The Biggest Loser

Jan. 5, 2011
Does the industry need to revise its methods for designing hydronic heating systems and rethink conventional methods for sizing circulators?

For most of the past four decades, my hydronic training centered on choosing a circulator that met or exceeded the required system flow rate, while overcoming the system's head losses in each zone. Our hydronic piping zones were like fat wide highways where traffic was light and with very little need on our part to pay close attention to those kinds of details.

In addition, there were few choices for residential circulators. Pretty much one size fit all. Zone valves were prone to failure and leaking, so I became a devout advocate for using circulators, which were reliable and long-lived, unless you over-oiled the motor bearing cups.

New mixing strategies emerged: PEX tubing with radiant heating; high-head-loss boilers; injection temperature zones; 4-, 3-, and 2-way mixing valves; and the need to comprehend Cv values (coefficient of velocity) corresponding to the required GPM (gallons per minute) flow rates, each of these factors dictated which circulator was chosen, based on the manufacturers' hydraulic curve.

The need to properly size circulators to their corresponding zone of responsibility became much more critical and model choices expanded exponentially. Our focus was centered on providing customers with high-efficiency heat sources, while utilizing heat emitters designed for efficient delivery of comfort energy.

Time was, electricity was cheap and abundant, as were fossil fuels. If I were to place a wager, I'd bet 95% of all installed circulators are grossly oversized, wasting giga-Watts of power if viewed as a whole. From start to finished hydronic systems, the CYA (Cover your Ass-sets) process layers on the energy fat: heat-loss design programs build in a cushion to account for construction anomalies; Cv values for valves add a bit more CYA; piping friction loss calculations add still more fat; heat emitters were oversized designers often add their own CYA; circulators are then chosen based on the fattened total, and I suspect their flow charts from the manufacturers incorporate a bit of fat as well; and when in doubt, system installers tend to use the next larger, more powerful size.

But no one complained, because the systems designed and installed have virtually all worked. No one paid attention to the energy consumed while transferring thermal comfort from our 95% efficiency boilers to the heat emitters. We always knew there was some CYA built in from conception to delivery, but how much remains a mystery: 50% to 95% perhaps?

My eyes were opened during trips to the ISH trade shows in Germany where system-wide energy use was a focal point. At one show, a wall of ECM (electrically commutated motor) variable-speed 5- to 45-Watt circulators stopped me dead in my tracks.

Fast forward to today

Modulating-condensing (modcon) boilers squeeze virtually every last penny out of the combustion process. Fossil fuels have long ceased to simply be cheap and abundant, and starting in the 1970s, we have witnessed ever-tighter building envelopes.

As the boxes we live in became more frugal with energy losses/gains, our heating appliances also started an efficiency climb upwards. Over the past five years, we've witnessed efficiencies nearly reach 100%, which are rapidly becoming the accepted norm. When coupled with a low-temperature delivery system (radiant floors, walls, ceilings; radiant panels; freestanding cast iron radiators; etc.), both comfort and efficiency are enhanced. However, there remained a weak link in this chain of efficient production and use of energy for comfort: the delivery system.

In 1993, we built our new home, and I was determined it would be heated using a hydronic radiant system, with every room having its own zone. My high-efficiency condensing boiler did not modulate, so a buffer tank was required to accommodate my 10-zone system. Outdoor reset was accomplished by an external control that overrode the boiler's control to alter its high-limit setting. The burner and all my circulators were simple on/off devices. While gas consumption was a concern, little thought was given to the power consumption of my 13 circulators (10 zone circulators; one indirect water heater circulator; and twinned high-head circulators to overcome the high head loss through the boiler).

In 2005, I installed our first modcon boiler, a 93%-efficient model. Outdoor reset was now an internal function that modulated both the burner and outlet temperatures. An immediate increase in our comfort was noticed and without prompting, my family asked what I¡¦d done to create the difference? Changes in delivery temperature were much more gradual and glided up/down as outdoor weather changes occurred. One other thing I noticed: run-times for my burner and system circulators increased to almost constant use. We also noticed an increase in our electric utility bills.

Ghost loads and PV solar

By early 2007, I'd already installed solar thermal for our home's domestic hot water system and began focusing on my home's power consumption. Plans to incorporate a solar PV (photovoltaic) system were begun and, as they say, the devil was in the design details.

Ghost-loads can be a hidden problem for PV installations and the fact that a $1.00 reduction in power consumption equaled a $3.00 reduction in the cost for a solar PV system convinced me to purchase a Kill-a-Watt meter to aid in putting my home on an energy diet, a Biggest Loser contest of sorts.

I was surprised to find that my home's ghost-loads (toaster, coffee pot, computer, TVs, wireless router, etc.) totaled just 28-W when not in use, which accounted for only $2.25 of our monthly energy bill; pennies instead of nuggets of gold. Aside from lighting, where CFL light bulbs were able to cut 100-W to 26-W, a 74% reduction in energy use per fixture, and purchasing Energy Star-rated appliances, there wasn't much else I could do to trim my home's apparent appetite for energy. Or was there?

Focusing on parasitic losses

Imagine my shock when I first checked my wet-rotor circulators and discovered each one was using from 87 to more than 130-W. I should stress that I was using three separate brands of wet-rotor circulators. Our three relay-control boxes were consuming 10-W each per hour year-round, while my 10 zone circulators enjoyed extended run-times because I was using a well-adjusted outdoor reset curve. Turn on all 10 zone circulators and the one primary circulator, and my power consumption was a whopping 1,186-W! I'd found the mother lode of fat to be trimmed from my home's energy.

