Best Practices for Exterior, Interior, and
MEP Data Center Security
Follow these guidelines to secure data center operations
By Sean Brady
April 11, 2020
Data center security is more critical and complex than ever before. Physical security plays a
crucial role in preventing unauthorized access to facilities, equipment, and data.
When it comes to physical security, there are many factors to take into account. However, four
crucial areas must be addressed when considering best practices for data center security: the site;
building exterior; mechanical, electrical, and plumbing (MEP); and interior white space.
While several of the approaches covered here can be applied to more than one area of the
property, each solution will only be addressed once to avoid redundancy.
Securing the Data Center Site
The front line of defense is protecting access to the data center site, and the first step is to
implement multiple layers of security. Begin by evaluating the site with the goal of mitigating
risk of damage from natural disasters, such as floods, tornadoes, and hurricanes. Human risks,
including airplane flight paths, chemical plants, force majeure, and easements, must also be
taken into consideration.
If possible, establish a 100-foot buffer zone around the property on all sides. The existing
landscape may serve as a natural barrier, or this can be achieved by planting trees, placing
boulders, and constructing gullies and/or grass berms around the perimeter. Surrounding the site
with a 10-foot K-rated fence that is strong enough to withstand the force of an 18-wheeler
traveling at 60 mph will provide added security.
Limiting the number of entry points is critical for maximum control. Establish a single entrance
to both the data center site and the building itself and have surveillance in place to carefully
monitor who enters the facility and when. Install 24/7/365-manned security posts in each
location as well as in the loading dock area to authenticate visitors. Position one or more
retractable crash barriers and a bomb detection device at all entrances and install video
surveillance cameras with infrared and motion sensor detection around the entire perimeter of the
site. Recorded information should be maintained for no less than 90 days and up to 12 months
(this applies to all three areas covered in this article).
Anyone entering the facility must be authenticated multiple times. Ideally, employees, vendors,
and visitors should be authenticated three times (when entering the site, building, and data hall).
Visitors and vendors must always be accompanied by an employee. Depending on their status,
authentication options for employees, vendors, and/or visitors can include access cards and
identification badges; combination locks and/or keys; or biometric identification using
fingerprint, hand, face, or retinal scanning. Physical entry logs should be utilized and kept for 12
months.
Building Security Best Practices
Maintaining the highest level of building security requires many of the same practices and
techniques used to secure the overall site. Before the facility is constructed, building materials
should be chosen with security and protection in mind. This includes 12-inch steel-reinforced
concrete or Kevlar walls and/or ballistic walls and windows.
Protect outdoor MEP yards by surrounding them with bollards and concrete walls topped with
fencing or barbed wire. The roof should be secured from the inside and the outside so that only
authorized personnel have access. Depending on where the site is located, the roof should be
rated for 120-mph winds or higher. Air handlers must be protected against a biological,
chemical, smoke, and/or radiological event. The system should be able to shut down outside air
and recirculate internal air. In addition, all fire exits should be alarmed, and they should not have
a handle on the exterior of the door.
The importance of establishing one main entrance and posting security guards to authenticate
persons entering the building cannot be overstated. If a loading dock area offers secondary
access to the building, security personnel should be stationed in both locations. All deliveries
should be inspected for bombs at the loading dock.
Camera surveillance TVs should be at each entrance, so when one guard steps away, a second
guard can monitor the same areas. Everyone on the site should have a set procedure for entering
and exiting the building, and personnel should have access only to the area or areas they are
authorized to enter (the facility’s access list should be in real time). Background checks should
be performed on all employees and vendors, with standards reevaluated every 24 months. All
internet devices that have an IP address should be encrypted.
Maintaining Interior and MEP Security
Walls in the data hall and MEP rooms should be built slab to slab with wire mesh and/or Kevlar.
This is to ensure the walls cannot be penetrated, as well as to protect encased wiring or pipes.
Install separate restrooms for visitors and employees — visitor restrooms should be near the
loading dock, and employee restrooms should be near the main entrance to the building.
Data halls, a/c galleries, PDUs, UPSs, generators, switch gears, and transformers should be in
separate, secure rooms that are not side by side. Ceilings and raised floors should be secured with
smoke, water, and motion detection systems and monitored at the guard station and/or the
network operations center (NOC).
Each individually secured area should require more than one form of authentication and access
control. Depending on the sensitivity of the data and equipment involved, consider enforcing
specialized security measures for each room and area.
Mantraps should be installed at the entrance to the building, secured areas, and/or the data halls.
There are several types of mantraps that perform different functions, and the design of the site
and level of security required will depend on the design and function of the mantraps.
In the absence of a mantrap, two methods of authentication, such as a cardkey and a
finger/hand/face/retinal scanner, should be required to gain access to the data hall. Cabinet layout
should be done by department, and cage access should require at least one authentication.
Locking cabinets should be installed inside the cage. Surveillance cameras in the data halls
should be able to view multiple sides of all cabinets. Data center operators should also have a
manned NOC with the same security cameras monitored around the clock.
