Real-World Applications: ABB Variable Frequency Drives


Many are not aware of the full potential of an ABB VFD. Most of the time, the VFD is just a follower device—hanging on the wall waiting to be told what to do. Start. Stop. Speed up. Slow down. This is because a higher power—a building automation system (BAS)—is involved. Regardless of brand, automation systems all seem to run on the same concepts; computing input data and making decisions. But, what happens if you don’t have a BAS or it is being utilized to its limits? This provides an opportunity to use some of the potential, inherent (AKA free) control capabilities of ABB VFDs.

For example, let’s say you have a BAS and recently added a VFD to a hot water pump in a mechanical room on an end of the building being updated. Previously, the pump was on a constant velocity system. The pump motor was operated by a contactor that pulled in during a call for heat. Thus, the pump runs flat out all the time. Another update to the system was swapping old three-way valves for two-way valves on all end devices. The idea is to run this pump as slowly as you can while distributing an effective amount of hot water. To accomplish this, you install a differential pressure sensor on the end of the system piping allowing you to determine whether to speed up or slow down the pump.

What if your BAS has been installed in that portion of the building? You are short the physical control points needed for operating the drive and the differential pressure sensor, but you’re in luck! Your BAS controllers are capable of BACnet MS/TP (RS485) communications. So are ABB VFDs! With something as simple as a two-wire BACnet comm link wired back to the BAS, the BAS can utilize many different capabilities of the VFD.

Primarily, the start, stop, speed, feedback and fault functions can all be used over a communications system. Secondly, the differential pressure sensor (you thought I forgot about it, didn’t you?) can be wired to one of the VFD’s analog inputs. As long as there’s a suitable input signal, the BAS can read the value of our analog or digital inputs through the BACnet communications. The BAS can take that data, compute and decide what to do from there. During this, the ABB VFD’s control board basically became a universal expansion panel.

The VFD doesn’t need to do PID regulation to be handy. It is also possible to use the VFD’s inherent (FREE) control capabilities as a signal relay device of sorts. Imagine a rooftop unit with the supply fan being driven by an ABB ACH 580 VFD. The BAS could feed the control signals (speed, start, stop, etc.) via the BACnet interface. Multiple sensors (outside air AHU supply temperature, etc.) could be wired into the VFD with the BAS reading their values of the same BACnet system. All this data is conveyed over a simple pair of wires vs. a gang of costly, longer wires going to a junction box.

Hopefully these simple, real-world examples generate other possible applications for the standard control capabilities of an ABB ACH 580 VFD.


What You Need to Know: Double-Walled Heat Exchangers


To safeguard from cross contamination of potable water in the event of heat exchanger failure, many states and municipalities have special system requirements. The solution is a double-walled heat exchanger constructed in order to make cross contamination impossible. For decades, Bell & Gossett (B&G) has offered such heat exchangers which perform well in a variety of facilities. Over the years, they’ve added to the sizes, types, and materials available in double-wall heat exchangers.

Since the beginning, B&G has made their double-walled heat exchangers a true double wall noting that in the event of ANY failure of a connection, wall, or joining point, cross contamination would NOT occur. Many other vendors claim to have a double-walled unit only to have one or more vulnerable points where a failure would result in contamination of potable water.

Originally, double-walled heat exchangers were constructed from a single tube fitted inside another. The inner tube was knurled with multiple grooves to provide a leak path in the event of either tube failing. The cross-hatched grooves gave this series of heat exchangers its name “Diamondback”. The U-Tube configuration units can utilize water/glycol as a heat source (Model WU) or steam (SU) and are available in sizes up to 12” diameter shells and 10-foot long tube bundles.

Responding to designers’ desire for better performance from smaller units, plate and frame heat exchangers (GPX Series) were modified to double-walled configurations. While looking different and being capable of operating at lower spreads between mediums, Bell & Gossett plate and frame heat exchangers are a true double-wall unit. These units are available in applications ranging from 1” NPT to 8” flanges.

Dive deeper with these great resources


ASHRAE, the American Society of Heating, Refrigerating and Air-Conditioning Engineers, is dedicated to advancing the arts and sciences of heating, ventilation, air conditioning, and refrigeration to serve humanity and promote a sustainable world. Click the logo at left to learn more.


