Calculating Your Building’s Heating and Cooling Load: Where the Peak-Load Analysis Comes In

In both commercial and residential settings, a heating and cooling load calculation is critical to finding and installing HVAC equipment that will work at its best possible level of efficiency and effectiveness. As part of your building’s heating and cooling load calculation, you should also have your HVAC professional conduct a peak-load analysis. This assessment will give you additional information on your building’s heating and cooling demands that will help you reduce building loads even further, saving energy and reducing your ongoing utility bills.

Why Do a Heating and Cooling Load Calculation?

A properly performed heating and cooling load calculation tells you and your HVAC professional exactly how much heating and cooling is needed to keep your indoor spaces at the temperature you prefer. When you know this important information, you will be able to confer with your contractor and choose a furnace, heat pump, air conditioner, boiler or other temperature-control system that will produce the level of indoor comfort that is required.

Characteristics of a Heating and Cooling Load Calculation

A heating and cooling load calculation should be performed using industry-accepted standards and procedures, such as the processes set forth in Manual J, “Residential Load Calculation” or Manual N, “Commercial Load Calculation,” both published by the Air Conditioning Contractors of America (ACCA). These manuals and the accompanying software provide sophisticated tools for assessing the thermal characteristics of your home or commercial facility, and using those characteristics to determine the structure’s heating and cooling load. They will take into account factors such as:

• Local weather and climate.
• Building seal and energy-efficiency features.
• Directional orientation of the building.
• Number and orientation of windows.
• Occupant temperature preferences.

After an on-site inspection and taking of extensive measurements, the data collected will be entered into a computer program that performs the complex mathematics and delivers the final load calculation.

The Importance of the Peak-Load Analysis in Heating and Cooling Load Calculation

A peak-load analysis adds an additional layer of evaluation to your load calculation that can help you determine when your heating and cooling equipment will be most likely to function at its highest capacity, and what can be done to reduce energy usage during those times. Peak-load analysis can help you and your HVAC contractor account for situations such as:

• Changes in peak cooling months and how that affects use of natural lighting: Indoor lighting is a significant source of heat, and in many cases, natural daylight will be used to offset these lighting-based loads. When changes in natural lighting occur during seasonal changes, the peak cooling month might shift from sometime in the summer to October. This occurs because the position of the sun in the sky still creates enough heat in the daytime to require indoor cooling, but reduces the effectiveness of shading systems and overhangs.
• Sources of largest cooling loads: The largest cooling loads in your building may occur because of sunlight-based gains through windows on the west side of the structure. The peak-load analysis should show you if this is occurring. Solutions include installing insulated window units or low-emission glass, putting shades on windows that receive excess sunlight, or adding outdoor shades or landscaping features that block sunlight.
• Sources and types of peak loads that occur in winter: In the winter months, the building’s peak load may occur in the morning when the structure is warming up. If this is happening in your building, you can solve it by installing a heating system that will take care of this morning load but work at a lower level at other times. Adding shades and screens or reducing the number of windows on the west side of the building may also be an effective solution.

Our goal is to help educate our customers about Plumbing, HVACR, Fire Protection and Alarm Systems in Mechanical, Commercial and Residential settings. For more information on heating and cooling load calculations and the importance of the peak-load analysis, or to view projects we’ve worked on, visit our website!