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The importance of heat load calculation in HVAC design

Calculating the heat load is crucial for HVAC design

By HVAC BlogsPublished 2 months ago 5 min read

In the HVAC industry, heat load calculation is a must-have skill. Space cooling is a major drain on building budgets during the warmer months. The goal of heat load calculation is to determine the total amount of heat that must be dissipated from a given space.

A building's heat can originate either from within (via appliances) or without (via the sun). When calculating the heat load, all of the potential contributors are taken into account.

Introduction to the Primary Sources of Thermal Energy

There are many direct and indirect sources of heat within a building, but the following are some of the most common:

Gain of Heat from the Sun

The sun's heat can enter a building through any of these three pathways: conduction, convection, or radiation. Because of the temperature differential between the interior and the warmer outdoor environment, heat is conducted through the walls and roofs of a building. The term "convection" is used to describe the process of heat transfer that occurs when hot air from outside or air of varying temperatures inside moves past different surfaces. Lastly, radiation is a direct form of heat transfer that occurs when sunlight enters a building through windows or other transparent surfaces. Interactions between radiation, convection, and conduction can occur at the surfaces of walls and roofs. The sun is the primary source of heat for a lot of structures.

Think about how the sun moves across the sky throughout the day, and you'll see how important orientation is when calculating solar heat gain for a given room. Surfaces and windows facing east receive the most sunlight in the morning. At noon, surfaces facing south receive the most direct sunlight, while in the afternoon, west-facing surfaces receive the most. Reduced solar heat gain occurs on north-facing walls.

The effects of solar heat gain can be felt instantly or over a period of time, depending on how it occurs. The effect of solar heat penetrating glass windows (radiation) is instantaneous. If, on the other hand, heat is gained through conduction across walls, that heat is stored by the walls and gradually released throughout the night.

Energy produced by human bodies:

A significant amount of heat is generated by the occupants of a building as well. Think about how a person burns off some of the hundreds of calories they consume daily through metabolic processes. When humans engage in strenuous physical activity, they generate even more body heat than usual (sweating).

Keep in mind that the amount of people in a space has an effect on the temperature as well. Therefore, in large air-conditioned spaces like halls, auditoria, theatres, cinemas, and airports, the human contribution to the total heat load can be especially high.

Radiant heat from the outside air:

Outdoor air, also known as atmospheric air or simply air, is the warmer air found outside of climate-controlled spaces. The average indoor temperature rises when cooler outdoor air enters a room.

Although it is natural for air to circulate through a building when doors and windows are opened, unconditioned air can also enter habitable spaces through cracks in the building envelope. Aside from the sun, vehicles and other structures can also contribute to the temperature of the air outside.

Electric and electronic device heat:

Lighting, televisions, coffee makers, water heaters, and other electrical and electronic appliances fill indoor spaces. In conditioned environments, these appliances still generate some heat and waste electricity. The heating effect of appliances can be reduced by using ones that use less energy.

How to Figure Out Heat Load

If you want to know how much heat your building needs, you need to do a thorough survey of every room and record every heat source you find. The HVAC designer then makes recommendations on the type and capacity of air conditioning system needed based on the calculated heat load. This method aids building owners in avoiding the pitfalls of both undersized systems that fail to provide adequate cooling and oversized systems that incur unnecessary initial and ongoing costs.

Only a trained HVAC technician should attempt to calculate a building's heat load because doing so is a complex and time-consuming process. Achieving optimal building performance requires this step as it lays the groundwork for choosing an air-conditioning system of the appropriate type and capacity for the application at hand (e.g., a home, a school, a church, an airport, a movie theatre, etc.).

As a building owner, you should know that HVAC specialists frequently ask for supplementary data, like a copy of the structure's blueprints. Once all required information has been collected, the calculation procedure can begin. A HVAC heat load calculation can be performed either manually or with the help of specialised HVAC software.

Procedure by Hand:

Predefined equations and tabulated parameters are applied to the data obtained from the building survey and supporting documentation. The geometry, materials, and appliances/systems installed in the building inform the selection of the appropriate equations and table values. The HVAC designer uses these numbers to advise on the best type and size of air conditioner to install.

The Role of Software

Residential Heat load calculation are typically done in software such as Trace 700 and HAP (Hourly Analysis Program) by today's HVAC designers. There is a need for a high level of technical expertise, but much of the mundane, time-consuming work can be done mechanically. Inputting the information from the building survey, architectural plans, and other sources is all that's required. It is much simpler and quicker thanks to the HVAC software, which calculates heat loads automatically and suggests the necessary air-conditioning system capacity.

Both the individual room heat loads and the overall building heat load are calculated. In order to provide technical recommendations for peak performance, HVAC designers and consultants can use these calculations.

Conclusions and Suggestions

In reality, investing in professional design services is a wise choice. A properly engineered HVAC system provides sufficient cooling for the building it serves at the lowest possible cost to the building's owner. Code compliance and paperwork, both of which can be time-consuming in York City, are two other benefits of hiring professionals.

If your home or business has a sizable roof, solar energy may be an option for you. New York has great rebate programmes, and by taking advantage of them, you can lessen the impact of solar heating while adding a green energy source to your home.

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