Innovative injection pumping systems: Using circulators

instead of mixing valves to modulate temperature

 

Today’s precisely modulated and maintained indoor comfort is a lot more than just a collection of linked equipment parts generating and distributing heating or cooling within a building. Today’s hvac systems are sophisticated systems where the sum is greater than the parts. This is particularly true of pumping systems for radiant heating and cooling systems. Recent innovations to pumping systems have successfully addressed the need for a hydronic system to supply different water temperatures to different parts of an hvac system, particularly those in a radiant system.

 

Traditional hydronic systems generate high temperature from the boiler and low temperature water from the chiller and employ mixing valves to either mix down or mix up water temperatures at the terminal units at the other end of the system. Newer, more efficient radiant heating and now cooling systems for residences and light commercial applications use water at different temperatures than those generated by the boiler or chiller. For example, a radiant heating system will typically use water between 100º to 120º F at the radiant panel even though the boiler water temperature is generated between 160º to 180º F. In a similar fashion, radiant cooling systems typically provide water to radiant ceiling and wall panels (chilled beams in commercial buildings) in a temperature range between 55º to 60º F while the chiller supplies chilled water at 40º to 45º F.

 

How then do you best achieve, in an energy efficient manner, this temperature differential between the generation source and the terminal units? Traditional hydronic systems have used mixing valves to mix down high boiler water temperatures supplying radiant floor or wall panels. In radiant cooling applications, mixing valves mix up the lower water temperature supplied by the chiller to the radiant ceiling panels. But mixing valves consume energy. Can circulators more efficiently perform the mixing function instead?

 

The answer is, yes. Today’s circulators are more reliable than control valves and consume less energy. With the introduction of smaller, more reliable wet rotor circulator technology this mixing function can indeed be performed by circulators more efficiently than mixing valves using less pump energy. Replacing energy consuming control and balancing valves with small, low kW circulators results in lower pump head and less power needed to move system water. The pumps help deliver the water where it needs to go instead of forcing the water where it doesn’t want to go.

Taco, for example, now offers innovative radiant injection pumping packages for radiant and other applications. The Taco Radiant Mixing Block (rmb) is a complete injection mixing system that combines a variable speed injection mixing circulator, constant speed zone circulator and air elimination all in one unit. On the cooling side, the brand new Taco LoFlo Injection Mixing Block combines a constant speed zone circulator with a variable speed injection circulator — again all in one unit.

 

Using variable speed/variable volume injection pumping to mix water temperatures up or down instead of using mixing valves with constant volume pumps is more efficient, even if the constant volume pump is more efficient than the variable volume pump. The variable volume pump responds to the load whereas the constant volume pump does not.

 

Information supplied by Taco, Inc.

 

Primary-secondary pumping — A 1940s innovation that’s still making hydronic systems more efficient

 

BY LARRY KONOPACZ

 

Sixty years ago, hydronic heating circuits in residential and commercial buildings often used constant flow pumping to move water from the boiler to the radiation and back. Although constant flow pumping was a simple system, it sometimes did not produce uniform heating within the building, nor did it provide opportunities for savings in material costs and energy.

 

That was the way it was before Gil Carlson came on the scene and began four decades of influencing the ways in which hydronic systems operate. After earning an engineering degree from Purdue University, Gil started to work at Bell & Gossett. Never satisfied with conventional answers to problems, by 1950 he was taking a fresh look at heating systems that weren’t operating to the higher standards that he had set for himself, and in the process he devised a concept that within a short time would become a common practice in the industry.

 

Primary-secondary pumping was Gil’s way of solving a difficult problem that he encountered in a particular heating system. Then, over the years he applied the principle to more and more applications until they filled a complete textbook. That textbook is still used in hydronic heating training classes around the world.

 

To understand the benefits of primary-secondary pumping, we need to start by reviewing the operation of the constant flow pumping design.

 

Constant flow pumping

 

For years, constant flow pumping was the simple and accepted method for moving water from the boiler to radiation. As seen in Figure 1, in this system a single, large circulator pump moves water through a hundred or more feet of pipe and possibly dozens of pieces of radiation. The result: uneven heat from one end of the loop to the other and wasted energy. Adding independent zones from the boiler was an attempt to solve the problem, but those zones only added to the complexity and cost of the system.

 

Primary-secondary pumping

 

Enter Gil Carlson’s primary-secondary pumping idea. The use of primary-secondary pumping eliminated the zone control problems created by the interaction of system components and multiple pumps. Plus, primary-secondary pumping offered a bonus. Since it is a system featuring flow-independent — or “decoupled” — piping loops, the pumps, pipes and other fittings can be reduced in size — and therefore cost — especially in new or retrofit radiant panel systems.

In a typical primary-secondary system (Figure 2), the common piping is designed for very low pressure drop by installing two tees close together at points “A” and “B”, and sizing the pipe between them for very low pressure drop. Design tables or a SystemSyzer (a calculator wheel, also designed by Gil Carlson) will help the designer or installer choose the right pipe size for the design flow.

