Research

 

Study on DC Power Systems in Buildings

 

Through research on DC verses AC power supply systems in buildings, it is found that in the case of the BAM Fisher building it is not feasible to have a DC power system. The reasons for recommending against using a DC power system are as follows:

 

• Lower voltage means higher current. Higher current requires larger wire sizes and thus more copper usage, which is expensive.

• Many large appliances and HVAC systems, which use a majority of the building’s energy (fig. 1) run on very high voltage. These systems would need the DC power converted back into AC power to run. This will create losses, which the DC power system was aimed to reduce.  Although LED lighting could be run on DC only power (instead of having a driver) the overall percentage of building energy from lighting is relatively low in comparison, especially when using LEDs and meeting Standard 90.1 codes.

• Electronics and other low voltage systems that currently use a same AC to DC transformer on the plug head (i.e. a laptop charger), run on different voltages. Therefore the supplied DC power would still need to be transformed from DC to DC instead of AC to DC. Again, creating the losses the system was to avoid. Electronics also do not contribute a significant about of energy to building systems. (See Figure 1)

• In addition, all Electronic items would face an issue with economies of scale. These items would need custom chargers, plugs, etc, as they do not come with DC options as a standard option at this point.

• Renewables create DC power, which when converted to AC use occurs loses. However, as there are only a small purposed amount of renewables on the building, these loses are negligible when looking at the entire building load.

• Power line pole mounted transformers transform high voltage AC power to a usable level for homes. They are very high in efficiency. At this time the AC-AC conversion is the highest efficiency. It is unlikely DC-DC transformers would perform as well. Again, creating more loses.

• From a distribution standpoint, high currents and long distances (i.e. more electrical resistance) will create significant voltage drops.

 

From these points, DC power will likely not reduce loses and create a more energy efficient building. At least, not at this time. Perhaps, as we evolve as a society we may develop a universal standard around 12 volt DC for all electronics, develop a standard wall plug for 12V, or revise the current wiring codes to reduce the number of 110V outlets and circuits required. However, at this time it is not feasible.

Another thought was to create two systems, one DC and one AC for the building to split the loads between the two. All low voltage systems such as LED lighting, lighting controls, computers, telecommunication, and security systems would run on the DC power. However, based on the points above, this is also deemed unfeasible. In addition, from a construction standpoint, it would be incredibly important to ensure none of the wiring got accidentally wired to the wrong system. Also, electrical contractors are not familiar with wiring DC only systems. Finally, more electrical equipment would be needed; two main distribution panels, etc.