MNCEG, Minnesota Chief Engineer’s Guild, is an association for employees of the State of Minnesota who are actively engaged in the planning, management, and maintenance of public facilities, grounds, equipment and systems. Come see us at the 2019 MNCEG Conference & Trade Show September 4-6! Click the logo at left to learn more.


According to NIST, the National Institute of Standards and Technology, gas is the more eco-friendly option—for now—to heat and cool an energy-efficient home. Click the logo at left to read the study.

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Registration is open for the 2020 AHR Expo. Learn about industry trends, best practices, and solutions from the people creating them. Register now and come build relationships that will grow your business as the “Super Bowl of HVACR” converges in Orlando.

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Lochinvar and EC POWER, the top European producer of residential and commercial combined heat and power products, today announced the launch of XRGI25, one of the most cutting-edge cogeneration products to ever be released in North America.


In the two-plus years since the Department of Energy issued the Energy Conservation Standards for Pumps, the commercial pump industry has been moving toward January 2020 compliance—updating testing procedures, adding reporting methods and other practical matters.

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Mechanical contractors, specifying engineers, and building owners have many options when it comes to heating and cooling buildings. Learn more about important factors to consider when selecting which system to install.


ASPE joins ASHRAE and NSF to develop standard on managing disease risk in building water systems.


2019 Top 150 Workplaces

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Great workplaces start with great people.

We’re excited to announce that—for the second year in a row—Mulcahy was named one of Minnesota’s 2019 Top 150 Workplaces by the Star Tribune. This year, a record-breaking 140,000 employees were surveyed from over 2,000 invited companies about their workplaces’ leadership, values, culture, benefits, and employee engagement.

The Mulcahy team is one of a kind. Their dedication to quality and excellence drives innovation and growth for our partners and clients. We can’t thank them enough!

The Mulcahy team is one of a kind. Their dedication to quality and excellence drives innovation and growth for our partners and clients. We can’t thank them enough!

Mulcahy Company has been a fast paced and laughter-filled family to me for the past 4 years. I think our ability to collaborate on complex projects is a direct result of the community that has formed. Through team events, cookouts, and office banter, we form a company that enjoys working together to better serve the HVAC industry.

—Derek Johnson | Technical Sales

Choosing the Right Flue Vents

Boilers and furnaces are engineered to efficiently extract the most possible energy from fuel combustion. After the energy is extracted, the waste product—flue gasses—must be exhausted outdoors. Several products and systems exist to perform this function, but how do we know which products provide the best performance and which to stay away from?

Boiler and furnace manufacturers dictate the size and length limitations of the flue pipe in their certifications. These are listed in the product’s installation manual and must be complied with completely.

For years, the gold standard material for high-efficiency appliances has been AL29-4C Stainless Steel. It carries the highest temperature rating of all the common materials and is proven in the real world. Its only drawback is a higher cost. As a short-term, cost-saving measure, some manufacturers certified their units to be vented with non-metallic (plastic) materials. The units pass laboratory tests, but the real world isn’t a controlled environment.

At present, a boiler manufacturer can list a material for use as a flue pipe even if the pipe manufacturer never intended it to be used in that way. Therefore, the pipe manufacturer holds no blame if problems arise, as they never state it’s a suitable use of their product.

PVC and CPVS pipe are an example of this. Manufacturers generally don’t list tables, charts, or limitations for their products as a hot gas transport material, but somehow boiler and furnace manufacturers are able to list it as an allowable flue vent material.

This is where independent certification becomes important. Underwriters Laboratory (UL) and other independent entities provide various standards to dictate performance requirements for flue gas venting applications. For example, if a pipe manufacturer references that its product is built to UL-1738, you know it is intended to be used as a flue pipe for a Category VI boiler or furnace. Because the product is intended for use as a hot gas transport, the manufacturer will be there to help if problems arise.

Polypropylene is a certified non-metallic product. It handles temperatures upward of 110°C—much hotter gasses than PVC—and carries the UL rating to prove it was built with the intention of being used in flue vent applications.

Want to know more about boilers, furnaces, and flue venting? Mulcahy Company has some exciting educational opportunities coming up that will prepare you to make informed decisions.


Do Sensors Make $ense?

Many options exist in the marketplace to control variable speed pumps in hydronic systems. The increased capability and price reduction of microprocessors has allowed the basic centrifugal pump to become smart.Some manufacturers have decreed, with no explanation, that the new ways are the best ways. While new methods offer some advantages, in the end they still come up short in many ways.

