Carbon12 wrote:Agreed on the BTU content. The equation gets more difficult when consideration for amount of heat extracted from the coil at different fan speeds is added. Higher fan speeds result in less heat per CF of air being transferred to the air. Not enough fan speed doesn't move enough BTU's. Each coil has a sweet spot between fan speed and water temperature. I've been recording coal usage per degree day. Will see if the fan speed change makes any difference. The fan seems to run for a shorter amount of time each time the TT call for heat. That also means the stoker is running for a shorter amount of time to satisfy the call for heat. I'll be watching it closely. Slower fan speed uses less electricity and is easier on the fan, especially if the external static pressure is decreased. Haven't tested that yet. Delta T across the coil is almost exactly 20 degrees now. I believe that's desirable. House is nice and toasty and that's what, ultimately, really matters
The A/C circuit ramps the fan up to high speed regardless of how it's wired for heating. I did put a note on the furnace jacket alerting anyone working on it to what I did,.....and to remind myself! Lol!
Carbon12 wrote:Here's an interim report: With the lower fan speed my external static pressure is .5 WC instead of almost 1 WC. .5 is where the furnace manual says it should be. According to the fan curve chart, the high static pressure reduced CFM so even though I lowered the fan speed I'm essentially moving the same amount of air. With the higher register temperatures it appears I'm moving a lot more BTU's into the heated space. Higher fan speeds apparently don't necessarily equate to higher air flow. It depends on many factors. Will continue to monitor the amount of coal I'm burning per degree day. It may be more, less or the same. Curious to determine which FYI,.....all this static pressure, fan speed, flow rate crap is making my head hurt,......I do find it interesting so it's all good.