Low-Flow Shutdown Sequence for Pressure-Boosting Systems

By | Energy Savings, Pressure

shutdown boosting systems

According to ASHRAE 90.1, Domestic Water Booster Systems must shut down during periods of no flow demand. Operating pump systems when there is little or no demand wastes energy and increases wear and tear on the pump and piping system. While this sounds simple, it is one of the most challenging control sequences for a Booster System.

Domestic Water Booster Systems are used to supply water to commercial buildings to be used in restrooms, kitchens, and to make up water to Hydronic Systems like Cooling Towers. The demand for water will change throughout the day and the pump system must be able to respond to these changes. In commercial office buildings, for example, there can be long periods of little or no water demand overnight when the building is empty or even in the middle of the afternoon when the building is occupied.

For a pump system to perform a low-flow shutdown, it must first be able to measure the flow demands in the system. Flow Switches and Flow Meters are mechanical means of measuring flow, which can work, but both require proper installation in the system piping for proper readings. Space and piping constraints can limit the installation of switches or flow meters.

System Controllers like the Grundfos CU352 on the BoosterpaQ can calculate system flow using feedback from the pump Variable Frequency Drives (VFDs) and pressure readings from the system headers, eliminating the need for additional flow sensors. Once the CU352 detects low flow, it will start the Low Flow Shutdown Sequence by ramping the pressure up above the set point for a preset period. This ensures the entire piping and bladder tank are pressurized before the pump package shuts down.

Hydro-pneumatic or bladder tanks are used in the piping system either at the pump discharge or off the main riser on the upper floors of a building. With a proper air charge (typically 5 to 7 PSI below system pressure at the tank), the bladder tank will maintain the system water pressure while the pumps are off during low flow. Water from the bladder tank can handle a small water demand such as a toilet flushing or a sink being used. Once the water from the bladder tank is used and the system pressure drops, the pump system will turn on briefly to re-pressurize the system and the bladder tank, then shut down again. This process will repeat until normal flow demands resume in the building and the CU352 Controller will operate the pumps normally.

A bad or improperly charged bladder tank and poor controls cause pumps to short cycle during low-flow demands. Pumps will turn off, only to have the system pressure drop immediately, causing the pumps to turn back on. Short cycling pumps in this manner will increase wear and tear on the pumps, motors and piping components, leading to early mechanical failures.

A pump system with a good low-flow shutdown sequence and properly sized bladder tank will provide constant water pressure with reduced energy savings and system wear. As part of a Building Assessment, Cougar USA reviews existing pump systems for low-flow shutdown controls and properly installed bladder tanks.

Design Considerations for Water Pressure Reducing Valve (PRV) Stations in Commercial Buildings

By | Pressure

prv design

Pressure Reducing Valve (PRV) Stations are an important component of a water-distribution system in a commercial building. The 2015 Uniform Plumbing Code Section 608.2 states that PRVs are required at any point where the system static pressure exceeds 80 PSI. Typically, this applies to mid- and high-rise buildings when the pressure boost required at the ground floor to serve the upper floors in the building is over 80 PSI. When you need to design a PRV Station, you must consider the station pressure drop, water flow, and safety devices.

To calculate the Pressure Drop across the PRV Station, we have to determine the inlet and outlet pressures. The inlet pressure is determined by the PRV location in the building. The lower the PRV is in the building, the higher the static inlet pressure will be. Typically, the PRVs are fed by a Pressure Boosting System that feeds the entire building, so the inlet pressure may also fluctuate a little, depending on the demand in the rest of the building.

The outlet pressure is determined by two factors. First is the number of floors the PRV Station is serving, and the second factor is whether the station is feeding the floors above or below the station. A good rule of thumb is that each floor will result in a pressure change of 5 PSI. If the floors fed by the PRV Station are the floors above, then you would need a higher outlet pressure at the PRV Station (around 65 to 75 PSI) because the pressure will drop about 5 PSI each floor higher in the piping. If the PRV Station is feeding the floors below, the outlet pressure would need to be lower (around 40 to 50 PSI) because the pressure will increase 5 PSI for each floor lower in the piping.

