prog. therm. and heat pump questions

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snipped-for-privacy@ece.villanova.edu wrote:

Not following what you are saying Nick. If what rises above dewpoint?
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The coil. If it's well-controlled, always between freezing and the dew point, moisture will not re-evaporate.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

Fixed metering system, in a matter of a few seconds of that compressor shutting off that coil is going to warm up. Pressures equalize pretty fast.
Non bleed TX system, that air will warm up the coil fairly quick.
Your window shaker runs the fan steady as it has a sensing bulb for the thermostat. Next summer wire your window shaker to a remote thermostat that kills controls a contactor that kills the power to the whole unit. The fan will then cycle with the compressor. Watch RH drop compared to letting the fan run all the time.
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snipped-for-privacy@ece.villanova.edu wrote:

Abby did say "running the fan constantly". There's a difference between running it somewhat more than the compressor and running it 100% of the time. So actually, I think the two of you are talking about different things.
- Logan
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Running the fan when the compressor is off is a bad idea in a humid climate in cooling mode.
Nick mentioned running the fan steady on low speed and cycling the compressor. Lower speed will result in more latent removal, but the coil will warm up quick when the compressor is off either by pressures equalizing in a fixed metering system or just from rapidly picking up heat from the room air.
Even having the blower cycle off 60 seconds after a compressor stops to ring the last sensible BTU out of the thermal mass of the coil is a bad idea with respect to humidity control.
Logan Shaw wrote:

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wrote:

It sure will!
Especially if the face velocity is below the carryover threshold. It is a critical design paramater for dehumidifiers. :-)
But since you are not reheating the air with the condenser, it acts more like an oversized system (coil) than a dehumidifier. And I doubt if short cycling does squat for efficiency (in fact I think it hurts, both efficiency and the compressor).
P.S.: Why is this crossposted to misc.consumers.frugal-living? I read all three groups, but I don't understand... this is an engineering question, or a frugality issue?
(Maybe except for the fact that it is unfrugal to waste energy and/or thrash an HVAC system.) ;->
-- -john wide-open at throttle dot info
~~~~~~~~ The time to repair the roof is when the sun is shining - JFK ~~~~~~~~
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Well Nick never believes anything I say but maybe if some of his cronies say the same thing he will believe them.
I went to a seminar put on by the Florida Solar Education Center, and as a guest speaker, they brought in an aquaintence of Nick. As soon as I heard the guy talk, I knew that he had to know Nick. I ask the guy and sure enough they even collaborated on magazine articles. The seminar was on PV panels, but if these guys say something concerning humidity it surely must be the gospel as far as Nick is concerned.
Maybe check out this link, http://www.fsec.ucf.edu/bldg/science/mold/index.htm , and look for the heading "Practises That WIll Minimize Mold Growth" with the subheading "Air Conditioner Operation".
Note you hear the same things from HVAC Criminals, except the criminals go on to say that the practise of running the fan constant while the compressor cycles on/off can even dry out the drain pan.
Logan Shaw wrote:

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my bad, it's the Florida Solar ENERGY Center
Abby Normal wrote:

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Stretch wrote:

Yep the lower the temperature source the lower the heat output.

Yep not arguing there, 75 is on the high side tho for a winter set point. A setpoint of 68 to 70 set back to 60-65 overnight will be similar tho. Running without heat strips will take a long time to bring temperature back up and would need the help of the sun, unless of course the heat pump is sized for triple the heat load .
I have seen ground source sized to the heating load in Canada and end up being 100% oversized for cooling. In this situation the summer humidity was still low enough as to not be problematic and create an overly humid, mold condusive indoor environment in the summer.
A system sized for the full heat load, in a warmer climate with a hot humid summer most likely will be oversized for cooling and enf up with high indoor RH in summer. Just imagine what something sized for 3 times the heating load will do in summer.

No arguement there. A unit oversized to the point of not needing heat strips to recover from a setback would short cylce in heating as well as cooling.

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