Xylem study analyzes life-cycle cost of HVAC systems
Hydronic systems outperform VRF, analysis finds

Introduction
Upfront costs and energy consumption are primary drivers when selecting a commercial HVAC system in new and retrofit projects. A new study commissioned by Xylem underscores the importance of evaluating total life-cycle cost in the selection process to adequately identify pros and cons of the various system types.

To anecdotally compare and contrast HVAC systems according to their 30-year life cycle cost analysis (LCCA), the Xylem study analyzed seven elementary and middle schools located in South Carolina Climate Zone 3A, a humid, warm climate. The cost analysis includes upfront installed cost, replacement cost allocations and ongoing energy and maintenance cost of the following system types:

• Variable refrigerant flow heat pumps (VRF)
• Water source heat pumps (WSHP)
• Ground source heat pumps (GSHP)
• Direct expansion rooftop units (DX RTU)
• Water cooled chillers (WCC)
• Air-Cooled Chillers (ACC)

With HVAC systems dictating as much as 50 percent of the overall energy use of K-12 buildings, according to ENERGYSTAR, the results of the Xylem study serve to inform decisions and promote maximized energy savings across the commercial construction industry.

Methodology
Over a three-year period, utility cost (electric and natural gas) and average maintenance cost were collected. For a more accurate comparison, construction costs were estimated according to the year each building was built, and utility rates and square footages of these facilities were also normalized to remove any other outside factors. The average electric rate ($k/kWh) and natural gas rate ($/therm) from the sample buildings were multiplied by each building’s electric and natural gas consumption to calculate a normalized energy cost ($/SF) for each building. Each building’s square footage was also considered when calculating maintenance and installation cost.

Findings
From a life-cycle cost perspective, the primary drivers of a purely economic decision of all HVAC system types are installation and energy cost. However, these costs are often interrelated with a maintenance department’s unfamiliarity and uncertainty with any given system, eventually showing in the form of increase utility cost from overrides and other changes to the system design.

The study’s findings resulted in the following ranking in life-cycle cost analysis from lowest to highest.

As exhibited in Figure 1, replacement allocations had an impact on the life-cycle cost analysis (see yellow bars) and drastically reduced the cost effectiveness of equipment with 15-year life expectancies.

Figure 1

Conclusion
As design engineers, building owners and mechanical contractors strive for more sustainable and energy-efficient practices, these findings shed light on the differences among systems, particularly hydronic and VRF systems. Considerable benefits of hydronic HVAC systems include lower energy usage intensity and cost, wider range of maintenance flexibility and longer life expectancy.

Specifically, the schools with WSHP and GSHP systems displayed energy use levels that were 30 percent (40.7 kBtu/sf) and 41 percent (34.4 kBtu/sf) better than the national median for elementary and middle schools (58.2 kBtu/sf), respectively. The replacement cost allocation also acknowledged that the tested hydronic systems operate effectively for approximately 25 years. The tested VRF systems require replacement a decade earlier because of their tendency to work harder during heating cycles, ultimately bringing proof of long-term cost savings to the forefront of the conversation surrounding sustainability and hydronic HVAC system efficiency.

Click here to download the pdf

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About Xylem
Xylem (XYL) is a leading global water technology company committed to developing innovative technology solutions to the world’s water challenges. The Company’s products and services move, treat, analyze, monitor and return water to the environment in public utility, industrial, residential and commercial building services, and agricultural settings. With its October 2016 acquisition of Sensus, Xylem added smart metering, network technologies and advanced data analytics for water, gas and electric utilities to its portfolio of solutions. The combined Company’s nearly 16,000 employees bring broad applications expertise with a strong focus on identifying comprehensive, sustainable solutions. Headquartered in Rye Brook, New York, with 2015 revenue of $3.7 billion, Xylem does business in more than 150 countries through a number of market-leading product brands. The name Xylem is derived from classical Greek and is the tissue that transports water in plants, highlighting the engineering efficiency of our water-centric business by linking it with the best water transportation of all – that which occurs in nature. For more information, please visit us at www.xylem.com.

The post Xylem study analyzes life-cycle cost of HVAC systems appeared first on Xylem Applied Water Systems - United States.

Volume 6/ Issue 3/ October 2019

The well-known Domestic Pumps from Xylem can handle up to 212ºF of boiling condensate, without cavitating, without vapor locking and in many cases even without elevating the tank. Units will do their job and transfer the condensate back to the boiler room, or to the boiler itself. The condensate will travel through pipes, fittings, ups and downs, before reaching its final destination. If it is a boiler feed pump then overcoming the operating pressure of the boiler should be accounted for, too. All the pipes and fittings along the way will try to give our pump a hard time because of the pressure drop along them.

To calculate this pressure drop you have to take into account how far you’re going, and how high you’re going. Sounds simple but it may not be. How far includes not only the distance but also the equivalent distance for each fitting, each valve, each elbow, and the losses for all the piping. How high refers to elevation, but elevation can be both positive and negative. This means careful review of plans, or specifications that have already taken all of this into account and determined what the total losses to the pump are in the discharge piping before the pump delivers its condensate to where it needs to be.

