Calculating the heat load is a crucial skill for HVAC consultants and designers. Keep in mind that one of the biggest energy consumers in buildings, particularly in the summer, is space cooling. However, in order to appropriately size a space cooling system, we must first determine the amount of heat that must be removed. Calculating the heat load serves this function.
Buildings can generate heat from both interior (from electrical appliances, for example) and external (from the sun) sources. Calculating the heat load takes into account all available sources and calculates their combined impact.
Summary Of The Principal Heat Sources
The following are some of the primary sources of heat generation in building interiors, while there are numerous other direct and indirect methods as well:
1) Solar Heat Gain
Heat from the sun can enter interior spaces by conduction, convection, and radiation, among other methods. Due to the temperature difference between building interiors and the warmer outside environment, conduction happens over walls and roofs. Convection is the term for heat transfer caused by hot outdoor air moving in large quantities or by hot inside air moving over cold surfaces. The last type of heat transfer is radiation, which happens when sunlight enters structures through windows or other transparent surfaces.
Conduction can interact with radiation and convection at the surfaces of walls and roofs. The sun is the main source of heat for many structures. Given that the sun’s location in the sky fluctuates throughout the day, the direction or alignment of a room has a significant impact on how much solar heat gain it receives. East-facing windows and walls receive direct sunlight in the morning. In the midday hours, south-facing surfaces and west-facing surfaces are both directly exposed to the sun. The least solar heat gain is experienced by walls that face north.
The impacts of solar heat gain may be felt right away or gradually, depending on how it happens. For instance, solar heat (radiation) that enters through glass windows has an instantaneous impact. On the other hand, when heat is gained through conduction through walls, the walls themselves act as heat storage devices, releasing heat within throughout the night.
2) Heat From People
Inside of buildings, people are a primary source of heat. Take into account that a person consumes hundreds of calories of food each day, and that some of this energy is converted into heat during metabolic processes. When engaged in vigorous physical exercise, humans produce much more heat through perspiration (sweating).
Take into account the fact that human heat gain varies with occupant density. As a result, in big air-conditioned places like halls, auditoriums, theaters, cinemas, and airports, people might contribute a lot more to the overall heat load.
3) Outdoor Air Heat
Also known as atmospheric air, outdoor air is the warmer air found outside of climate-controlled facilities. The average room temperature tends to rise when outdoor air enters indoor rooms because of its greater warmth.
Outdoor air can also enter conditioned spaces through leaks near doors, windows, and other building envelope components, even though some air exchange occurs naturally when doors and windows are open.
Although the sun is a major source of the heat in outdoor air, additional sources include moving objects and other structures.
4) Heat from Electrical And Electronic Appliances
Electrical and electronic appliances, such as light fixtures, television sets, coffee makers, water heaters, etc., are ubiquitous in indoor settings. In air-conditioned areas, these equipment use electricity and produce some heat. Reduce the heating effect of your appliances by using energy-efficient models.
Procedure For Calculating Heat Load
A survey of every room in the building is required to determine all the heat sources present in order to calculate the heat load. The HVAC designer then suggests the kind of air conditioner suitable for the application and its necessary capacity based on the heat load calculations. This strategy aids property owners in avoiding undersized systems that provide insufficient cooling as well as oversized systems with greater initial and ongoing costs.
Only a licensed HVAC specialist is capable of performing the extremely specialized, time-consuming, and complex task of calculating heat load. It also serves as the foundation for choosing an air conditioning system with the right type and capacity for the application at hand, such as a residential building, hall, auditorium, theater, cinema, airport, etc., and is crucial to achieving optimal building performance.
If you are a property owner, keep in mind that HVAC contractors frequently need additional information, like the building’s architectural drawings. When all of the required information has been acquired, the computation process begins. A heat load estimate can be done manually or with software, which are both viable options.
Predefined equations and tabular parameters are used to analyze the data obtained from the building survey and related documentation. Based on the building’s geometry, the materials used in its construction, and the appliances and building systems located inside, the precise formulae and table values to employ are chosen. The HVAC designer suggests an air conditioning system with the appropriate kind and tonnage based on these estimates.
To calculate heat loads today, the majority of HVAC designers utilize programs like Trace 700 and HAP (Hourly Analysis Program). Although this still takes a substantial amount of technical knowledge, many tedious and repetitive procedures have been automated. The information from the building survey, architectural blueprints, and other relevant material gathered must only be input. The process is made simpler and much quicker by the software’s automatic heat load estimates, which also indicate the necessary air-conditioning system capacity.
All regions of the building’s heat load are calculated, and the overall building load is also established. HVAC designers and consultants can offer technical solutions to attain peak performance based on these calculations.
Although they may appear to be an expense, professional design services are actually an investment. The cooling requirements of the building are met by a well-designed HVAC system at the lowest possible ownership cost. Working with specialists also ensures adherence to codes and streamlines paperwork, which can take a long time in smany cases.
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