 

Low pressure drop in the common pipe means that flow in the primary circuit cannot cause flow in the secondary zone, making flow in each loop independent. A circulator pump in the secondary loop will cause flow in that loop, diverting water from the primary to the secondary at one tee and returning it at the other. If the secondary pump is off, low pressure drop in the common pipe will allow primary water to bypass the secondary. When the control system turns on the secondary pump, water will automatically be diverted into the secondary loop to provide heat. This results in a very simple “on/off” method for controlling temperature in the secondary loop. The check valve symbol in Figure 2 represents a Bell & Gossett Flo-Control™ valve used to prevent gravity circulation of lighter, warmer water from the primary loop into the secondary loop when the secondary pump is off. Flo-Control valves are used with secondary pumps that operate on or off. Flo-Control valves should not be used in secondary systems that use a constantly operating pump and valves that vary the flow because they would close at low demand flow rates. In systems that don’t use a Flo-Control valve to prevent unwanted gravity circulation, thermal traps - formed by keeping the hot loop at least one foot higher than the connection to the cold loop - can be used.

 

Two-pipe systems

 

Figure 3 depicts a two-pipe primary-secondary system in which each secondary zone can get the same primary supply water temperature. The common pipe is part of a “zone bypass” or “cross-over bridge” between the primary supply and return. A balance valve in the zone bypass sets the primary flow in the bypass, but the balance valve cannot be installed in the common pipe because that would increase the pressure drop in the common. If that happens, flow in the primary loop will always generate flow in the secondary, and the two loops would no longer be independent.

Although Gil Carlson is no longer with us, his great ideas continue to grow.

 

Many people in the hydronics industry recognize the him as an innovator and problem solver. As director of Technical Services at Bell & Gossett, he developed many of the tools and products that are used every day in the design and installation of hydronic heating systems. A holder of numerous patents, his innovations include the Circuit Setter® balance valve, the Red Ring Monoflo® fitting, the Triple Duty® valve, and the SystemSyzer® calculator. And of course, one of his most lasting contributions to the hydronics industry is the concept of primary-secondary pumping.          n

 

Larry Konopacz is manager, Training & Education, ITT, Morton Grove, Illinois. He may be reached at 847-983-5841.

 

Innovative pump design spawns the ALPHA

 

The new alpha from Grundfos Pumps has been introduced — a 115-volt circulator for hydronic heating applications in residential and light-commercial applications, and is now on the North American market.

 

“As is our custom with a new product, we did our due diligence with the alpha in the United States, taking two full heating seasons to be certain it would perform as well here as it has in Europe. Our objective is to verify the alpha as a stable pumping platform for the North American market for many years to come. Europe’s hydronic systems are different that ours. As a result, pumping requirements are different, too. Our larger systems require larger flow rates, so we had to do our homework, making critical adjustments to the hydraulic design of the alpha,” said Bob Reinmund, senior product specialist, Grundfos Pumps.

 

The alpha’s permanent magnet motor design that will avoid motor slippage problems common to induction-type motors, while delivering a starting torque four times higher than a standard induction motor.

 

The autoadapt™ function automatically modulates circulator performance to match ever-changing system demand, cutting power consumption by a minimum of 50%, as compared with other circulators in its class.

 

And, the circulator’s design makes the alpha the most compact circulator offered by Grundfos. Rather than being bolted on, its sophisticated electronics are fully integrated within the motor, simplifying installation in tight spaces.

 

“If the installer is not familiar with piping layout, he may decide the best way to avoid a callback is simply to oversize the pumps. Alpha creates a colossal opportunity to address this oversizing tendency. The circulator will automatically find the lowest possible operating-efficiency point to meet changing system demand. Then it will continuously adjust that setting to achieve optimal comfort at minimal power consumption — all without direct human intervention. The pump can operate with an input as low as five watts, as compared with a minimum of 80 watts for a conventional circulator of comparable size,” said Reinmund.

 

“The previous circulator consumed between 55 and 70 watts during periods of peak usage. Using the autoadapt feature, the alpha went as low as 7 watts and as high as 22. It installed easily, and we never had a problem with it,” said Phillip Hughes, principal, Hughes Plumbing & Heating, Inc., Harrod, Ohio.

 

Its easy-to-read led (light-emitting diode) display offers a range of unique, user-friendly features:

 

• Large, real-time display alternates readings between energy consumption (Watts) and estimated flow indications (gallons per minute).
• One-touch, button-type interface permits the user to toggle quickly and easily among seven different hydraulic operating modes: three fixed speeds, three levels of constant pressure, and one automatic setting — the autoadapt.
• Plug-and-play convenience: Six-foot-long alpha plug connects the circulator to a wall outlet, with no wiring required, eliminating the need to open a terminal box to make electrical connections.
• Installer-friendly pipe connections: Standard two-bolt flange with a built-in nut-capture feature holds the bolt steady during tightening, so the installer has a free hand to hold the circulator in place.

 

“As the valves in the different sections open or close with rising or falling demand, my alpha automatically ramps up or down to meet the load without any adjustments on my part. It’s pretty much a set-it-and-forget-it proposition. The circulator has worked so well for me, I’m looking forward to specifying it in my various company projects, as well,” said Paul Seward, Principal, Seward Mechanical Systems, Louisville, Colo.