YES AND NO...

Vent temperature is only half the equation, the other half is volume of air coming through the events. If you simply try to match the evap core freezing temperature a given blower speed you won't be happy;most never are.

You need to remove so many BTU's per minute or hour, and if the vehicle is absorbing more BTU's you'll never chill. If you have a stock blower fan control chances are you wont' be happy. If you have a stock condenser set up, stock evaporator, you won't be happy.

So, if you have a stock setup, Ideally you want to increase the volume of air coming through the vents as much as practical by either increasing the total vent area or increasing evap blower output; this will create a higher rate of evaporation in the cockpit.

I love me some wwest. What a great idea.

It is well understood that the greater the difference between the 2 mediums exchanging temperatures the greater will be the transfer efficiency. Second..the LONGER your milk remains in the fridge the closer it will get to the lowest temperature...so, SLOW airflow...

Our problem is that we "feel" better, psychologically, about the operation of the system with that high rush of airflow to the face and upper body.

If the speed of the blower rises so high that it brings the temperature of the evaporator above the highest heat transfer level, 33F, then you are defeating the efficiency of the process.

psychologically?

Nope!

its physio...

You feel better "physiologically" with a greater air movement because of an increase in evaporation of moisture off your body.

Not only that but your skin feels colder too.

http://forums.pelicanparts.com/uploa...1344272458.jpg

"So, if you have a stock setup, Ideally you want to increase the volume of air coming through the vents as much as practical by either increasing the total vent area or increasing evap blower output; this will create a higher rate of evaporation in the cockpit."

One can also improve evaporator capacity of the stock system (i. e. a more fully flooded evaporator) by doing the super heating elsewhere. Friday - I received a report on a modified Carrera A/C system (but with stock blower motor and fan wheel and cleaned, flushed stock evaporator core and condensers) as it passed through Needles, CA. The A/C had to be turned down as it was getting too cold. Engine oil temperature was normal - car has a cage-type external oil cooler without a fan.

Yes, subcooling with greater condenser function (air movement or area) usually works.

Well, that's a yes, maybe NO.

The COLDER the evaporator surfaces are, and longer it takes for the air to flow through the evaporator, the DRYER the exit airflow will become. The DRYER the system airflow is the more rapidly will be the rate of evaporation from your body surfaces.

And the whole idea is to get the cabin temperature down to the point wherein you need no perspiration for body cooling.

And it's at that point wherein cool and dry airflow, especially HIGH VOLUME airflow, becomes more discomforting than otherwise. Most of us then turn the airflow direction elsewhere having already lowered the blower speed. That's why most modern day system's use the reheat/remix technique to moderate (modulate?) the outlet airflow temperature while at the same time getting the greatest level of dehumidification

WAIT!

That's my line....

Wild,Wild, West, Tell you what. I will let you have the last word regardless of how funny it is.

But... not to let you off the hook so easily, on your concept of air movement I'll share my Rennlist response on the concept of deck lid fans, enjoy

Griff

I would venture to guess, depending upon the year of the 911, the avg (varies depending upon the year) liters per second
at 6100 rpms would something like 1335 ls (60 seconds per minute) or 80,100 lm .. per minute.
There are many quotes and charts.
Converted to cfm would be 2828 cfm at 6100 rpms.

The typical 911 condenser is 9"x27.5" of effective area, or 247.5" sq in.
So in a perfect world you might have 2828 cfm pulling across 247 sq in
of condenser at 6100 rpm, and if the correlation between rpm and cfm
was linear it might look something like this:

0 rpm = 0 cfm
1525 rpm = 707 cfm
3050 rpm = 1414 cfm
6100 rpm = 2828 cfm
or ... .46 cfm per rpm

Let's assume at idle, maybe a nominal idle of 850 rpm, the cfm
is equal to 391 cfm (850 x .46). Well use the relationship later on here.

Ideally the largest diameter pancake electric motor puller fan you can mount under the condenser is a 9" nominal. Provided you had a minimum 12vdc and the amps needed, 1 fan pulls 543 cfm under 0 static pressure. However, it is not pulling 543 cfm across the entire condenser:
Effectively 1 fan does not pull 9" of diameter, or 63.6 sq in, across the surface as the fan motor is typically 4.375", or 15 sq in (no fan blades), so the effective surface the fan works on the condenser is 48.6 sq. in.
Let's multiply that by 2 fans for 97" nominal sq in of working area,
or 39% of the condenser area.

