Pressure Boosting Systems – Pt3

By | Pressure

With few exceptions, the water demands of a Commercial Building are significantly overestimated, which has negative impacts on the long-term performance, reliability, and efficiency of a Booster System.  At Cougar USA, we design our systems to be most efficient at the partial load of the building, which improves performance & reliability and reduces operating costs.  In this Tech Talk, we cover the pump and system selection for Booster Systems.

Make sure to check out Parts I & II!

Pressure Boosting Systems – Selection – Part 3 Tech Talk Transcript:

Hi, I’m Tim Zacharias with Cougar USA, on this Tech talk we’re going to be going over system selection for pressure-boosting systems in commercial building applications. This is part three of a three-part series. So please check out Parts one and two if you haven’t already.

Now that we’ve determined our flow in our pressure for our building, we can take those and make an actual pump system selection. Based on our fixer unit counts for the worst-case scenario and specialty applications we have a potential load requirement thereof 300 gallons per minute, but we do want to take into consideration that partial load and that diversity factor that we talked about, the 15%. So we’re looking at about 50 GPM, there, is really where this pump is going to be operating most of the time. We want to pick our pump selections based on this 50 gallons per minute and not necessarily 300 gallons per minute.

In order to be covered, we want to make sure that we have enough pumps to cover that worst-case scenario if needed. So with the Grundfos Hydro MPC system boosterpaq, you can go up to five or six different pumps, so we can really get in, dial-in that pump selection to get it where we need it to be.

So what we don’t want to do is Select that pump, you know, let’s say we want two pumps, we want some redundancy. Set two pumps at 300 GPM each, so we’re going to be 100% redundant there. But, really, those pumps want to operate way out here and not back here at this partial load. A pump that is going to be efficient out here at this 300 GPM, is not going to want to operate back here at this 50 GPM where we’re going to see that load most of the time. So, instead, we’re going to pick based on this 50 gallons per minute and have multiple pumps. So we can do that, we can break this up into thirds, we can do 33-33-33 each at 100 gallons a minute. We could do 50-50-50 pumps at 150 gallons a minute each, or you can do four pumps at whatever, you know, 60 or 75 gallons a minute, start to add up your redundancy.

Now, when we’re looking at the redundancy, you know again this 300 GPM is going to be the worst-case scenario. Probably never going to hit that, so even if you were to go in this case, we’re going to do three pumps, each at 100 GPM, and really where that redundancy is going to come from is the diversity factor in the building. If you wanted to have an n + 1 you could go 4 at 100 or we could do a 3 at 150, but in any case, we really want to keep that pump selection to 100 to 150 GPM per pump because those are going to operate best at that partial load condition. They’re going to be able to run at this reduced speed and still be efficient, still be within their preferred operating range.

A couple of different options to give you some redundancy there, just depends on, you know, having a type of risk or how close are you going to be to the actual worst-case scenario there. But again, we would advise that you go with smaller pumps and had more of them to cover the redundancy rather than doing less larger pumps.

Okay, so that would be our flow right here, any of those selections would work well. When we’re talking about pressure now, remember we have to consider that pump versus the system boost. We want to make sure that our pump boost is correct, and in the city of Houston, that’s going to match the system boost because we’re starting from zero and that was 150 PSI or about 350 feet based on our example and again that’s represented here. But we want to look at when we’re selecting our pump, where we are going to be operating at these partial loads. It’s easy to select the pump out here where we are running it at 100% and we are satisfied that that Duty point, but ultimately again, we’re going to be operating back here somewhere at these partial speeds. So these could be in 95-90-85-80 even lower, potentially, depending on your flow rate. Where that pump is going to operate as the demand slows down so as that the man reduces the pump speed is going to slow down to maintain that constant pressure at the different flow rates

So we would like to see the pump be able to maintain Pressure at 80 to 85% speed at the partial loads. So if we can get to this 50 GPM and maintain 350 ft at about 80 -85% speed. That’s where we’re going to want to be, that’s going to give us the additional flow that we need as the demand increases. It also gives us some additional head in the system if we need it for whatever reason if we need to increase our set pressure.