We recommend keeping the pressure drop across any single PRV to below 100 PSI to avoid poor performance, cavitation, noise, and valve damage.

prv design

The water-flow demands of a PRV Station depend on the number of fixtures being served by the station and can be calculated using Hunter’s Curve, which unfortunately doesn’t account for diversity in the system demand. If the building’s water flow is overestimated, PRVs tend to be oversized and do not perform well at partial load conditions. Combining two valves in parallel with High and Low Flow Valves helps to keep both valves operating within their design conditions across all load demands. 

When a Pressure Reducing Valve fails, high-pressure water will be allowed to pass through the station to the fixtures downstream. By code, an expansion tank or relief valve is required downstream of the PRV. We recommend the use of a direct-acting relief valve, along with a control system to shut down water
flow. A pressure switch senses the high pressure downstream of the PRV and signals the control panel to close the block valve. The control panel also sends the alarm signal to the building management system to alert the building engineers. As with Level Control Systems, we always recommend monitoring these alarm outputs.  

Cla-Val has a Factory Sizing Program that provides Pressure Reducing Valve selections that handle the pressure drop across the entire flow range of the station without excessive velocity or noise. At Cougar, we take the valve selections from Cla-Val and combine them with our control system to provide the best design for Water PRV Stations.

For more information, or to request PRV sizing, please contact us here.

Avoiding Cavitation in Water Pressure Reducing Valves

By | Pressure

High-rise buildings present multiple challenges for water distribution due to the high pressures required to reach the top of the building. The high pressures in the lower levels of the building cause high-pressure drops across Pressure Reducing Valves (PRVs), over 100 PSI or more, creating the potential for cavitation within the valves.

Cla-Val explains cavitation in this white paper, saying “Cavitation occurs when the velocity of the fluid at the valve seating area becomes excessive, creating a sudden, severe reduction in pressure that transforms the fluid into a vapor state, resulting in the formation of literally thousands of minute bubbles. The subsequent decrease in velocity and pressure rise that occurs after the valve seating area, when the pressurized condition resumes, causes these vapor bubbles to collapse at the rate of many times per second. Should this occur in close proximity to any metal surface, damage can take place. Over time, this can lead to valve failure.”

The damaging effects of cavitation include excessive noise, erosion of the valve and eventual valve failure. When designing a system with pressure drops greater than 100 PSI, there are two ways to avoid cavitation.

Cla-Val Cougar

The first is to use the Cla-Val Anti-Cavitation Trim option on the 90-01 Pilot Operated PRVs. The Anti-Cavitation trim controls the water flow through the disc and seat of the valve in a way that dissipates cavitation and its effect and allows the pressure drop to be taken across a single valve.

Cla-Reg Cougar

The second option is to use multiple valves in series to reduce the pressure in stages so that the pressure drop across each individual valve is less than 100 PSI. In the example above, the station pressure drop is 150 PSI (200 PSI to 50 PSI) with the first PRV reducing the pressure from 200 to 110 PSI, and the second from 110 to 50 PSI. Both the High Flow (Blue 90-01 Valves pictured) and the Low Flow (Bronze CRD-L’s) are configured in series for the staged pressure drop.   

The choice to use the Anti-Cavitation Trim or Valves in Series will depend on each application. Cla-Val has a Factory Sizing Program that provides PRV selections that handle the pressure drop across the entire flow range of the station without excessive velocity or noise. At Cougar, we take the valve selections from Cla-Val and combine them with our control system to provide a complete solution for Water PRV Stations.

For more information, or to request PRV sizing, please contact us.

Break Tank Fill Valve Types – Float Versus Electronic

By | Level, Pressure

Many commercial buildings use storage tanks for Domestic (Potable) and Fire Water Applications, especially in Houston where it is required by Houston Amendments to the Uniform Plumbing Code Section 607. As water is used in the building, an automatic system is required to replenish the water and maintain a constant level in the tank. In domestic applications, this process can repeat multiple times an hour during peak demand loads. An automatic level-control system has two main components, Fill Valves and Controls.

Float Controlled Valves (Cla-Val model 124-01) are widely used on break tanks in commercial buildings. Float valves operate on the same principle as the valves in the back of a toilet: a float attached to a rod moves up and down with the level of the water in the tank. Float valves are simple and effective, but there are drawbacks in commercial applications. Most valves are installed on the top of tanks with the float rod directly attached to the valve, making them difficult to access and maintain. Tank-water-level adjustments are also difficult because the float rod length and float position must be changed on the valve itself.

