69 Buick Riviera 430 ci dyno 7hp/9ftlbs less with A6 compressor using R12 engaged @1500 RPM.
How much HP does the A / C actually draw?
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Originally Posted By: brianl703
Originally Posted By: CaspianM
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
The air conditioning is not producing anything, it's moving heat from one place to another.
In the real world, air conditioners move much more than one BTU of heat for each BTU of energy used.
Yes it takes more work than it can produce. Again those are the base design numbers and mechanical losses are added to come up with final size. Only the manufacturer knows what the inefficies are based on experimental valus.
Originally Posted By: CaspianM
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
The air conditioning is not producing anything, it's moving heat from one place to another.
In the real world, air conditioners move much more than one BTU of heat for each BTU of energy used.
Yes it takes more work than it can produce. Again those are the base design numbers and mechanical losses are added to come up with final size. Only the manufacturer knows what the inefficies are based on experimental valus.
Originally Posted By: meep
Originally Posted By: CaspianM
Originally Posted By: brianl703
Originally Posted By: CaspianM
But ball park numbers are:
1 ton cooling power =12k btu/h
If it is a two tone unit then it draws 24k btu/h of energy.
That's not quite right. There is no properly functioning AC unit that is so inefficient that it needs one BTU of energy to move a BTU of energy.
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
1 ton cooling = 12k BTU/hr | units conversion
one BTU/hr = 0.293 watts of heat | unit conversion (not power consumed)
one ton cooling = 3.516kw of heat | unit conversion (not power consumed)
in generic numbers, 1 ton household A/C requires 1.4 kw/hr, which equates to ~2+hp in an efficient 1 ton system...
Which thus suggests that vehicle A/C is grossly inefficient when engine-driven compressor is used. maybe the electric-pumped A/Cs can optinmize for greater efficiency...
Are they really installing electric compressors in cars as posted above? I thought electrical systems were going to 36 or 48 volts in order to support that, which I haven't yet seen? hello 300+ amp alternator...
I posted 4.7 hp needed for 2 ton unit hence 2.35 hp is needed for 1 ton.
Originally Posted By: CaspianM
Originally Posted By: brianl703
Originally Posted By: CaspianM
But ball park numbers are:
1 ton cooling power =12k btu/h
If it is a two tone unit then it draws 24k btu/h of energy.
That's not quite right. There is no properly functioning AC unit that is so inefficient that it needs one BTU of energy to move a BTU of energy.
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
1 ton cooling = 12k BTU/hr | units conversion
one BTU/hr = 0.293 watts of heat | unit conversion (not power consumed)
one ton cooling = 3.516kw of heat | unit conversion (not power consumed)
in generic numbers, 1 ton household A/C requires 1.4 kw/hr, which equates to ~2+hp in an efficient 1 ton system...
Which thus suggests that vehicle A/C is grossly inefficient when engine-driven compressor is used. maybe the electric-pumped A/Cs can optinmize for greater efficiency...
Are they really installing electric compressors in cars as posted above? I thought electrical systems were going to 36 or 48 volts in order to support that, which I haven't yet seen? hello 300+ amp alternator...
I posted 4.7 hp needed for 2 ton unit hence 2.35 hp is needed for 1 ton.
Originally Posted By: brianl703
Originally Posted By: CaspianM
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
In the real world, air conditioners move much more than one BTU of heat for each BTU of energy used.
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
Originally Posted By: CaspianM
It actually is the other way around. If it take 1 unit of work to produce 1 unit of work then it is 100% efficient. Eff=output/input.
I just posted theoretical values and also said that mechanical losses such as internal loss and belt are extra which reduces eff of the unit.
In the real world, air conditioners move much more than one BTU of heat for each BTU of energy used.
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
An automotive A/C system definitely does not draw 25 HP, its more like 2 or 3. If the engine made 100 lb/ft of torque (which it absolutely does not, 25 lb/ft, about 4 HP, would even be optimistic) at idle it would only be making about 15 HP and the engine would not run.
The HP loss varies with speed and temperature.
But 4-6 HP loss is a good range to expect.
With a small engine, this is proportionately more of it's total power than a large powerful engine, so we feel it more.
