similar to the Microsoft Paint program that comes on all Windows computers and that you probably have spent some time goofing around with.  You can use it to draw straight lines, curvy lines, boxes, circles, just about anything.  The best part though, is that you can easily change what you have drawn previously. In my opinion the most important thing is that the design can be easily changed.  When done, just print off as many copies as you need.  One of the most common CAD programs is AutoCAD but there are also other popular programs used by design professionals.

A newer form of CAD is called Building Information modeling or BIM.  While CAD can be done in 2D or 3D, BIM takes 3D modeling of a building to the next level by having the different disciplines work in the same environment so that they can see each others work.  For example, if I am designing the HVAC ductwork I can see on the computer where the electrical designer has placed the light fixtures and can avoid putting a diffuser at that location.  This saves coordination time and helps to ensure a building can be built with less surprises in the field.  While most BIM models still get printed out as traditional documents, the technology is there for a contractor to simply open the file on a computer or tablet and build straight from the designers original model.  The same company that makes AutoCAD also makes a program called Revit which is one of the leaders in BIM design.  This is also my favorite way to design a building!

It wasn’t always so easy, though.  Have you ever heard of the term blueprint?  It’s still widely used to describe design drawings and gets its name from an old process for making copies.  The original design would be drawn on a piece of translucent paper.  Special blueprinting paper would be placed under the translucent original drawing.  The blueprinting paper was coated with chemicals which, when exposed to light, would turn blue.  Since the lines on the original drawing would block the light, you would get a copy that showed white lines on a blue background.  With the advent of photocopiers, the need for this process died off.

Forward Engineers uses both AutoCAD and Revit as well as other computer-based tools to complete our designs.  The use of CAD and BIM allows us to provide a high quality final product while remaining flexible to design changes.  If you are seeking to work with an engineering firm that is client-centered and strives to provides services that are on time, on budget and exceed expectations, please contact us. We would love to work with you on your next project!

While flying on a recent trip, I got to wondering about how the air in the cabin was conditioned.  I assumed it had to be either warmed or cooled in some way and fresh outside air would need to be introduced at some point, but how is the fact that the cabin is pressurized affect all that?  My curiosity led me to do some research and here is what I found.

Similar to commercial HVAC systems, the conditioned air in the cabin is a mixture of recirculated and fresh air.  A normal commercial system is usually designed with about 10-15% of the air coming from outside while an airliner’s system is around 50% outside air.  Commercial building systems are usually limited by the humidity that they have to remove from the air (called the latent load).  This isn’t really a factor for airplane systems as there is very little humidity at high elevations.  In fact, the relative humidity in an airliner cabin while flying can be around 12% which is less than ideal to say the least.  Also, the occupant density of an airplane is a bit higher than your normal building so it makes sense that you would want more fresh air anyway.

The fresh air doesn’t just come through a grate on the side of the plane, though.  It is bled off of from the compressor sections of the engines.  These compressors have pressurized the air and, as a byproduct of the compression, made it very hot.  You may recall from a previous article on humidity, that by heating the air any measure of relative humidity that was present is now even lower.  The hot dry air now goes through the air conditioner’s evaporator and is cooled down to a comfortable temperature.  These air conditioner units are known as “packs” in the aviation world.  From there the air is mixed with recirculated air (which came through a filter from the cabin, just like in a building system) and blown into the cabin.  Excess air, which has to get out somehow or else the cabin pressure would continue to increase, is let out through a device called the pressurization outflow valve.

On the refrigeration side of the system, the refrigerant goes through the refrigeration cycle just like it would in a system on the ground.  The evaporator absorbs the energy from the air into the refrigerant turning it into a vapor.  This produces the needed cooling effect on the air.  It then goes through a compressor (powered by the engines) raising its temperature and pressure.  Next it’s piped to the condenser that has air blowing over it which cools the refrigerant back into a liquid.  The last step is for the liquid pressure to be lowered by using a thermostatic expansion valve which gets the liquid ready to evaporate in the evaporator.

When sitting on the ground with the engines off, the airplane will simply get connected to a mobile air conditioning unit or connected to a central system in the terminal.
While a bit different from your everyday home or business air conditioner, you can see that the components and basic operation is very similar.  One big difference is if your air conditioner stops working at your home or office you can usually just open a window, but I can’t recommend trying that on a plane.

At Forward Engineers, we seek to not only be a design and consulting firm but to also educate our clients about engineering technology. While doing so, we inevitably refresh our own knowledge and sometimes even learn something ourselves. If you are seeking to work with an engineering firm that is client-centered and strives to provides services that are on time, on budget and exceed expectations, please contact us. We would love to work with you on your next project!

As I mentioned in my last newsletter, the 179d federal tax deduction for energy efficient buildings expired on January 1 of this year.  Any project completed before this date can still be certified for a deduction on your 2016 taxes.  Congress continues to discuss extending the tax deduction, but little formal action has been taken.  All of the current extension bills are awaiting action in various committees.  Stay tuned to our website for any updates on the extension efforts.

As you may know, we regularly post links to our articles on our Facebook and LinkedIn pages.  This month we added a Twitter account which you can follow to get updates on new posts.  Here’s what we were talking about this month:

1. Variable Speed Fans on HVAC Units – One of the most common recommendations we make to clients is to consider installed variable speed fans on their HVAC equipment.
2. Why not Take the Train? – A friend asked me how much coal it takes to get to Maine. I’m not that kind of engineer but I took on the challenge.
3. Humidity and Healthy Air – You may already know the effects of humidity on comfort, but did you know it can also influence your health?
4. Cooling off with Sunscreen – Ever notice how a spray can is cold after use? You just experienced a principle of refrigeration.

Be sure to check our website regularly for updates or follow us on Facebook, LinkedIn or Twitter.  We wish you the best this month and if you ever have need of any of our services, please don’t hesitate to contact us.   Have a great day!

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