When two float valves are used, there is no alternation between valves. The lead valve (shorter float rod) will always operate first, with the lag valve going long periods without use. This combination will eventually cause failures in both valves without proper preventative maintenance. Also, these systems typically provide little or no feedback to the Building Management System.

fill valve

Cougar recommends using an Electronic Solenoid Actuated Fill Valve and a Level Control Panel to avoid all of these issues. The Cla-Val Model 136-01 fill valve uses the same base valve as the 124-01, but it uses an electric solenoid valve to open and close the valve rather than a float rod. This allows the fill station design to be improved in multiple ways.

Cougar recommends using an Electronic Solenoid Actuated Fill Valve and a Level Control Panel to avoid all of these issues. The Cla-Val Model 136-01 fill valve uses the same base valve as the 124-01, but it uses an electric solenoid valve to open and close the valve rather than a float rod. This allows the fill station design to be improved in multiple ways.

First, the valves no longer need to be installed on top of the tank and can be wall- or rack-mounted down at a level that is easy to reach. Instead of a float rod, a level sensor assembly is installed on the tank to provide level feedback to the control panel.

The levels at which valves turn on and off, or levels for Low- and High-Level Alarms, can all be easily viewed and adjusted on the Control Panel Touchscreen Interface. Level adjustments require a few touches on the screen instead of a ladder and tools.

The Level Control Panel also provides automatic alternation of multiple fill valves, thereby ensuring even wear. During each fill cycle, the lead fill valve alternates between valves; however, any valve can be manually run or taken out of service if required using the Open-Close-Auto Switch on the control panel.

The Cougar Systems Level Control Panels have Tank Alarms and Level Outputs for the Building Management Systems to monitor. It is crucial that level-control systems be monitored for Low Level (loss of water) and High Level (tank overflow) alarms to prevent equipment failures and potential flooding. For more information on overflow and flood protection, see our blog post here.

Electronic Fill Valves and Level Control Systems improve the operation of the fill station, will extend the life of the valves and provide building engineers with greater visibility of their system. For more information, please contact us.

Why are Break Tanks Required in Houston for Pumping Applications?

By | Level, Pressure

break tanks houston

Some call them House Tanks, others Break Tanks, Storage Tanks, or Buffer Tanks. If you have been in the pump room of a building in Houston, you’ve seen these large water tanks, but why are they used? The Houston Amendments to the Uniform Plumbing Code Section 607 states that upstream from a pump system, an atmospheric storage tank with an air gap between the tank and city water supply must be used. This applies any time the city water pressure is insufficient to supply a building for both Domestic (potable) and Fire Water applications and the addition of pumps is required.

The City of Houston is one of a few municipalities across the country with this requirement for both Domestic and Fire Water Pumps. The tank air gap effectively separates the building’s water supply and consumption from the city water lines. This should stop any contamination from a building from getting back into the city supply and affecting others. Also, large sudden demands in a building (i.e., fire pumps) shouldn’t affect the water supply to those around it.

While a tank is an effective backflow prevention method, it does add some complications. Tank size and design, water-level controls, pump pressure design calculations, and system maintenance all must be considered when using a storage tank.

The National Fire Protection Association (NFPA) Standard 22 has requirements for Fire Water Storage tank sizes. However, there is no minimum tank size for domestic water. There are multiple options for tank construction. Steel tanks with coatings for potable water are widely used, but over time maintenance on steel tanks and coatings can be expensive and time-consuming. Alternatives to steel are fiberglass and plastic, both of which carry NSF61 ratings without the need for coatings. The modular design of the FTC FRP Tank is ideal for the tight space requirements of most pump rooms.

In order to maintain a constant water level in the storage tank, fill valves and controls must be used. A simple method is to use a Float Valve on top of the tank. For more control, electronic valves and a control panel are used. A quality level-control system can prevent tank overflows and flooding or dry tanks and the building from losing water. It is crucial that the building management system monitor the level-control alarms for potential issues.

When using an atmospheric storage tank, the city supply pressure cannot be used in the booster pump pressure calculations; this is referred to as Flooded Suction as opposed to Pressurized Suction. Pump selections must also consider the low Net Positive Suction Head provided by the atmospheric tank. The Grundfos CR Multi-Stage Pump is an ideal selection for Flooded Suction pressure-boosting applications.

