In addition to the most significant heat source in a building, i.e., the sun, other heat sources are generated inside the building, the so-called internal heat gains.
There are three kinds of heat sources inside the building: people, lighting, and equipment.
The amount of thermal energy produced by these three sources is calculated similarly, similar to the calculation of the solar gain mentioned in the previous lesson. It is always the amount of energy in W, multiplied by the time during which the energy is released. And that’s it! It is important that you truly understand what is calculated. If a building is larger, it is logical to have more occupants, lighting bodies, and devices to produce more thermal energy. That’s why this calculation is connected to the unit of area.
Let’s discuss in more detail how these data are obtained.
We all know that our bodies release a certain amount of thermal energy depending on our activities. When calculating the amount of energy obtained from the occupants, the most crucial information is the purpose of a building. For example, it is not the same if two buildings with the same surface area have 10 or 100 occupants and if those people sit at a computer or do a sport. An entirely different amount of energy will be released per m2 or ft2 in the same space. This information is usually found in ready-made tables and information on the type of buildings, and we’ve prepared one such table as a bonus for you.
So, as we said, this information is multiplied by the number of working hours per day and the number of working days per month to precisely calculate how much thermal energy is obtained from the users for a month.
Information on average installed power density for lighting and equipment per area unit is also found in ready-made tables. These data also depend on the purpose of the building. For example, an office building where lighting and computers are on for most of the day and a private house whose users spend most of the day outside won’t receive the same heat from these two sources. These data can also be found in projects for the systems if you want precise figures or in ready-made tables, but you must understand the essence of what is calculated.
Let’s repeat. The gains from both lighting and equipment are calculated precisely the same way by multiplying thermal energy with the period of use monthly or annual.
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To include the building size factor in this calculation, heat emission and average installed power density are usually expressed by area unit, i.e., in W/m2 or W/ft2, and then multiplied by the heated area to calculate heated gains kWh on a monthly or annual basis.
When these heat gains are calculated, they are added to solar heat gains to calculate the total heat gains.
And that’s it. It’s not complicated.