Control logic has always been a key element to any successful variable speed fan or pump. Many systems didn’t reduce speed in fear of not supplying enough flow to a system, thereby not achieving the primary goal of an HVAC system—comfort. Systems wasted energy to avoid the possibilityof complaints. The industry now realizes that this approach is unacceptable and doesn’t meet owner expectations or the energy code. So, how do we control hot water and chilled water pumps?

The Old Way

Differential Pressure

In this system, a differential pressure sensor is installed on the critical circuit which maintains a minimum differential pressure across that point (remember, the pump head is based upon the friction of that flow path). If the critical path is satisfied, all other paths are satisfied. This system is very simple to understand and operate. A major advantage of a sensory system is that it automatically removes the excess capacity of the pump, whether it’s due to oversizing or reduced system demand.

There are two common enhancements that can improve this efficiency of this system:

  1. A multiple sensor system is used when a system’s load is so diverse that its critical path could change based on usage. For example, a school auditorium is empty while students are in classrooms, but hours later the reverse could be true. Parts of the system could be fully loaded while others remain at minimum load.
  2. Resetting the differential setpoint was recently added to ASHRAE Standard 90.1. Building Automation Systems can monitor the position of all the control valves in a system and make real-time decisions to alter the differential pressure setpoint in order to get all modulating control valves to be nearly wide open. If a circuit is slightly throttled, it is under control.

The New Way

Control Curve

Although control curves can be employed with different approaches, all follow the same theory—at a certain flow the pump will be operated at a specific pump head. Some operate off a flow meter or DP sensors at the pump, some use VFDs programmed with the pump’s operating data. No matter the method, a microprocessor decides the pump speed based on system flow. The problem is that these systems don’t know where the flow is going. Close loads? Far loads? Split? In the end, a control curve system’s only feedback comes in the form of a comfort complaint which results in the system being adjusted to operate at a higher speed.

The Punch Line

We all must follow the laws of physics and one simple formula ends up determining the largest cost of ownership for a pump—energy consumption.

head * gpm

Pump Power = ______________

3,960 – (pump eff)

GPM is how much heat transfer a system needs. Head is the friction needed to move that flow through the system. Any system that minimizes those factors will draw less HP and cost less to own. Pumps with 2-3 HP can be demonstrated to save enough energy to justify the cost of the sensor.

All design choices are a series of tradeoffs. DP sensors cost a little more money and effort to install, but allow a pump to operate at the lowest HP for a given set of conditions. However, it’s not always cost effective to install them. For a low HP system or a system that is difficult to access, a control curve might be the best choice.

Burner Replacement – When and Why

In this article we are going to talk about burner replacements. When do we replace them and what are the benefits?

First, we need to understand that every situation is different and there is no sweeping answer to when or why.

Let’s Start with the Age of the Existing Burner

We know that things do not last forever and that eventually the burner will need to be changed. We’ve seen burners 30-40 years old still in operation, but that comes at a cost. Older burners can start to become unreliable and then you have unwanted service calls. The other problem is that the burners are not supported by the manufacturer. Manufacturers are continuously making their products better and more efficient, thus moving older lines to the wayside.

In some cases, the manufacturer is no longer in business. This creates its own set of problems because you are still able to get parts (usually online), but the online store is limited. You have to know the part number you are looking for or you have to measure the part and match it to a similar part, which can be problematic. If your blower wheel comes apart it is hard to match something that is in several pieces. You are taking a big risk to run this equipment. It never fails to break down when you need it most.

Complete Burner Replacement Will Create Better Efficiency

Another reason to replace your burner is because of efficiency. This can be broke down into a couple segments. In some cases, if you have a burner that is not that old and you can retrofit linkageless controls. This is a nice upgrade from a linkage type burner as linkages tend to drift over time and negatively impact combustion. Another big reason is you are able to separate the 2 fuels, gas and oil. Linkageless retrofits can typically increase the gas side turndown to 4:1-5:1 vs 1.75:1. Consult the burner manufacturer to determine what turndown you are safe to run.

New burners have 10:1 turndown ability and they can also run low O2. This is where your savings are when changing your burner. With linkageless controls you can run a low O2 fuel curve across the entire firing rate with little to no PPM CO.

