From when I took some AC courses, "sensible heat" is when you add or remove BTU, and it makes a temperature difference. For example, you heat or cool dry air. The temp goes up or down.
Latent heat is adding or removing BTU, which doesn't make a temperature change -- in other words, humidity. An example is running an AC which condenses out a lot of water, but doesn't change the temp. We'd call that "reducing latent heat".
Or, so it was explained to me.
Well stated. Design makes a considerable difference in the ratio of latent to sensible as does airflow and run time. Also, as the humidity level of the air increases so does the ratio of latent condensate change of state heat absorbed increase. Studying the graphed charts illustrated in the link below, clearly reveals this relationship ratio equation. As the humidity level goes up the condenser discharged heat which includes the latent heat goes up as the sensible temperature drop goes down.
This is Turtle.
Go with the contractor that did the Manual J and go along with the 4 ton 14 seer / propane back up because some contractor have dought about the Manual J reading and will up a 1/2 ton in there recommendations to remove errors.
i just can't picture Southern Maryland being a hot area of the country but could see a humid area.
TURTLE
Turtle, we know that they should size for the latent humidity load as well as the sensible load. That is especially true in a high humidity area like he lives in. The latent load is a major critical factor toward efficiently achieving the human comfort zone.
When the humidity is high the latent load will take a lot of BTUs away from the sensible capacity of the evaporator; which will also provide more needed run-time. However, they should be careful not to oversize, --because it takes adequate run-time to get the humidity percentage down.
If they have the blower speeds to do it,-- they could use a relay operated by a dehumidistat to go to 350-cfm per ton airflow for a colder coil, when needed until the dehumidistat is satisfied. - udarrell
If it's a piston metered coil, then how are you going to charge the system? In low or high speed? What happens to superheat when the blower speed changes?
hvacrmedic
That is what the rule makers' should have eliminated instead of the 10-seer. For those high humidity conditions we ought to pump the system down and tear out the flow-rator-pisser crappers and replace them with TXVs.
Well, we know what can happen with low temperature heatloads combined with low CFM; freeze-ups and slugged compressors. Some hot blooded babes that get all sweaty in bed doing it, run the RM-TH at 68 or lower at night when it's real cool outside.
Of course, that provides us with more work. I always told her or him to buy a big floor fan and run it on high if they were going to be doing it most of the night. Some laughed and some got pissed off but then usually started laughing. One fine lady just rolled her big blue eyes blushed then looked away. (That's all I'm saying here.) - udarrell
I'm not touching that :)
hvacrmedic
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