For low pressure boilers less than or equal to 50 psi the discharge pump pressure needs to be greater than the losses by a minimum of 5 psi. If losses are 10, we take 15. For systems where boiler pressures are greater than 50 psi, your discharge pump pressure needs to be greater than the losses by a minimum of 10 psi, in order to be on the safe side. If we run the unit under vacuum then another 5 psi should be added on top of the above rule, since the pump will be pumping out of an average of negative 5 psi. Sizing the pump is vital for proper operation.

Domestic Pump has standard solutions to overcome up to 100 psi of back pressure and this is more than enough for most steam heating applications.

But what happens when the pressure drop along the discharge piping is higher than 100 psi? Such applications can be found in industrial facilities or in larger steam heating systems with longer and more complex return piping. The solution to that is coming from our large Xylem family, and it is the Gould’s e-SV stainless steel multi-stage pumps. Utilizing the e-SV multi-stage delivers a great solution for high pressure condensate and boiler feed units with an efficient and easy-to-maintain multi-stage pump.

B&G Domestic Elevated Boiler Feed Units CMED

Here are just a few benefits from the synergy between Domestic Pump and e-SV:
• Pumps up to 500 psi discharge pressure
• Stainless steel multistage pumps
• Flexible pump solutions

Most importantly we make sure that the selected e-SV pump models will also transfer boiling water without cavitating and without the need to oversize them. This is achieved by selecting those models that meet the same required net positive suction head (NPSH) like the ones of the Domestic Pumps. All of our units are vented to the atmosphere. This means that the max. temperature of the condensate is 212ºF and it is a matter of atmospheric pressure and available water column at pump inlet to provide the required NPSH at pump inlet. We have taken care of that and the design of the units, including tank elevation and types of pumps, will meet the application requirements. Like with Domestic Pump, the e-SV models also have a low-NPSH version to transfer condensate with temperatures at the higher end.

Custom condensate return unit, model CED-e-SV

In addition to the standard pump options, like discharge pressure gauge, 60 or 50Hz applications, and motor enclosures, we can also add different pump discharge connection styles and different materials for the volute and seals.

Currently there is a number of standardized CMED-e-SV boiler feed models available. Customized units are always available for both Condensate Return and Boiler Feed Units utilizing a range of cylindrical and/or elevated receivers.

Please feel free to reach out with your custom unit inquiry and questions.

Check out our products on www.domesticpump.com

Click here to download the October 2019 SteamTeam pdf file

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Volume 6/ Issue 3/ October 2019

When a steam trap failed open, and allows live steam to pass by, it is easy, and convenient to ignore symptoms or place on our never-ending list of “things to do.” After all, what harm is it besides wasting little energy that cost a few bucks? The boiler is still running, building is heated, tenants are not complaining, and everything seems to be fine. However, a failed trap will cost you more than just the loss of a small amount of steam. It will cost you a lot more.

The Cost of Lost Steam
Let’s examine how a trap passing steam can affect the whole steam system. First, you need to determine how much the loss of steam really costs. Since the steam is being lost at saturation condition (0 psig from the vented tank receiver) we can determine amount of energy (Btus) that will not be recovered. 0 psig steam contains 970 Btu/lb. So, for every pound of steam we don’t recover, we lose 970 Btu’s. But we’re losing more than just that latent energy. This is only a part of energy wasting. We are also losing sensible energy. Having lost that pound of steam, we must now replace it with a pound of water and we have to add energy to the new water just to bring it up to saturation condition (for water it is approximately 1Btu/lb°F). Let’s say the water we are introducing is 60°F. Because we lost our steam through a vented receiver, we have to raise its temperature to 212°F. And because the steam we lost had already been treated, there is the additional cost of treating the new water. Now let’s see how much it can cost you.

Single trap with 3/8” orifice discharging 100 psig of steam to atmosphere will cause a steam loss of 652 lb./hr. Since each lb. of steam is equivalent to about 1,000 BTU/hr. Loss will be 652,000 BTU/hr.

On gas fired boiler, operating at 70% efficiency will produce about 70,000 BTU for each Therm of Natural Gas. The gas required to replace the lost of steam will then become 652,000 BTU/hr. ÷ 70,000 BTU/Therm. or 9.31 Therms per hour.

If Natural Gas cost $1.27/therm. (US average June 2018 bls.gov) the money wasted due to the faulty trap becomes $11.82/hr. (9.31 * 1.27). If the boiler is operating 241 days/year. October 1st – May 1st 10 hours/day it becomes $28,486/year.

The significance of these savings becomes rapidly higher when you consider that an even small steam system usually has several traps, and larger system can have more than 1,000 traps.

Other Effects of failed Traps
Having this information we are able to calculate the energy loss associated with losing steam through a bad trap. However, there are other indirect costs related to the failed trap that are more difficult to calculate. One is the damage caused by water hammer. As steam enters a condensate return line, there is the chance steam will mix with the condensate and some of the condensate may flash into steam and collapse into condensate, causing water hammer…remember this banging pipes? Water hammer can cause serious damage to steam system. One failed open steam trap may destroy the rest of the traps, (Remember when you are replacing a thermostatic element it is extremely important to replace all before restarting the system).

