What information needs to be coordinated with electrical?
In this series we’re going to cover what information electrical designers and engineers need from us, and secondly, what information do we need from them. Today we are going to be talking from the perspective of a Fire Protection consultant or a fire sprinkler contractor designing a suppression system.
So, what information does electrical need from us?
Generally, electrical engineers and designers are most concerned about our power needs. Ideally, the earlier we can coordinate, the better. It’s smoother overall and the electrical engineer and the electrical contractor don’t have to make changes late in a project.
So what needs power?
Well, let's think about all the components of a sprinkler system and the multidiscipline coordination required for, let's say, fire pumps, jockey pumps, air compressors, nitrogen generators, pre-action or other sprinkler system releasing panels, and some other coordination items we'll talk about later.
Let us consider one of the largest electrical demands that a sprinkler system can require, and that would be looking at fire pumps.
FIRE PUMPS (POWER, PHASE, VOLTAGE, STARTER TYPE)
We have two types of fire pumps, electric and diesel. Both have electrical demands, but they impact electrical system design differently.
First, let's look at electric fire pumps. Electric fire pumps have power needs for the electric motor driving the pump. This demand is measured in horsepower or kilowatts and is based on the size of the pump. The more pressure and flow needed from the pump, the more power the pump needs, and the higher the electrical load.
Then there is voltage and there are different advantages to selecting different voltages, however, the voltage of this motor needs to be coordinated with electrical to make sure that the selected power type is available in the building or if a transformer is required to convert to a particular voltage. If we only have single-phase, 120V coming into a building, then we cannot use a 460V, three-phase fire pump. There’s no supply for that. Often, when we have a large fire pump on a project – the coordination conversation often takes the form of asking what phase and voltage is available to the building, and then using that to specify or select the phase and voltage for our fire pump.
In some cases, early electrical coordination with the electrical engineer can help out their design for voltage. If only one or two items could benefit from three-phase supply, but then we add a large fire pump into the mix – well perhaps that changes the overall picture electrically – to the extent that they choose to bring in three phases to the building.
We also have the starter type and there are several starter types to choose from. These include Across-the-Line, Wye Delta open, Wye Delta closed, a soft start, and variable speed drives. Each one of these starters provides an advantage to electrical demand at the startup of a pump. Electric motors have a large amp draw to start the motor and these different starter types allow for the design to tune the impact to the electrical system for fuse and conduit selections. We’ll talk plenty on this in other segments.
In general, the electrical engineer or the electrical contractor will want to know five things about a fire pump; what is the horsepower (or kW rating), what phase and voltage is it using, what is the starter-type, and where is the location for the controllers. The power rating is dependent on the rated pressure and flow for a fire pump. If you want to approximate the horsepower from a very rough quick calculation method, take the rated pressure of the pump in psi, and the rated flow of the pump in gpm, and multiply those together and divide by 1,200. Your end result is in the rough ballpark of what the resulting horsepower for that pump would be.
The best way to really dial-in horsepower for a fire pump is to first determine the hydraulic demand on the system and actually make a selection. Even as a consultant, you are required to do enough homework to select a fire pump pressure and flow rating, select a fire pump model as a “design basis”, and then gather the listed horsepower for that pump.
Some manufacturers will publish fire pump selection books to match pressure, flow, and horsepower in tables. You simply determine the size and look up the power needs from the book.
If you’re less confident on making a selection yourself, contact a local fire pump sales representative or the fire pump manufacturers themselves. Let them know you’re wanting to establish a “design basis” for your project and share your pressure and flow data with them. They have access to all their data, so they would be able to help provide the power needs that you need to coordinate with.
REASONABLY CONSERVATIVE NEEDS
One warning here related to electrical coordination for fire pumps is power ratings for pumps only come in specific tiers. You likely will not find a 28-horsepower fire pump. They’ll be in nominal sizes. These sizes count by 5s from 15 to 30, so that’s 15, 20, 25, and 30. Then, size by tens up through sixty. So, you have 30 HP, 40, 50, 60. Then it increases by 25, so you’re looking at 75 HP, 100 HP, 125, and 150, and beyond that, it goes up by 50s until you reach 500 horsepower, and then it increases by 100 HP increments. If you’re in the early planning stages for a project and not making a final pump selection, then it’s important that you clearly communicate any ambiguity with your electrical engineer.