Install an asset-tracking system in all IT equipment. This tag transmits real-time data that
includes temperature, humidity, and other environmental information, and it can even indicate
when a server cabinet is opened. This information can be monitored in the NOC or by cellphone,
but mobile applications should be avoided, as they may compromise site security.
Increasing the redundancy to a minimum of an N+1 MEP design makes the site more secure and
is categorized as a Tier III data center. Increasing to Tier IV brings the site to the top redundancy
level, which includes dual utility feeds that can come from separate substations and/or from two
different utility companies. It is best to install these electrical lines underground; alternatively,
they can be 50 feet apart on the poles leading into the building or from two separate sides of the
building. The Tier IV solution is the most secure for a data center operation.
Fiber should come into the building from two sides and into two separate meet-me-rooms
(MMRs) located at least 50 feet apart. The site operator should also consider two separate telco
providers taking separate paths to service any vital location. These rooms should be monitored
continuously from the NOC.
IMPLEMENT AND VERIFY
Data center operators are advised to perform an annual security audit and review of the site’s
security policy for all three areas addressed here. A simpler spot audit is suggested every quarter
or when there is personnel turnover. Keep in mind that the tier rating for the site does not reflect
the level of security required or outlined here.
Data centers play a critical role in an organization’s operations and productivity. While data
center security is complex and multifaceted for enterprise and colocation sites, it is crucial to
ensuring smooth and safe operations. Addressing these three key factors effectively is what will
separate preferred operators from the pack.
Ideally, employees, vendors, and visitors should be authenticated three times (when entering the
site, building, and data hall).
A pipeline to a cooler data center
July 23, 2012
By
Larry Thau
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Archived Content
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correctly.
When consulting engineers Hilson Moran designed the cooling system for a financial
institution’s data center in Essex, UK, it originally drew a conventional welded and
threaded HVAC system. Key issues for the client were completing the installation on
time at a reasonable cost, without sacrificing quality of product due to the critical
applications involved in the project.
The system required long (60m) runs of large-diameter piping – up to 350mm. Because
this would be time-consuming and costly to weld, the engineers sought an alternative to
meet the client’s needs for a speedy, clean and cost-efficient installation.
HVAC systems play a major part in the whole-life performance of data centers. A
traditional HVAC system can account for up to 54% of a facility’s energy consumption
but a thoughtfully designed system using efficient installation methods and high-quality
components and controls can reduce this to 22%.
For many years, air-cooled systems provided sufficient cooling capacity, however,
increased computing density produces more heat and requires more efficient cooling. In
larger data centers, the most cost-effective method is a chilled water system. According
to the Science of Aquatics, water is 4,000 times more efficient than air. This is why, in
recent years, companies like IBM have developed methods for bringing cooling water
directly into server racks.
In a chilled water system, cool water is pumped out of the mechanical room and into
computer room air handlers by way of under-floor water distribution lines. The air
handler then removes heat and humidity by drawing warm air through coils filled with
circulating chilled water. The water absorbs the heat from the air and circulates back to
the chiller where the heat is transferred to a condenser water loop and eventually
released through a cooling tower.
Hard piping utilizing carbon steel pipe or copper tubing is common in a chilled water
system. Traditional pipe joining methods for hard piping systems consist of welding,
brazing or flanging which generally work well in data centers. But, with increased loads,
frequent changes, and system expansions, these joining methods have become
problematic. They are not easily accessible, feature limited design flexibility, introduce
fire hazards to the jobsite and require lengthy system shutdowns to perform routine or
unplanned maintenance activities.
This is where grooved mechanical piping technology comes into play – a method of pipe
joining that requires no flame, with reduced deployment time, providing an easily
adaptable system and reducing downtime during routine or unscheduled maintenance.
Hilson Moran installed a flame-free system of grooved-end pipe joining for the 350mm
chilled water and ice water piping systems for its Essex client. “Trying to weld that size
of pipework would have meant quite a considerable increase in labour time and costs so
we recommended an alternative,” Hilson Moran contracts manager, Peter Dulieu says.
“Using grooved mechanical piping speeds up the process and has the added advantage
of cleanliness over welding.”
How grooved piping works
To form strong and reliable joints on large carbon steel pipes, a Victaulic Advanced
Grooved System (AGS) was used. This is wider and deeper than standard grooved
systems. The wider gasket gives more contact area for sealing. The two-piece housing
of the coupling speeds up handling and installation time, and a union at every joint
makes for easy adjustment, system maintenance or expansion.
Over the operating life of a data center, a piping system requires three basic categories
of maintenance: routine inspection and maintenance, physical changes or expansion,
and unscheduled repairs.
Grooved couplings provide a union at every joint, which allows for easy system access,
maximum field flexibility for on-site decision making and flexibility for future system
expansion. To access the system, a worker needs to de-pressurize it and simply
unscrews two nuts.
To complete the job, the gasket is re-installed, coupling placed back and bolts are
tightened.
Welded systems don’t have unions; to repair the piping system workers actually have to
cut out the damaged pipe section. Because grooved mechanical pipe joints can be
installed on wet lines there is no time required to let the system dry out.
