Heating and Cooling Loads: Learn the Fundamentals
What are heating and cooling loads?
The HVAC industry describes the amount of conditioning homes need as heating and cooling loads (also known as thermal loads). The load refers to the amount of work any system must do to keep the structure comfortable.Heating loads refer to the amount of heat energy required to be added to an area to maintain the temperature in an adequate range. On the other hand, cooling loads refer to the amount of heat energy that needs to be removed from an area to maintain the temperature in an adequate range.
Before learning about the different types of heating and cooling loads, it’s important to distinguish between load and capacity. If you’re new to the HVAC system, it’s easy to get confused between the two.
Load means the amount of heating or cooling required by a building. Capacity refers to the amount of heating or cooling an HVAC system can offer.
Thermal loads consider the following factors:
- Your home’s construction and insulation (including walls, floors, and ceilings)
- Your home’s glazing and skylights (which are based on performance, size and overshadowing)
What are the different types of heating and cooling loads?
HVAC professionals base the size of the systems they install on their capacity to satisfy three different kinds of heating and cooling loads.
Before buying new HVAC equipment, it’s important to have a deeper knowledge about these three types to ensure that you’re purchasing an appropriate capacity.
Three Types of Loads
- Design load
- Extreme load
- Part load
Design loads are directly linked to the designated design specifications in your home. In other words, calculating the amount of heating and cooling load your HVAC system requires depends on the predetermined winter and summer temperatures of your area. For example, the design temperature in Florida is around 90°F in summers and 65°F in winters.
The most influential load HVAC engineers consider is the design load of structures. This load includes the layout of the building, its overall energy efficiency and orientation to the sun. Homes that have adequate insulation, thermal windows and little air infiltration have lower design loads. Two-story homes have different conditioning loads than single-story homes.
The extreme load refers to the hottest and coldest temperatures any given place experiences. Unlike the design load, this load carries little weight when HVAC contractors calculate the size HVAC equipment needs to be. Extreme weather conditions seldom last long enough to have a measurable impact on the overall performance or comfort of a properly sized HVAC system.
The part load, combined with the design load, weighs heavily on calculating the heating and cooling loads in terms of its capacity, along with the type of system selected. In our region, humidity factors into the part load, and in the cooling mode, humidity makes a difference.
Humidity adds to the amount of work an air conditioner or heat pump has to do to cool the air. Besides calculating the cooling load for homes, HVAC pros use software tools to evaluate the suitability of a system to manage the latent heat load, which describes heat plus humidity. The sensible heat load is the air temperature only.
Florida has a high latent heat load. When upgrading your HVAC system, insist that the HVAC contractor calculate the heating and cooling load.
How to Calculate HVAC Load
The most appropriate way for sizing an HVAC unit is the Manual J residential calculation. This calculation is mostly carried out through complex computer programs, which require energy, time, and money. For this reason, contractors have made the BTU calculator a rule of thumb. In the heating and cooling industry, BTUs are used to measure the amount of heat that an air conditioning unit can remove from a room per hour. By measuring BTUs (British Thermal Units), technicians can define a general estimate while in the field. A perfectly sized HVAC unit will make sure that the desired space can reach the right temperature without wasting energy.
Step 1: Find the square footage of your home
You can determine the square footage of your home by looking at the blueprint or measuring the entire place room-by-room. Begin by calculating the length of each room, and multiply those measurements to estimate the square footage of that room. Add all the calculations you get from each room for your final result.
Another method of finding square footage is by calculating exterior measurements of the whole house and subtracting the square footage of any area of the home that you don’t want to be heated or cooled, like your basement or garage.
Don’t forget to measure the height of the rooms. Rooms having tall ceilings likely require more BTUs as compared to the ones with a standard height.
Step 2: Consider factors that influence insulation
Look to gauge what grade of insulation the home was built with. If you’re not quite sure, U.S. Standard Insulation is a good resource. Other crucial points to take into account are windows, sunlight, and airtightness for the whole house.
Points of reference include:
- Add 100 BTUS for every member of the household
- Add 1000 BTUS for every window
- Add 1000 BTUS for every exterior door
Step 3: Imagine how your living space is being used
Does your house or a specific room have heat-producing devices? How many members occupy the area you are calculating, daily? This should also define the HVAC load that will be enough to heat or cool the particular space.
Let’s put theory into practice. Let’s say your house is 2500 sq. ft. and has 10 windows, 3 exterior doors, and is occupied by 5 members.
Follow the formula below:
- 2,500 x 25 = 62,500 base BTU
- 5 members x 500 = 2,500
- 10 windows x 1,000 = 10,000
- 3 exterior doors x 1,000 = 3,000
- 62,500 + 2,500 + 10,000 + 3,000 = 78,100 BTU
Ready to estimate the thermal loads of your home?
Heating and cooling load calculation is an essential skill for HVAC designers and consultants. We all know that heating or cooling space is the biggest energy expense. To estimate the size of a heating or cooling space, we must be aware of the amount of heat that must be added or removed.
To learn more about heating and cooling loads, contact Rinaldi’s Energy Solutions, providing outstanding HVAC services for Orlando area homeowners since 1969.