How to Prove Your HVAC System Designs Perform Well

Some HVAC designers believe the system image they create on their computer screen mirrors how the system will perform when its installed in the field. However, once the system is built and started-up, the complaints can roll in. Let’s take a look at several diagnostic tests designers can use to resolve HVAC system performance issues discovered after system start-up.

Design Assumptions
Whether you design a new system or redesign an existing one, your customers expect it to deliver a satisfactory level of comfort, that’s quiet and efficient. A floorplan is the foundation of a system design and should include relevant building components, internal loads, and occupant activity. Based on this information you interpret the data, organize facts, and make some assumptions to create your design.

Today, you can reduce many of these assumptions. There are software programs that enable you to walk through the project before its built and identify troublesome conflicts in advance. Unfortunately, because of normal construction conditions and field realities, you cannot find and correct all flaws ahead of time.

The truth is, what’s on your screen at design time, may not match field installation conditions.  

Customer Complaints
Upon start-up or occupancy, there is usually an initial punch list of items that need correction. Many of these are oversites and defects caught-up in the whirlwind of construction. The installing contractor will take care of most of these. Or, if the project was designed and built in-house, the service department resolves these issues. Rarely will the designer catch wind of these problems. 

Trouble begins when customer complaints persist. This is when things get sore and liability raises its ugly head. When others can’t resolve the issues, eventually finger pointing ensues and everyone wants someone else to make the problems go away. That’s when the crosshairs fall on you.

This is the moment where you, as a designer, either blame someone else for the problem or step up and find the solution. Guess which approach pays the biggest long-term business benefits?

Use the following process to troubleshoot and resolve HVAC problems. They will prove your design and improve system performance, regardless if you’re a third party or in-house designer, contractor, or salesperson. 

Prove Your Design, Solve the Problem
If you’re the designer, your best approach is to solve your customer’s complaint. First, acknowledge the plans and specs are different than the installed system. This fact brings clarity to the resolution process.  

First, acknowledge the plans and specs are different than the installed system. This fact brings clarity to the resolution process.  

Employing diagnostics will make you a design authority and move you past others in your field. It will also improve your ability to design better HVAC systems. 

To make a valuable contribution to the project, use one or more of the diagnostic tests below to pinpoint system defects and prescribe needed solutions. Your solutions will place you in a position of authority and will direct the cost and responsibility of making the needed repair to the correct party.

Most Common Design Complaints, Diagnostics, and Solutions
See how many of the following complaints have been blamed on your design in the past. Then consider how to prove your design with diagnostics and then prescribe solutions to eliminate the installation issue. 

“The equipment you specified is too small.
Diagnostic – First, verify the equipment nameplate to assure the correct equipment was installed. It’s surprising how often the wrong equipment gets loaded on the truck before it leaves the shop.

Verify the equipment nameplate to assure the correct equipment was installed. It’s surprising how often the wrong equipment gets loaded on the truck before it leaves the shop.

Second, check for return duct leaks from an unconditioned space. Measure return grille air temperature and equipment entering air temperature. Subtract to find the temperature difference.  If it’s more than five degrees, you’ve found the problem. The equipment appears undersized because of unconditioned air entering the system through return duct leaks.  

Solution – Either replace equipment with the specified model or repair return duct leaks. Repairing leaks often, magically, makes the equipment become the right size. 

“The family room won’t cool.” 
Diagnostic - First, the system and your design may be fine. This could be a building insulation problem.  Use an inexpensive infrared thermometer to scan the ceiling and outside walls. If the ceilings or walls are unusually hot or cold, then building insulation may be missing. 

Measure room airflow with an air balancing hood and compare your findings to your specified airflow.