In a traditional flanged system, multiple bolts are needed to create the seal, and
removing these is a time-consuming process. When the multiple bolts are removed and
the flanges pulled apart, the gasket will tear and need to be replaced.
With mechanical coupling, the compression loads on the gasket are different than the
flange – it has a C-shaped cross section seal that is pressure responsive and designed
to handle cyclical loading. Systems can be pressurized and depressurized repeatedly
for many years without fatiguing the elastomer material. This also means expansion
projects can be completed in occupied buildings without vacating the space because
mechanical grooved piping does not release noxious fumes or introduce a fire hazard.
The grooved mechanical pipe joining system also accommodates movement and
deflections within the piping system, reducing the need for periodic product repair or
replacement.
The surge in popularity of grooved mechanical piping is due partly to the everincreasing demand to save installation time on site and to engineers’ desire to build
reliable, maintenance-friendly systems from day one.
Case study: Data center
piping
A data center required robust piping to transfer chilled
water for cooling
BY SAAHIL TUMBER, PE, HBDP, LEED AP, ESD, CHICAGO SEPTEMBER 17, 2019
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A data center located in the Midwest was undergoing expansion. The project involved a new data
hall with an initial load of 1,300 kilowatts and capability to scale up to an ultimate load of
2,600 kilowatts. An air-cooled chilled water plant was designed to serve the expansion space.
The plant comprised of three 225-ton chillers piped in parallel to provide N+1 redundancy with
the capability to add two additional 225-ton chillers in the future.
The heat transfer fluid was 40% ethylene glycol for freeze protection; each chiller featured a
design flow of 380 gallons per minute and the chilled water pumping configuration was variable
flow. The day one design flow was 760 gallons per minute and the ultimate design flow was
1,520 gallons per minute. Design chilled water temperature was 60 F supply and 76 F return.
The system design pressure was 150 pounds per square inch gauge.
It was critical that the piping system serving the data center be robust. A piping system
comprised of 8–inch schedule 40 steel pipe (ASTM A53, Grade B, Type E) with welded
joints and fittings was used to create chilled water supply and return pipe loops beneath the
raised access floor. The 8–inch pipe loops incorporated lugged butterfly valves at strategic
locations to ensure that the piping system was concurrently maintainable — i.e., pipe segments
could be isolated for maintenance activities without impacting the critical loads. Flanges were
limited to valve and equipment connections. Figure 1 indicates the 8–inch chilled water supply
and return loops. Also visible is 3–inch chilled water branch piping and ¾–inch condensate
piping from the computer room air handling units.
The piping system above the suspended ceiling was supported from the roof structure by using
clevis hangers and metal framing system was used to support the piping system on slab beneath
the raised access floor. Pipe supports were provided every 10 to 12 feet in compliance with the
applicable code. Additional supports were provided at heavy pipe accessories such as air
separators per manufacturer requirements. Figure 2 indicates the lugged butterfly valves at the 8–
inch chilled water loops and the supports for the piping system beneath the raised access floor.
Based on day one design flow of 760 gallons per minute, the maximum flow through an 8–
inch pipe segment was 380 gallons per minute during normal operation, which corresponded to a
pressure drop of 0.3 feet water column per 100 feet of pipe and a velocity of 2.4 feet per second.
Based on ultimate design flow of 1,520 gallons per minute, the maximum flow through a pipe
segment was 760 gallons per minute during normal operation, which corresponded to a pressure
drop of 1 feet water column per 100 feet and a velocity of 4.9 feet per second.
In the event a pipe segment had to be isolated for maintenance during an ultimate design
condition, the maximum flow through the active pipe segment was 1,520 gallons per
minute, which corresponded to a pressure drop of 3.9 feet water column per 100 feet and a
velocity of 9.8 feet per second. In all scenarios, the pressure drop and velocity were within the
recommended limits.
Thermal expansion of the pipe system was reviewed. During normal operation, the
minimum chilled water temperature was 60 F. In the event the data center was offline
for an extended period and the chilled water system was disabled, the maximum water
temperature was anticipated to be 95 F — i.e., the maximum temperature differential was only
35 F and the pipe loops had adequate capability to accommodate thermal stresses.
There were multiple locations where dissimilar pipe connections were necessary. For
example, the CRAH units serving the data center had copper pipe connections. To reduce the
potential of galvanic corrosion, dielectric flanges were used to connect steel pipe to copper.
Chlorinated polyvinyl chloride was initially considered for condensate drain piping from the
CRAH units. However, few CRAH units were equipped with an integral humidifier and the
units also used the condensate piping for humidifier blowdown. Due to the potential of elevated
water temperature in the pipe, CPVC was deemed to be unsuitable for the application and 1–
inch copper pipe (ASTM B306 Type DWV) was used per CRAH unit.
The closed–loop system incorporated expansion tanks to accommodate fluid expansion, air
separator to vent air from the system, glycol feeder to fill the system with glycol solution, sidestream filter to remove suspended solids from the system and chemical feeder for periodic
injection of water treatment chemicals such as biocides, scale inhibitors and corrosion inhibitors.