McDonnell & Miller float destroyed by water hammer

A failed trap can pressurize the return main resulting in insufficient differential pressure across other traps draining into the same main as the failed trap. Consequently, condensate will back up in the processes the traps are associated with. Someone will wrongly diagnose these traps as being defective, possibly even replacing a good trap and still not getting the desired results. Frustrating! Because the trap has no differential pressure due to the pressurized condensate line, there is also the possibility of water hammer occurring in the heat transfer device that cannot drain. Again, the mixing of steam and condensate can cause water hammer.

Higher Steam Temperatures Problems
This is not the last of the problems that a trap passing steam can cause. With steam passing through the trap, the return condensate is at a higher temperature, which sounds like we are saving energy by not having to add as much sensible heat to the condensate to bring it back up to saturation conditions. But the warmer the condensate is, the more flash steam. Even worse, the pumps will handle hotter condensate, and this can have a negative effect on the pump seals (Viton seal will only help in the short run). And, the higher the temperature, the less NPSH (Net Positive Suction Head) we will have available at our pump suction. Less NPSH available, increases the chance for cavitation to occur in our pump.

Impeller destroyed by cavitation

So, the indirect cost of a trap passing steam may be great. The best solution is to under­stand the operation of your traps, survey and test them on a regular basis, and repair or replace the traps when they fail. The cost will always be justifiable.

The next time you have problems, look at the whole system. Remember that even if the process is still working, a bad trap may actually cause other, more serious problems.

To determine if the trap failed open may require some special tools and some experience.
1. Start your work with a plan. (It is always a good idea to have plan).
2. Use tags to identify traps.
3. Form to record trap data.

You will need to have test equipment. Thermometer (You can use an Infrared Thermometer), stethoscope or ultra-sound. Now you can start your traps testing.

Make sure the steam system is on. Use a thermometer to measure the inlet and outlet temperature. If the trap failed open the temperature reading will be the same. Use a stethoscope or ultra-sound device to listen for steam blowing through trap. If a trap failed open it will have a low pitch whistle. A steam trap working correctly will have a wet gurgling sound.

Below you can see typical trap installation. If your installation is equipped with a Test and Pressure Relief  Valve you can use it to determine what passing traps steam or condensate.

For help with any steam problems, contact your local Bell & Gossett sales representative. They have the answers to all of your questions.
http://bellgossett.com/sales-service/

Click here to download the October 2019 SteamTeam pdf file

The post When a Steam Trap failed open appeared first on Xylem Applied Water Systems - United States.

Volume 7/ Issue 1/ January 2020

This article is intended to simplify the selection of components for a steam heating system. The majority of steam boilers used in heating systems are rated on the BTU heat output. Selections are based on modern steam boilers, many older steam boilers had sufficient water storage capacity to fill the heating system with steam and then wait for the condensate to return. Modern steam boilers have much less usable water capacity that can cause boiler flooding or low water conditions to occur.

The tables recommend that a boiler feed unit should be used on all boilers over 300,000 BTU. The boiler feed receiver then becomes the reservoir for the system. The net usable storage capacity of the boiler feed receiver should be between 10 and 20 minutes. The minimum capacity shown in the tables is 10 minutes. Single level buildings that are spread out over a large area should be increased to 15 or 20 minutes.

The Xylem “Steam Team” includes a wide range of steam products. When it comes to expanding, upgrading or repairing your steam system it pays to have a partner like Xylem. We make the parts. We build the system, and we know them inside and out.

Our “Steam Team” representatives are experts in steam heating systems and have the answers you need to get the job done right. They’re the only ones that handle a full line of products that include Domestic Pump condensate handling equipment, Hoffman Specialty air vents, supply valves and traps, and McDonnell & Miller boiler controls. Consult your local representative for more information.

Piping layout and suggested product for one pipe gravity return systems based on system size

Gravity Return Systems

• All steam boilers are shipped from the factory with aLWCO. This could be a 67 or a ‘PSE’ unit, which you can specify when ordering the boiler.
• A 47-2 feeder/LWCO could be installed in place of the factory supplied LWCO on boilers less than 250,000 BTU.
• For boilers over 250,000 BTU, the factory supplied LWCO should be left in place as a secondary LWCO when installing a 47-2 or 51-2 feeder.
• Voltages of feeders, 101A and WFE Uni-Match, should be the same as the voltage at the LWCO cut-off they are being controlled by. For example, purchase and install a WFE-24 for installation on a boiler with a PSE-802-24 LWCO.
• The 67, 64 or series PSE-800 LWCO operates the electrical make-up water feeder and serves as a LWCO.
• We recommend that systems with 10 horsepower or larger boilers use a boiler feed unit.

