How to size fire pumps?

You understand how important a well-maintained fire sprinkler system is for any building if your sprinkler system activates, but the water pressure is insufficient to cover every part efficiently. This demonstrates why accurate fire pump sizing is critical. The key to a functional sprinkler system is a fire pump that can provide enough water to cover the entire structure. The sprinkler system is nearly useless without enough water pressure to successfully put out a fire. The kind of fire you are prepared for and your particular project will play a major role in selecting the best fire pump. Several factors influence the selection process, with temperature being an important one.

An undersized pump cannot supply the required water volume and pressure. On the other side, a large pump can be both costly and inefficient. A low-temperature fire pump may be better suited for projects with high temperatures to prevent water from boiling and causing harm. This article will guide you through the basics of fire pump calculation and cover some tips and tricks to consider during your selection.

Fire pump sizing calculator

The gallons per minute (GPM) that your fire pump must maintain will depend on the size and design of your structure. The standpipe method or sprinkler area calculations can be used to establish the pressure needed for the fire pump. Generally speaking, the minimum pressure for a fire sprinkler system’s sprinkler head should be no less than 7 psi. By doing this, it is certain that in the event of a fire, the sprinkler head’s heat-sensitive bulb will crack and water will be released. Below is how to determine the appropriate pump sizing using these two techniques:

A. The Standpipe Method

NFPA 14, Standard for the Installation of Standpipes and Hose Systems, defines the standpipe method to assess fire pump pressure requirements.

• This applies to buildings with both sprinklers and firefighter standpipes.
• The first standpipe requires a pump capable of delivering 500 gallons per minute.
• Adding a standpipe raises the pump size required by 250 gpm.
• This method requires a maximum of 1,000 gpm.

B. Sprinkler Area Calculation

Larger buildings and buildings with a variety of fire hazards benefit from the more complex method of calculating sprinkler area requirements for fire pump size.

• It examines the building’s material type, including low and high fire risks.
• Use a fire code reference to determine the “density” value of the materials.
• Multiply the density number by a specific building area, often 1,500 square feet.
• Include the water required for firefighting hoses in this estimate.

The water volume needed by the fire pump depends on the risk degree of your building:

• Low-risk buildings, such as churches or museums, contain a few easily combustible things.
• Moderate-risk buildings have some combustible things that are not tightly packed or tall, such as kitchens or laundry rooms.
• High-risk structures have a lot of extremely flammable materials or liquids, like paint shops or airplane hangars. Higher risk needs more water delivery from the fire pump.

Following is a simple approach for estimating water requirements:

1. Evaluate your building’s risk level.
2. Select a small region (1,500 square feet) within your building.
3. Check the risk level against the appropriate density number.
4. Multiply the area by the density number.
5. Include a set number of firefighter hoses.
6. This calculation produces the expected water flow rate for your fire pump.

For a 30,000-square-foot building, the fire pump’s total flow rate is 475 GPM, calculated by multiplying 1,500 by 0.15 (density) and adding 250 (hose demand).

These calculations help you determine the optimal size, flow rate, and pressure for your fire pump.

Common types of fire pumps

Fire pump sizing and selection are critical because of the different pricing and uses of the fire sprinkler system. The most common types of fire pumps are:

• The most common type of fire pump is an electric centrifugal pump, which has a single-stage impeller mounted on a shaft.
• The original fire protection systems used horizontal split case pumps. They direct water to both sides of the impeller and have flow rates ranging from 250 to 5000 gpm.
• Inline fire pumps have a compact, space-saving design that reduces installation expenses.
• Diesel engine centrifugal pumps are driven by a diesel engine and can be base-mounted or skid-mounted at the point of usage.
• Vertical turbine pumps are made up of a multistage impeller mounted on a vertical shaft and powered by an electric motor or diesel engine. They are utilized when the water supply is below the suction flange, as NFPA fire pump rules require positive suction pressure for a fire pump.

How can I identify the size of the fire pump I need?

When putting in or repairing a fire pump, it is critical to choose the appropriate size. Here are three key elements to consider:

• Pressure requirements
• Total flow rate
• Pressure loss during piping

Local fire rules will specify the minimum discharge pressure for your building, so start by estimating your pressure requirements based on those guidelines.

Next, calculate any friction loss in your system. This includes calculating the number of elbows, fittings, and vertical rise of the pipes.

Then, determine the required flow rate. Some pumps have a maximum flow rate that they can handle. If your system’s flow rate surpasses this limit, it will be necessary to look for a different pump.

Remember to take into consideration any pressure loss due to pipes.

Finally, choose the power source for your fire pump. Pumps are offered in both diesel and electric versions. Choose based on criteria such as cost and maintenance requirements.

How much capacity does the fire pump have?

Its capacity is something you should be aware of to maintain the health of your fire pump. This is determined by the amount of water delivered at a certain pressure, which is commonly expressed in gallons per minute (GPM) or liters per minute.

The actual capacity may vary depending on your system; however, here are some broad guidelines:

Your fire prevention system should be powerful enough to fulfill any water demand, taking into account both hot and cold weather as well as any changes in building use.

The supply line must be sized to provide the required water flow per minute. Calculate this by summing all potential simultaneous water uses, such as all sprinkler heads running at the same time, and then adding two gallons per minute for every 10 minutes.

Additional tips on assessing the size of a fire pump

Here are some tips for measuring the size of a fire pump.

• Inspect the label for any information written on it. Examine the nozzle size, as it determines the amount of liquid used to extinguish fires. Check the labels on your fire pump to determine the appropriate nozzle size.
• If your pump has an adjustable nozzle, adjust it to figure out the gallon capacity, which is normally listed on the label.
• An undersized pump can cause property damage and even death, whereas an oversized pump can result in wasteful expenses.
• Measure the amount of water and pressure required to reach various portions of a fire pump to evaluate its size.
• After you have these numbers, use the following calculation to get horsepower (HP): flow (GPM) / pressure (PSI). The nameplate of your fire pump motor should have the horsepower value written on it.

Essentials of Fire Pump Codes

Take into account these crucial code criteria for fire pumps while choosing pumps and creating system designs.

• On a split-case fire pump, maintain horizontal elbows or tees at least 10 pipe diameters away from the suction flange to guarantee smooth flow.
• At the suction flange, always keep the suction pressure positive.
• Provide fire pump controllers with two hours of fire-rated electrical connections.
• Refrain from maintaining pressure with fire pumps.
• The code permits pumps with variable speeds.
• Put in fire pumps in rooms that are rated for two hours or longer.”

Final Take

It is wise to consult a fire protection expert for accurate fire pump sizing. Anchor Fire Protection Inc. professionals can evaluate your building and sprinkler system thoroughly, considering factors like layout, occupancy, water supply, and calculations to find the right pump size.

A well-sized fire pump is crucial for a reliable sprinkler system, potentially saving lives and property during a fire. You can use fire pump sizing calculators for initial estimates or seek a fire protection engineer for a detailed analysis to prioritize proper sizing.

In summary, fire pump sizing and selection are vital for a functional fire sprinkler system. Your system may need to be stronger or underperforming with the right design and size.