Pipe connections with isolation valves and blind flanges were provided to ensure that future
chillers and CRAHs could be incorporated without disabling the system. Pipe dead-legs were
limited to 2 feet in length.
8 Do’s And Don’ts Of Mission Critical
Plumbing
What to avoid and what to tackle.
By John Nieman
FIGURE 1. Data hall raised floors can reach 3 ft-0 in. in height, as shown in this construction
photo. Floor drains installed under the raised floors protect the data halls from filling up like a
bathtub if a water leak occurs.
FIGURE 2. Install solenoid valves with by-passes in an accessible location, always remember to
coordinate with other trades. The use of solenoid valves with leak detection will shut off
underfloor water distribution if a water break occurs.
FIGURE 3 and FIGURE 4. Data center duplex sewage ejectors will be more costly than
backwater valves to install. These cost concerns are eased due to the confidence instilled
knowing they will not fail due to their redundancy and BMS monitored operation.
June 18, 2018
Let’s face it, plumbing is an afterthought in most buildings — especially mission critical —
where cooling and power take center stage. But, that’s a mistake. When it comes to data centers,
plumbing is an essential support to every other critical system.
For one, mechanical systems rely heavily on plumbing water supply and drainage infrastructure
in data centers to do their job efficiently. There’s also the challenge of locating and designing
plumbing infrastructure to avoid, and protect, electrical systems and equipment. Consider these 8
Dos and Don’ts when designing mission critical plumbing systems.
1. Don’t let your data center fill up like a bathtub. Raised-floor data halls can fill up like a
bathtub if proper drainage is not provided. For one, there are often 3-in. perforated holes in a
raised data center floor to enable the cool air to rise into the space. In the event of a fire, sprinkler
discharge, or a mechanical or plumbing system leak, the raised floor area would need to be
drained. In multi-story data centers, sitting water in a raised floor could directly affect the data
hall tenant below, and at the very least, will cabling and power systems routed underfoot. By
providing floor drains, located to minimize piping runs on the floor below, with leak detection,
water damage will be minimized and building operators will be notified to investigate the leak.
2. Do protect the building’s sanitary sewer from backups. In larger metropolitan areas, data
center sanitary systems may be connected to combined public sewers (sewers conveying both
storm and sewage). In order to protect the data center from back-ups during high-rainfall, the
sanitary system is completely reliant on sewage ejectors or backwater valves as a means to
protect the building.
Sewage ejectors are reliable, but costly, and not permitted by code when there is a means to drain
the building by gravity. Work with the local authority having jurisdiction (AHJ) and explain the
critical nature of the building. Because there’s no guarantee that the sewers will not have
backups, which could cause tremendous damage to the building and its stored data, it is not that
difficult to convince local authorities to permit sewage ejectors. When you do outfit the data hall
and or other areas of the building with sewage ejectors, make sure you:
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Size the ejector for the total load while also taking into account the effect a sprinkler
discharge could have
Coordinate with structural, architectural, and electrical disciplines as they need to be on
emergency power
Connect the ejector to the BMS to monitor its operation
Make sure the pump is provided with 2N redundancy
Oversize the gravity sewers the pump discharge is routed to in order to handle the load
from both pumps
3. Do use solenoid valves with leak detection and water dams for your domestic water supply
system. The use of electronic solenoid valves to respond to leak detection is gaining popularity,
and can help wherever there is an unwanted water break. While it can be costly, employing
solenoid valves can be very effective.
For example, when designing one mission critical control center in the Midwest, the owner of the
112,000-sq-ft facility was intent on not suspending water piping through the ceilings of the
facility. In this case, the water supply and mechanical piping were routed under raised floors in
the main corridors. But what if there was a leak or pipe rupture? To minimize damage, ESD
coordinated with the architect to create water-proofed dams in the command center hallways.
Going one step further, the pipes were controlled with solenoid valves connected to leak
detection. The valves were programmed to automatically shut off should a leak be detected under
the raised floor and send a signal to the control center’s building automation system (BAS) to
notify the building. This gives the maintenance personnel a chance to survey the leak to
determine its origin. Manual bypasses were also installed so that unaffected water systems could
be restarted while the leak is being repaired.
4. Do use automatic electronic trap primers or trap seal devices to protect trap seals on floor
drains. Some data center floor drains may receive little to no waste. The traps on these inactive
drains will eventually dry out due to evaporation. Dry traps will result in gasses and odors being
released out of the drainage system.
There are two types of devices to employ when protecting trap seals, and there are pros and cons
to both:
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An automatic electronic trap primer is a solenoid valve that distributes water to floor
drain traps via a manifold and tubing system. It is controlled by a timer and at least once
a day the valve opens and injects water into the drain to protect the trap. Since they need
electricity, the automatic trap needs to be wired and programmed, and the primer tubes
also need to be routed from the manifold to the floor drains. Things to consider: cost,
power source hookup, connection to the BAS, tubing coordination and installation.