Piping layout and suggested product for one pipe pumped return systems based on system size

Pumped Return Systems

• All steam boilers are shipped from the factory with a LWCO. This could be a 67 or a ‘PSE’ unit, which you can specify when ordering the boiler.
• A 47-A Pump Controller/LWCO can be installed in place of the factory supplied LWCO on boilers less than 250,000 BTU. The 42S-A is connected to the boiler utilizing the sight glass tappings.
• For boilers over 250,000 BTU, the factory supplied LWCO should be left in place as a secondary LWCO when installing a pump controller/LWCO such as the 42S-A (sight glass tapping installation) or 42S (equalizing pipe installation).
• For any motor larger than 1/3 HP, a motor starter should be used to stop/start the pump to prolong the life of the switches in the M&M pump controller.
• The boiler feed units are selected for 10-minute storage, some applications may require a larger tank. Horizontal units are also available which provide a lower inlet connection.

Piping layout and suggested product for two pipe gravity return systems based on system size

Gravity Return Systems

• All steam boilers are shipped from the factory with a LWCO. This could be a 67 or a ‘PSE’ unit, which you can specify when ordering the boiler.
• A 47-2 feeder/LWCO could be installed in place of the factory supplied LWCO on boilers less than 250,000 BTU.
• For boilers over 250,000 BTU, the factory supplied LWCO should be left in place as a secondary LWCO when installing a 47-2 or 51-2 feeder.
•  “A” Dimension. Pressure Drop + Static Head + Safety Factor. Typically 26-28”.
•  Voltages of feeders, 101A and WFE Uni-Match, should be the same as the voltage at the LWCO cut-off they are being controlled by. For example, purchase and install a WFE-24 for installation on a boiler with a PSE-802-24 LWCO.
•  The 67, 64 or series PSE-800 LWCO operates the electrical make-up water feeder and serves as a LWCO.
•  We recommend that systems with 10 horsepower or larger boilers use a boiler feed unit.

Piping layout and suggested product for two pipe pumped return systems based on system size

Pumped Return Systems

• All steam boilers are shipped from the factory with a LWCO. This could be a 67 or a ‘PSE’ unit, which you can specify when ordering the boiler.
• A 42S-A Pump Controller/LWCO can be installed in place of the factory supplied LWCO on boilers less than 250,000 BTU. The 42S-A is connected to the boiler utilizing the sight glass tappings.
• For boilers over 250,000 BTU, the factory supplied LWCO should be left in place as a secondary LWCO when installing a pump controller/LWCO such as the 42S-A (sight glass tapping installation) or 42S (equalizing pipe installation).
• For any motor larger than 1/3 HP, a motor starter should be used to stop/start the pump to prolong the life of the switches in the M&M pump controller.
• The boiler feed units are selected for 10-minute storage, some applications may require a larger tank. Horizontal units are also available which provide a lower inlet connection.

Domestic pump and Hoffman Specialty pump has a complete line of condensate transfer pumps, boiler feed pumps and vacuum return units

Quick selection materials list with part numbers and description.

Xylem offers the most complete line of products needed for steam systems. The SteamTeam includes Bell & Gossett Domestic Pump, Hoffman Specialty and McDonnell & Miller.

Domestic Pump and Hoffman Specialty
Provides the full line of condensate transfer equipment including condensate transfer units, boiler feed units, vacuum heating units, clinical vacuum units and low NPSH pumps.

Hoffman Specialty
Offers a complete line of steam traps, regulators, vents and accessories.

McDonnell & Miller
Delivers reliable performance and safety in boiler and level control products for over 95 years.

Click Here to download the January 2020 SteamTeam Newsletter

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The new Bell and Gossett e-HSC pump boasts an advanced seal chamber design. This paper outlines the benefits in reduced downtime this technology provides in water applications.

The seal is undoubtedly one of the most important parts of a centrifugal pump. Of course there are many critical aspects of pump performance, but when it comes to mean time between failures, it remains that 60% to 70% of centrifugal pump maintenance is seal related (Lobanoff & Roass, 1985). The fact that mechanical seals can only be replaced once the pump has been shut down (and in many cases drained) also means that this can be an expensive repair, depending upon timing.

Pump and seal design must adequately address the potential for abrasive particles which may shorten seal life due to seal face erosion or seal cavity clogging (Shiels, 2004). Double suction pumps, which historically relied on packing as the primary sealing option, transitioned to mechanical seals to eliminate the fluid leakage and the increased power consumption related to gland packing. However, with that transition came the increased seal replacement time, placing even more emphasis on mechanical seal life. Many designs continue to use a stuffing box capable of accepting either packing or a mechanical seal.

Plans for maintaining seal chamber conditions have long been standardized by the American Petroleum Institute (API) in their Annex G piping plans. Figure 1 provides details behind the plans typically employed in water applications. Plan 02 and Plan 11 are not effective at limiting contaminant buildup and seal wear. Plan 31, however, flushes utilizing pump discharge pressure and filters utilizing a separator in order to limit contamination. While a stuffing box design allows for handling many industrial process fluids because of the flexibility to employ even more complex plans such as 32, 41, or 53, there are more effective and less complicated approaches for water applications. An API plan 31 needs to consider a balance between seal cavity pressure and flush cooling flow through sizing the throat bushing and adjusting the flush orifice (Shiels, 2004). This can be more of a challenge considering the variable flow and pressure in today’s variable speed environment.

