Mowing How much horse power is sufficient for A/C?

[Redlands Okie]

If your mowing a lot consider having the windows tinted. Makes a big difference on the cooling.

 

[skipmarcy]

I learned many years ago when doing my apprenticeship at Cadillac that they engineered a/c systems according to glass surface area. I also learned that the old Fridgidaire A6 compressors required 12 hp to operate within proper head pressure range.

 

[marchanna]

I think in general, it's a non-issue. If you look at a common window a/c unit the conversion of electrical energy to mechanical energy it works out to 2.4hp. I don't think a tractor or car a/c is going to even be in the neighbourhood of those power requirements. So I officially retract my earlier guesstimate of 5hp. I think i might just buy an A/C unit for my tractor.

 

[shui5612]

On a side note,
I may be wrong on this but...
I don't think it's fair comparing the household ACs as equivalent to car ACs. Yes a window unit uses about 1300-1500W which is 2.some HP, but don't forget it is also running on 110VAC, this reduces the amp draw when compared to the same unit that would have used 12VDC

A car or tractor unit is mostly belt driven, means there is an inherent loss in the belt known as slip and energy that gets lost in heat buildup.

I've disassembled one AC compressor off a tractor and it was pretty much like an 8cylinder orbital engine... it takes a lot of power to "compress" fluid.

Seeing how its belt driven then it is probably engine RPM dependent too. So while running it on idle takes up a percentage of power (I would say a higher percentage as the engine isn't producing a lot of hp at idle yet the ac has a minimum demand of x hp to spin). At higher RPM the percentage of power lost is decreased due to the engine making more power and the compressor only needing abit more power to spin faster (most likely just an increase in friction).

A home AC runs on a different kind of power, and the motor inside the unit spins at a fixed RPM and the coil, condensers, ac pumps are all optimized for it.
The only thing that changes from low to high is the fan speed not the motor speed.

Seeing how a car or tractor AC doesn't run at a constant speed, the AC was designed for a variety of changing RPMs, meaning it could be overpowered in order to be able to sufficiently cool the cabin at idle or high idle RPM.

Also we can't forget that with the AC there is also a couple other components that drain power too. Such as the fans, sensors, etc which draw electrical current from the alternator, therefore it is easy to assume that the combination of everything draws around 4HP.

And to be fair, we are all arguing that the AC takes up anywhere from 2.5 to 6HP and at this point, it shouldn't matter all that much since if it draws 4HP average, will someone even feel an increase or decrease of 1HP while mowing?

@OP. Look at what the mower deck recommends in terms of power, I suggest stay in the 60-75% minimum of the range (I.e. the mower says anywhere from 10 to 25HP, I'd recommend atleast having 16HP while 20HP would be ideal, this will optimize cut speed, then take into account a 4HP AC power loss and a 1.5-2HP electrical loss (headlights, flashers, radio, etc) transmission loss and then add that up. Will you be close to your 33hp engine capacity? If so get the higher up engine and your engine will work ever so slightly less, meaning potentially less cab noise, less consumption and less wear on all of the components.

 

[Gary Fowler]

As most of you know, switching on the AC in your car will briefly stall the engine a bit until the computer compensates for the additional load. What that load is, I am not going to discuss. HP being HP, with my tractor at idle, switching on the AC doesn't seem to affect the engine at all. RPM doesn't seem to change and no load up can be detected by the engine sound. My tractor has a 70 HP engine but it sure isn't producing that much at idle.

With all that being said, I don't think the OP will notice the HP drop from his tractor at all. I don't see a 33 Engine HP tractor using a 60" mower being in any kind of load from the mower, HVAC or alternator. Go with the tractor that you feel most comfortable with in price and comfort whether it be the small one or larger one.

 

[shui5612]

As most of you know, switching on the AC in your car will briefly stall the engine a bit until the computer compensates for the additional load. What that load is, I am not going to discuss. HP being HP, with my tractor at idle, switching on the AC doesn't seem to affect the engine at all. RPM doesn't seem to change and no load up can be detected by the engine sound. My tractor has a 70 HP engine but it sure isn't producing that much at idle.

That is kind of ironic because I have a 115HP tractor and when I switch the AC on, I hear a slight noise and the tach goes down by a blonde one. If in idling at 800RPM, switching on the AC brings it down to maybe 770RPM. While if I turn it back off but leave the fan on, it jumps back up to 800.

Is this a noticeable power loss? Absolutely not. But when you only have a limited amount of HP, every bit counts.

Now do I personally think that OP will notice a difference with the AC on or off? Maybe very slightly.

But I personally would get the bigger HP tractor due to better hydraulic pumps, bigger loader and 3PH capacities and it will have more room for expansion than the smaller unit.

Today it's a 60 inch MMM but tomorrow it's an 84inch brush cutter in the rear..

OP has not mentioned the price difference between the two, but if it's only a thousand $ more and it's a tractor with more options (I.e. more hyd outputs, larger tires,etc ), why wonder if you'll have enough power for x or y when you can be confident about your machine, while also having the better resale down the line...