If, for instance, with the information you have, you’re about 80% sure that the fire pump will be 75 HP or below, but it could be 100 HP, well, share that information with your electrical engineer. They may need to plan on the 100 HP to complete their design.
That’s different than if you’re an installing contractor and you’re making a final pump selection, where you’re the party selecting the exact model to be installed. Obviously, you’re bringing much more certainty on the power needs, so if you do have a 75 HP pump, well that’s the size the power supply needs to handle.
SERVICE FEED LOCATION
Also, one item often overlooked is the service feed. Many fire pumps are fed from concrete-encased conduit from the utility transformer, underneath the fire pump room, and to the fire pump controller. In order to do that, the electrical engineer needs to know where the fire pump controllers are going to be located. This is something they will likely want to know; so, having a good idea on where the fire pump will be located and where their controllers will be will be very helpful to the electrical designer.
So, for electrical fire pumps – the electrical engineer will need to know size, phase, voltage, and starter type. They should have a pretty good handle on emergency and standby power needs, but you may also get asked about that. Fire Pump secondary power supply is a deep topic and we’ll visit in a lot more detail separately.
What about diesel? The advantage of a diesel fire pump is that it substitutes an electric motor for a diesel-powered engine. This reduces the impact on the electrical infrastructure of an existing building or a remote building that has limited available power. However, diesel fire pumps have an electrical component, too, they require startup and battery charging. These electrical requirements are still critical to coordinate with electrical engineers. While the demand is significantly less than an electric fire pump, the electrical engineer or contractor will still need to provide power to these locations.
Accompanying every fire pump is a jockey pump. A jockey pump is a much smaller pump that maintains pressure on the sprinkler system. Generally speaking, these pumps may be a fraction of a horsepower up to a few horsepower or kilowatts, they also require a starter, like any motor, and have the same coordination items required for a larger fire pump. Unlike the fire pump, however, jockey pumps are provided for pressure maintenance only.
They kick on so that the bigger fire pump doesn’t have to. Because they’re not a required part of the system, they are often not required to be on emergency or standby power. Just be cognizant that if a jockey pump isn’t served by backup power, the fire pump may kick on during an extended power outage if the pressure in the system dips, which would very much not be wanted. So, is a jockey pump required to be on a backup power? Not necessarily. Would it be a good idea to do so? Yes, very much so.
AIR COMPRESSOR POWER
We’ve talked a lot about fire pumps thus far. That’s a huge coordination item with electrical engineers. But what about the rest of the system?
A sprinkler system may be a standard wet pipe design or it may be a dry pipe style of system which requires an air compressor, maybe a nitrogen generator, or any other sort of pre-action or sprinkler releasing mechanism. When we look at air compressors, they have an electric motor. Air compressor motors can be similar in size to, let’s say a jockey pump motor. They are often in the range of a fraction of a horsepower to a few horsepower or kilowatts. Air compressors are also often accompanied with pressure sensors and control panels that contain the logic to operate the system and can tie into a building management system.
An electrical engineer will want to know what the size of the air compressor will be. And for contractors – that’s an easy answer. We can look at the volume of our system, select an air compressor or nitrogen generator, and provide the power needs.
If we’re a consultant trying to coordinate this early, dialing in an air compressor power need is a little trickier.
One way to get a rough approximation is to look at air compressor or nitrogen generator product brochures and show different volumes of a system with different size air compressors. If we have a very small dry system, let’s say a tank-mounted air compressor might be as small as a 1/6th of a horsepower. And a medium-volume dry system, maybe 500 gallons might be around a ¾ horsepower compressor.
But what about a large system? Or a very large system of 2,000 gallons or more? Well, we could be looking at a 5 HP compressor or multiple air compressors. If we’re planning in these early stages, we want to plan to be reasonably conservative and make sure that there are available options that may actually work for our system before handing over power needs.
NITROGEN GENERATOR POWER
Today, when there is an increased focus on corrosion control. Many Fire Protection designers and engineers opt for nitrogen generators. Which are? Well, they’re just more complex air compressors that filter out the oxygen and impurities to provide compressed nitrogen. You can have a nitrogen generator downstream of an air compressor, or you can have a built-in unit that compresses air, filters out the nitrogen and supplies it to a tank or the system. When a nitrogen generator is provided, electrical coordination for the type of generator that is being selected is required because it may have a separate control panel to supervise.