Figure 1
American Petroleum Institute seal plans typically seen in water applications
(extract from Flowserve FTA160eng Rev 9-17)

In May of 2014 the American Petroleum Institute amended Annex G piping plans to include a tapered bore seal chamber (Plan 03). This was the result of successful application of large bore tapered seal chambers in extending seal life without the complexity of pressurized flush and particle separation. In fact, an extensive study comparing the traditional Plan 02 stuffing box configuration with a variety of enlarged and tapered seal chambers was conducted for the Tenth International Pump Users Symposium with the expressed purpose of improving the uptime of centrifugal pumps. The study concluded that tapered or flared bore chambers without throat restriction allowed for maximum heat transfer with the pumped product, reduced gas in the seal chamber under start/stop conditions and reduced solids concentrations without the need for external flushing (Adams, Robinson, & Budrow, 1993). The study further found that “some form of rib, strake, or protrusion extending axially along the chamber wall could reduce the high azimuthal velocity and impart an inward radial velocity to the particles…this change in velocity and direction would then allow the particles to exit the chamber with the outflow” (Adams, Robinson, & Budrow, 1993). The study was focused on end suction centrifugal pumps, and it did find that there were some impacts on the effectiveness of the seal chamber design created by impeller features such as balance holes and pump out vanes designed to mitigate axial thrust.

Bell & Gossett has incorporated the best aspects of all these design features into a double suction pump. It has an enlarged tapered seal chamber for internal flush that actually opens into the entire suction chamber of the pump. Due to the balanced thrust inherent in the double suction design, there are no balance holes or pump out vanes adding pressure back into the seal chamber against the flow for particle removal. The seal chamber pressure is dictated by the lower, more consistent suction pressure rather than re-circulated flow from the discharge. There is no need to monitor and adjust external flush pressures or install and maintain particle separators. This design brings more consistent performance and lower install cost than a traditional plan 31. In addition, this stuffing box allows for side access to the seal for faster replacement than traditional stuffing boxes where the upper casing must be removed for seal access. The design even includes an axial rib from the CFD (computation fluid dynamics) model to impact the radial velocity of the particles just as the study indicated. Pump downtime is ultimately best reduced by this type of focus on advanced design that increases mean time between failures and reduces repair times on the number one reason for pump failure.

In the above cutaway photograph of the mechanical seal chamber you can see the tapered bore which opens into the suction chamber of the pump. You can also see the axial rib above the seal that impacts the flow within the suction chamber.

Adams, W. V., Robinson, R. H., & Budrow, J. S. (1993). Enhanced Mechanical Seal Performance Through Proper Selection and Application of Enlarged-Bore Seal Chambers. 10th International Pump Users Symposium (pp. 15-23). College Station, Tx: Texas A&M University.

Lobanoff, V. S., & Roass, R. R. (1985). Centrifgual Pumps Design and Application. Houston, TX: Gulf Professional Publishing.

Shiels, S. (2004). Hidden Dangers in Centrifugal Pump Specification: Part One. In S. Shiels, Stan Shiels on Centrifugal Pumps: Collected articles from “World Pumps” magazine
(p. 275). Oxford, UK: Elsevier Advanced Technology.

Click here to download the pdf

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About Xylem
Xylem (XYL) is a leading global water technology company committed to developing innovative technology solutions to the world’s water challenges. The Company’s products and services move, treat, analyze, monitor and return water to the environment in public utility, industrial, residential and commercial building services, and agricultural settings. With its October 2016 acquisition of Sensus, Xylem added smart metering, network technologies and advanced data analytics for water, gas and electric utilities to its portfolio of solutions. The combined Company’s nearly 16,000 employees bring broad applications expertise with a strong focus on identifying comprehensive, sustainable solutions. Headquartered in Rye Brook, New York, with 2015 revenue of $3.7 billion, Xylem does business in more than 150 countries through a number of market-leading product brands. The name Xylem is derived from classical Greek and is the tissue that transports water in plants, highlighting the engineering efficiency of our water-centric business by linking it with the best water transportation of all – that which occurs in nature. For more information, please visit us at www.xylem.com.

The post The Benefits of Advanced Seal Chamber Design in Double Suction Pumps appeared first on Xylem Applied Water Systems - United States.

The newly designed Bell & Gossett e-HSC pump standardized on a stainless steel shaft and impeller. This paper outlines the benefits of stainless steel in performance and product life.

In 2014 Bell & Gossett launched modernized versions of its Series 1510 base mounted end suction centrifugal pumps. This began the “Power of e” campaign and the “e” designation denotes improved performance characteristics. Since then there has been a re-design of the inline pumps and most recently the horizontal split case pump. Each of these re-designs utilized computational fluid dynamics (CFD) analysis to optimize efficiency and minimize net positive suction head requirements (NPSHR). Most recently, Bell & Gossett launched the e-HSC pump, which broadened and standardized the horizontal split case line while incorporating the latest design technologies.