Will OP be OK with the 33hp model? Most likely, but for all the times OP will have to drive a tiny bit slower or have issues going through a patch of grass, they will most likely would regret not getting the higher HP model.

If you have all the time in the world then you can use a 20 inch 5HP gas mower, but since you only want to spend the least amount of time on the field then the bigger, comfier option is probably the right choice.

Bigger engine, maybe a bigger mower, even less time spent on the field.

Just my 0.02$

 

[marchanna]

On a side note,
I may be wrong on this but...
I don't think it's fair comparing the household ACs as equivalent to car ACs. Yes a window unit uses about 1300-1500W which is 2.some HP, but don't forget it is also running on 110VAC, this reduces the amp draw when compared to the same unit that would have used 12VDC

A car or tractor unit is mostly belt driven, means there is an inherent loss in the belt known as slip and energy that gets lost in heat buildup.

I've disassembled one AC compressor off a tractor and it was pretty much like an 8cylinder orbital engine... it takes a lot of power to "compress" fluid.

Seeing how its belt driven then it is probably engine RPM dependent too. So while running it on idle takes up a percentage of power (I would say a higher percentage as the engine isn't producing a lot of hp at idle yet the ac has a minimum demand of x hp to spin). At higher RPM the percentage of power lost is decreased due to the engine making more power and the compressor only needing abit more power to spin faster (most likely just an increase in friction).

A home AC runs on a different kind of power, and the motor inside the unit spins at a fixed RPM and the coil, condensers, ac pumps are all optimized for it.
The only thing that changes from low to high is the fan speed not the motor speed.

Seeing how a car or tractor AC doesn't run at a constant speed, the AC was designed for a variety of changing RPMs, meaning it could be overpowered in order to be able to sufficiently cool the cabin at idle or high idle RPM.

Also we can't forget that with the AC there is also a couple other components that drain power too. Such as the fans, sensors, etc which draw electrical current from the alternator, therefore it is easy to assume that the combination of everything draws around 4HP.

And to be fair, we are all arguing that the AC takes up anywhere from 2.5 to 6HP and at this point, it shouldn't matter all that much since if it draws 4HP average, will someone even feel an increase or decrease of 1HP while mowing?

@OP. Look at what the mower deck recommends in terms of power, I suggest stay in the 60-75% minimum of the range (I.e. the mower says anywhere from 10 to 25HP, I'd recommend atleast having 16HP while 20HP would be ideal, this will optimize cut speed, then take into account a 4HP AC power loss and a 1.5-2HP electrical loss (headlights, flashers, radio, etc) transmission loss and then add that up. Will you be close to your 33hp engine capacity? If so get the higher up engine and your engine will work ever so slightly less, meaning potentially less cab noise, less consumption and less wear on all of the components.

I understand your point, however in an "ideal scenario" whether it's mechanical energy from the engine or 110vac the same amount of energy is required to transfer "x" number of BTU's. So let's throw out an absolutely ridiculous efficiency loss on the mechanical unit like 50%, and assuming the 110vac counterpart is 100% efficient and it is consuming 100% of the line load 1,800watts, that mean the absolute power draw the mechanical counterpart would be 3.6hp. As an additional note, that other article cited above, indicated that the average vehicle A/C draws 400watts, so I do think now that even 4hp is an significant over-estimation.

 

[shui5612]

I understand your point, however in an "ideal scenario" whether it's mechanical energy from the engine or 110vac the same amount of energy is required to transfer "x" number of BTU's. So let's throw out an absolutely ridiculous efficiency loss on the mechanical unit like 50%, and assuming the 110vac counterpart is 100% efficient and it is consuming 100% of the line load 1,800watts, that mean the absolute power draw the mechanical counterpart would be 3.6hp. As an additional note, that other article cited above, indicated that the average vehicle A/C draws 400watts, so I do think now that even 4hp is an significant over-estimation.

I have looked up online and the general consensus is that a cars AC draws anywhere from 3kw on smaller cars to 12-15kw on large yukons. With the majority running around 5-6HP.
They are significantly overpowered as compared to a house AC as they cool a fairly small volume but VERY quickly and cars heat up very quickly too.

Once you turn off your car and let it sit in the sun for 10 minutes, think of how hot it gets in there. While driving the AC needs to combat the fact that the outdoor air temperature is high, potentially high humidity and that it still manages to cool the car down to around 16C for the lowest setting or say a comfortable 20C.
How fast does your car cool down? 5minutes? 10? It goes from essentially 120F down to 60F in 10 mins let's say while a house unit takes an hour or two to bring the temperature down from 68 to 65f.

Lastly, the post quoted to have an AC run being 4-500 W sounds like they just took the load of the FANS blowing air. If we take the 3.6HP that you stated the mechanical counterpart consumes and add the fans and loses from the fans blowing (and the alternator which is a giant loss of energy that simply becomes heat) the total would be close to 4HP as per my original post...

Many sources claim a cars AC impact on HP has many variables yet the general small size car is 4hp or 3kw, while a tractor cab is smaller than a car it has way more windows that cause a greenhouse effect, almost no insulation , and many leaks ( where all of the shifter, knobs, hyd outlet levers exit from).


