A/C cooled water for Air-Water Aftercooler... Doable??
02-15-2002, 11:17 AM
#11
Registered User
Thread Starter
Join Date: Oct 2000
Location: Santa Cruz, CA
Posts: 1,664
Likes: 0
Received 0 Likes
on
0 Posts
UL,
It is indeed an assumption on my part that the AC is not a drag on the engine when the engine is operating at high loads.
If it turns out that it is a drag then that changes everything... I dont know if a cooler charge can compensate for a 20 HP drag.
No doubt that this setup would generate more heat from the engine than otherwise... One way to see the possible effect would be to see how coolant temp behaves at the track with and without the AC running in a SC'd car. Thats something I can record on my laptop and may give it a try at SoW.
Hopefully someone here can come up with thermal capacity numbers for the AC system. But, I dont think the goal of the AC system is to remove all the heat from the intake charge to bring it to ambient temps. I only see it as a supplemental cooling in addition to the Aftercooler radiator, that may have the combined ability to take the charge temp to or below ambient.
At this point i think we need some numbers...
It is indeed an assumption on my part that the AC is not a drag on the engine when the engine is operating at high loads.
If it turns out that it is a drag then that changes everything... I dont know if a cooler charge can compensate for a 20 HP drag.
No doubt that this setup would generate more heat from the engine than otherwise... One way to see the possible effect would be to see how coolant temp behaves at the track with and without the AC running in a SC'd car. Thats something I can record on my laptop and may give it a try at SoW.
Hopefully someone here can come up with thermal capacity numbers for the AC system. But, I dont think the goal of the AC system is to remove all the heat from the intake charge to bring it to ambient temps. I only see it as a supplemental cooling in addition to the Aftercooler radiator, that may have the combined ability to take the charge temp to or below ambient.
At this point i think we need some numbers...
02-15-2002, 11:21 AM
#12
Registered User
Join Date: Feb 2001
Location: El Sobrante
Posts: 444
Likes: 0
Received 0 Likes
on
0 Posts
For drag applications and street starts, you could use the AC system to cool your reservoir to below freezing (using some antifreeze mixture) then disable the AC during high load. Depending on the size of reservoir, and heat of the intake charge, this could work for a while. For long track sessions, it wouldn't be practical if there's a large parasitic loss due to AC.
02-15-2002, 01:23 PM
#13
Registered User
Dave,
According to the FSM, the stock A/C system has a cooling capacity of 13,170 BTU/hour, or 3320 Kcal/hour
With the stock blower on full speed (15,200 ft^3/hour or 430 m^3/hour) this is enough to lower air temps by 30 degrees at 20% humidity, or 16 degrees at 80% humidity.
Hope that gets you started.
UL
According to the FSM, the stock A/C system has a cooling capacity of 13,170 BTU/hour, or 3320 Kcal/hour
With the stock blower on full speed (15,200 ft^3/hour or 430 m^3/hour) this is enough to lower air temps by 30 degrees at 20% humidity, or 16 degrees at 80% humidity.
Hope that gets you started.
UL
02-15-2002, 01:57 PM
#14
Registered User
Dave,
I just ran some rough calcs, someone will need to check my work, but:
If you are circulating a total coolant capacity of about 5 kg (1.5 gallons or so) of water, you would have the ability to reduce the temperature of that reserve by about 11 degrees C/minute.
The numbers are as follows: 3320 Kcal/hour = 55.3 Kcal/min
Specific heat of unpressurized water = 1 Kcal/kgC
Thus, 55.3/5 = 11.6 C/minute
Keep in mind that the amount of water isn't too important for this calc since less water will run at a higher temp to begin with, but you'll be able to take out more heat, so you'll end up at a similar temp. More water is good as a thermal reserve though and you don't want temps to reach boiling.
So, if you were sitting at the strip you could really chill the water down in 5-6 minutes (although keep in mind that heat is still being added while the car is running till its at equilibrium, so the actual drop may be less, need to figure out the input heat as the temp calc assumes equilibrium state). It would probably be easier to ice the reservoir.