If it takes 25-30 HP to propel a small car at highway speeds, then the extra 5 HP loss or so is more evident.
But 4-6 HP loss is a good range to expect.
With a small engine, this is proportionately more of it's total power than a large powerful engine, so we feel it more.
If it takes 25-30 HP to propel a small car at highway speeds, then the extra 5 HP loss or so is more evident.
I just added a V-Tech sticker to my car (good for 15whp on Honda/Acura and 10whp on everything else except Camaros, in which case it's
-50whp)
Problem solved
-50whp)
Problem solved
Last edited:
Originally Posted By: KrisZ
I just added a V-Tech sticker to my car (good for 15whp on Honda/Acura and 10whp on everything else except Camaros, in which case it's
-50whp)
Problem solved
Yes, that raises the impression ratio. I'm impressed.
I just added a V-Tech sticker to my car (good for 15whp on Honda/Acura and 10whp on everything else except Camaros, in which case it's
-50whp)
Problem solved
Yes, that raises the impression ratio. I'm impressed.
Oh, and by the way. It's VTEC, not v-tech. Those stickers only provide 5 whp.
Originally Posted By: CaspianM
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
The heat energy already exists long before we've applied any power to the AC unit. All the AC unit is doing is moving that heat energy from one place to another. It's not producing more heat than the energy input; it's taking that heat from the evaporator coil, which is why it gets very cold, and moving it to the condenser coil, which is why that gets very hot.
In the case of a heatpump, the amount of BTU output drops as the outdoor temperature does, because there is less heat for the system to move. At some point, the temperature has dropped so much that the heatpump can no longer work effectively and the resistance heating (aka emergency heat) has to be used. This is why heatpumps aren't used in the northern states.
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
The heat energy already exists long before we've applied any power to the AC unit. All the AC unit is doing is moving that heat energy from one place to another. It's not producing more heat than the energy input; it's taking that heat from the evaporator coil, which is why it gets very cold, and moving it to the condenser coil, which is why that gets very hot.
In the case of a heatpump, the amount of BTU output drops as the outdoor temperature does, because there is less heat for the system to move. At some point, the temperature has dropped so much that the heatpump can no longer work effectively and the resistance heating (aka emergency heat) has to be used. This is why heatpumps aren't used in the northern states.
Originally Posted By: brianl703
Originally Posted By: CaspianM
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
The heat energy already exists long before we've applied any power to the AC unit. All the AC unit is doing is moving that heat energy from one place to another. It's not producing more heat than the energy input; it's taking that heat from the evaporator coil, which is why it gets very cold, and moving it to the condenser coil, which is why that gets very hot.
In the case of a heatpump, the amount of BTU output drops as the outdoor temperature does, because there is less heat for the system to move. At some point, the temperature has dropped so much that the heatpump can no longer work effectively and the resistance heating (aka emergency heat) has to be used. This is why heatpumps aren't used in the northern states.
It is true that AC unit removes the heat from inside and dump it outside but in the process refrigerant goes thru two cycles and work needs to be done on it to get the phase changed. I stand behind what I said.
Enery cannot be increased nor destroyed. It is always converted. The total work to get a job done is always greater than output due to either mechanical losses i.e. thermal loss.
"First law of thermodynamics:
Energy can be neither created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system."
Originally Posted By: CaspianM
Can you explain? I am at loss!
It takes more than what it produces due to losses(inefficiecies) air conditioners or what have you no exceptions.
The heat energy already exists long before we've applied any power to the AC unit. All the AC unit is doing is moving that heat energy from one place to another. It's not producing more heat than the energy input; it's taking that heat from the evaporator coil, which is why it gets very cold, and moving it to the condenser coil, which is why that gets very hot.
In the case of a heatpump, the amount of BTU output drops as the outdoor temperature does, because there is less heat for the system to move. At some point, the temperature has dropped so much that the heatpump can no longer work effectively and the resistance heating (aka emergency heat) has to be used. This is why heatpumps aren't used in the northern states.
It is true that AC unit removes the heat from inside and dump it outside but in the process refrigerant goes thru two cycles and work needs to be done on it to get the phase changed. I stand behind what I said.
Enery cannot be increased nor destroyed. It is always converted. The total work to get a job done is always greater than output due to either mechanical losses i.e. thermal loss.
