Of all the processes that our industry seems to struggle with, completing a legitimate load calculation seems to be one of the most contentious. The load calculation is the cornerstone of the entire design, install and service process. If done properly it can significantly reduce many of the issues that prevent equipment from operating at it’s rated capacity and efficiency. Conversely, loads that are done improperly, or perhaps overlooked completely, are a primary reasons why we run into those poor performing systems where no matter what we do, we’re just not able to make them operate properly and/or provide comfort for the occupants. Key points of information provided by the load calculation include:
- An accurate assessment of individual room and space loads throughout the home that gives us the data to allocate the capacity of the fan correctly for duct design. (Sorry, there is no such thing as so many Btu’s per square foot.)
- A target CFM for selecting the actual equipment to serve the load.
- A latent and sensible load for cooling that is required for proper coil selection.
- Advance notice of room and space loads where zoning may be required.
More importantly, it’s a fact that as SEER values rise, so does the amount of time required for indoor coils to reach an operating pressure and temperatures where they are capable of reducing the moisture content of the air stream flowing across the coil. Additionally, short-cycling associated with oversizing equipment only makes dehumidification more difficult to achieve.
Obviously, there are lots of other reasons to complete an accurate load. And it is certainly one of those functions where we only have one chance to get it right.