Trap seal devices are rubber inserts installed in the drain outlet or strainer throat. Gaining
popularity for use in mechanical rooms, the rubber insert minimizes evaporation and,
should it dry out, prevents gasses from leaking out. Maintenance workers typically like
mechanical traps, as they’re not automated, are easier to work with, and more
economical.
5. Do consider plumbing requirements for mechanical systems. Generally, when mechanical
equipment is specified, it may have special plumbing requirements. If so, find out from the
mechanical engineer: What water pressures are needed? Is treated water necessary? What are the
drainage requirements? Where should drains be located? Are there condensate or clear-water
wastes? Is make up water needed? What types of backflow protection is required? The answers
will be more specific to the equipment than code.
6. Do separate waste. When coordinating utilities leaving the building, some jurisdictions require
separate clear water and sanitary connections. Check with the local AHJ, specifically in the
Northwest U.S., to see what is required. They may also offer industrial treated water (ITW) for
non-potable usage. There is a cost benefit to doing this, as the data center may pay less for ITW
than potable water. While the infrastructure may be more for additional incoming and outgoing
systems the utility rates will often be less. Return on Investment (ROI) depends on the utility’s
ITW rate.
7. Don’t route water atop data halls. As a rule of thumb, keep water away from anywhere there’s
electricity. Typically, roof drainage is routed to gutters and scuppers along the perimeter of the
building to avoid electrical areas. Coordination of hose bib locations on data center rooftops is
also critical so as not to route water over a data hall full of servers. In colder climates non-freeze
hydrants will be needed, and typical hydrants will require a drain connection. Some hydrants
have a reservoir for drainage, but that may first need to be reviewed and approved by the local
AHJ due to concerns about water contamination.
Today, many mission critical facilities are built with future expansion in mind. For this reason,
be cognizant of where the plumbing is routed. Owner demands may change as well even before
the project is completed, altering room functions. What was supposed to be a storage room may
now become an electrical room, and re-routing the plumbing may be necessary. While electrical
and mechanical designs drive mission critical facilities, the plumbing is directly affected. Be
aware of potential changes and how they can affect every discipline.
8. Don’t forget about tomorrow. Take future use of the facility and site into consideration when
building out and sizing plumbing infrastructure today, especially when it comes to domestic
water booster pumps. If this is a site where there will be future data centers built out, make sure
the necessary plumbing base building infrastructure is added now. Always include provisions for
future booster pumps to ensure that there will be enough water pressure to serve the building for
years to come.
For example, when designing an 800-ft-long data center in Virginia, water system calculations
determined that there was enough pressure to serve hose bibs and mechanical humidifiers at the
farthest end of the building on day one. However, should the building expand or the surrounding
site fill with additional data centers, the demand for water will increase, and therefore likely
decrease the water pressure at the ends of the building. When considering potential future needs,
piping stubs and an allocation of space was provided for a future booster pump.
Eight steps to determine
plumbing system
requirements
In nonresidential buildings, engineers should pay close
attention to local codes, the Uniform Plumbing Code
(UPC), and International Plumbing Code (IPC) when
sizing water supply piping systems.
BY JEREMIAH JOHNSON AND KRIS KALKOWSKI OCTOBER 18, 2017
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Learning Objectives
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Explain water supply and distribution system sizing methods used in plumbing codes.
Provide basic calculations and examples for engineers to use when sizing water supply systems
for various types of commercial buildings.
Several codes and standards are used when sizing water supply piping systems for commercial
buildings. Various local authorities have adopted codes and standards that dictate methods of
sizing systems. Currently, two of the major codes used in many jurisdictions within the United
States are the 2015 editions of the Uniform Plumbing Code (UPC) and the International
Plumbing Code (IPC). As there are multiple sizing methods and various system conditions, this
is not intended to be an exact guideline for sizing all water piping distribution systems. There are
multiple published standards for plumbing systems and water distribution systems that explain
conditions and problems that arise when sizing various water piping systems.
The first step in determining plumbing system requirements and pipe sizing is to understand the
building occupancy and plumbing fixture requirements. Plumbing fixture quantities are
determined by the project architect based on code requirements as well as project-specific
requirements that may exceed code. Building-occupancy types and associated plumbing fixture
quantity requirements are dictated in the UPC, IPC, and the International Building Code (IBC).
Each of these codes have slight differences in regards to plumbing fixture quantities based on
occupancy types and the quantity of people that will be occupying the space. Once the quantity
of required plumbing fixtures is determined, the architect will be able to design the various
restrooms and associated plumbing fixtures for the building. Restroom groups may not be the
only fixtures/appliances in the building that will require water supply. Food service areas,
equipment make-up water, washing systems, and other appliances may also require water supply.
Determining the required flow for all water supply fixtures will be required in order to properly
size the water supply piping.
Starting with the basics in water pipe sizing, the basic flow equation is Q = VA, (Q = flow, V =
velocity, and A = Area). This equation can be used to determine the required pipe size based on
flow rate and velocity limitations. The UPC and the IPC dictate velocity limitations in water
supply systems, and the values in the codes range from 4 to 5 ft/second for domestic hot water
and a maximum of 8 ft/second for domestic cold water. The values in the UPC are better defined
for the specific application. It is important to note that other factors may contribute to velocity
limitations, such as acoustical requirements for sound-sensitive areas and corrosion and erosion
in piping due to water quality.
