I received a disturbing call the other week from an aspiring baker in Vancouver. She was young and excited at opening her own bakery. To keep costs low, she was working with the landlord to determine if the existing electrical supply was enough to power her new store. She had spent 3 weeks doing an electrical load calculation before becoming exasperated.
As electrical consultants, stories of struggle from our clients are not fun to hear. She was struggling with electrical engineering calculations as much as I struggled with baking a birthday cake. Our attempts at each other's speciality did not go well.
When she heard that we could complete her electrical task in less than one day, she was immediately relieved.
Electrical load calculations require:
Electrical load calculations need to account for all equipment including heating, ventilation and air-conditioning (HVAC) equipment. These two redundant units are in a 7-storey office building in Edmonton.
- knowledge of the Canadian Electrical Code,
- detail workings of how the rules apply to various commercial and industrials loads,
- understanding of single phase and three phase power distribution systems,
- experience with determining realistic demand factors.
Load calculations are one of the first steps in the design process of a building's electrical distribution system. To determine the correct size of the incoming power supply, we talk and listen with the client to find out what equipment they have and how it's going to be used.
How to do Electrical Load Calculations in Canada
Knowing how to correctly size commercial and industrial loads is an essential skill for electrical consultants.
The Canadian Electrical Code Section 8 lists the general rules for electrical loads. Table 14 documents the demand factors and Watts per square meter for different types of buildings and occupancies. A bakery is going to use a lot less power than an autobody shop.
Electrical Load Samples
Every business uses electricity in different ways. Here are some of the rules, as stated in the CEC, that we apply when determine the size of main service for your specific business:
Arc Welders (Section 42) - For light-industrial shops, a number of welders can be used at the same time. The following demand factors are listed in Rule 42-006 (2):
- 100% of the two largest calculated currents of the welders in the group plus
- 85% of the third largest plus
- 70% of the fourth largest plus
- 60% of the remaining.
As electrical engineers, we discuss with our clients if such usage is realistic. Sometimes we can use our engineering discretion to lower the demand factor to realistic levels.
Electric Space Heaters (Section 62) - For residential buildings, the first 10 kW of electric baseboard heating shall be calculated at 100%; 75% demand factor for the rest.
These are realistic values even for Edmonton and Calgary where the electrical heaters will cycle off and on during the cold winter, but rarely will they all be on simultaneously.
In Kelowna and Vancouver, with the mild winters, we still have to apply to Rule 62-116(2) while keeping in the back of our mind that there is an extra margin here.
Electric Hot Water Tanks (Section 62) - The demand factor for connecting electric hot water tanks shall be calculated at 100% demand factor.
Elevators (Table 62) - The demand factor decreases as the number of elevators and dumbwaiters increase in a building. For some buildings, like wineries and hotels with 1 elevator, we have to follow the CEC and assume a demand factor of 1.
This means that it can be used continuously (i.e. during the busy morning checkout time) and must always have a readily available amount of electricity. People have got to kept moving!
This older electrical room in Calgary was redesigned and upgraded after an electrical load calculation was completed.
Commercial laundry - This was a shocker on our first design of a commercial laundry. There are no mention of demand factors or derating for this type of commercial space so we had to design for the appliance nameplate. We had to assume that at peak usage, (i.e. after a long weekend), that all machines could be running simultaneously and continuously for more than 3 hours in a 6 hour period (Rule 8-104(3)(b)). The main service was HUGE for these commercial washer and dryers!
Commercial Kitchens - Most restaurant kitchens in Alberta and BC are gas-powered which cost less to operate (gas and exhaust systems are designed by mechanical consultants). Gas-powered fryers, ovens and grills reduce the overall demand of more expensive electricity. For the electric ranges, 'the demand shall be considered as not less than the rating', (Rule 8-300(3)).
Lighting and Building Signs - The Canadian Electrical Code requires a minimum load per square meter for general lighting. This allowance varies by type of occupancy. However, speciality lighting is considered a separate line item. With Canadian winters having long hours of darkness, we generally consider specialty commercial and industrial lighting designs as continuous loads.
General Demand Factors
We need to understand how a client's business operates to design an appropriate electrical distribution system that's customized for your business.
We design for realistic conditions and not the maximum connected load to avoid over-provisioning and to save money. For instance, when electric space heating is installed (only used during the winter) and an air-conditioner is also installed (only used during the summer), we can safely assume that both will never run simultaneously. Then our calculation need only take into account the largest electrical demand of the two instead of both.
Demand factors for recreational vehicle parks and Marinas are completely different and have separate rules due to their transient demand.
Calculating Electrical Load on Existing Buildings
It's impossible for clients to remember the electrical requirements of their equipment. In this case, when we do tenant improvement projects that are additions to an existing installation, we are permitted to add to the maximum demand load as measured over the most recent 12-month period while still respecting the other CEC rules. Or we may conduct an electrical load monitoring test. Huh, you may ask? Don't worry, we'll take care of the electrical design for your business expansion.
Every profession is specialized. Bakers are valuable because they know how to bake. Electrical consultants are specialized because we understand how to design power distribution systems for commercial and industrial clients. An electrical load calculation is one skill we use to make building power systems that are reliable, safe and compliant to code.