Instead of air-compressor selection charts, we just look at the product data for nitrogen generators and their associated control equipment and get their power needs. Many nitrogen generator manufacturers will work with you to estimate your system size and provide a “design basis” generator for you, which will list all the power needs.
RELEASING PANEL POWER
If we were to look at a pre-action system, a deluge system, or even a clean agent system, they all have a listed releasing panel and detection requirements. In general, these releasing panels will use 120V single-phase power, and will require a dedicated circuit to supply it. So, the actual load of the panel might not be as critical as simply coordinating a circuit to supply it.
If you have any specialty components that need power? Well, it’s in your hands to coordinate. The electrical engineer or the electrical contractor might be able to make a few assumptions, but they’re not experts in suppression systems. So, it’s just as much on us as it is on them to make sure that we coordinate what those power needs are going to be.
FIRE ALARM / SPRINKLER MONITORING PANEL POWER
So what else actually needs to be coordinated beyond electrical motors and control panels? Even if the sprinkler system is a plain old standalone suppression system without a pump, well it’s required to be monitored. And there are several different devices or strategies to monitor a sprinkler system. And we cover this in a whole lot more detail over in our fire alarm series.
If the building does not require a fire alarm system, the sprinkler system will still often have a fire sprinkler monitoring panel. This would be considered a Dedicated Function Fire Alarm System under NFPA 72. Generally speaking, the fire alarm or the fire sprinkler monitoring panel is going to supervise and power all the devices and appliances under its umbrella. Tamper switches? Flow switches? Smoke detectors? That’s generally going to be low voltage, such as 24V, and powered by the fire alarm or sprinkler monitoring panel.
When would we need to coordinate those items with the electrical engineer? If something needs 120 volts – say a standalone waterflow switch or a standalone 120V duct detector or a 120V horn/strobe for waterflow notification – well that’s when we’ll have to coordinate with electrical.
In every case, the electrical demands for the sprinkler system are required to be protected with emergency power or a reliable means of secondary power to allow the critical life safety systems, like a fire pump, to remain active in the event of power loss.
Where the fire pump has secondary power, then it will need an automatic transfer switch to automatically transfer the pump from the main source of power to the emergency circuit upon power failure. We’ll talk on this in more detail in separate segments.
Beyond electrical sizing, sometimes it is a good idea to coordinate with the electrical team where the incoming electrical service comes into a building or where the ideal location for backup generators will be. This will help to determine if locating the fire pump near the electrical service or generator is possible because the emergency power supply from that location to the fire pump is required to be protected in either concrete encasement, a fire-rated enclosure, or really expensive fire-rated cable.
This is all information that we can provide the electrical team or drive the conversation, but…
WHAT DO WE NEED?
What information do we need from electrical?
We need to know the available voltage to select the right fire pump, jockey pump, air compressor, or any other electrical component.
We need a reflected ceiling plan showing the location of lighting, size of light fixtures, location specific lighting controls, speakers, or fire alarm devices to attempt to avoid them while laying out our sprinkler design, or at least identify areas to coordinate if too congested.
Also, if the electrical designer or engineer can provide the locations of panels, switch gear, transformers, or other electrical equipment, in order to avoid routing piping over the panels, then we can avoid any issues in the field or coordination items in our model.
What information needs to be coordinated with electrical?
Power needs for anything needing power. That would include a fire pump, jockey pump, any releasing panel, air compressor, nitrogen generator, any 120V component, and the locations of the power service, emergency power source, light fixtures and panels.
Coordination is a two-way communication path that requires early and frequent discussion. Providing a preliminary pump or motor size early on in the design process can assist the electrical team in sizing their system, which can be refined throughout the entire design process. Waiting until the last minute can cause some costly changes and a lot of headaches for the design team.
We have a high-level overview in our performance-specification cheat sheet below, but you can always construct a coordination checklist or template form custom to you or your company to remind you of all the information you and the electrical design team need at each stage of the design or during the construction process.
In our next segment, we’re going to get into specifics about routing pipe near electrical equipment.
I’m Ben Brooks, this is MeyerFire University.
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