Energy efficiency measures normally have an upfront cost, which means there is a payback period involved. However, some low-cost measures achieve a payback of less than one year. Recommissioning is a good example, since it only involves skilled labor and the reconfiguration of existing components. In addition, energy efficiency brings a benefit that is not always considered: it reduces the load on electrical wiring.
When energy efficiency is deployed in an existing building, the wiring ends up oversized thanks to the reduced load. However, energy consultants do not recommend a circuit replacement in these cases: rewiring with smaller conductors has a cost, while leaving the existing circuits is free. The outlook is different in a new construction, since circuit capacities can be optimized before starting the project.
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A wiring replacement is recommended with energy efficiency measures if the existing conductors are damaged. For example, the insulation of old wires can harden and crack over time, exposing live conductors. Electrical faults are much more likely under these conditions, and safety can be improved with new wiring.
Wiring Size Reduction Example: LED Lighting
LED lighting is typically recommended after energy audits, since it achieves an attractive return on investment in most buildings. LED lamps consume less power than those they replace, while lasting much longer. As a result, they achieve both power bill savings and maintenance savings.
Thanks to the high efficiency of LED lamps, they reduce the current that must be carried by lighting circuits. Upgrading one lamp does not have a noticeable effect, but the cumulative current reduction can be significant when many lamps are involved.
As an example, assume a distribution center uses 500 metal halide fixtures that consume 440W each. When all the lights are on, the total power consumption is 220 kW. With a 220V power supply, this results in 1000A in a single-phase installation, and 577A in a three-phase installation. Consider the effect of replacing all these fixtures with an equivalent LED product that consumes 150W:
- The total power consumption is reduced to 75 kW.
- The total current is reduced to 341A for a single-phase installation, and 197A for a three-phase installation (assuming 220 V in both cases).
With such a reduction in current, wiring costs can be reduced significantly. It is also possible to use more lamps per circuit, reducing the number of circuit breakers needed to protect the entire installation. The cumulative effect of many energy efficiency measures can also allow the use of smaller transformers, achieving additional savings. To summarize, an energy efficiency installation can use smaller conductors and protection devices with a lower rated current.
Energy Efficiency Increases the Capacity of Existing Wiring
As previously mentioned, there is no need to downsize the wiring when energy efficiency measures are used in an existing building. New circuits have a price, while existing installations have already been paid. In fact, reducing the load on existing conductors brings an advantage: spare circuit capacity is obtained without new wiring.
For example, if a 220V circuit can deliver a current of 30A, it can power 15 of the 440W metal halide fixtures. However, this same circuit can power 44 of the 150W LED lamps. In this case, the LED upgrade has essentially tripled the circuit capacity.
These examples use lighting circuits because they are simple, but the same principle holds for other types of electrical equipment. Energy efficiency measures for mechanical ventilation, pumping and air conditioning systems also reduce the current drawn by equipment. All this load is subtracted from the required capacity of conductors, protections and electrical service equipment. As a result, the electrical installation becomes less expensive.
How Energy Efficiency Adds Value
The benefits of energy efficiency extend beyond power bill savings and less expensive wiring. Buildings that use efficient equipment may also be eligible for rebates or other financial incentives, which help cover the cost of upgrades. Developers who offer residential and commercial spaces for rent can also use energy efficiency as a marketing tool: paying less for electricity and gas is an attractive deal for tenants.
New York City has taken a very proactive stance with building energy efficiency. Properties covered by the benchmarking law will required to publicly disclose their building energy grades starting from 2020, and the NYC Green New Deal sets a 40% emissions reduction target for 2030.
Since each property is unique, the effectiveness of energy efficiency measures varies. To identify the most cost-effective measures for a building, the best recommendation is getting a professional energy audit.