The “Rules of thumb” to get full flexibility from your AHU design solution

The title is, of course, a paradox (and I’m sure you realized it).

In this article I’d like to speak about real and well-defined rules (the opposite of “rules of thumb” mentioned in the headline) to help AHU manufacturers to afford the issue linked to flexibility demands.

Flexibility in AHU design

As a modern AHU manufacturer, I’m sure you dealt with the following (or similar) issue many times.

You customer has space constraint: this means that your AHU must fit a reduced and well defined room. In many cases, your standard units catalogue doesn’t help at all: you need to design a bespoke AHU.

This means that if in your standard unit catalogue you have sizeN and sizeM models (for which you have predefined the frontal size, all the drawings needed for the production and for which you know very well the costs), in the specific case you need to design a new unit, with a new “sizeY” that is in the range “sizeN- sizeM”.

I’m pretty sure that, thank you to your experience, you managed to cope with this situation in different ways. For example, your technical department engineers can use the 3D solid model (if any) of a predefined unit and “stretch” it to get the needed dimensions. They can also take the existing 2D CAD drawings and adapt them to the new constraint and generate the documentation needed in the manufacturing phase.

Whatever is the workaround solution you adopt, some important drawbacks can be identified; among the others, I’d like to underline the following:

  • Lack of cost control: most likely, you can say that the cost of new unit sizeY of our example will be between the cost of sizeN and cost sizeM similar unit, but you can’t be more accurate than this;
  • Lack of time control: the process is slow, because you need to do it manually.

As alternative, you can ask you AHU design software to do the job for you.

Custom unit design with a generic AHU selection software

Some generic software for AHU design available in the market can manage the concept of custom unit dimensioning. This can happen with different level of accuracy and complexity.

The very basic approach to custom AHU management consists in giving the user the possibility to specify customized external size for the unit: the printout generated by the software will report the new dimension, but internally to the unit nothing changes if compared to standard units (no components recalculation is done, no internal metal sheets are recalculated, and so on). I wouldn’t consider this solution enough for an advanced AHU manufacturer, for obvious reasons.

More sophisticated software rely on big database table in order to store all possible dimensional information related to all possible unit sizes and models. This approach requires a big initial effort by manufacturer in order to fill in all the required information. But these information are only data, that are well known by the technical office. Some manufactures states that “after an initial effort, then the software works!”.

I would like to underline a couple of important drawbacks of this kind of solution:

  • The “initial effort” required to fill in all the needed data can be very big: on average it can requires 4 to 6 months at least, to be optimistic;
  • The approach has important limitation from the maintenance point of view: as soon as the number of model and sizes will increase, it will be very difficult to maintain the consistence of the information in the database, especially if you need to introduce a change in your production. A small change in your unit need to be replicated in all models and unit sizes in the database. Sooner, you will have easily tens of table with hundreds of fields to be changed and to be maintained consistent one each other.

It is a time consuming and a not easy task (unless you are happy that your technical department engineers will dedicate many hours of their time to database programming and maintenance, instead of concentrate to their core activity, that should be design new products and optimize the existing one).

Custom unit with an engineered solution based on “rules”

It is possible to think about an alternative approach in order to cope with the issues mentioned above and to guarantee a full flexibility for the selection of custom units. This alternative is based on the concept of rule.

A rule is nothing more than a synthesis, expressed in mathematical form, that formalize the way you create your units. The production rules will be in general expressed as a function of the (customized) frontal dimensions of the unit.

Rules can be used to calculate the main values that influence the cost of the unit and the that are, apart the cost of the internal components:

  • Units sections length;
  • Components position inside each unit section (taking in consideration also the components coming before and after each component);
  • The unit structure elements (panels dimensions, profiles length, omega profile length, etc.);
  • The internal metal sheets (blank off plates) flat pattern dimension (and holing);
  • Roof metal sheets flat pattern dimension and basement (either metal sheets flat pattern or profiles length, whatever is the way for the production);
  • Manpower times calculation.

As a consequence, the calculation of the cost and weight of the unit will be always calculated as much as accurately as possible. Only with the use of rules you can get a such level of accuracy and flexibility.


But the real value of rules definition is not in the benefit coming from the usage in the software development.


The definition of the rules is therefore an effort in charge of the manufacturer’s technical department engineers, that leads to clear benefits to the whole company in terms of optimization of AHUs production processes.

The software solution is only in charge of automate the application of the manufacturer’s design criteria, optimized and standardized under form of rules.

Among the advantages inherent in the definition of the rules, I can surely mention the EASINESS OF MAINTENANCE process: a change in a rule has immediate impact on all unit sizes. This is not certainly is not the case having to update data in a table (as you will have to edit the same data for each unit size involved).

The definition and collection of rules, anyway, require a strong cooperation between the manufacturer and the partner company that has in charge the development of the software solution for the automation of unit design and production.

I collected for you some important directives, based on our long experience in AHU design and production  solution development, about how the process should work, in order to get the best results in the shortest possible time.

Ideally, this should be the process:

  • Rules SHOULD BE COLLECTED FROM THE PARTNER, and then implemented in your solution;
  • The first release of the software will be COMPLETE AND READY TO USE;
  • In this way, you save time-consuming data entry activities (at least 4-5 months of effort can be required, if done by you in an independent way);
  • The rules will be included in databases, that can be EASILY CHANGED BY YOU AT YOUR NEED.

To sum up the main concepts for you:

  • Rules definition is the ONLY way to have a true custom units design by a selection and production automation software solution;
  • Rules are useful, as a first step, FOR THE OPTIMIZATION of your AHUs production processes. It is not only for the software, but it brings real benefits to the whole company;
  • Rules should be collected by your partner, the engineering company in charge of  our software solution development, with your contribution. They should be implemented in the first version of the software and should be easily modifiable by you.


If you would like to know how a long experienced engineering company can implement the rules concept in your next solution for AHU selection and production automation, please click on the following link on today, we will contact you immediately:


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