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04-06-2011, 07:16 PM #14Regular Guest
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04-06-2011, 07:34 PM #16Regular Guest
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04-07-2011, 10:29 AM #17
Added the *0.0167 Factor in Formula to calculate Infiltration
If you wanted to use a calculated air infiltration rate I didn't put the full formula factor on the other posts. (Sorry about that!)
Estimating infiltration CFM per minute: Some rate infiltration CFM using .4 for lowest Air Changes (per) Hour (ACH).
SQ.Ft., area conditioned 2000sf*X's Ceiling Height 8 16000cu.ft. air* ACH * either .4 lowest; or *.7 average; 11,200 or 1.0 poor for high infiltration. then multiple that figure by * "0.0167" = Cu.ft.per minute 187.04-CFM; for cu.ft.per houir * 60-minute 112,224-cu.ft per hour.
Then, at specific temperatures, you find the grains of moisture per lb of air & figure how much latent & then the sensible in-coming loads add when reduced to room temp & humidity levels.
FINDING The LATENT HEAT OF CONDENSATION
The amount of heat energy in BTU's that must be removed to change the state of one ounce or one pound of a vapor to one ounce or one pound of liquid at the same temperature.
At an evaporator condensing temperature of 55ºF the latent heat transferred to the cooling coil's boiling refrigerant is close to 1,062 BTU per pound.
What is helpful in regulating conditioned space %RH is that: as the percent of Relative Humidity rises "the ratio of latent" to sensible, goes way up!
Latent capacity is not static.
E.G.; a 28,538-Btu/hr system: That would be 10,559 of sensible and 17,979 latent or, only 37% sensible and around 63% latent. This would have to be at a very high indoor Relative Humidity. (Ballpark projections here.)
The usual latent/sensible split on a 2-ton 13-seer A/C unit at a high 70% RH, is around 55% latent and 45% sensible, or 13,200 latent and 10,800 sensible.
For example, use an alarm timer set for 15 minutes, if you collect 18-ounces in 15 minutes, that's 72-oz/hour or 4.5-lbs an hour. (4.5-lbs X's 1065-btu/lb 4,792.5-BTUH) of latent heat transfer per hour.
At very high humidity levels a reduction of 50 or even 100-cfm/ton or, 300-cfm/ton Vs 400-cfm/ton doesn't make much difference in latent capacity over time! With proper Btu/hr sizing producing sufficiently long run-times, reducing airflow, too low, may be counterproductive!
The reason is that more cu.ft. of air is being moved through the indoor coil; a critical factor how cold the coil is, the entire coil & fins must be well under the dew point temp. If you see errors, let me know.
Last edited by udarrell; 04-07-2011 at 10:31 AM. Reason: Delete Double cheers again...
04-07-2011, 12:09 PM #18
Factors *X's Infiltration CFM to get Latent & Sensible BTUH
[B]SQ.Ft., area conditioned 2000sf*X's Ceiling Height 8 16000cu.ft. air* ACH * either .4 lowest; or *.7 average; 11,200 or 1.0 poor for high infiltration. then multiple that figure by * "0.0167" = Cu.ft.per minute 187.04-CFM ; * 31.96 = 5,977-BTUH latent Infiltration load.[/U]
The sensible-infiltration-load use 187.04-cfm * 22 = 4,115-BTUH Sensible.
Ballpark numbers @ Design conditions: 75-F indoors; 95-F outdoors 50% RH, 95-F holds a lot of gains/lb air added to indoor air; Total added BTUH 5,977-Latent + 4,115-sensible = 10,092-BTUH Infiltration load, nearly a TON.
Software would do it easier, faster & more accurate.