The UPC and IPC provide similar methods in sizing water distribution systems. The sizing
methods noted below conform with the UPC and IPC and note the key differences.
As previously mentioned, the first step in sizing any water distribution system is to work with the
project architect to understand the building-use type, occupancy type, and quantity of people that
will be occupying the building. Once the building program is developed and the architect has
provided the required quantity of plumbing fixtures and appliances, the next step is to develop
the diagrammatic piping layout in the building to serve each fixture/appliance as required. With
the piping layout complete, pipe sizing can then be determined using the appropriate plumbing
code section.
The 2015 edition of the UPC provides multiple sizing methods. Method one is outlined in
Chapter 6, Section 610.0, and uses Appendix A. This method is used in this article for medium to
large commercial-type projects. It is worth noting that Chapter 6 also provides sizing methods
for flushometer valve piping systems; however, this typically applies to smaller projects.
The 2015 edition of the IPC provides sizing criteria in line with the UPC Appendix A. This
information can be found in Chapter 6, Section 604, and using Appendix E. The UPC and the
IPC’s sizing methods can be broken down into eight steps:
Step 1: Available water pressure
The first step in sizing water supply pipes is to determine the available pressure, static, and
residual, if available. In many cases, this can be determined by calling the local water authority
and requesting the domestic-water service pressure at either the required area or cross streets for
the project site. Based on the available pressure at the city’s connection location, hydraulic
calculations can then be completed to determine the available pressure at the building. Plumbing
engineers typically deal with the plumbing systems within the building up to a point of 5 ft past
the exterior wall. Therefore, it is good practice to discuss available pressures with the civil
engineer, who may be completing a hydraulics analysis of the water piping from the city’s
connection point to the building. The civil engineer may be able to provide the available high
(static) pressure and expected low (residual/dynamic) pressure at the building, which already
would have taken into account any site piping losses, meters, and backflow-prevention devices
being provided. The anticipated high and low pressures are important to understand so the
plumbing systems are operating properly. High system pressures can damage piping, equipment,
and fixtures or, more importantly, exceed the maximum allowable pressure (80 psi) dictated by
the plumbing codes. Low system pressures can affect fixture performance or system flow during
peak periods. If this information is not available from the civil engineer, then the plumbing
engineer can check with local utility authorities for site pressure information and then complete a
hydraulics calculation to estimate the pressure losses through the site piping, including meter and
backflow-prevention losses as required. For the purpose of this article, it is assumed that the civil
engineer will provide the high and low water pressures at the building by completing their own
hydraulic calculations for site piping and components.
Step 2: Determine the pressure requirements
The second step is to determine the pressure required for the building and all plumbing fixtures.
As previously stated, plumbing codes dictate a maximum pressure of 80 psi to any plumbing
fixture. Minimum pressures depend on the fixture or service type. For example, flush valve water
closets can require as low as 25 psi for proper operation, as opposed to flush tank water closets,
which can operate at much lower pressures. Mechanical make-up water systems may require 30
to 40 psi for proper make-up. For plumbing fixture requirements, it is recommended to review
the manufacturer requirements for minimum operating pressures. If no specific pressure is
required, a general guideline is to select 30 psi as a minimum pressure to each fixture. For the
purpose of this article and the sample calculations, the assumption is that the required pressure is
to be between 30 and 80 psi. Flush valve water closets and shower valves are the most stringent
fixtures that require a minimum of 30 psi.
Step 3: Water supply demand
Next, the required water supply demand needs to be calculated for the entire building. The 2015
UPC, Table 610.3, and the 2015 IPC, Table E103.3(2), provide water supply fixture unit values
for various types of plumbing fixtures. To determine the total demand, first tabulate and
summate all of the water supply fixture units for all fixtures within the building. Water supply
fixture-unit values can be converted into a flow rate using Hunter’s Curve, which takes into
consideration the plumbing fixture flow, duration of operation, and the probability of
simultaneous operation of all fixtures. The curve was developed by Roy B. Hunter in 1940 for
the U.S. Department of Commerce and has been used in water supply pipe sizing ever since.
This is a big topic of discussion in the plumbing community, as Hunter’s Curve is very
conservative and tends to oversize water supply piping systems—especially taking into
consideration how plumbing fixtures have evolved over the years and low-flow fixtures are
commonly used in many buildings. Hunter’s Curve is provided in Figures 1 and 2 for reference.
An example for using Hunter’s Curve is as follows:
1. The project architect determined the required quantity of plumbing fixtures: (20) gravity tank
water closets, (30) lavatories, and (4) mop sinks.
2. Total fixture units for these fixtures from UPC Table 610.3 for a public occupancy equals 92;
however, using IPC Table E103.3(2) for a public occupancy results in 172.