Run-hours and outdoor reset: My heating zone (southeastern Pennsylvania) indicates we can expect 2,250 run-hours per year for older-style, on/off equipment. By downloading a day-by-day low/high temperature chart for the past 12 months, it was easy to determine if any heating might be required and project run-hours based on that information. Each month's heating degree days confirmed there was a potential for 4,200 hours of heating when utilizing an outdoor reset curve adjusted to virtually match our home's heat loss.

Assuming a 70% run-time for my primary circulator (because the 10 zones would overlap their extended run-times) granted an approximate 3,000 run-hour projection for the primary loop circulator. If I allowed for a 67% run-time average for my zone circulators, they each would see 2,800 run-hours. One last item to add that uses power, the zone control panel(s).

Crunching the numbers

We currently pay 11 cents per kWh (kilowatt hour): 1 kWh = 1,000 watts. If my run-hour projections were correct, our hydronic radiant heating system's power consumption would look like this (Chart 1):

We would consume 3,526.8 kWh and that would cost $359.04 per year. If I assume a 50% increase following deregulation on Jan. 1, 2011, of electric utility rates, my new rate will be 16.5 cents per kWh and, absent any changes, my cost to move thermal energy from boiler to radiant floors would increase to $538.56. (Chart 2) Yikes!

Watt to do? Looking back at ISH while looking forward caused me to learn more about ECM vs. induction-motor circulator technology and how they each work. Last but not least, would investing in ECM circulators make cents? Here's what I learned: AC (alternating current) induction motors run at one set speed using full power. The majority of induction motor circulators are substantially oversized, which compounds the wasted power consumption. Hydraulic erosion and audible noise issues often result, which can lead to premature failure of system components and customer complaints.

DC (direct current) ECM motors use a brushless permanent-magnet rotor with variable-speed inverter-drive (converts AC to DC) technology. These motors run much cooler, often at surrounding ambient temperatures. ECM motors are a great choice for those who want to increase the circulator efficiency, dramatically reduce power consumption and conserve energy. Software-enhanced control of an ECM motor can reduce energy use by more than 80%!

Grand experiment

Pruning my energy tree meant searching for the lowest Wattage devices available. Taking this one step farther, I wanted to gauge costs based on what we would typically charge a customer.

I found zone valves for $105.54 each that utilize just 3-W of power when on. The ECM 5- to 45-W circulators work seamlessly by ramping their speed up and down as zone valves opened and closed; their selling price would be $315.02 apiece. A second circulator was required to handle our lower floor's low-temperature slab system. If I were selling this as a retrofit system to one of our customers, their investment would look like this (Chart 3).

Where the rubber meets the road: My newly designed system with the two ECM 5- to 45-W circulators and the 10 3-W zone valves was up and running for the entire 2009-2010 heating season. During this time, data logging with the Kill-a-Watt meter indicated my run-hour projections were on target.

Initially, both of the ECM circulators ramped up to 45-W. But as the circulators began learning my zones' system curves, the Watt readouts fell until they settled into an established pattern.

Testing has confirmed the zone valves use just 3-W each. The ECM circulators have varied their Wattage use considerably: from 5-W to a maximum of 28-W to date, as zone valves open/close; but, on average, less than 16-W. As Chart 4 documents, last winter I cut my thermal-transfer power use by 93.4% over 2008-2009: 375.05 – 24.83 / 375.05 = 0.9337, or 93.4%

In terms of simple payback with the electricity increase in 2010 and an annual 5% bump in the rate, I'm looking at a bit more than six years.

If the return on investment calculations in Chart 5 don't get your attention, let's look at long-term investment based on a 5% annual increase in the cost for electricity following deregulation. We will also include this first year with its 11 cents per kWh rate. After 20 years, my system costs should look like the numbers in Chart 6.

Given these returns, would you say no to this new style, energy-miser system? Would you ignore the savings potential? Mine was a retrofit that replaced a functioning 10-zone hydronic system. What if we were to consider the cost differences between installing a typical six-zone system from scratch? Let's start over.

Starting from scratch

The labor won't be any different, so we'll look at the cost difference in materials only. Six wet rotor circulators versus the combined six 3-W zone valves and one ECM 5- to 45-W circulator. Using standard markup rates for all materials, the cost difference is just $398. While I've increased the initial system cost, the ROI in my 11 cents per kWh year just skyrocketed to 42.2% (see following tables).

The comparison between the old style energy-hog and new-style energy-miser systems can be seen in Charts 7 and 8.

In terms of simple payback, I'm looking at less than two years to recoup the added $398 investment.

It's clearly a win-win scenario for everyone involved. I've reduced my system's thermal-energy-transfer consumption by a bit more than 93%, slashed my operating costs and virtually eliminated parasitic energy losses. In addition to having a much greener carbon footprint, I have a fatter wallet.

But this Grand Experiment has raised two questions:

Do we, as an industry, need to revise our methods for designing hydronic systems to more accurately reflect actual values? Do we need to rethink conventional and accepted methods for sizing circulators?

ECM circulators are new for North America hydronic system designers/installers, but this technology has been used for more than 10 years in other countries. Longevity isn't the issue: Acceptance and adopting a new mindset was my own personal challenge. After this first heating season's performance, I am convinced ECM-driven circulator technology offers a true win/win for everyone involved. The technology in use in my home revealed dramatically that my 11-circulator system was on an electrical power trip in spite of my having matched each zone circulator to the conditions indicated during the design process 18 years ago.

That's why, from my point of view, both of the above questions raised can be answered with a resounding "yes."

Dave Yates owns F.W. Behler, a contracting company in York, Pa. He can be reached by phone at 717/843-4920 or by e-mail at [email protected].

About the Author

Dave Yates

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