When you’re updating your home’s heating and cooling systems, accurate equipment sizing is essential to prevent problems with performance, efficiency and comfort. There are two terms related to sizing that you may hear mentioned: capacity and load. Capacity refers to equipment output, while load is the amount of heating or cooling your home needs. To help you understand how equipment is properly sized, you should be aware of the three types of heating and cooling loads used in capacity calculations.
Design Load
When sizing new equipment, an HVAC contractor uses Manual J software that factors in constants like solar orientation and insulation levels. To arrive at the correct equipment capacity needed, it’s also necessary to input the seasonal outdoor and indoor temperatures for our area, or the design conditions. This determines the design load, or the amount of HVAC equipment output needed under design conditions. Even though design conditions aren’t often met during day-to-day heating and cooling, they provide a vital sizing guideline.
Extreme Load
Our area of Ohio has a humid continental climate with hot, muggy summers and cold winters. Summertime temperatures have hit 104 degrees, and they’ve dropped to a low of -22 in the winter. These are the extreme load conditions your HVAC equipment may have to face, but they typically occur about 1 percent of the time so they aren’t an accurate metric for sizing. To avoid oversizing the equipment by using the extreme load, Manual J software increases the design condition temperatures by 15 to 20 percent to compensate for these relatively rare situations.
Part Load
For the remaining 99 percent of its life span, your HVAC equipment doesn’t use its full capacity; instead, it runs on part load. This occurs whenever the thermometer reading doesn’t match the design load temperatures. Since most HVAC equipment operates at a fixed output, part load conditions can cause temperature variations and humidity problems. Opting for a variable-speed air handler or installing a whole-house dehumidifier can help overcome these issues.
To learn more about heating and cooling loads, contact the Lorain home comfort pros at Energy 1 Heating & Air Conditioning .
Our goal is to help educate our customers in Lorain, Ohio about energy and home comfort issues (specific to HVAC systems). For more information about heating and cooling loads and other HVAC topics, download our free Home Comfort Resource guide.
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