"First law of thermodynamics:
Energy can be neither created nor destroyed. It can only change forms.
In any process in an isolated system, the total energy remains the same.
For a thermodynamic cycle the net heat supplied to the system equals the net work done by the system."
That does not change the fact that a typical AC system moves more than 1BTU of heat energy per BTU of mechanical energy input. If this weren't so, nobody would bother heating their houses with heatpumps, they could just use 100% efficient electrical resistance heating which costs a lot less to manufacture than the parts for a heatpump.
A heat pump is a refrigeration system. Only thing that is reversed are the position of the condenser and evaporator coils.
Is it your contention that an AC system cannot move more than 1BTU of heat energy per 1BTU of energy input?
If so, that is demonstrably false.
If not, what exactly is it that you disagree with me about?
Is it your contention that an AC system cannot move more than 1BTU of heat energy per 1BTU of energy input?
If so, that is demonstrably false.
If not, what exactly is it that you disagree with me about?
What you are missing here is the total energy used.
In heat pump the supplied electrical energy is only part of the total energy. The rest is outside in form of heat.
The difference between systems is like flow of water.
In cooling system you are forcing the water in upward whereas in heat pump is downward therefore less energy is needed as the gravity is supplying the rest of energy to move the water.
In all the total energy needed to conver energy from one form to another is grater than outputed energy.
In heat pump the supplied electrical energy is only part of the total energy. The rest is outside in form of heat.
The difference between systems is like flow of water.
In cooling system you are forcing the water in upward whereas in heat pump is downward therefore less energy is needed as the gravity is supplying the rest of energy to move the water.
In all the total energy needed to conver energy from one form to another is grater than outputed energy.
Quote:
If it is a two tone unit then it draws 24k btu/h of energy.
That's what I disagree with. I can only assume that you meant that it actually consumes 24kbtu/h of energy to turn that compressor--if that's not right, then please correct me.
The measured power consumption of my 2-ton unit with an outdoor temp of 78F is 1.8kW. 1.8kwh=6146BTU/h. So for my particular central air unit, it takes only 6146BTU/h to move 24,000BTU/h. 6146BTU/h equates to 2.41HP.
(Right now, with an outdoor temp of 96F, the power consumption is 9.9A@235V=2326W=7942BTU/h=3.12HP).
If it is a two tone unit then it draws 24k btu/h of energy.
That's what I disagree with. I can only assume that you meant that it actually consumes 24kbtu/h of energy to turn that compressor--if that's not right, then please correct me.
The measured power consumption of my 2-ton unit with an outdoor temp of 78F is 1.8kW. 1.8kwh=6146BTU/h. So for my particular central air unit, it takes only 6146BTU/h to move 24,000BTU/h. 6146BTU/h equates to 2.41HP.
(Right now, with an outdoor temp of 96F, the power consumption is 9.9A@235V=2326W=7942BTU/h=3.12HP).
I don't disagree with your statement, if that's what you intended to state, that someone could design an AC system so inefficient that it uses as much power as you state. However, it is possible to design better and, given fuel costs, it behooves the engineer to do so.
I'm not sure about the amounts of the draw, but the AC in the Toyota/Lex hybrids is interesting. It's a purely electrically driven system and has no direct connection to the gas engine at all. It sucks juice from the traction battery, which powers a variable speed compressor which runs only when needed (of course) and when on, runs only as fast as necessary to provide the desired cooling. Of course, there's no free lunch. When the AC is really working, the battery clearly drains faster, and mileage will drop some (how much depends but it doesn't seem to change by more than about one mpg).
From an operational (driver's) perspective, what's really nice is how you simply never, ever feel any of the grab-and-fade, even in the Prius with its small I-4. And it always provides max cold air on demand, even if you're sitting in traffic just idling.
Drawbacks? The systems are all automatic only, with no manual option for those who'd prefer it.
From an operational (driver's) perspective, what's really nice is how you simply never, ever feel any of the grab-and-fade, even in the Prius with its small I-4. And it always provides max cold air on demand, even if you're sitting in traffic just idling.
Drawbacks? The systems are all automatic only, with no manual option for those who'd prefer it.
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