Emission Upgrade Requirements

Lastly, emissions upgrades could be yet another reason to change your burner. Depending on your location and requirements, you may be required to install an O2 trim system and Flue Gas Recirculation (FGR) system to help reduce NOX. This will also allow you to run even lower O2s in some cases. The downside is that you will have more maintenance because you will have flue gas monitors running at all times.

Selecting the Right Burner

Now that we have gone over why we would change your burner, we want to understand what we would look for when selecting the right burner for your application. First, we need to understand if the existing boiler it too big or if it is sized properly for the application. This may be a good time to put a smaller burner on and go with a high turndown burner. This will help reduce cycling and still have enough BTU/HR during the cold months.

Is the boiler compliant? With a new burner comes a new gas train. This will be code compliant for whatever size boiler burner you are working with. LWCO controls and the manual reset high limit should also be looked at. We also need to make sure we have proper combustion air. If we don’t have enough, we could put the room into a negative and that could cause nuisance burner failures.

Other items to consider are not code related but can help if there is a failure or other problem. This would include a lead-lag system and draft controls. With a touch screen lead-lag system, it can be programmed to alert you (email or text) if there is a failure and it will automatically bring on the lag boiler. You are able to trend your steam flow or water temp which is a good tool to have. We have been able to solve quite a few system problems with this feature. There are many different options to choose from. Some are simple, and some are quite extensive. This is a conversation you should have with the customer to decide which way to go.

Mulcahy Can Help

Now that you have an idea of what the customer would like or need you can reach out to us and we can start putting together a package for you to discuss. We will need to know incoming gas pressure which dictates the gas train size. There could be some savings if we can use a smaller gas line. Electrical is another big must have. We can add a control circuit transformer. So only one power feed to the burner is needed. Will there be any emissions requirements? If so, what is the PPM NOX requirements? In some cases, we can meet emissions with the proper burner without the need for O2 trim or FGR. Once we have this info, we can start putting together pricing with all the components you need.

Thank You, Steve Norberg!

On January 4, Mulcahy bid farewell to a fixture in the engineering community. Steve Norberg dedicated decades of his career working for engineering firms including Erickson Ellison, Dunham, and KFI. His work emphasis was on school and healthcare projects in the state of Minnesota, along with work at the airport for many years. At Mulcahy, he continued that work in the design and support of HVAC systems for over six years to the benefit of the engineers, contractors, and facilities with whom he worked. He built lasting relationships in organizations like the Minnesota Educational Facilities Management Professionals and the Minnesota Healthcare Engineers Association. Head to one of their conferences with him and you won’t get two feet before he stops to great someone with a familiar smile.

On behalf of Mulcahy, we want to thank Steve for his years of service in the engineering community.

Steve plans to do some warm-weather travel with his wife Ivonne, and keep up on his poker game at Running Aces. Don’t be surprised to see him around in the fall when conference season heats up. We wish Steve well in his well-deserved retirement. Congratulations, Steve!

Mulcahy Recommends: Zupa Toscana Soup Recipe

You’ll love this Italian soup loaded with sausage and potatoes. This recipe is a personal favorite from one of Mulcahy’s own.

What You’ll Need

  • 1 pound of Italian sausage
  • ½ Tbsp. red pepper flakes
  • ¼ cup chopped white onion
  • 2 cloves of garlic
  • 4 tbsp. bacon pieces
  • 8 cups of chicken broth
  • 2 cups water
  • 1 cup of half & half
  • 2 large potatoes (sliced thin)
  • 1 cup kale
  • Salt & pepper

How to Make It

  1. In a large soup pot, brown the sausage with red pepper flakes.
  2. While the sausage is cooking, slice up your potatoes nice & thin then quarter the slices.
  3. Chop up your onions and mince your garlic.
  4. Once the sausage is cooked, remove from pan and drain. With a small amount of oil remaining in pot, add onions, garlic and cooked bacon pieces. Saute until onions are transparent.
  5. Add the broth and water to the soup pot.
  6. Carefully pour in your potatoes. Bring to a boil and then Reduce the heat and simmer until potatoes are tender (around 10 minutes or so).
  7. While potatoes are cooking, rinse and chop your kale.
  8. Once your potatoes have cooked through, add the half & half and Italian sausage. Cook the soup until heated through.
  9. Add the kale. Remove from heat and serve.

Serve with bread sticks.