Another key enhancement to all of these pumps has been the transition from bronze to 304SS impellers. Bronze had been the industry standard for many years based on economics and manufacturing technologies available at the time. Although bronze performs adequately, stainless steel has always been the superior material. The widespread use of stainless steel was cost prohibitive and the manufacture of stainless steel impellers was possible only in specialized facilities working on custom projects. Mass production of these components was not an option. Stainless steel was reserved for only the most demanding applications for this reason. Advances in manufacturing technology and reduced costs for stainless steel material versus bronze have finally made stainless steel use possible on a widespread basis.

In clean water applications bronze remains a suitable choice, but bronze does not offer the same corrosion resistance properties of stainless steel and has a greater potential for degradation. Over time the surface characteristics of bronze can cause it to wear faster than stainless steel – leading to reduced pumping efficiency.

Figure 1
Impeller eye of a bronze sand cast double suction impeller with vane cleanup (left) compared to a stainless steel investment cast impeller (right).

The common bronze alloy used in impellers is especially susceptible to a process called dezincification in which chlorine dissolves the zinc material (4-12% of volume) from the metal. There are specialty grades of bronze with comparable corrosion resistance to stainless, but they are higher cost and harder to manufacture.

The stainless steel impellers are made as “investment castings1 ”. These are created using a lost-wax process that results in a significantly improved surface and part quality than the more common die-cast process or the sand-cast process historically used on bronze casting. The end results of this process are greater efficiency, consistency between impellers, greater durability and more sustainable hydraulic performance. As shown in figure 1, a sample sand cast impeller (left) typically require grinding to address surface imperfections. Investment cast impellers (right) have cleaner edges and a more consistent surface. Impeller performance is not only dictated by the geometric design, but performance enhancements based on surface improvements can also be modeled (figure 2). In order to offer both stainless and bronze impellers, two sets of tooling would be required. By making stainless steel the standard offering and leveraging economies of scale, the benefits of stainless steel are available for all applications without increased cost.

Figure 2
CFD modeling assists in the design for optimal energy transfer

We can also compare the two materials by the numbers. In figure 3 you can see that stainless steel is equal in strength, but has superior crack resistance when compared with bronze. Data also shows the stainless
steel material to be harder than bronze, resulting in equal or less wear and longer life. Stainless steel also has equal or better corrosion resistance for many fluids. Most importantly, stainless steel has no added lead, eliminating the concerns of lead contamination in the pumped fluid which exists with some bronze materials.

The transition from bronze to stainless steel impellers has leveraged the latest manufacturing technologies and offers the power savings, corrosion resistance and reduced wear of stainless steel without the cost penalties that kept this out of reach in the past.

Figure 3

1 Available on impellers up to 18”

Click here to download the pdf

Follow Bell & Gossett on social media:

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• Twitter: @BellGossett
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About Xylem
Xylem (XYL) is a leading global water technology company committed to developing innovative technology solutions to the world’s water challenges. The Company’s products and services move, treat, analyze, monitor and return water to the environment in public utility, industrial, residential and commercial building services, and agricultural settings. With its October 2016 acquisition of Sensus, Xylem added smart metering, network technologies and advanced data analytics for water, gas and electric utilities to its portfolio of solutions. The combined Company’s nearly 16,000 employees bring broad applications expertise with a strong focus on identifying comprehensive, sustainable solutions. Headquartered in Rye Brook, New York, with 2015 revenue of $3.7 billion, Xylem does business in more than 150 countries through a number of market-leading product brands. The name Xylem is derived from classical Greek and is the tissue that transports water in plants, highlighting the engineering efficiency of our water-centric business by linking it with the best water transportation of all – that which occurs in nature. For more information, please visit us at www.xylem.com.

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Volume 7/ Issue 2/ April 2020