Edit, according to your math of 1800w at 100% efficiency, we're looking at 2.41HP
And 50% efficiency would mean 4.83HP for the mechanical counterpart.
Now let's reduce the efficiency on the electric one and increase it on the mechanical one, your numbers will hover in the mid to high 3hp ratings. Plus other factors, still the same 4HP. My old tractor (deutz allis 7085) had the exact same compressor as an 80s peterbuilt truck. Same model numbers same manufacturer.

 

[buickanddeere]

A properly maintained tractor will not injest dust. Nor will it loose power to any noticeable level for thousands of hours of use. I really wonder where people come up with some of this crap.

I agree 100%

 

[buickanddeere]

No offense to Jeff....but I agree...I hear some statements on here that are made that people just DO NOT need to worry about.....and 1 huge one is a diesel engine loosing horsepower.

I am also having a hard time buying (although I can't back it up) that a small tractor A/C uses 4 diesel horsepower to run.

If we knew the btu´ , we could ballpark the HP within a few percent .

 

[buickanddeere]

Here is a ball park number . The numbers sound about right for all that glass and heat from the transmission . Tractor Cabs and Cab Enclosures - AIR CONDITIONING - REGULAR DUTY - ENGINE COMPRESSOR DRIVEN Sims Cab Depot

 

[Texasmark]

As guys get older, they turn up the cab radio volume. This sucks more power off the engine. Instead, turn off the rap music and get an 84" mower. This cuts down on mowing time which results in less suds cooldown after the job is done. Besides, a bandana and a bucket off cool water to soak it in is less sissy.

1 HP is 746 watts. If you had a 1 hp boom boom box in that tractor turned up to 1 hp, if it would go that high, I guarantee you, you wouldn't be inside the cab! The OEM radio is more like 5 watts per channel.

 

[joeu235]

Are you buying the tractor for commercial use or for personal use? If it's personal use and it gets too hot, just mow the grass some other time. If it's commercial use, get something bigger because lost income is worse than some incremental increase in the purchase cost.

 

[TheMan419]

Are you buying the tractor for commercial use or for personal use? If it's personal use and it gets too hot, just mow the grass some other time. If it's commercial use, get something bigger because lost income is worse than some incremental increase in the purchase cost.

Except sometimes in personal use that is the time you have to cut the grass. It is the weekend or the one night where the family does not have an activity etc. Sometimes you just got to get stuff done. That means (in relation to OP's question) if you get the 33 hp unit either sweating it out or going a bit slower.

Of course the A/C is going to draw some power. Will it be enough for OP to notice? Depends on what he is doing with the machine. I was told no way no how would a 5 foot tiller work behind my 25 hp tractor. Guess what? Works like a charm. Would I want to run that commercially? Heck no. Takes too long. But it got done the job I needed to get done. Sure it took a while but I got her done.

My point is that we get hung up on OMG we need a huge tractor so that we can do the job FAST FAST FAST. Well sometimes just getting the job done is what counts.

Anyway off my rant box. Sorry did not mean to rant at you

 

[bdog]

My mini excavator has 23.3 hp and a cab with AC. I notice no difference in performance with the AC on or off. I ain’t pulling a plow with it though.

 

[shui5612]

My mini excavator has 23.3 hp and a cab with AC. I notice no difference in performance with the AC on or off. I ain’t pulling a plow with it though.

A mini ex works on mostly hydraulic fluid, so gpm and psi.

A loss in engine HP will result in a slight loss of GPM which you probably wouldn't feel, plus if there's restrictions and whatnot the hyd hose will heat up more, etc. Same thing goes when you lose some rpm, it will turn a hair slower. Yet it will probably turn the same hair slower as when it's a hot summer day and the hyd fluid is HOT

 

[RickB]

A mini ex works on mostly hydraulic fluid, so gpm and psi.

A loss in engine HP will result in a slight loss of GPM which you probably wouldn't feel, plus if there's restrictions and whatnot the hyd hose will heat up more, etc. Same thing goes when you lose some rpm, it will turn a hair slower. Yet it will probably turn the same hair slower as when it's a hot summer day and the hyd fluid is HOT

Give your keyboard an Imodium.

 

[chim]

............. it takes a lot of power to "compress" fluid.....................

You're correct with that statement, but it's gas that's being compressed.

No compressors are 100 percent efficient. There are losses whether running with an electric motor or with a belt. I'm sure a genuine engineer could give information on that.

 

[Rock Crawler]

Last time I checked, fluid can not compress. It can accept pressure, but it does not compress. Gasses will compress. They will change in volume based on applied pressures. Fluids maintain the same volume no matter the applied pressure.

EDIT: What I was taught 30 years ago in aircraft school is wrong. You can slightly compress fluid with a huge enough force:

Can you compress hydraulic fluid?

Contrary to popular belief, liquids are compressible. For hydraulic oil, a rule of thumb is that it will compress 0.5% for every 1000 psi that is exerted. However, for most applications this side of a flight simulator, we can consider it incompressible

 

[Sawyer Rob]

I think mowing heavy grass in 100* heat with the AC blasting with a small tractor, I would be more worried about over heating the tractor than running out of power...

SR