BS at BS Summer Camp
I’ve been thinking about good HVACR system design a lot lately, and I believe I had an experience that really brought it all together for me. While attending the 26th Westford Symposium on Building Science, I ran into Greg Stockton from Little Rock, AR, an ACCA member from Today’s Building Science, LLC. He shared an interesting story with a group of us that led to a great conversation at our table. Greg posed a question that I consider the best kind of question—one that included not only the query but also came with receipts.
Documentation
While I would have preferred a photo of the thermostat showing an indoor temperature of exactly 75°F with 50% relative humidity, I had to work with what I had. (NOTE: For all the perfectionists out there, I did confirm with Greg that the home was able to maintain exactly 75°F at 50% RH on a design day.) The design temperature in Little Rock is 96°F for the location of the structure. Based on this, I would say the system can achieve the Manual J® required target.
The photo of the thermostat shows that the house conditions are acceptable, and it was reassuring to see the duct leakage test report included, confirming that the duct system passed the required tightness for its location. It brings more confidence to see the Manual S® report capacities land within the guidelines.
The Question
At this point, I have to ask: What do you think Greg’s question was going to be?
I often say, “Nothing surprises me anymore,” and this is a perfect example of why that’s true. Greg had been keeping track of this job with photos because, believe it or not, the customer complained. They thought their system should maintain a lower temperature and that it shouldn’t have to run as much as it does. Before I go any further, I want to clarify that Greg’s company only does the designs, not the installation—another company installs the equipment. When Greg first asked for my opinion of the design, based on the receipts, I literally gave a chef’s kiss and exclaimed, “Nailed it.” I couldn’t think of a better example of how crucial it is to inform people about what to expect.
The Talk
This brings me back to the topic of managing expectations. I honestly don’t know if the homeowner had anyone manage their expectations. If they did, then explaining that the system is performing as it should be an easy conversation. If no one explained what the expectations should be, then a much more difficult conversation will be needed. This serves as a good reminder that, company-wide, there should be consistent explanations provided to everyone who interacts with the homeowner.
Misinformation
There is so much misinformation easily accessible to the average consumer right now, but I’m sure you’re already aware of that. The idea of square footage per ton is never going to disappear, so I’ve accepted that people will continue to bring it up. My calculations, depending on location, are usually 150% to 200% less than their preferred numbers. As for the argument about systems running too hard or too much, there might be some truth to it if they’ve got a solar pool cover piled on top of the outdoor unit or if the cottonwoods are in bloom. However, I don’t buy into the idea that the system works harder under typical conditions. And finally, bigger is not better—oversizing raises the dew point in the house, which reduces comfort and can cause potential problems.
Conclusion
There are countless things we can get wrong, but the most critical mistake is installing the wrong size equipment. It’s incredibly difficult to fix that after the fact. I’d much rather have a conversation with the homeowner upfront, so they know what to expect, rather than try to explain why they’re dissatisfied later. Given the choice, I would prefer to manage any disappointment about the temperature in their home when it exceeds design conditions, rather than take on the liability of a raised dew point due to insufficient runtime caused by an oversized unit. Nobody likes leaving money on the table, but everyone loves running away from problems. We need to protect ourselves—bigger units don’t make things better, but quality installation and managing expectations does.
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