# Thread: Indoor humidity VS Evaporator Split

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## Indoor humidity VS Evaporator Split

Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?

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Compared to what?

55% RH seems like it would yield a reasonable TD in the 18 to 20 territory.

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Compared to 30%.

4. Originally Posted by greenhorn520
Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?
Split meaning, return air verses coil temperature- 55%RH @ 75^F, a 60^F dew point return equals 49^F coil temperatue, a 55^F dew point supply air??
Is this what we are talking about?

Regards Teddy Bear

5. Originally Posted by greenhorn520
Will 55% indoor humidity and a dew point of approximately 66* with 78 dry bulb reduce a split?
Split meaning, return air verses coil temperature- 55%RH @ 75^F, a 60^F dew point return equals 49^F coil temperatue, a 55^F dew point supply air??
Is this what we are talking about?

Regards Teddy Bear

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In that case, 30 percent rh return air will yield a hight temperature drop then a 55 rh

By how much?

Use this formula to find target outlet temp based on return air conditions

[(3wb+2db)-112]/4.

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18* to 24* is normal td lets first see what the units doing. If its 90* outside and return is 90* we all no the problem lets.get.some dr y bulb temps.

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Split meaning RA vs SA temp. 97* out door ambient. 78* RA. I was using the check and charge app it was matching up. Just surprised a split can be reduced to 12* from humidity. I actually found some air gaps around the evaporator and was able to improve it to 15* split. 78/63.

9. Are the supply ducts in a hot attic or a cool basement/crawlspace? This is an inaccurate method of judging the measure the cooling, sensible/latent heat. Temperuature/%RH or temp/dew point temp is better way to determine the amount of sensible/latent(moisture). If your target is 50%RH in the home, the cooling coil should be low enough to lower the dew point of the air passing through the cooling coil a minimum of 6^F. An example is 75^F, 50%RH, a 55^F dew point return with attic ducts may have a 60^F, 70%RH, a 49^F dew point at the supply grill. With a basement supply duct, the supply may be 55^F, 85%RH, also a 49^F dew point. Both have enough moisture removal to maintain <50%RH during peak cooling loads. Dew point or grains of moisture per Lb. of air is the more accurate is measure of a good a/c setup.
This also explains why the %RH goes high when there is low/no sensible cooling, the outdoor dew point is high, plus the home is occupied by moisture generating occupants. A small whole house dehumidifier combined with a well setup a/c setup/sized for the desired condition is ideal.
Keep us posted.
Regards Teddy Bear

10. I saw no mention of airlfow in any post. Too much or too little will swing your delta T. At a 15 Delta I would guess you are moving more air than you need to. Did you take any static readings or check an air flow chart for the system?

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Could be short of gas or piston size / coil size isn't matched. Need pressures and temps of lines.

12. a simple measurement of DB delta is meaningless!

if you truly want to begin to understand the liquid we call air, get Psychrometrics without tears, by Eugene Silberstein, and read read read! it's a good, basic introduction to air. if you want to learn more, there's a whole other world of AC out there!

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