Modern structures now house an ever-growing array of electrical devices, and this surge in technology is driving up the need for electrical power to sustain these integral components of contemporary business operations. This article will delineate the fundamental considerations when assessing the electrical load for residential and commercial buildings. It is imperative to have a realistic estimation of operating load requirements to attain a well-engineered electrical distribution system.
During the initial planning phases, it is improbable to possess exhaustive details about the equipment destined for installation in a building, irrespective of its intended purpose. To enable the progression of planning, engagement with utility companies, and the formulation of decisions necessary for specifying critical components of machinery and service equipment, the design engineer must possess the confidence to generate accurate load estimates. These estimates should draw from experience and a comprehensive database of actual operating loads from comparable projects, or a schedule shared by the clients.
The client has a responsibility to ensure that all designers and contractors participating in the project have access to pertinent pre-construction information related to their respective roles. This information encompasses details regarding the site and its impact on the construction work, insights into the intended use of the structure as a workplace and the lead time granted to contractors appointed by the client for planning and pre-construction preparations.
Electrical Loads within buildings, residential and commercial, can be classified into these categories
- Lighting
- Small power and fixed loads
- HVAC loads
- Lifts and escalators
Lighting
Light is a form of energy that may be transmitted through space without the need for any material or substance to help propagate it. Such energy transfer is known as radiation.
The objective of any lighting installation is to meet all the lighting needs of the people using the area being lit whilst consuming a minimum of energy. The basis of energy efficient lighting is to provide the right amount of light, in the right place, at the right time with the right lighting equipment.
The table below gives the lighting load capacities for broad planning purposes.
| Building Type | Minimum Load Capacity (W/m2) |
| Residential Building | 8 |
| Office | 16 |
| School | 8 |
| Hospital | 6.5 |
| Church | 4 |
| Hotel | 6.5 |
Small Power and fixed loads
Small power typically encompasses devices that are either plugged into electrical sockets or permanently connected within a building. These items are usually brought into the building by its occupants, rather than being selected by the building services designer. The demand for small power varies significantly across different areas within a building; some spaces such as dining areas, and receptions may have minimal small power requirements, while others, such as kitchens or offices with computers, may exhibit relatively high unit loads. In cases where specific areas are known to have substantial loads, it is advisable to consider a higher average load for those areas
The table below gives the small power load capacities for broad planning purposes.
| Building Type | Minimum Load Capacity (W/m2) |
| Residential Building | 22 |
| Office | 44 |
| School | 22 |
| Hospital | 18.5 |
| Church | 11 |
| Hotel | 18.5 |
HVAC Equipment
Heating, Ventilating and air conditioning equipment in modern buildings can account for 40-50% of the total electrical load of the building. The nature of the building materials also affects the expected load for the building, fresh air requirements, equipment to be cooled, appliances to be used etc. The highest load of either heating or cooling should be used for broader system calculation since they are usually not simultaneous. In a typical heated and cooled office building, the electrical load could be estimated at 40-50W/m2.
In conclusion, during initial design calculations, it’s recommended to base unit loads on a W/m2 (Watts per square meter) basis. To do this, use the gross area of the building but subtract known non-usable spaces like shaftways and voids. When you’re estimating loads, there’s no need to get overly precise by factoring in the thickness of exterior walls or columns. Typically, the difference between lettable areas and building gross areas won’t significantly affect equipment selection, unless you’re using unreasonably large unit loads for your calculations.
For precise load calculations, it important to note that operating loads rarely equal the sum of installed load capacity. Electrical systems can be broken into groups of smaller branches with several other smaller branches. Diversity usually occurs because not all loads can be connected/operating simultaneously. Demand factor on the other hand takes into consideration the maximum power rating of a point to the connected load. This is usually a unit less than 1. Example a 13A 240V socket outlet with a connected TV of 100W will have a demand factor of 0.03 (100/13*240). Will publish an article to further elaborate this topic.
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