Comparing a given surface of the condenser, engine fan at idle vs. electric fan at idle, 391/543, the electric fan is a 38% improvement. But....

Going back to 'at idle', the stock engine cooling fan is pulling 391 cfm across
100% of the condenser surface. Whereas 2 electric fans are pulling 543 cfm across only 39% of the condenser. So, at idle, you are not seeing a 38% improvement with electric fans but rather 38% improvement over only 39% of the total condenser surface. Let's just say for simplicity a 15% improvement at idle using electric fans.

If the electric fan can only pull a maximum of 543 cfm, is it logical that at some point the electric fan could reduce the work done by the engine cooling fan? Logically yes! When the engines cooling fan's cfm exceeds that of the electric fan, that would take place around (543cfm/.46 per rpm) 1180 engine rpms. But wait! ... something else is in play we discussed earlier..
the almost non effective working surface of the electric fan's motor, 15 square inches (x2 fans) 30 square inches is impeding upon the work being done by the engine's fan (or 15/247 or 6% of the engine deck lid condenser is now ineffective because of the electric cooling fan motors).

And, wait... it does get worse...unfortunately:
We assume all cfm's are noted for 'static' pressure. Static pressure in simple terms means there is nothing in front of the fan, no condensers, no deck lid grills, no bugs in the soup. So... above 1180 engine rpms the electric cooling fan's blades become an increase for static pressure (air cannot move as easily past them).

Although car owner 'experience', may feel, or seem or show some improvement when adding electric cooling fans, whether subjective or proven empirically, the reality is that near of just below 1180 rpms,
add on electric cooling fans would only be effective at near idle conditions such as when sitting at traffic lights or in very slow moving (at a crawl) traffic. And, if you were to observe the minutes or hours spent during the course of an average drive while your AC is turned on, that period or percentage of your drive (at or near idle) is probably less than 5% for the average driver.

So, in summary, the idea of adding electric cooling fans under or above the deck lid condenser may sound like a great idea, a simple solution, a less expensive solution, the bottom line is NOPE!

"Yes, subcooling with greater condenser function (air movement or area) usually works."

Stock condensers, evaporator and fans that had a hard life in Houston - the front chin condenser looked like it had been used to plow sand on a beach (cleaned packed, chemically cemented sand out of the fins and flushed to refurbish). Hot high pressure lines going forward converted to 3003 aluminum - 1/2 the weight of standard hose and much smaller in diameter.

http://www.nrel.gov/docs/fy00osti/28960.pdf

Looking at comfort related graphs 4 and 5 it would appear getting the heat out as fast a possible is what counts as far as people's comfort sensations are concerned - so whatever product of air flow and air temperature achieves this best would be the goal. I'll go for maximum air flow through the evaporator until the person is chilled down.

"the reality is that near of just below 1180 rpms,
add on electric cooling fans would only be effective at near idle conditions such as when sitting at traffic lights or in very slow moving (at a crawl) traffic."

Incorporating a triplex pressure switch in place of the required R-134a conversion hi/lo cut-out switch on the compressor output will engage the electric rear deck lid fans only when condenser pressure is at a higher intermediate pressure such as at idle or in slow traffic. Some OEM systems have this or an equivalent set-up.

Maximum airflow does not, in this case, necessarily result in the fastest cabin cooldown.

+1

The heat gain inside the car parked in the sun is huge. We want to be able to cool the cabin as quick as possible. Max airflow thru a thicker and more surface area across the evaporator on new cars can do this.
On an older car, it is a struggle. I usually open the windows first and cool down the interior for the first 1 or 2 miles, then close the windows.

Yes, since the late 80's most systems, even RWD, have a pressure switch dedicated to bringing on extra cooling (fans/speed) if the high side pressure exceeds a certain level.

What would be helpful would be a solar powered ventilation fan system custom configured for a 911 to continually vent it out when parked in the sun. Put the PV panel on the back parcel shelf? I don't like leaving my windows rolled down for various reasons starting with thunderstorms.

The lowering the rear windows slightly in that situation has been common practice, even recommended in most owners manuals, for many years. And don't forget to over-ride the absolute stupidity (NipponDenso idiots at work again) of the system automatically going into recirculate mode in this situation. Drive OUT the HOT atmosphere, cool down the cabin surfaces somewhat first and only then put the system in recirculate for optimum A/C cooling capacity.

But....it WORKS..!!

The bumblebee FLYS.....