In terms of how beneficial it would be on the track, not much. You'd be able to reduce temps in the reservoir by about 0.2 C/second. So, a few seconds under braking, or whatever wouldn't get you much reduction.
But again, check my numbers. I'm no thermodynamicist.
UL
I just ran some rough calcs, someone will need to check my work, but:
If you are circulating a total coolant capacity of about 5 kg (1.5 gallons or so) of water, you would have the ability to reduce the temperature of that reserve by about 11 degrees C/minute.
The numbers are as follows: 3320 Kcal/hour = 55.3 Kcal/min
Specific heat of unpressurized water = 1 Kcal/kgC
Thus, 55.3/5 = 11.6 C/minute
Keep in mind that the amount of water isn't too important for this calc since less water will run at a higher temp to begin with, but you'll be able to take out more heat, so you'll end up at a similar temp. More water is good as a thermal reserve though and you don't want temps to reach boiling.
So, if you were sitting at the strip you could really chill the water down in 5-6 minutes (although keep in mind that heat is still being added while the car is running till its at equilibrium, so the actual drop may be less, need to figure out the input heat as the temp calc assumes equilibrium state). It would probably be easier to ice the reservoir.
In terms of how beneficial it would be on the track, not much. You'd be able to reduce temps in the reservoir by about 0.2 C/second. So, a few seconds under braking, or whatever wouldn't get you much reduction.
But again, check my numbers. I'm no thermodynamicist.
UL
02-15-2002, 03:12 PM
#18
Registered User
Originally posted by RT
UL, what are you using for the Delta T's in the calcs? (the A/C to water and the water to charge air)
UL, what are you using for the Delta T's in the calcs? (the A/C to water and the water to charge air)
Keep in mind too fellows that even operating at 100% efficiency it takes almost 6 hp to operate a system with the cooling capacity of our AC system. Considering the real efficiency is probably closer to 1/3 that and you see the issue. According to some more rough calcs, you could reduce the temp of the intake air from the supercharger by about 7-8 degrees if you did a direct cooling system. Good for 1-2% gains in power or 3-6 hp on Dave's car. Wouldn't even make up for the power to drive the A/C which is why a storage system (as Dave has proposed) would probably be better.
UL
02-15-2002, 03:15 PM
#19
Registered User
Thread Starter
Join Date: Oct 2000
Location: Santa Cruz, CA
Posts: 1,664
Likes: 0
Received 0 Likes
on
0 Posts
jschmidt,
You bring up an interesting point about latentcy. I had initialy assumed that the stock AC system didnt contained a collector (reseviour for compressed freon) or whatever you call it. However, looking at the AC diagram in the manual shows a canister called the "Receiver/Dryer" at the proper location in the circuit to store precompressed freon. That makes me wonder what kinda of duration you could acheive running off the contents of that canister after the compressor has disengaged. Certainly the DeltaT provided to the charge air would be greater with an AC evaporator as the AfterCooler core. That would also allow you to do away with the water tank, pump and radiator. I would think that to make the system more effective, increase duration, you'd want a larger collector. hmmmm....
As RT says I live for the road track but i also do my fair share of spirited driving... I would imagine that a system that utilizes the AC in some fashion will work significantly better during spirited driving than compared to the track. But i think the most important aspect of the system will be in increasing the duration as you call it.
You bring up an interesting point about latentcy. I had initialy assumed that the stock AC system didnt contained a collector (reseviour for compressed freon) or whatever you call it. However, looking at the AC diagram in the manual shows a canister called the "Receiver/Dryer" at the proper location in the circuit to store precompressed freon. That makes me wonder what kinda of duration you could acheive running off the contents of that canister after the compressor has disengaged. Certainly the DeltaT provided to the charge air would be greater with an AC evaporator as the AfterCooler core. That would also allow you to do away with the water tank, pump and radiator. I would think that to make the system more effective, increase duration, you'd want a larger collector. hmmmm....
As RT says I live for the road track but i also do my fair share of spirited driving... I would imagine that a system that utilizes the AC in some fashion will work significantly better during spirited driving than compared to the track. But i think the most important aspect of the system will be in increasing the duration as you call it.