3. Using Hunter’s Curve, 92 fixture units with a flush tank system is equal to approximately 41
gal/minute per the UPC. Using Table E103.3 from the IPC, the building would require 58
gal/minute. The IPC’s Table E103.3(3) converts water supply fixture-unit values to flow
rates. This table is like Hunter’s Curve as described above.
As shown in the example above, fixture-unit values differ between the UPC and IPC. It is
imperative to confirm the correct code that will be used based on locally adopted codes to
properly size piping systems to conform with the local code.
Step 4: Pressure losses through building supply systems
The fourth step is determining pressure losses through the interior-building supply systems. As
mentioned above, it is assumed that the civil engineer is providing the high and low water
pressures at the building connection. Additional losses through the interior-building supply
system will include piping friction losses, elevation losses, equipment losses, and other
miscellaneous components with pressure losses.
Piping friction losses can be calculated by knowing the piping material, pipe size, and flow rate.
The Darcy-Weisbach equation provides a method for calculating friction loss in a pipe. This
formula was used to derive the charts in the UPC’s Appendix A and the IPC’s Appendix E,
which provides friction loss in head (psi) per 100-ft pipe length. The UPC and IPC include charts
for copper tubing smooth pipe (type M, L, and K), fairly smooth pipe, fairly rough pipe, and
rough pipe. These charts can be used to determine the velocity in feet per second and the friction
loss per 100 ft of pipe length. These charts will be used in the next step to determine pipe sizing
based on flow and allowable friction loss.
Elevation losses (or gains) occur when there is a physical change in elevation in the piping
system. Each foot of vertical rise is equivalent to 0.434-psi pressure drop or vice versa (each foot
of vertical drop in elevation is equivalent to 0.434-psi pressure gain). For example, if the
incoming water supply pipe is at an elevation of -4 ft below the finished floor and a plumbing
fixture is being served at Level 2 with an elevation of 16 ft above the finished floor of Level 1,
then this will be equal to 20 ft x 0.434 = 8.68-psi pressure drop. Therefore, if you have an
entering pressure of 60 psi, this would result in 51.32 psi at the Level 2 fixture (assuming static
flow with no friction losses or other losses in the system).
Equipment losses are determined based on the type of equipment and associated pressure drops
per the manufacturer. Common equipment that may have pressure drops include water-softening
equipment, water-filtration devices, instantaneous water heaters, etc. It is common for watersoftening system equipment to have a pressure drop between 15 and 25 psi for continuous to
peak flow. Pressure drops through all equipment need to be coordinated with the manufacturer
based on the required flow rates.
Miscellaneous component losses include various appliances, fixtures, equipment, etc. Common
items include backflow-prevention devices, water meters, point-of-use water filters, etc.
Backflow-prevention devices and water meters can result in a large pressure drop that needs to
be accounted for in the overall building pressure-loss calculations. These pressure drops are
typically indicated in the manufacturer’s literature based on the required flow rate.
Step 5: Longest developed pipe length
This step will determine the longest developed pipe length to the furthest hydraulically remote
fixture/appliance. It is important to note that the furthest fixture from the main-entry water
service may not be the furthest hydraulically remote fixture. For example, a fixture on Level 2,
which is closer to the main-entry water service, may still be more hydraulically remote than a
fixture further away on Level 1. Consider a water closet on Level 2 that is approximately 100 ft
away from the main-entry water service versus a water closet that is 200 ft away from the mainentry water service on Level 1. The water closet on Level 1 will have a longer pipe length;
however, the water closet on Level 2 will have a higher pressure drop to reach this fixture due to
the elevation losses. Another example would be a flush valve water closet versus a flush tank
water closet. Again, the flush valve water closet will require a higher pressure to operate than a
flush tank water closet, therefore it may be the furthest hydraulically remote fixture. This is
worth considering when evaluating longest developed lengths and required water pressures at
various fixtures.
The longest developed length is calculated by determining the overall piping distance from the
main-entry water service to the furthest hydraulically remote fixture. For example, the furthest
hydraulically remote fixture is a water closet on Level 2, which is approximately 500 ft away
from the main-entry water service.
In addition to the overall piping distance to the furthest hydraulically remote fixture, pipe fittings
need to be considered to determine the overall developed longest run. Depending on the piping
materials and required fittings, additional losses will occur at each fitting. Manufacturers
typically provide information for pressure losses in fittings and valves, which is represented in
the equivalent length of pipe. For example, a 1-in. copper pipe with a standard 90-degree elbow
will add approximately 2.5 ft of equivalent pipe length. Therefore, calculations can be completed
based on the piping layout design and anticipated fittings, types of fittings, and pipe sizes to
determine the additional losses through fittings and valves.
Calculating friction losses through every fitting and valve can be time-consuming, especially
when the pipe sizing needs to be determined to review the losses through each fitting and valve.
Not to mention that the final installation of piping from the plumbing contractors may differ
from the diagrammatic design drawings, which will change the friction losses through the piping
system. A good rule to follow is to use between 15% and 50% of the overall piping distance. For
example, a standard commercial project with minimal changes in direction may only require an
additional 15% added to the overall piping distance to determine the overall developed longest
run. However, a project with a significant quantity of fittings and changes in direction may
require upwards of 50% added to the overall piping distance. This total will provide the overall
developed longest run.
