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.