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Letters: May/June 2013

May/June 2013
This article originally appeared in the May/June 2013 issue of Home Energy Magazine.
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The Fracking Dividend

Thanks for Alan’s editorial “Home Energy and the Fracking Dividend,” (HE Mar/Apr ’13, p. 2); it’s an important and timely topic. But I wonder if you didn’t end a couple sentences too soon. The perception of low gas prices in the future may be more important than the reality. What happens to efficiency programs (both electric and gas) if regulators feel that they are no longer needed? It doesn’t take much interruption in programs to make for a very difficult restart.

Shouldn’t we be finding ways to capture the social dividend of lower gas prices and divert them from wasteful consumption today to long-term reinvestment in energy efficiency—investments that also help to stretch those gas supplies even further?

Jeffrey Harris
Senior Vice President for Programs
Alliance to Save Energy
Washington, D.C.

All Electric in New York

Alan’s editorial “Home Energy and the Fracking Dividend” (HE Mar/Apr ’13, p. 2) definitely brings up an important topic.

Some homeowners in upstate New York are changing their homes to all electric because of their opposition to fracking. They are also switching their electrical supplier to all renewable, which often adds 1-2 cents per kWh. These folks are prime candidates for efficiency and conservation retrofit measures.

With fuel prices relatively low compared to periods with a stronger economy, now is the best time to invest in energy conservation and energy efficiency; before prices go up. If a homeowner is planning on being in their home for decades, then payback should be based on the life of the measure. Measures such as air sealing and insulation should outlast the mortgage payments in a house that is well maintained.

Dale Sherman
Development Specialist
New York State Weatherization Directors Association
East Syracuse, New York


Static-pressure probe


Straight tube bracket

Bent or Straight Static-Pressure Probes?

Thank you for Paul Raymer’s great article discussing the best probe to use when testing draft pressure in flue pipes of combustion appliances (“Static-Pressure Probes: Measuring Combustion Draft,” HE Jan/Feb ’13, p. 6). Articles about tools and equipment are incredibly valuable to technicians and business owners. 

In the article, Paul references Pure Energy’s research, stating that we decided to use straight probes for our draft pressure tests. I want to clarify that Pure Energy uses the bent static-pressure probes when doing postwork QC inspections, not the straight probe. This is because we want to be sure the draft pressure is adequate, so we test conservatively. However, we also will test using a straight probe if our static-pressure probe test indicates a lower draft pressure than the contractor’s recorded draft pressure. This is because we want to be fair to the contractor—giving him or her the benefit of the doubt—while still ensuring a healthy and safe postwork home.

Tamasin Sterner
President and Chief Coach
Pure Energy Coach, LLC
Lancaster, Pennsylvania

What Is a Safe Level for CO2?

I read “Deep Energy Retrofits” (HE Jan/Feb ’13, p. 24) a couple of times and enjoyed the author’s journey through these buildings. I do have a concern with one of the comments in the article:

Terry Brennan, of Camroden Associates, pointed us to research that indicates that an indoor CO2 level of about 1,100 ppm is a pretty reliable sign of healthy indoor ventilation rates.

In my training and experience, CO2 levels above 600 ppm need to be addressed. The goal is to keep indoor levels below 600 ppm. The 1,100 ppm number is certainly alarming. I don’t know where Terry Brennan got his numbers.

Here are some guidelines from ASHRAE:

Properly ventilated buildings should have carbon dioxide levels between 600 ppm and 1,000 ppm, with a floor or building average of 800 ppm or less. If average carbon dioxide levels within a building are maintained at less than 800 ppm, with appropriate temperature and humidity levels, complaints about indoor air quality should be minimized. If carbon dioxide levels are greater than 1,000 ppm, complaints may occur. Therefore, 1,000 ppm should be used as a guideline for improving ventilation. If a building exceeds this guideline, it should not be interpreted as a hazardous or life-threatening situation. An elevated carbon dioxide level is only an indication of an inadequate amount of outside air being brought into a building. The level cited in this document should only be used as a guideline to determine the amount of fresh outside air entering a building.

Dick Rome 
Technical Specialist - HVAC 
Pacific Gas and Electric-Energy Training Center 
Stockton, California

Coauthor Paul Eldrenkamp replies:

Thanks for your note.

The research that Terry Brennan pointed us toward originated with 19th-century German scientist Max Joseph von Pettenkofer, who hypothesized that an indoor CO2 level of about 650 ppm or so more than outdoor ambient was a reasonable proxy for adequate indoor ventilation (to oversimplify a bit). In 19th-century Germany (as elsewhere), the primary ventilation concern was odor control; in the 21st century we’ve come up with lots of additional reasons to ventilate. 

I’m intrigued by this relatively simple metric, because in our work my coauthor Mike Duclos and I are trying to move toward a quantifiable performance standard for ventilation rather than the sort of prescriptive approach that ASHRAE 62.2, for instance, takes. Most of the important building performance characteristics are easy to measure—temperature, relative humidity (RH), energy consumption, water consumption. But air quality and ventilation effectiveness are not in that category, unfortunately. Yes, you can easily calculate whether a home meets 62.2, but it’s difficult to know whether following that prescriptive path is actually providing enough fresh air. When Mike and I have measured CO2 levels in various rooms in a house that meets 62.2, we find that they’re all over the map. It’s not unusual to reach 3,000 ppm in a master bedroom, for instance. There are lots of variables that affect CO2 levels, and ASHRAE 62.2, ironically, seems to be down the list a ways. 

I also have to acknowledge that I’m not sure that 1,100 ppm is the right number to aim for. I consider it a hypothesis rather than a conclusion. That being said, I’m pretty sure that a reading of 1,100 ppm should not be considered “alarming,” given that we find that level is exceeded in one room or another in pretty much every house we’ve measured. Let’s just say that if it is indeed alarming, retrofitters have a lot more work to do than they realized.

I’m also not yet sure that CO2 levels are the best measure of ventilation effectiveness available to us. ASTM D6245-12 has what I think is a really good summary of the drawbacks of attempting to use indoor CO2 concentrations to evaluate indoor air quality and ventilation. The good news is that we can log CO2 levels pretty easily, with only about $600 worth of equipment; tracer gas testing, on the other hand, is rarely an option because of the cost and time required. Monitoring CO2 levels because it’s relatively easy to do so might be analogous to looking for the car keys under the street lamp because that’s where the light is, but my sense is that it’s more useful than that. So far, we’ve found a good correlation between CO2 at around 1,100 ppm and occupant comfort, well-managed RH year-round, and moderate run times of the ventilation system. But we don’t have anything close to a statistically significant data set. 

Finally, I realize there will probably never be a really good way to know how much ventilation is the right amount. We’re dealing with a complex system—a house—and its interface with an even more complex system—the human body. We’ll probably never have consensus on what the best strategy, or best level, or best way to measure will be for every situation. 

I am grateful you took the time to respond to our article and provide your feedback based on your experience. It’s always important to Mike and me to hear what other practitioners are doing to deal with the same issues we face in our work; we always learn something. I hope we can continue the dialogue.

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