When outages hit your commercial customers, lives and money are on the line. That makes having a reliable source of backup power critical. Yet for large buildings with many applications drawing power, finding the balance between enough energy to keep essential services running and what the budget can accommodate is often a challenge.
Construction pros like you play an important consultative role in this process. To do so effectively requires anticipating the risks customers face in the event of an outage — whether that’s spoiled product or loss of life.
When is backup power necessary?
Those risks vary by application. For example, many schools double as emergency shelters and should be equipped with sufficient backup power, says Michael Kirchner, senior sales training manager for Generac Industrial Power. Emergency lighting and signage should also be backed up to help ensure a safe evacuation. (In retrofit construction these general applications typically have a battery backup, while in new construction they are tied to the generator.)
Retailers and storage facilities, too, must be prepared to safely evacuate workers and customers during an outage. Therefore, ensure emergency lighting, elevators, escalators, and automatic doors are connected to backup power, says Nicole Dierksheide, senior product manager at Kohler. Cold storage is typically billed as a critical load due to the potential for product damage.
Retailers may also want to continue operations during outages, especially in areas where they are frequent or if the store expects to be in high demand during and after storms. Think grocery and home-improvement stores. That means backing up point-of-sale systems, general lighting, and HVAC as well.
Multifamily projects back up elevators and emergency lighting, along with critical loads for each unit. Those typically include a refrigerator and a single outlet in each dwelling so residents can charge mobile devices.
Healthcare facilities prioritize life-safety loads, including emergency rooms and intensive care units, Dierksheide says. More states are requiring air cooling as well. In June 2018, Florida began requiring nursing homes and assisted living facilities to have at least 96 hours of backup power. The rule followed the deaths of 12 elderly nursing home residents during a power outage caused by Hurricane Irma that led to sweltering indoor temperatures.
The desire to preserve occupant comfort and safety — not to mention the regulations that mandate it — are often best addressed with whole-building backup. “Comfort and sustained operation will tend to take you down the path of a whole-building application,” Kirchner says. “Those with limited budgets will tend to want to leave cooling out of the scope. People are realizing buildings can’t sustain extended outages without cooling.”
Projects in outage-prone areas or whose business spikes during storms are also advised to back up all systems, he says. And depending on the company, losses from just one outage can encourage a building owner for whom standby power is optional or partial to switch to full backup.
Sizing the backup load
“A good rule of thumb is for the generator to be sized for 80% of total load demand,” says Dierksheide. Standby generators are typically rated to run at that level for an unlimited time and at 100% for short periods of time. So if the peak demand load is 800 kW, then a 1,000 kW generator is ideal, she says.
Generators not sized to handle peak demand should be set up to add and drop noncritical loads as needed during an outage to ensure sufficient power for critical loads. It’s worth noting that features such as cold storage and air conditioning increase backup power demand significantly. When calculating the backup load, Kirchner recommends assuming 1 kW per ton of cooling.
One way to determine the backup load is by taking the sum of all loads to be used during an outage. And be sure to consider the extra current needed to kick-start nonlinear loads, such as motors and pumps. “By staggering the startup of multiple nonlinear loads, the peak demand of inrush current can be controlled and the motor starting demand on the generator can be reduced,” Dierksheide says.
“A good rule of thumb is for the generator to be sized for 80% of total load demand.”
Knowing the minimum expected load is also important. Dierksheide gives the example of a manufacturing facility that runs two shifts a day and shuts down during the third. “If there is a loss of utility during the first or second shift, the load demands are large, but during the third shift they are minimal,” she says — although they still must be covered.
Diesel generators typically don’t operate at less than 30% of peak load to avoid a condition called wet stacking, in which the generator doesn’t create enough heat to burn off all the fuel particulates and fuel then enters the exhaust system. “Gaseous generators do not have this concern and can be a great consideration in applications that see great variations in load demand,” Dierksheide says. They can also be oversized to accommodate expansion.
Kirchner advises sizing 20–25% above the highest 12-month utility peak demand.
Today, applications above 500 kW tend to opt for diesel-fueled standby generators, while natural gas dominates the market below 150 kW, Kirchner says. Propane is typically used for the latter group of projects, which can include several critical community spaces including nursing homes, schools, government buildings, multifamily, retail, and other light commercial projects. (To determine what fuels are allowed for backup power in your project, refer to the National Electric Code.)
Propane offers several advantages for backup power. It can be stored on-site, which is required for some applications that have Level 1 (life safety critical) loads, Dierksheide says. It can also be an advantage in areas vulnerable to seismic activity, which can cause the natural gas lines to be shut off. Plus, gas tends to produce fewer pollutants than diesel, a common generator fuel option.
To learn more about the advantages of propane-fueled standby power and to start the conversation with your customers today, download our commercial generators brochure and check out our Propane Training Academy course on commercial backup power.