Advice for Matching HVAC Load and Capacity

Advice for Matching HVAC Load and Capacity

Calculating load appropriately is extremely important for efficiency and comfort

Advice for Matching HVAC Load and Capacity When selecting heating or air conditioning equipment, it is very important to make sure that the equipment has the capacity to generate enough heated or cooled air to suit the needs of the space, aka the “load.”



…There is more than one way to calculate the load.

Here are 3 possible ways to think about a building’s HVAC load:

Design Load

The design load is meant to represent the average capacity that the HVAC system in a given property will need. First, the HVAC designer considers the attributes of the building such as the building design, orientation, insulation R-value, and air leakage. Data on these attributes is usually taken from the architectural plans so it will be based on an ideal measurements and conditions.

Then, the designer calculates how much heating and cooling power is needed to produce appropriate indoor temperatures in that specific building on an average winter or summer day. For Los Angeles, the winter design load is calculated assuming we need to achieve an indoor temperature of 70F when the outdoor temperature is 40F. The summer design load assumes an indoor temperature of 75F and an outdoor temperature of 89F.

Extreme Load

Of course, there will be summer days when it is much hotter than 89F outside in LA and winter days when it might be colder than 40F. On these days, it might not be good enough to have HVAC equipment with the capacity to merely meet the design load.

This is where the concept of the extreme load comes in. The extreme load is calculated based on what HVAC capacity is necessary on record-breaking days.

However, it is important to remember that there is some lag between when the outside temperature hits a peak and when the inside temperature starts warming up. Often, so long as the building is reasonably well sealed and insulated against air leaks, and your equipment has been successfully keeping indoor temperatures stable, you will never really have your HVAC equipment working against that top number.

Part Load

Extreme temperatures are rare. In the real world, your HVAC equipment will be operating at conditions that are actually less extreme than the design conditions the majority of the time. This can create a real issue with your HVAC equipment actually being oversized for your property’s load, and you may experience comfort and efficiency problems.

Ask an HVAC Expert for Help

The bottom line here is that the determination of the appropriate HVAC capacity for your property’s load is actually quite a nuanced calculation. It needs to be done by a professional who understands the concepts involved and can help you arrive at the right solution for your property.

So next time you are in the market for a new furnace or a new air conditioner, you might not want to just purchase the same size model you had before. Instead, call the pros at Econo West Heating Air & Plumbing for an expert load and capacity calculation.

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