Tuesday, August 26, 2014

Following ACEEE Blog, Furnace Fans As Energy Hog

I'm just a seventy-year old educated person doing weatherization of homes by myself as I see fit, learning and sharing methods and concern over policy issues. I blog. I maintain web sites. I have leading-edge insights in things I pursue, such as fast adoption of better LED down lighting. Writing on 8-26-2014, I am obsessed with an impending meeting in Portland, Oregon, on about 9-30-2014, a hearing of Oregon's Public Utility Commission in turmoil over strange assessment of weatherization cost-effectiveness . I have a lot to learn, if I am to have a contribution to a better outcome. In my research I see valuable writing by ACEEE, the American Council for an Energy-Efficient Economy. They have a blog, and near top I find this post :

June 25, 2014 - 12:12pm

By Joanna Mauer, Technical Advocacy Manager, Appliance Standards Awareness Project (ASAP)

The Department of Energy (DOE) issued new efficiency standards today that will dramatically reduce the energy use of a little-known home energy hog. Furnace fans, which circulate heated and cooled air throughout a home, consume more than twice the electricity in a year as a typical new refrigerator. The new standards will cut the cost to power furnace fans by about 40% and also deliver improved comfort.
Most furnace fans come as part of a furnace. But in homes with central air conditioning, the fan circulates cooled air during the summer in addition to the heated air during the winter. Furnace fans consume about 1,000 kilowatt-hours per year, or almost 10% of the total electricity use of an average U.S. home. And yet, while the energy use of furnace fans is significantly higher than that of other common home appliances (see below), because furnace fans are inside a furnace, their energy consumption is hidden to most consumers.

And, I comment:

Your furnace fan likely consumes more than twice the electricity of your refrigerator. In time a new furnace will implement some cost savings for you. But, please think. In most homes, most of the load on that fan is in hacked-in D-boxes entering and leaving a furnace. We must NOT continue to build heating systems where ducting is an afterthought of the arriving installation crew. We must install intelligently-designed hydrodynamically-efficient plena . These plena must not be judged solely upon higher installed cost, to be avoided.
The fan is not simply the hog. It is the summation of fan with leaky and stupid ducting. We should replace that ducting now. When your furnace fails, and that is the cost-effective time to replace it , be ready with the better ducting already in place. Your installer won't give much thought to your ducts if called in an emergency, perhaps not offering improvement under any circumstance. Fix ducts now, upon your own initiative! The engineered plena and strongly-attached, zero leakage ducts, will only make your furnace more serviceable. In the deal, get rid of heat capacity in ducts , acting just like leakage.

At 9/28/2015, admit that electricity draw by a furnace with a squirrel cage fan goes down , if ducts are more resistive and blower flow is reduced. Added cost with poor duct design is in longer run times, and greatly increased run times to cope with an important room that has inadequate register flow. The savings in motor electrical efficiency are very large , but this is not associated with a campaign for better ducts. In time, I will rewrite the previous paragraph. I will not relent in campaigning for well-built ducts, asserting that octopus D-box ducting is foolish.

At 9/27/2016, begin reporting of experimental measurements of blower behavior as function of duct resistance. Here is a setup to measure furnace electrical power draw, as one of the efficiency parameters:

This Kill-A -Watt meter is in series with all electrical power draw of my furnace with very-efficient ducts. The display here is of 7 watts dead draw. In a heating cycle, the power steps up to 130 watts while firing and then to about 450 watts (5.2 amps) while the blower runs. 

If I fully cover the return air filter with cardboard, I hear rumbling complaint, and power draw falls to 400 watts. The lesson is that duct inefficiency will have little effect on momentary power draw, yet large impact on fuel and electrical energy consumed, in proportion to cycle time, inverse to blower flow rate.

My challenge in assessing savings from improvement of duct efficiency will be to sense change of blower flow rate with logical reduction of duct resistance.

Squirrel cage blower flow rate impact of reduced duct resistance 

Find AMCA, Air Movement and Control Association International, Inc. , via Wikipedia at top of the search. I hope that AMCA can help me in test setup for the myriad of home situations I will face. I am advised by excellent blower manufacturer Rosenberg USA , that flow rate is not easily or accurately inferred from static pressure measurements. I don't expect to get much help from any furnace manufacturer.

I can reach some conclusions about operation with variable duct resistance, from two non-obtrusive holes in my furnace ducts. Operate my new Testo 510 digital manometer in scale Pascals, Pa. I don't need any heat in warm late-September, but run the thermostat up to force heating cycles.

With furnace firing and blower running, read 33 to 35 Pa across the filter. Close 75% of floor registers and read 27 to 28 Pa, corresponding to a 10% drop in flow through the filter. After firing stops, and with registers again open, observe 32 to 33 Pa filter pressure differential.

Extreme changes to ducts aren't likely to change blower flow by more than 10%. Where reduced flow is with same heat input, the temperature at registers will go up, and cycle time will change little.

I learn here that measurements of operating cost effect, may not help to justify duct innovation. Perhaps it is enough to offer such for reasons of getting ducts buried, out of harms way. and for better regulation of equal register flows without need of dampers and their confused settings. In the process, ensure there is zero leakage of ducts, and a minimum of the leakage-like effect of needless thermal mass of steel, swinging with furnace cycles.

Where I offer sealing and insulation improvement along with duct innovation, I despair of making sense of measurements now possible with my investment in instruments, from long-term monitoring of expected home energy savings. 

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