coolling the house with basement air?


Does anyone know anything about the possibility of just using the fan to recirculate the air, and hoping it will cool during the time it is in the basement? I have output vents for the HVAC in the ceiling of the basement, and the floor of the first and second floor.
But I think the only input is in the basement, by the stairs. ??
Would it have been of any value if the input was for example, in the laundry room instead of by the stairs?
Meirman -- If emailing, please let me know whether or not you are posting the same letter. Change domain to erols.com, if necessary.
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meirman wrote:

i run my fan 24/7 and it does cool off. I have no intake vents in the basement, but the ducting seems to cool the air since the basement is cool. It makes my house much more evenly cooled. But it does raise the humidity a bit. Oh, and I have A/C too.
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CL Gilberthttp://www.rigidsoftware.com/Chess/chess.html
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meirman wrote:

It will cool a little, but remember once the cool air is out of the basement, it will be replaced with warmer air and then it will no longer cool. You also should consider that the air is also likely to be humid and it may not be all that comfortable. But it is cheap to try, your particular conditions will determine how well it may work.
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under no circumstances should return air ever I repeat ever be ducted from a laundry room or area. If you need to replace your furnace in the near future I can assure you that this will happen. The chemicals contained in the cleaning agents in your laundry room will make a lovely little acid when combined with the furnace gases. Will eat a nice hole right through the heat exchanger in no time. If you wish to use basement air the best solution is to take the blower door off the furnace and run a full time fan. Be sure to put the door back on come heating season or you will be drawing combustion gases in through the system. Best recomendation is to install some form of A/C system
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It will cool. The deep ground temp is about the same as the average yearly air temp, 54.3 F where I live near Phila...

But warmer air can extract more coolth from the soil, and soils have thermal conductance: min 5.4 Btu-in/h-ft^2-F for sands, 11.4 for silts, 7.8 for clays, and 6.6 for loams, according to the ASHRAE Handbook of Fundamentals. So a 2400 ft^2 basement floor with a U1.5 film conductance near Phila might provide (70-54.3)2400x1.5 = 56.5K Btu/h of immediate cooling to 70 F air, (like 11 window ACs), and less (but not zero) as the ground warms up.
Soil's heat capacity is about 30 Btu/ft^3-F, so after the basement has provided 30x2400(70-54.3) = 1.1 million Btu of coolth, warming the first foot of clay soil, it can still cool at (70-54.3)2400/R2.2 = 20K Btu/h.

Run the AC at the same time.
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

True, but will the available surface area be able to transfer enough heat fast enough to do much? Best way is to try it out. Also as time goes on the soil around the foundation will warm and acting as an insulator it will slow heat transfer as well. Again the answer is try it and see.

True enough, but the extra moisture will make the AC less efficient and effective, again this is easiest tested by trial and error. There are just far too many variables to bother trying to calculate them all.

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Please note the 2400 ft^2 above.

Please note the 20K Btu/h above.

If water evaporates from the basement floor, it provides house cooling. IMO, the AC would become MORE efficient, with condensation on the cold fins dramatically raising their heat transfer rate.
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snipped-for-privacy@ece.villanova.edu wrote:

Thats my experience. The high humidity makes the A/C appear to do more since its both droping temperature AND humidity. Nevertheless, overall you may have to lower your thermostat setting since the house humidity will still be up. Unless of course your thermostat also detects humidity. Still can save some money I suppose. Especially if you are in a less humid area.
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snipped-for-privacy@ece.villanova.edu wrote:

Which will be countered and then some by condensation at the evaporator, robbing the system of sensible capacity, more than was gained by the initial vaporization on the floor.

I don't follow that logic. How does heat transfer rate equate to efficiency?
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Wrong. They are exactly equal.

You are an HVAC "professional"? :-)
Nick
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snipped-for-privacy@ece.villanova.edu wrote:

The increased head pressure due to the added heat load will result in a loss of volumetric efficiency. There will be a net loss of capacity. You can cite a reciprocity between vaporization vs. condensation, but that wasn't the point. OTOH, these won't be exactly equal, since the evaporation in the basement occurs at a higher temp and lower latent capacity. The condensate will be colder, coil skin temp, and this is wasted capacity unless you want to run it through a heat exchanger and recover it :)

Yes. Not always correct but always eager to learn. If you disagree with my points, then I encourage you to flame away :)
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About 1000 Btu per pound of sensible house cooling...

If the AC provides 1000 Btu of coolth to condense that pound of water vapor, there's no net loss of capacity.

Tiny potatoes... 1000 vs 70-40 = 30 Btu per pound. An energy frugalist might run the condensate through a little tempering tank before letting it leave the house...

Maybe I shoulda wrote "heat transfer coefficient," ie more air-to-refrigerant thermal conductance which raises the cold side temp, compared to a system with less condensation. This raises the Carnot efficiency, like using a larger evaporator coil or increasing the evap coil airflow or raising the room temp.
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snipped-for-privacy@ece.villanova.edu wrote:

But does this feel like cooling? The air temperature is reduced but the air humidity is correspondingly increased. And the human body feels 'heat transfer' not true temperature correct? And the heat transfer is increased in humid air? Or is it that our skin stops evaporating its liquids which makes us feel a bit warmer?
Either way, water evaporation may fool the thermostat, but not the human body. Bottom line, no energy is removed.
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....1000 Btu/lb of sensible cooling, and more from the cool basement floor.

Not if it's removed by an AC.

Sort of... 70 F water feels a lot cooler than 70 F air.

No. It's decreased.

Yes, evaporation slows down.

No.
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snipped-for-privacy@ece.villanova.edu wrote:

Which releases as much heat as it cooled in the first place, so why not just cool with the AC?

At a cost.

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

The statement above said nothing about 1000 Btu/lb. it was about evaporation of water from the floor.

Yes, but we are talking evaporation only. Of course A/C cools the house, that exactly what it was designed to do...
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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1
On Sun, 31 Jul 2005 21:40:51 -0400, "CL (dnoyeB) Gilbert"

Hell, if the basement is a swamp, why not turn it into a swamp cooler?
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-john
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snipped-for-privacy@ece.villanova.edu wrote:

I doubt it. By your reasoning then, a unit running with an indoor wb of 100 will run more efficiently than the same system at 60 indoor wb.
While the capacity will have increased because of the increased mass flow, the instantaneous EER will have dropped. The reason that a two speed compressor will run more efficiently in low speed (or unloaded) than in high is not because of the higher SST that ensues, but because wrt low speed the condenser coil is grossly oversized. In your example above however, you haven't changed the relative condenser coil size, and since you did not, the head pressure will run higher, not lower; net efficiency will drop.
hvacrmedic
like using a larger

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RP wrote:

The Carnot efficiency (ideal) of heat transfer processes increase with decreasing temperature differential between cooled media and the reservoir media. Surely you realize that increased load isn't equivalent to increased media temp. And we also have to remember that the typical resi system is far from being Carnot's ideal heat pump.
I'll grant that within a narrow range a higher indoor temp "can" result in a higher efficiency on a "real" system over that range, that is, until the temp reaches a value at which the efficiency curve peaks. The problem with "real" systems is that as head pressure rises the systems become less and less ideal, and can even begin to cease cooling altogether at some arbitrarily high indoor temp. People who actually work on systems in such extremes, such as in industrial applications, don't need Carnot for this lesson. Carnot is still involved however, if applied correctly to all of changes that occur to the system throughout the range of temperature values encountered. Much too deep of a discussion for this forum, and in any case, it can be found in books on the subject :)
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