Step 6: Allowable friction loss
The next step involves using the information from previous steps to determine the allowable
friction loss in the piping system. The allowable friction loss will be used with the charts from
Appendix A of the UPC and Appendix E of the IPC to determine pipe sizes and flow-rate
requirements.
Reference the previous example of a commercial building with (20) gravity tank water closets,
(30) lavatories, and (4) mop sinks. Assuming this is a 2-story commercial building with fixtures
on both levels, the first step is to determine the available pressure. For this example, the civil
engineer has provided the plumbing engineer with a 3-in. domestic-water service at an assumed
low pressure of 60 psi (dynamic) and a high of 70 psi (static). The high static pressure is within
acceptable pressure limitations per the UPC and IPC (does not exceed 80 psi). As there is no
drop-in elevation (no basement or lower level within the building), there will not be an increase
in pressure due to elevation drop. This example will focus on the low pressure of 60 psi and will
use this value to determine the allowable friction loss. A meter loss of 10 psi is assumed.
Next will be to determine the required pressure from Step 2. Although all of the water closets are
gravity tank type, it is good practice to maintain a minimum of 30 psi at the most remote fixture.
For this example, 30 psi will be used for the minimum pressure required.
Now using Step 4, friction losses can be determined for the building supply system. At this time,
piping friction losses will not be calculated as this step is to determine the allowable friction loss
over the entire system. Elevation losses as described in Step 4 will be used for this example, with
a vertical rise of 20 ft which is equal to an 8.68-psi pressure drop.
Step 5 will then be used to determine the overall developed longest run. For this example, 500 ft
will be used as the overall piping distance from the main-entry water service to the furthest
hydraulically remote fixture on Level 2. This building has various changes in direction but an
overall majority of straight pipe runs. Therefore, the plumbing engineer will agree to add 25% to
the overall piping distance to account for losses in fittings and valves. Therefore, the overall
developed longest run is equal to 625 ft.
Finally, calculating the allowable friction loss per 100 ft of pipe run is completed by multiplying
the pressure available after all losses and required pressure at furthest hydraulically remote
fixture by 100 ft, then dividing the total by the longest developed run; see the calculation in
Table 1.
For this example, the allowable friction loss per 100 ft is equal to 1.8112 psi. This value will be
used in Step 7 to develop the pipe sizing chart per the tables from the UPC and IPC.
Step 7: Pipe size and flow requirements
This step uses Charts A 4.1, A 4.1(1), A 4.1(2), and A 4.1(3) from Appendix A of the UPC and
Figures E103.3(2), E103.3(3), E103.3(4), E103.3(5), E103.3(6), and E103.3(7) of the IPC. These
charts provide the correlation between pipe size, velocity, flow, and friction loss per 100 ft for
various pipe materials (copper tubing, fairly smooth pipe, fairly rough pipe, and rough pipe).
Depending on the piping material to be used for the project, the correct chart can be used. For
domestic-water piping, fairly rough piping is used frequently. This chart will be used to further
develop the pipe-sizing requirements based on the example used in Step 6.
Using the allowable friction loss per 100 ft, which from the example above is 1.8112 psi/100 ft,
the chart can be used to find associated flow-rate limitations and velocities for various pipe sizes.
Keep in mind that the velocity limitation for cold water is 8 ft/second and for hot water is 5
ft/second.
These values can then be converted into a table for reference related to pipe size, flow, and
velocity using Hunter’s Curve to convert flow to water supply fixture units, as shown in Table 2.
Step 8: Pipe sizing
The final step is finalizing the pipe sizing on the associated plans. This includes summing up the
water supply fixture units for all fixtures and totalizing the water supply fixture units through the
entire piping system. The example markup plan in Figure 3 shows summation of the water
supply fixture units using the UPC through the hot- and cold-water piping systems back to the
main water supply. The same method would apply for the IPC, with changes to water supply
fixture-unit values as required. For fixtures with cold-water supply only (i.e., urinals, water
closets, hose bibs, etc.), this will be equal to the total water supply fixture-unit value from Table
610.3 of the UPC. For fixtures with hot and cold supplies, the notes at the bottom of UPC, Table
610.3, permits using 75% of the total supply fixture units to calculate flow. The IPC provides
fixture-unit values for both cold- and hot-water-serving fixtures.
Once the water supply fixture units are totaled through the entire piping system, then the table
developed in Step 7 can be used to provide the proper pipe size for each pipe segment.
The 2015 editions of the UPC and the IPC provide similar water-pipe-sizing methods for large
commercial buildings, although there are clear differences between methods used in each code.
Numerous published standards are also available for support in sizing of plumbing systems and
conditions/problems that can arise. Using the correct code adopted by the local jurisdiction is
required to complete proper sizing of the domestic-water systems. Understanding the basics
behind pipe-sizing principals is vital in understanding how to use the proper code and properly
design the water distribution systems for commercial buildings.