When we think of our Condensate Return Units the first one that comes to mind is our standard CC unit. As with any packaged unit, there are times when field conditions create a non-standard installation and operation environment. As a result, questions arise on what can be done. One scenario encountered involved a Model 306CC with a 36 gallon receiver. The location where this unit was installed required the vent pipe to run a horizontal distance of approximately 200-250 feet to reach an outside wall. “Will this be an issue?” is the question that must be answered. To provide the answer, we start by noting the “CC” series of Condensate units are rated for a maximum condensate temperature of 200°F. If the Overflow is piped and primed, the maximum is increased to 209°F. Next, it is important to ask a few additional questions about the installation to verify the “CC” is the correct Domestic Pump series choice. First question, “What is the expected condensate return temperature?” If above the “CC” maximum rating, the “CB” or “CBE” style should be considered. Regardless of final selection, a unit receiver, whether cast iron or steel, is not designed to act as a pressure vessel, and therefore must have proper venting. If the installation site has the potential to allow a condensate return temperature higher than 200°F (209°F), provisions must be made in the field to reduce it to, or below, the recommended maximum prior to entering the receiver. The receiver vent is sized to maintain atmospheric pressure conditions within the chamber at all times. If condensate at, or above, 212°F enters the receiver under this condition, “Flash” steam will develop, which can overtake the vent’s ability to maintain neutral pressurization, and thus lead to potential receiver or pump damage, and the discharge of live steam out the vent. The most common method of condensate cooling prior to the receiver inlet is the installation of a vented ASME rated flash tank, which can handle flash steam, allowing the removal of additional sensible and latent heat from the condensate, lowering its temperature to an acceptable level. Other suggested cooling methods include using a heat exchanger with external cooling source, or a dedicated cool water supply piped to the inlet pipe (or the receiver) with a temperature regulating valve to blend the two fluids for a mixed temperature below recommended maximum. While not recommended from Domestic Pump, as a last resort, we have seen the unit receiver oversized to increase the time between pumping cycles, allowing the condensate to cool. Our next question, “Where will the unit be located?”. With the request to run a 250’ vent line, this answer could reveal possible alternate solutions. If the unit will be isolated from pedestrian traffic, and in a location that does not have additional mechanical or electrical equipment, such as a crawl space, then venting right in the space may be an option, provided condensate temperature is controlled as discussed earlier. Another possible scenario may involve tapping into an existing vent line for other equipment, provided a thorough analysis is done to determine it is adequately sized to handle the equipment it already serves plus our unit, or that it is not subjected to any positive static pressure that can prevent the free flow of air from our unit, or possibly push harmful contaminants into our receiver.

When experiencing any kind of a horizontal run with the vent line, a 1” pitch is ideal (angled back towards the receiver) for every 20’ of pipe. So for a 250’ run, we need a total vertical height difference of 12.5” from the wall penetration back to the receiver vent elbow or tee. (NOTE: The elbow/tee will most likely be roughly 12” above the inlet threaded opening in the receiver, so looking for at least 24” of head space from top of receiver to wall penetration.)

In addition, with the distance to be traveled by the vent line, consideration to upsizing the pipe 1-2 sizes larger than our threaded vent connection size is recommended. This is due to resistance of air moving through the pipe. Over 250’, it is possible the air would run out of energy, and stall somewhere in the pipe before reaching the wall penetration. All the moisture in the air will condense inside the pipe, and no doubt cause corrosion. Overall, for proper instructions and recommendations on condensate units please reference our Domestic Pump Vented Condensates unit’s instruction manual and brochures on the Domestic pump website. There you will find more information about our units, and how to properly install them out on the field.

DN0158F instruction manual

Domestic Pump Series CC Condensate Unit brochure

Click here to download the April 2020 SteamTeam newsletter

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Volume 7/ Issue 2/ April 2020

Back in the days of coal and wood fired boilers, heating contractors used vacuum air vents to help them get the maximum efficiency out of their steam heating systems. They called these old systems “Vapor/Vacuum,” and the principle that made them work was a simple one: At very low pressure, steam takes up about 1700 times more space than water. When that steam condenses, it will create a vacuum if air can’t get back into the system. The old timers let the steam expand naturally. It pushed air ahead of itself, through the vacuum vents and out of the system. When the steam condensed in the radiators, it contracted to 1/1700th its size. Air couldn’t reenter the system through the vacuum vents because they have check valves at their outlets. If the piping was tight, a deep vacuum would form throughout the system. The nice thing about a vacuum is that it lowers the boiling point of water. If the system was set up right, a vapor/vacuum system could continue to make steam, even after the water temperature dropped as low as 140ºF. The old timers could take advantage of every bit of heat from the coal or wood fire as it burned down to embers. They wasted almost nothing. However nowadays most of us fire our steam boilers with gas or oil. Coal and wood fired boilers are still around, but they’re the exception to the rule.

Natural gas and oil are convenient fuels however they’re not a good choice for systems using vacuum vents because gas and oil burners cycle on and off. This ON/OFF cycling creates problems in systems that have vacuum vents. The vacuum quickly forms when the burner shuts off. Any air that doesn’t get vented on the first cycle expends greatly, blocking the movement of the steam “vapor” to the radiators, and because gas and oil burners shut off completely between firing cycles, there’s no longer a hot bed of embers to keep the low temperature water boiling. When you mix vacuum vents with gas or oil burned boilers you usually end up with uneven heat through the building, condensate that doesn’t return quickly enough from the system, and that can lead to problems with overfilled boiler or flooded system.

Hoffman Specialty stopped offering most of vacuum vents more than 25 years ago. Today, we only offer one vacuum vent – the #76 Main Vent. We continue to make this vent for the two pipe coal fired systems that remain.

If you have a two pipe, vapor/vacuum system running on gas or oil, you should be using our #75 Main Vents near the end of each dry return. The steam will push the air through the radiators, into the dry return and out through #75 Vent. The system won’t drop into vacuum as long as your radiator traps are working as they should, your old vapor/vacuum system will heat evenly at very low pressure. It usually takes no more than 12 ounces of pressure (0.75 psig). If you suspect your steam traps aren’t working as they should, test them with a contact thermometer or a temperature-sensitive crayon. You should see 10 to 15ºF drop in temperature across the thermostatic trap if it’s working correctly. If the traps are passing steam into the returns, you’ll have uneven heat, high fuel bills, boiler water level problems and water hammer noise.