So really two important takeaways here are going to be that our pumps are between we’re looking to try to select our pumps that do about 100 to 150 gallons a minute and add multiple to get redundancy and our worst-case scenario covered and then on the speed on the head side. We want our pumps to be able to maintain our set pressure at about 80 to 85% speed at that partial load condition.

If you have any questions on systems selections or anything that we’ve covered please reach out to us or check out our other videos. Thanks.

Pressure Boosting Systems – Pt2

By | Pressure

The primary purpose of a Pressure Boosting System is to maintain constant pressure in the building (surprising, right?!).  In Part II of this Tech Talk, we explain the factors to consider when determining the pressure requirements for a building. 

Pressure Boosting Systems – Pressure – Part 2 Tech Talk Transcript:

Hi, I’m Tim Zacharias with Cougar USA. On this Tech talk, we’re going to be talking about calculating the system pressure required for a pressure boosting application of a commercial building. This is part two of a three-part series, so if you haven’t seen part 1 on the flow calculation, make sure to check that one out as well.

When we are looking at the pressure required for a pressure boosting system in a commercial building, the first thing we wanted to look at is our static pressure. Now, this is going to be literally what the weight of the water is to fill up the riser in the building and get it to the top of the building. So our very nice and friendly building over here is 20 stories at 231 feet so if we were to convert that to pressure, that would be 100 PSI. So if we filled this riser in this building with water, but it wasn’t under pressure we would see 100 PSI on our gauge, that would be our static pressure. Now, a little trick that we use a lot of times on existing buildings is a lot of times we don’t always know what the actual height of the building is, so we can kind of back into it by looking at the number of floors of boost. So if we assume that every floor is about 10 to 12 ft that’s going to be about 5 PSI per floor, and you can see our math works out pretty well in this one to be similar to 100 PSI not always going to be the case and all buildings, but it will get you close.

So for this example, we have 100 PSI as our static pressure. Now, the residual pressure is anything else that we need on top of our static pressure to make the water usable at the top. Our cooling tower is going to be one of the main reasons that we need this additional residual pressure up at the top. It could also be for our flush valves, it could be to go to water heaters, whatever it is, make sure that you have that residual pressure. We’d like to see a minimum of 45 PSI, that’s going to be able to get you through backflow preventer, and then out to the cooling tower, you know, if you got to go also through a softener and things like that and you might want to have a higher residual pressure than that.

Another thing to consider is going to be friction loss. Now, to calculate the actual friction loss in the building you’re going to want to have the length of pipe and any set fittings, things like that, to be able to convert those two equivalent lengths of pipe and then look at your flow rates to see what your actual friction loss is. When we’re dealing with pressure boosting applications, typically, we are going to be looking at lower flow rates most of the time, you know, 2200 gallons per minute, and if we have decent pipe sizes (2 inches and larger) the friction loss and can be pretty minimal. So we do have some, but for this example, we’re going to go pretty low and just have the 5 PSI there for friction loss, so that would give us a system pressure of 150 PSI. Now what that means is that we need that pressure here, at the bottom of the building, we need to have 150 PSI on the discharge of our pumps to be able to see this 45 PSI up here at the top for it to be usable.

So that’s what we’re going to want to see in the discharge of our pump system. And the other thing that we need to consider once we have our system pressure is, what are we getting from the city supply? Now, this gets a little bit complicated when we working in the city of Houston, because we have the code requirement to go through the atmosphere storage tank. So inside the city limits of Houston, our City supply is going to be zero effectively. We do get whatever the head is in the tank, but for these purposes, we typically use a zero as our suction pressure.

If you were in a municipality that did not have that code requirement, you could take whatever the city supply pressure is from the city and subtract it out from this here. So I will show you what that looks like. Let’s say that we have a 50 psi coming in from the city, we would have 50 PSI that we would subtract from our system pressure there, meaning our pump boost is only 100 PSI. So out of the 150 PSI required for the building, the pumps are only responsible for 100, the city pressure is taken care of 50 of that. But what we are dealing with most of the time here in Houston is where we have zero pressure coming in from the city because we were starting from that storage tank.

