Grundfos (and Wilo) "Smart" Circulator Pumps for Hydronic Heating
For the past couple years, I've been helping All Soul's Church in West Brattleboro, Vermont, save energy. While developing a plan to improve the performance of the building envelope of this early-1970s, heavily glazed and horribly inefficient building, one of our committee members found out about a grant program from the state that would support a heating system upgrade.
To make a long story short, we replaced the massive oil-fired boiler with a compact Buderus model that takes up just a fraction of the space; we got rid of the 6,000-gallon underground storage tank, replacing it with two 330-gallon tanks in the boiler room; we replaced the failed zone valves with new thermostatically controlled, electric zone valves; we stopped using the boiler to make hot water for three small lavatory sinks (for which the boiler would operate off-and-on all summer); and--the topic of this blog--we replaced the constant-speed, 1-horsepower (hp) pump with a high-tech pump from Denmark that should dramatically reduce the electricity we use for circulating hot water.
The pump we installed is a variable-speed Grundfos Magnawith ECM motor and a unique AutoAdapt feature that uses an integrated logic board to "learn" the building's usage patterns and calibrate the pump operation accordingly.
To understand why this pump is pretty cool, let me explain how the hydronic heating system used to "work" at the church ("work" is intentionally in quotes). The oil-fired boiler heated water that was circulated through a primary loop in the basement and crawl space. Zone valves (which were user-adjusted at the baseboard radiators) employed a paraffin material to passively open when heat was called for and close when heat wasn't needed (at least that was the theory). The 1-hp pump operated nearly continuously throughout the heating season, and because most of the old zone valves were stuck open, the church was kept fully heated most of the time. The church used about 6,000 gallons of oil per year.
The replacement electric zone valves now allow the hot water flow to be cut off to radiators, so we can actually set back the temperatures in different rooms in the church. That improvement, alone, should produce very significant energy savings.
But the new, high-tech pump is also pretty neat and will result in significant electricitysavings. A 1-hp pump uses about 750 watts when its on. Operating 24/7, such a pump uses about 550 kilowatt-hours (kWh) per month--about $70 worth at our current electricity rates. The variable-speed Grundfos pump we installed senses how hard it has to work to circulate water around the building, and it doesn't work as hard when less water is being circulated.
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At night and during other periods when heat isn't being called for, water is circulating only through the primary hydronic loop; the zone valves are closed so hot water isn't being diverted up into the church and through the baseboard radiators. In this condition, the pump controls throttle it way back, so water is circulated much more slowly and pumping energy is greatly reduced.
The Grundfos Magna pump has a sophisticated variable-speed drive as well as an "electronically commutated motor" (ECM) which makes it significantly more efficient.
The AutoAdapt feature in the Grundfos Magna (and a companion Alpha line for smaller residential heating systems) uses special algorithms in the processor to anticipate when heat will be called for and ramp the pump speed up or down accordingly. Frankly, I don't understand how this works, and I haven't been totally convinced of the benefits--but the company is very proud of the feature.
Grundfos is not the only company offering advanced, variable-speed ("Smart") pumps. German manufacturer Wilo (pronounced "veelo") has a similar product. The Wilo Stratos (for commercial buildings) and Stratos ECO(for smaller residential applications) pumps were actually introduced to the U.S. market a few years before the Grundfos Magna and Alpha pumps, and they work on much the same principle--though without the AutoAdapt feature.
A sales rep at Grundfos told me that their residential Alpha pumps are about three times as expensive as standard constant-speed circulators, while their Magna pumps cost about 50% more than standard circulators. Someone at Wilo told me the cost of their Stratos and Stratos ECO pumps are two to two-and-a-half times that of standard circulators. The payback for these pumps (assuming electricity savings only) can range from eight months to about three years, according to representatives from both companies.
These variable-speed, ECM circulators make a lot of sense for several reasons. One, they allow you to save pumping energy by varying the flow rate. Two, by reducing the flow they can increase the temperature difference between water leaving the boiler and water returning--which improves efficiency, so you use less heating fuel. (With a condensing boiler, this higher delta-T allows the boiler to truly operate in a condensing mode during swing seasons when less heat is being extracted out of the hydronic loop; often during those seasons, boilers stop operating in the condensing mode and their efficiency drops about 8%.) And three, these pumps compensate for the fact that circulator pumps are almost always significantly oversized.
According to Grundfos and Wilo, these variable-speed pumps with ECM motors can reduce pumping energy by 70-90 percent--and that's a lot of electricity savings. Worldwide, pumping accounts for about 22% of all electricity use, according to Steve Thompson, the vice president for building services at Wilo USA!
The point about oversizing pumps is an important one. In most buildings, according to hydronic heating expert Henry Gifford, the level of savings we will achieve with the high-tech (expensive) variable-speed pump can be more cheaply achieved simply by right-sizing a constant-speed circulator. The reality, however, is that most heating contractors don't do actual calculations for pumps (most probably don't even know how to do those calculations), preferring to cover themselves by significantly oversizing the pumps. For this reason, this new generation of advanced smart pump makes a lot of sense.
In the September issue of Environmental Building News, we'll be running a more in-depth article about smart pumps from both Grundfos and Wilo.
For more information:
Melrose Park, Illinois
See more on Grundfos Pumps in the GreenSpec Guide
See more on Wilo Pumps in the GreenSpec Guide
Alex Wilson is the executive editor of Environmental Building News and founder of BuildingGreen, LLC. In addition to this product-of-the week blog, he writes the weekly Energy Solutions blog. To keep up with his latest articles and musings, you can sign up for his Twitter feeds. Products covered in his product-of-the-week column are--or soon will be--listed in BuildingGreen's GreenSpec Directory.
(2010, August 12). Grundfos (and Wilo) "Smart" Circulator Pumps for Hydronic Heating. Retrieved from https://www.buildinggreen.com/blog/grundfos-and-wilo-smart-circulator-pumps-hydronic-heating