Picture this: An hvac designer really holds up a print in front of the computer screen, and says to the computer, “OK, tell me the system design.”

Not too long ago, I realized this isn’t a joke. Recent software developments have taken us to the point where this vision is coming close to reality.

New diagram-based software enables the designer to graphically drag shapes such as rooms, windows, and doors into the proper position. The program then instantly calculates loads; designs ductwork, radiant panels and hydronics; selects equipment; and finally generates required documentation including drawings, parts lists, sales presentation and a proposal.

Design-build contractors, particularly those involved in residential and light commercial buildings, are largely driven by the sales process, which demands at least a minimum system design as part of the proposal. In many cases, contractors can’t afford to keep a designer on staff, so they frequently hire sales people with limited design skills and provide on-the-job training.

Even the most skilled salespeople, however, are so pressed for time that they shy away from learning detailed design methods. What they need, and what nearly every contractor would like to provide, is a quick method of converting a simple building floor plan sketch into a complete hvac design.

Sketch to proposal

The new generation of diagram-based systems is finally bringing this vision to fruition. Instead of entering building dimensions and specifications into a form, the salesperson interacts with a simple floor plan diagram. Simply dragging and dropping a shape onto to the drawing can create a room.

Designers can then stretch the room to the proper shape and dimensions. Rather than entering each window and door by typing numbers in a form, doors and windows can be dragged into the proper orientation and stretched to the right dimensions.

At this point you may be thinking, that sounds like a CAD package and aren’t CAD programs complicated and difficult to learn? Yes, most CAD programs are complicated because of the inherent complexity that is required to specify a structure down to the level of detail that is required to construct or renovate it.

One of the key distinguishing characteristics of the new generation of diagram-based hvac design systems is that they don’t force the user to become immersed in the same level of detail required to design the building.

Instead, they use shapes that are very simple from a geometrical standpoint, yet possess the intelligence to understand their basic connectivity and thermal characteristics.


Rather than CAD, the new generation of hvac software uses an approach called diagramming. Unlike CAD, diagramming is simple, inexpensive, and has a short learning curve. Diagramming consists of selecting simple, pre-drawn shapes that have intelligence, such as knowing that the thermal properties of a wall with windows are different from a solid wall.

By embedding hvac design calculations in shapes, any change in shape, size, or materials instantly changes the loads, and hence the duct system, operating costs, etc. This intelligence is transparently passed on to the calculation engine that works in the background. All the hvac salesperson needs to know to design and quote a system is, basically, where are the walls, doors, and windows, and what are their thermal properties.

How do the diagrams described here relate to the conventional CAD drawing which may sometimes be available as input to the design process? The value of the CAD drawing to the designer is limited because it has very little of the information needed and a great deal of extraneous details may complicate the process.

What the CAD drawing does well is provide a reliable guide to the building’s layout and dimensions. That’s why developers of this new generation of hvac design systems have chosen to import the CAD drawing as a separate layer that can be used as a guide to construct the hvac shape drawing, while avoiding the need to work directly with the CAD data.

Background calculations

Once the user has created a simple diagram using the approach described above, the program takes over. It calculates the loads, sizes the ducts, and drops the registers into place on the floor plan that was created in an earlier step.

In some cases, the software will actually automatically draw out a fully sized duct system. The salesperson can specify a radial or extended plenum system and manually move registers into better locations than those specified by the computer.

Users can also create libraries of equipment from which the computer will automatically select, or can make their own choice based on the application. The software can even offer a choice of good, better and best selections.

The results produced by the current generation of hvac design software are trusted because they follow the same manual processes, such as Manual J, that have been proven over time and are accepted by regulatory authorities.

The new diagram-based programs produce reliable results by using exactly the same calculation methods as the old forms-based tools. For example, a room in a diagram-based program simply represents a hidden calculation of a Manual J column. The key difference is that the calculations stay behind the scenes, although the user can easily print the underlying calculations at any time.

Automatic proposals

The new diagram-based design programs can generate the full range of documentation to sell, specify, and build an hvac system. By setting up templates in advance, designers can define equipment and other system preferences to generate a materials take-off, eliminating another time-consuming aspect of the design process not addressed by conventional design tools.

Templates are a labor saver that help the user by presetting an entire set of characteristics for a project. They allow the user to enter default properties for various building types into templates that can be selected according to the job being quoted. The creation of custom libraries representing common construction methods in a particular geographic area may eliminate the need to give thermal properties a second thought.

Diagram-based programs provide useful types of output. Unlike conventional forms-based tools, diagram-based software can easily produce scaled design drawings. The diagram-based programs can also produce a quotation in a format defined by the user. They also generate useful sales information such as cost comparisons and return on investment calculations.

Finally, they give the user the ability to define custom reports such as permit submittals via a link to Microsoft Word and other word processing programs.

Wizards simply

The process is simple because the object-oriented approach of the new generation of programs makes it possible to harness their power to a wizard, such as the ones used to perform common tasks in Microsoft Office. The result is an even greater level of user friendliness.

For the high-speed sales process, this is a crucial win. The salesperson simply clicks on a proposal icon and the wizard walks him or her through the entire process. More advanced users may prefer the level of control that they gain from interacting with the program in its natural state. They will always have that option.

The wizard approach personifies the ability of this new generation of programs to fulfill the promise of converting a sketch into an hvac system design. Diagram-based programs serve as an equalizer by giving everyone else the ability to perform all of the calculations needed to ensure that an hvac system is properly designed for a specific building.