Cougar USA has worked in hundreds of buildings in Houston with break tanks, level controls, and booster systems. For more information or a free building assessment, contact us here.

Older Domestic Booster System Modifications Versus Replacement

By | Energy Savings, Pressure

domestic booster system

In Houston, there was a construction boom in the 1970s and ’80s, with hundreds of high-rise buildings adding to the skyline. Many of these buildings are still using the original mechanical systems for HVAC and pumping applications. Potential mechanical failure and energy savings are forcing building operators to choose between modifying their domestic booster system or replacing it all together.

Commercial buildings have seen a lot of changes in the last 50 years. The push for energy efficiency and a reduced carbon footprint affect everything in the building, from the exterior designs to the mechanical systems in the basement. Low-flow water fixtures, water recovery systems, and improving HVAC systems reduce water flow load profile today compared to years past.

Pressure Boosting System Design has also seen drastic changes in the same time period. Fifty years ago, large constant-speed, single-stage, centrifugal-pump systems were the design standard. These workhorses run 24/7, 365 days a year, regardless of the system demand in the building. This results in wasted energy and unnecessary wear on the pumps and piping. With smaller flow demands today, older pumps still in service are grossly oversized, making them much less energy-efficient.

Grundfos introduced the inline Vertical Multi-Stage Pump in 1971. It has multiple impellers, each one boosting the pressure higher, making them ideal for domestic pressure-boosting applications. However, these applications were not widely adopted in the U.S. until years later. Because they can create higher pressures, Multi-Stage Pumps typically require pressure control either through a Pressure Reducing Valve (PRV) or Variable Frequency Drive (VFD).

A PRV is a mechanical device used to reduce the pump pressure to the pressure required for the building. This is the equivalent of driving a car by flooring the gas pedal and using the brake to control the vehicle’s speed. No one would even think to drive their car this way, but until Variable Frequency Drives (VFD) and improved controls, the PRV was the best method of pressure control for booster systems.

The application of VFDs and Control Systems to booster pumps have transformed them from dumb workhorses to finely tuned Controls Packages. A VFD and Controller combined with Vertical Multi-Stage Pumps will only operate pumps at the speed required to maintain a constant pressure in the building. Operating a pump at a reduced speed for partial load demands creates massive energy savings. Due to affinity laws, power is proportional to the cube of pump speed. This means a 20% reduction in speed is not a 20% reduction in power consumption; it is a 48% reduction in power! 

So can you add VFDs to an old pump system and achieve similar energy savings and performance? Can you teach that old dog new tricks? In this case, the answer is almost always NO! The addition of new controls can’t overcome the underlying issues of the older single-stage pumps — they are oversized and not ideal for pressure boosting. The pumps were not designed to operate at reduced speeds, so adding VFDs to older systems usually yields very little energy savings as the pumps still operate at close to or at full speed most of the time.

Replacing older pump systems with new, properly sized systems with VFDs and controls will always generate more energy savings and a faster payback. For more information or for a free building assessment, contact us here.

Design Considerations for Pressure-Boosting Systems in Commercial Buildings

By | Design, Energy Savings, Pressure

More than 60 years ago, the late Dr. Roy B. Hunter developed a system for calculating water loads in commercial buildings. The estimated water demand of fixtures (water closets, sinks, etc.) is given a value called Fixture Units which have an equivalent demand load in Gallons Per Minute (GPM). The Fixture Units and Demand Load relationship is known as Hunter’s Curve and is still the basis for plumbing system design today.

Hunter’s Curve can be effectively used to calculate total system demand, but it has a glaring flaw. There is no consideration for diversity in the system demand. Using Hunter’s Curve for the basis of design of a Pressure Boosting System results in a pump system sized for all fixtures being used simultaneously, a scenario that will likely never happen. The pumps are grossly oversized for partial-demand conditions which make up 90% or more of total operation, causing poor system control and unnecessary wear on the pumps and piping system. In addition to Hunter’s Curve, Cougar USA uses field experience and data collection for system design.

