Thursday, August 20, 2009

Teaching Residential Design

One of the challenges that all HVAC/R educators face is convincing future contractors to ignore all the quick and easy rules of thumb for system sizing and duct layout and use design methods based on research. The problem with the ACCA standard design methods for sizing equipment and designing systems is that a considerable amount of time must be invested to understand how to use them. The first few systems someone does with Manual J and Manual D seem to take forever. Even using a computer design program requires the user to learn how to use the program. These methods appear overly difficult when compared to simple square feet per ton rules, or air changes rules. Still, the question really comes down to “do you just want an easy answer, or do you want a correct answer?” If you think from the customer’s perspective, they really want and need a correct answer. I believe that it is also in the contractor’s long term best interest to get correct answers as well. Avoiding a gaggle of unhappy customers that got the quick, easy, and wrong answer can be more time consuming than taking the time to get it right the first time.

I don’t think every Air Conditioning Technician needs to be able to whip out a Manual J load study, but I do think all technicians should be familiar with the overall concepts and general procedures used. Sometimes, the first step to learning is understanding how much you don’t know. Introducing technicians to the proper way to do a load study can be the light in the darkness that illuminates the path to greater understanding.

The truth is that the procedures are really not that difficult once you understand them. They will still take more time then dividing the square footage by a magic number, but an accurate load study on a typical residential home generally takes less than 30 minutes for someone who understands the process. It is true that you will have to invest hours of your time to get to that point, but that is really no different than any other skill that is required to perform HVAC/R work. The fact that time and effort are required to develop the skills and knowledge required to perform the job is part of what makes HVAR/R jobs valuable. The job is not as simple as memorizing a handful of rules of thumb.

Section 7 in Fundamentals of HVAC/R gives students the information they need to understand residential air conditioning application and system design with several unique features not found in other major air conditioning texts. The System Design, Sizing, and Layout section begins with Unit 54 which describes how buildings are constructed. It is important for students to understand how the air conditioning system fits into the building. Decisions about unit location, duct location, general duct design, and register placement are all very much affected by the building construction. Unit 55 shows students how to read and interpret drawings. Often, the first “look” an air conditioning technician has at a building will be in the form of a drawing. Teaching students how to interpret blueprints allows them to understand the building construction, even before the building is built. Unit 64 takes the students step by step through a manual J8 load calculation. Fundamentals of HVAC/R is the only major text to discuss the use of Manual J8, the latest version of ACCA Manual J, the ANSI standard for residential load studies. Unit 57 shows students the types the different types of duct systems available and how they fit different types of building construction. Unit 58 shows how to install duct systems and how to use friction charts and the ACCA Duct Calculator to design duct systems.

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