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Originally Posted by mason Switch it over to heat and use Btuh/ delta t x 1.08 If you know what kind of motor the unit is using then you can confirm if it's within "range" by using the static pressure. Residential psc motors max out at .5"w.c. and most ECM motors go up to .8"w.c. when does detaT calculate in initial starting or after stabilizing?can use this formula in 3phase and single phase fan? moideen-dubai
Originally Posted by chill67 Same fan speed and entire system is only a year old, no lint blanket on coil. I was shocked as to my findings as well. Wonder why there are no numbers calculated for air flow with wet coil?????? Define when the coil would be considered wet enough to test... Dry is dry. Wetness can vary. That's why York doesn't publish wet coil airflow data.
Originally Posted by bkmichael65 The square root of the static pressure x 4005 will give you flow velocity in ft/min. Multiply this by your duct cross sectional area in square ft. and this will give you air flow in cfm That should read "velocity pressure."
The square root of the static pressure x 4005 will give you flow velocity in ft/min. Multiply this by your duct cross sectional area in square ft. and this will give you air flow in cfm
I bet the source of the confusion is the way you are doing the math. If you use DB temp drop as the only factor - you will never get an accurate read on the airflow in cooling for 2 reasons. 1) the only time DB gives you a complete picture of heat going into or out of a system is in heating mode. If you try to say '3 tons is 36000 Btu - and my temp drop is 13 deg... that means the air flow is .......' You will be missing about 30-40% or more of the story, because cooling systems extract a lot of latent heat which only shows up with a WB temp difference. After taking WB and DB into and out of the system, you need to convert it to an enthalpy change using a chart, then use an adjusted formula to calculate Airflow. 2) a 3 ton refirgerant system does not always give you a real solid 36000 Btu's. Any refrigerant system will naturally have variations in output based on the Evaporating and condensing temperatures. basically, the closer the pressures are on both sides (high side and low side) the more heat your Refrigerant system will move. This means that just as sticklers will (correctly) insist that I cannot know my 150000 btu furnace is delivering the full amount without a combustion analysis test and tuneup (but the difference is USUALLY not enough to drastically throw off air flow calculations) so too, refrigerant systems are usually in the ball park, but not always. Even if it was working properly - which it may not be - charged properly - usually isn't - it may simply be suffering lower output because of low airflow, or high head pressure. Have fun measuring your airflow without a flow hood - really that is the only accurate way to do so, but you gotta do what you gotta do.
Originally Posted by Joseph'bidness Heat pumps are also simple e.e.r. Calc. And a temp rise for c.f.m. is generally with in ten percent from my experience. I have been seeing three and a half ton systems delivering nine hundred c.f.m.... 3.5 ton with 900CFM isn't uncommon. Oddly a 2 or 2.5 ton system can be hooked to the same ductwork and cool the house just as well with a much lower energy bill.. The larger systems tend to fall short on airflow. Peopel are quick to oversize the units, but not install the appropriate ductwork. When you think about the initial install which is charged to the builder by the ton it makes sense.
Originally Posted by doc havoc Just for clarification, when using this formula, make sure you use BTUH output, not input. Heat pumps are also simple e.e.r. Calc. And a temp rise for c.f.m. is generally with in ten percent from my experience. I have been seeing three and a half ton systems delivering nine hundred c.f.m....
Originally Posted by doc havoc Just for clarification, when using this formula, make sure you use BTUH output, not input. Then you need to clock the meter, if its a n.g system, to first verify actual input, so your output off of an efficiency value is projected by the afue unless an anylyzer is used.
Originally Posted by mason Switch it over to heat and use Btuh/ delta t x 1.08 Just for clarification, when using this formula, make sure you use BTUH output, not input.
Perhaps you are getting very low temps through the coil causing the air to be way off of .0075.. (I am being a smart ass here). All seriousness with all joking aside are there dip switches on the board, to select cubic feet per minute in cooling mode verses heat, like carrier infinity logic?
Is your coil oversized to the blower?
An AHE30B can't move 1200 CFM at a .1" ESP. I think your CFM check dry coil was way off.
York air handler md.# AHE30B3XH21A with X13 motor. At the time I ran my test air conditioner was not running and had not been running for days prior. Since I was not familar with the X13 motor I pulled outdoor disconnect at heat pump & made a call for cooling, obtained total cfm on all supplies. A week later I conducted same test after AC had been running for a couple days, hence the lower total cfm.
Originally Posted by chill67 Same fan speed and entire system is only a year old, no lint blanket on coil. I was shocked as to my findings as well. Wonder why there are no numbers calculated for air flow with wet coil?????? The coil has a pressure drop rating for dry/wet and the sytem has a max TESP, if both of those are within spec it should have the proper cfm.
What blower/furnace is it, and what model coil.
Same fan speed and entire system is only a year old, no lint blanket on coil. I was shocked as to my findings as well. Wonder why there are no numbers calculated for air flow with wet coil??????
Originally Posted by chill67 Good point bigtime. My air handler delivers 1202 cfm (checked at supply registers with Flow hood) with dry coil, 672 cfm with wet coil. Manufacture's air flow data is for dry coil condiitons and without filter on my York equipment. That is a pretty serious reduction in airflow, might want to do a pressure drop on that coil and a TESP on the system. Never hurts to confirm the fan speed setup first.
Originally Posted by beenthere Almost couldn't be. Or the coil is wearing a lint blanket.
Originally Posted by 54regcab 1200 down to less than 700 just from the coil being wet? Was the blower set at the same speed for both tests? Almost couldn't be.
Originally Posted by chill67 Good point bigtime. My air handler delivers 1202 cfm (checked at supply registers with Flow hood) with dry coil, 672 cfm with wet coil. Manufacture's air flow data is for dry coil condiitons and without filter on my York equipment. 1200 down to less than 700 just from the coil being wet? Was the blower set at the same speed for both tests?
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