Steam traps are as important on those old coal or wood fired systems as they are on more modern oil or natural gas systems. You can replace those old steam traps with Hoffman Specialty Thermostatic Traps or repair with Hoffman Specialty Dura-stat® Replacement Module.

Our replacement parts are built to last for many years under the toughest conditions. They fit most old fashioned steam traps, and they pay for themselves in no time with fuel savings and even heat and comfort. Your customer will be thankful for these upgrades.

When you think steam system, think Hoffman Specialty. We have the parts and the specialized knowledge to help you solve those tough problems – we are always happy to help you and we appreciate your business!

For all your steam system needs please contact our Factory Representative.

Click here to download the April 2020 SteamTeam newsletter

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VOLUME 8 / ISSUE 1 / JUNE 2021

Float and thermostatic (F&T) traps have an important role in distributing steam throughout a system. They allow air to pass through into a return line allowing steam to flow properly throughout the system. Air in a steam line will prevent steam from entering the line causing increased energy consumption and lower heat output.

Once the air the system, the F&T trap will close against the steam allowing it to pass the steam’s latent heat to the system. As condensate builds up, the trap will quickly open allowing the condensate to drain before closing again.

These traps setup the high and low pressure sides of the system that allow steam to flow. When traps fail, allowing steam to enter a part of the system it doesn’t belong, they can cause water hammer in the system damaging components and preventing proper steam distribution.

Because F&T Traps open based on water level and not temperature, using a thermometer to check whether an F&T trap is operating properly poses its own challenge. Condensate exiting an F&T trap can be the same temperature as the steam when it enters the trap.

A best practice for checking whether an F&T Trap is operating properly is to open a valve downstream of the trap’s discharge and check what is coming out. When your F&T trap is operating properly you will find a combination of flash steam and condensate. If the trap has failed you will usually find “live” steam and very little condensate.

It has been our best practice to produce our valves with two inlets and two outlets to be sure we provide options for the end user to utilize our traps in their steam system. You will always have a discharge port left over after piping is complete but this outlet can be utilized to test the trap. By adding a nipple and valve to the extra port you can test the trap as necessary with ease. As a safety precaution, be sure to put a plug in the outlet of the valve. This will ensure that, were the valve to be opened accidentally when not used for testing, no one gets injured.

Since these traps don’t vent air to the atmosphere but simply pass it through the line, usually to a vented condensate receiver, the left over port is also a great place to add a main vent. If there’s a location where the return line drops below the inlet of the receiver the piping will form a water leg and prevent air from venting. By using the left over port for a steam vent, you can vent right at the trap allowing the steam to quickly move throughout the system.

To make our traps even more reliable we use our Dura-Stat in our F&T Bear Traps®. These traps were tested through over 10 million cycles, resisting water hammer, without a failure. By providing all stainless steel internals and a wide range of capacities we ensure we not only have the trap you need but the most reliable trap as well. In many cases our traps exceed the ratings of those offered by our main competitors. Our traps will also work as direct replacements for some competitors’ traps.

Why choose a Hoffman F&T Bear Trap®? We’ve been designing our traps to be the most versatile and reliable for years. You’ll be able to take advantage of our traps’ features while your customers enjoy the added benefits. Click to learn more about the Bear Trap.

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VOLUME 8 / ISSUE 1 / JUNE 2021

A building management system (BMS) allows a building manager to monitor and control all the systems in their building or campus from a single interface and is most often applied in larger buildings with HVAC, mechanical, and electrical systems similar to the Domestic Condensate packages we provide. Our Domestic Condensate return units feature control panels that allow monitoring of your unit and system from your BMS to achieve your desired connection.

For example, sometimes the monitoring of pump status (on/off) is needed and in order to add this option you must include auxiliary contacts to the starters, which are available as a panel option and these contacts can later be connected to the BMS in the field. You can also an alarm with or without the silencing relay, and the alarm pilot light. Sometimes the need for a BMS connection is requested by our customers and the two options that Xylem can offer include the option to add an alarm allowing you to monitor your pump distantly with an optional additional terminal strip (ATS).

These two options work together with the high level float switch which triggers the alarm, alerting the user of the status of their unit’s water levels. To be able to see the alarm remotely, the end user must include the ATS option and you can contact your local Bell & Gossett (B&G) representative for pricing. The ATS panel option, which is an additional set of contacts, can be wired to the BMS to give you the ability to see your alarm remotely. Depending on your panel configuration, an electrician may add additional alarm terminals for distant annunciation per wiring diagram 1DW041; please contact your local B&G representative to get this wiring diagram. Wiring our units to your BMS system allows early detection of problems in your system, intelligent reporting, and effective monitoring.

The ATS is a very useful option and is yet another solution Xylem offers to help effectively manage your unit and system. Our Domestic Condensate return units are equipped with control panels that will aid in monitoring your unit and system for you, all while working with your building management system to make sure your system and unit are always being monitored.

You can work with your local B&G representative to have the ATS capability added to your system and you can find your local rep here.

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