Jim Bergmann gives his presentation on advanced combustion analysis for HVAC applications, including gas furnaces. He shows how to use BluFlame from AccuTools with measureQuick to get the most accurate results and protect yourself and customers from the hazards of carbon monoxide (CO).
To make sure your combustion analyzer is most effective, be sure to calibrate it outdoors with fresh air. When you measure CO in the home, you can keep the analyzer at chest height because CO doesn't stratify. Even though it's poisonous, you likely won't find CO without an analyzer because it's odorless, colorless, tasteless, and mixes well with the air.
Symptoms of CO poisoning resemble that of the flu and may include headaches, dizziness, nausea, fatigue, confusion, and shortness of breath. If you have those symptoms but feel okay outside your home, then your home likely has CO. CO is so dangerous because it displaces oxygen in the bloodstream. CO may come from the furnace, but you also have to think about other fuel-burning appliances, automobiles, and tobacco smoke.
At the appliance, you need to do draft and spillage testing. You need to do the draft test at least 12 inches above the draft diverter; the draft hood separates the appliance from the draft, preventing the fire from rolling out or nuisance pilot outages. A draft should be established within 5 minutes of starting a gas appliance. We want to avoid spillage when the flue becomes blocked or the chimney is cold; spillage is common on hot water tanks, and you can look for rusting or staining at the draft hood to identify spillage. Draft spillage is more likely to happen in undersized chimneys and when you have common vented appliances. Backdrafting can also happen when static pressure buildup causes the combustion air to spill through the smaller appliance.
When setting manifold pressure, you first need to understand how much fuel and air are required for complete combustion. After setting the fuel pressure, you must clock the meter. Heat content varies across the country per the Wobbe index, and clocking the gas meter allows you to adjust gas pressure and airflow accurately according to the manufacturer's specs AND the average heat content in your area. If you use measureQuick to help clock the meter, it will use its geolocation capabilities and do calculations to let you know if you need to resize the orifice to meet the target pressure.
Combustion testing varies by furnace efficiency; it is less critical on 80% furnaces than on 90%+ high-efficiency condensing furnaces. Higher levels of excess air can keep CO levels low, but when there is too much excess air, the flue gases can dry out and fail to produce adequate condensate. When you first start up an appliance, the combustion is very fuel-heavy, meaning that there is low oxygen and higher CO. As the excess air levels rise, the efficiency peaks and the CO should decrease as oxygen increases. You ideally want to be close to the middle of the target ranges, not close to the edges. You must do a combustion test on the undiluted flue gas in each cell (the same applies to boilers).
Combustion analysis can also help you distinguish combustion efficiency from AFUE; combustion efficiency does not account for standby losses and only tells part of the story. You should also verify that the base pan is sealed if the bottom return is not used.
MeasureQuick can also help you profile, benchmark, commission, and diagnose problems with gas appliances. After you profile the system, measureQuick helps you determine if your pressures and temperatures are within the targets. MeasureQuick also provides just-in-time education that allows you to learn about each reading and what it means.
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3 июл 2024
