Managing Expectations: Set the Table
Managing expectations is a big part of making customers happy. When it comes to an HVAC system conditioning a home, taking the time to prep end–users can go a long way. The paragraph below was taken out of Manual J®, as I have been regurgitating parts of it for a very long time.
Manual J® Wisdom
A6-9 Part Load Days Are More Important Than Design Load Days
“As a group, homeowners are overly concerned with extreme weather conditions that occur for a few hours per season and uninformed about the significance of the part-load conditions that occur for thousands of hours per season. This lack of understanding pressures contractors to install oversized equipment. This results in systems that are more expensive to install, less efficient, less comfortable for most of the season, and less reliable. In addition, the oversized equipment produces an unnecessary load on the electric and gas distribution systems. The solution to this problem is consumer education. Refer to Manual S® 2014 in general, and to Manual RS®, Section 10-4, for more information on this subject.”
One of the analogies that I use is as follows. If the occupant turns the system off and expects to return home after a day’s work to a house that they’ve allowed the temperature to rise to 85ᴼF, and then expects to be able to put a chicken in the oven at 5:00 PM and sit down to a fine meal at 6:00 PM in a house that is 70ᴼF, then they are not going to be happy with the system that I design and install for them. I say that slightly tongue-in-cheek, but it’s not that far off from some people’s expectations.
Do not allow yourself to be put in a position where you must defend the performance of a system that is working as designed. Just because it’s not instantly heating or cooling the space does not mean the system is deficient. It very well might be that the customer has unrealistic expectations. We need to manage those expectations. It is critical that a contractor has a poignant conversation with the occupant or end-user as soon as possible to find out what they expect from their air conditioning system. This can apply to heating systems also, but we are addressing air conditioning for this installment.
Proper sizing is required. Avoid the temptation to upsize. A larger system can help avoid the expected temperature increase we will get when we see temperatures above design, but the price we pay is less run time the rest of the time. Performance that is subpar most of the time is the trade-off for what amounts to a payoff that takes place statistically one percent of the time. It’s just not worth it. I must mention here that this is more of a humid/wet coil climate problem than we see in arid climates. But remember, run time helps with air mixing and all climate zones benefit from that.
Consider a two-speed or variable capacity system to help manage demanding consumers, but don’t ever let the phrase, “I oversized it, but it’s okay, it has multiple speeds,” be something you utter. There are slightly more generous sizing limits to those systems, but there still are “rules” (See Manual S® for specific guidance).
Let’s discuss what will happen if you decide to break the rules, which is not recommended, but we need to address it. Don’t just upsize with no strategy. We know that a larger system on part load days will increase our interior dewpoint. Ancillary dehumidification can address this. This is not a recommended strategy (To learn more about this, read Dehumidifiers That Don’t). Remember, if you create a problem, then you need to offer a solution.
Follow the design series in its entirety, where you perform a good load calculation, proper equipment selection, good duct design, and proper grill and register selection. When this is paired with an educational conversation with the end-user, you will reduce your callbacks and improve customer satisfaction. Remember, managing expectations should be part of your process on every job.
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