To generate an accurate demand load profile, we gather as much information as possible about the building. The type of building has a huge impact on the load profile; even with similar fixture units, hospitals, hotels, schools, and office buildings will all have different load demands throughout the day and week. Special applications, the height of the building, locations of equipment, and potential future expansion are all factors in creating the right Building Load Profile. Once the system requirements are determined, we must make the right equipment selection.

Pressure Boosting Systems are typically comprised of two or more pumps, suction and discharge headers, control panel, and bladder tank. The pump style, size, and quantity and are all dependent on the Building Load Profile. For most commercial building applications, the small footprint and multi-stage design make the Grundfos CR Vertical Multi-Stage pump the best selection. The pump size and quantity will be determined by partial load performance and the redundancy desired. Typically, a higher quantity of smaller pumps is more efficient at partial load conditions without adding much to the initial system price when compared to a duplex (two-pump) system of larger pumps.

A properly sized and charged bladder tank is crucial to the overall performance of the Pressure Boosting System. Based on the load profile and building height, we can determine the size and location of the bladder tank. In low- to mid-rise buildings, the tanks will typically be installed at the pump system discharge. In high-rise buildings, the tanks will be installed on the upper floors, off the main riser.

The last consideration is the level of controls required for the building. Critical applications like hospitals, research facilities, and high-rise buildings will require control features like those on the Grundfos CU352 used on the Hydro MPC Booster System. A graphical user interface shows feedback of the system and any alarms, as well as advanced control features like Proportional Pressure Control, Reduced Operation for Emergency Power, Soft Pressure Buildup, and Communications for Building Management Systems.

To effectively design for today’s buildings, we must look beyond Hunter’s Curve. Cougar USA has made hundreds of Booster System selections for commercial buildings, and not once have we been wrong.

energy savings

Building Assessments for Energy Savings and System Performance Improvements

By | Energy Savings, Pressure

In 2017, about 39% of total U.S. Energy Consumption was consumed by the residential and commercial sectors. In a commercial building, HVAC equipment (i.e., chillers, boilers, cooling towers, etc.) and lighting are the biggest targets for energy savings, but the capital costs for improving these may be prohibitive. There are many opportunities for energy savings and building performance improvements with other systems in commercial buildings.

Pumps are used in a variety of applications in commercial buildings, and 90% of them work inefficiently. There are three main reasons for pump inefficiency: pump type, size and controls. The proper combination of pump type, size and control will ensure the best system performance and lowest energy costs. Unfortunately, most pumps installed today are either improperly applied or sized and use outdated controls.

Domestic Water Pressure Boosting Pump Systems are required any time the city water pressure is too low to deliver water to a commercial building. Mid- to high-rise buildings almost always have pressure-boosting systems, and many single-story restaurants and medical facilities require high water pressure for special applications. In our experience, these systems usually suffer in all areas of inefficiency. Most are designed using fixture unit counts and maximum flow demands without looking at diversity factors and partial-usage loads. These calculations cause pumps to be oversized and incapable of performing well under partial-load conditions, which accounts for 90% or more of the total operation.

Even with the right pump type and size selections, high system performance is impossible without good controls. Variable Frequency Drives (VFDs) and integrated controllers will optimize the pump operation to meet changing building demands, only running the pumps as needed to maintain constant pressure to the building. Even with the perfect combination of pump size, type and controls, the most efficient pump is one that is not running at all.

Another key component to the Pressure Boosting System is a Hydro-Pneumatic Tank or Bladder Tank. Bladder tanks are installed in the system piping either at the pump system discharge or off the main riser on upper floors of a building. A bladder tank with a proper air charge is vital to the pump system’s Low-Flow Shutdown Sequence, a feature that will turn the pumps off during periods of little or no water demand. Allowing the pump system to shut down and still maintain water pressure to the building will greatly reduce energy costs and reduce wear and tear on the water system components (pumps, piping, pressure-reducing valves, etc.).

The energy savings potential with Pressure Boosting Systems in commercial buildings is 60% to 90% in most cases. An assessment of a building’s Pressure Boosting System will review the existing pump system information, but also account for the building type, size, special applications and potential for demand changes. Once these factors are reviewed, a new pump system can be selected, and the energy consumption calculated in comparison to the existing system. All the information is documented in a Building Assessment Report, provided at no charge by Cougar USA.

If you are interested in a Building Assessment, please contact us here.