13
Maintaining Backup Power to Critical Systems
5.8b Resilient Energy Systems:
Islandable Power.
 
13
Maintaining Backup Power to Critical Systems
During a power outage, backup power is vital to continue building operations and make repairs during and after a storm event.

Description + function

Larger, high-rise residential buildings are typically required to have backup power for critical functions, such as the operation of one elevator and a fire-suppression pump. Smaller buildings are not. Backup power becomes even more necessary if residents are sheltered in place during power outages.

 

Some buildings install a permanent exterior connection so it is easy to roll up a temporary generator and plug it into the emergency circuits.
 
During a large-scale emergency, generators, fuel and energy professionals will be in high demand and short supply.

Strategy into action

Outlets on the critical-load circuit can be
designated for emergency use only.
Image: Kristy Johnson

 

 

Sizing a generator.

Consider what systems will be connected to the generator’s emergency circuit. The higher the power needs, the more complex and costly the system must be.

Local codes frequently require that when a generator is installed, it powers emergency lighting, fire-suppression pumps, at least one elevator, at least one sewer ejector and other equipment.

In addition to the minimum requirements, consider adding:

  • Emergency outlets to charge cell phones and computers.
  • Electronic igniters for gas- or oil-fired heating systems.
  • Fans and pumps for heating systems.
  • Water-booster pumps to deliver potable water to upper floors.
  • Sump pumps.
  • Telecom systems.
  • Cable modems and wireless routers.
  • Alarms and security equipment.
  • A central washer and dryer.

Transfer switches.

  • When utility power fails it is essential to smoothly and safely switch to emergency power. Most systems include a transfer switch which makes this happen.

Automatic transfer switch (ATS).

  • An ATS continuously monitors electric utility power and automatically switches over to emergency power when necessary, then back to normal power.

Manual transfer switch (MTS).

  • An MTS must be activated by staff and takes much longer to switch power over than an ATS. Much less expensive than an ATS, an MTS is much more challenging to operate.
 

 

 

 

 

A place to charge cell phones is a high priority for residents during a disaster.
Image: Kiersten Chou.

Generator systems

 

There are many types of backup generators, each with advantages and disadvantages. You must consider the needs of your site when selecting an appropriate generator, including the location where it will be installed, fuel storage issues, the amount of emissions it will produce and your budget.

 

 

image

Gasoline Generators

  • Small, portable and used in single-family homes.
  • Store only a few gallons of gasoline. Need to be refilled daily.
  • Should never be used indoors. Emissions must be prevented from entering the building.

Storage

On-site, usually in small containers.

Quantity of Emissions

Moderate

Fuel Cost

$

Special Issues

Storage life limited; plan for cycling needed. Highly flammable. Tanks must be anchored.

 

image

Propane / LPG (Liquified Petroleum Gas)

  • For mid-sized systems serving multifamily buildings.
  • Work like natural gas generators, but fuel is stored on-site.

Storage

On-site, in tanks.

Quantity of Emissions

Low

Fuel Cost

$$

Special Issues

Highly explosive. Tanks must be anchored; larger tanks are usually buried.

 

image

Natural Gas Generators

  • Use piped, utility-supplied fuel rather than stored fuel.
  • Will not function if gas supplies are shut off during natural disasters .

Storage

Piped to site.

Quantity of Emissions

Low

Fuel Cost

$$

Special Issues

Gas pipelines may be shut off during disasters to avoid fires. Highly flammable.

 

image

Diesel Generators

  • Larger generators serving multifamily buildings typically use diesel fuel.
  • Usually permanent rather than portable, but can be delivered by trailer.
  • Can be mounted on roofs or upper floors to protect against flooding, if your building will accommodate this.

Storage

Onsite; must be protected from freezing.

Quantity of Emissions

High

Fuel Cost

$

Special Issues

Storage life limited; plan for cycling needed. Lower flammability than gasoline. Tanks must be anchored.

 

image

Biodiesel Generators

  • Work like diesel generators, but with fuel that is typically cleaner, generates fewer CO2 emissions and is less harmful if spilled or leaked.
  • Fuel must be stored more carefully and does not last as long as standard diesel.

Storage

Onsite.

Quantity of Emissions

Low

Fuel Cost

$$

Special Issues

Plan for cycling needed. Lower flammability. Tanks must be anchored.

 

image

Combined Heat and Power (Cogeneration) Generators

  • Used for larger residential buildings.
  • Waste heat from power-generation is used to heat water or make steam for space heating.
  • Can use fuel sources including: natural gas, propane, oil, wood chips or wood pellets.

Storage

Onsite; various fuel types.

Quantity of Emissions

Low

Fuel Cost

$-$$$

Special Issues

Extremely fuel-efficient.

 

image

Battery Storage

  • Primarily for short-term needs, such as uninterruptible power for computers, data systems and emergency exit lighting.
  • Becoming more efficient, but cost and maintenance are obstacles.

Storage

On-site; capacity limited.

Quantity of Emissions

None

Fuel Cost

--

Special Issues

Potential for solar battery charging.

 

This permanent backup generator is housed in a rooftop machine room, protected from the elements and far above the threat of flooding.
Image: John Gravelin.
 
Using backup power.
  • Employ only a licensed electrician to install and maintain a backup power system.
  • For larger systems, consult an experienced engineer to oversee installation and maintenance.
  • Install generators and the systems that support them (transfer switches, fuel pumps, etc.) above the DFE.
  • Ensure that your building is able to support the weight.
  • Minimize noise and vibration of generators to avoid disturbing residents and neighbors.
Balance advantages and disadvantages to best locate generators:

Generator Placed Indoors

Leaves, snow and other debris do not need to be removed.

Can cause noise and vibration problems for residents.

In cold climates, heating elements are not required to keep the generator ready.

Involves structural considerations to make sure the building frame can handle the weight.

Generator Placed Outdoors.

Can be located away from residents to minimize noise and vibration.

Exhaust can enter building through HVAC systems.

Saves valuable interior space.

Heating/cooling systems are required to keep the generator ready.

Operations + maintenance

Generator fuel must be carefully stored in code-appropriate enclosures and tanks.
Image: Samantha Yost.

 

Develop a maintenance plan that “exercises” the generator regularly and cycles through stored liquid fuel on a defined schedule so you can be sure it will be available and not stale when needed. Train facility staff in equipment operation.

Building codes typically require regular inspection and testing of generators.

Develop a maintenance log protocol, which can be used for manufacturer reimbursement in cases of system failure.

 

Estimated cost

 

  1. $
  2. $$
  3. $$$
  4. $$$$

 

Supporting strategies

Resources

 

Case Study: Rooftop Backup Power

Case StudyRooftop Backup Power

Background

Built in the early–1900s as a hospital, 318 Beach 85th St., Queens, NY is a 62,000 sq. ft. state-licensed residence operated by Services for the Underserved (SUS). It provides 71 units of supportive housing.

Less than 100 yards from Jamaica Bay, and 50 ft. from the Atlantic Ocean, the building is located within the FEMA AE flood zone, an area subject to inundation during a 100-year flood. After Superstorm Sandy, the first floor was flooded with 4 ft. of water and the building was without power for a month. Residents could not return to their homes for a year.

Strategy

SUS installed a natural gas-fired, 261 kW generator on the roof. The generator is connected to an Automatic Transfer Switch, and is sized to carry the entire electrical load of the building.

Cost

The generator and installation cost about $250,000. Funding came from a Community Development Block Grant, Disaster Recovery (CDBG-DR).

Image: Services for the Underserved.
318 Beach 85th St., Queens, NY
71 Units
$250,000
Back to top