So we’re going to show that example here, and the effect that has on the pumps elections if we assume, Zero here for incoming pressure, now our pump boost is going to be the same as our system pressure. So the pumps are going to be responsible for all of the Boost that is in that system pressure. It is very important to know if you have to go to the storage tank or not so you can see how much that affects the pump boost that is required.

Make sure you check out part 1 and part 3 of this series. Part 3 we’re going to look at how to take your flow and pressure calculations and turn them into a system selection.

If you have any other questions, please feel free to reach out or check out our other videos on our site. Thanks

Pressure Boosting Systems – Pt1

By | Pressure

Pressure Boosting Systems are essential for delivering water to high-rise buildings; however, the method for sizing these systems has not changed significantly in over 50 years!  Cougar USA’s High-Performance Design approach combines our extensive knowledge & experience with the best products on the market to deliver systems that provide constant water pressure with little to no downtime and the lowest Life Cycle Cost.  Check out this three-part Tech Talk series on Booster System Design to see how we do it.  We will cover the flow and pressure requirements of a building and pump & system selections to meet them.

Pressure Boosting Systems Design Part 1 Tech Talk Transcript:

Hi, I’m Tim Zacharias with Cougar USA on this Tech talk, this will be the first of a three-part series for sizing and selecting pressure boosting systems. On this one, we are going to be looking at the flow rate for a commercial building.

Now, a couple of different things that we need to take into account when we are looking at flow. The first place that we can start is Hunter’s curve in the fixture unit counts. This is a method that goes back to the 1960s. Basically, we can count up our fixture units in the building, look at the chart for what that says the equivalent flow rates are, and what that is going to give us is our worst-case flow rate for that building.

So if every fixture were to turn on and we needed that flow rate, what does that give us in terms of flow?

Now, the floor in Hunters curve is that it doesn’t take into account the diversity of usage and we’ve done flow audits on commercial office buildings, with and without cooling towers, we’ve done hotels, we’ve done hospitals, other types of buildings. And consistently we found that most of the time the usage is about 15% of what our worst-case scenario is for that building, meaning, 75% – 80% of the time we’re running at a partial load condition that is about 15% of what curve is predicting. Now, what that looks like on a pump curve, if we have our flow and head of our pump curve, is that if we were designing to this duty point here, that if that is our duty point, our design, you know, based on Hunter’s curve, really what we are going to see is an operation back here most of the time. This is where our partial load is going to be. So we really want to focus on the partial load condition when we’re selecting our pumps because that’s what they’re going to operate the most, that’s what we wanted to be most efficient because the pump that we select for this duty point is not going to be efficient or operate well at this point.

The other thingS that we have to take into consideration are any sort of special applications. Now, the number one in a commercial building is going to be make up to the cooling tower. Cooling tower, especially a commercial office building, even potentially in a hotel or other type buildings make up to the cooling tower is going to be the number one consumer of water, maybe anywhere from 20 to 80 or 100 gallons a minute, depending on the size of the cooling tower, the makeup line, the type of fill valve that’s used to make it up, but we need to take that into account when we are looking at our worst-case scenario in terms of consumption. So definitely want to make sure if we’re making up to the cooling tower that we have that covered.

Other things that could have large instantaneous demands, kitchens, dishwashers, you know, you could have sterilizers in the hospital, you could have a big sudden demand of all of these things if you have any sort of specialty processes in the building, you want to account for those and plug those into your worst-case scenario.

But if we’re talking, you know, very simple building, just has cooling tower, you know, men’s and women’s restrooms and a little kitchen on each floor, this 15% of our worst-case scenario is going to be a pretty accurate way to go when you’re determining your flow rates.

So, again, if we were to say that Hunter’s curve said that we needed, let’s just say it’s a simple building here, one hundred gallons per minute. You know what we’re really going to be wanting to design to is back in this 15 to 20 GPM range here.

All right. So we’re going to have two other videos as part of this to cover the pressure selection and then ultimately the pumping system selection for pressure boosting applications. So please check out those videos or reach out if you have any other questions.

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.