I Cycle of an air conditioner and power consumed

[Delta2]

I have an air condition that is 9.000 BTU and it states at the external unit that its Power is 1.2KW.

However because I know that an air condition has inductive loads (motors) its power factor is not 1 so I am not sure 1.2KW is the real power consumed.

I am thinking to calculate the power consumed via the number of 9.000BTU (I am not sure what this number is btw). I don't know a lot for Air Conditions. From Thermodynamics 1st law, for the cycle of the air condition it will be

$$Q=W$$

SO how can I calculate the Q per cycle (and thus the energy consumed per cycle) from the 9.000 BTU number.

 

[Delta2]

Ok well I found a BTU to KWh convertor in the web, it turns out that 9000BTU=2.637KWh. If anyone can give any insight on what exactly are the BTU (dont tell me it is just a unit of energy, ok I can infer that, I want to know how it relates to the thermodynamic cycle, is it the amount of heat lost or absorbed by the fluid for example?)how exactly we convert between BTU and KWh is more than welcomed.

 

[Motore]

Google is your friend:

Wikipedia is your friend:
https://en.wikipedia.org/wiki/British_thermal_unit

Many friends can be found in a span of a few minutes on the internet.

 

[Delta2]

Judging by what it is said at wikipedia BTU is for measuring heat not electrical energy.
Let me ask the question I have in the back of my head directly:
Can we say that an air condition that is 9000 BTU, consumes around 2.637KWh of electrical energy when it operates for 1hour?

 

[Lnewqban]

Most likely that value of 1.2 KW means Volt-Amps.
Check for a value of MCA on the nameplate of the unit for the actual amps that the unit withdraws when all motors are normally running (not during start ups).
Multiply that value for the voltage the unit is rated for.
As the compressor cycles, the amps value cycles as well (down to what the blower and other motors use in ventilation mode).

The BTU value is an optimistic estimate of how much heat the unit can move in ideal conditions (between two temperatures).

 

[russ_watters]

1. KW almost always just means kW. (Adding reactive power makes it kVA).
2. Input power is input power.
3. Heat (cooling) output is output. Also, the rating point is generally a challenge condition, not an optimistic one. An optimistic rating point would be arbitrary and worthless.

There are no conversions or other calcs required here except units. So:
4. 9,000 btu/hr is indeed 2.6 kW.

Then you next question might be: how can you do 2.6 kW of cooling with only 1.2 kW of input? Since air conditioners don't create heat, they just move it, they can do that. It's called coefficient of performance. This unit has a COP of 2.2:1, which isn't very good...

 

[Delta2]

Check for a value of MCA on the nameplate of the unit for the actual amps that the unit withdraws when all motors are normally running (not during start ups).

Cant find MCA reading in the plate it just says 1.25KW 220V

how can you do 2.6 kW of cooling with only 1.2 kW of input? Since air conditioners don't create heat, they just move it, they can do that. It's called coefficient of performance. This unit has a COP of 2.2:1, which isn't very good...

The unit is old, bought and installed on September 2004 (brand Bauer, I am sure you never heard it before lol ). Indeed my next question would be that. Cant we invoke the first law of thermodynamics to prove that the cooling done equals the mechanical work done by the compressor?

 

[russ_watters]

Indeed my next question would be that. Cant we invoke the first law of thermodynamics to prove that the cooling done equals the mechanical work done by the compressor?

Right, so, yes you can, but it isn't easy without more info and compressor work doesn't equal heat transfer anyway. There's no heat transfer at the compressor per se, just that work input.

 

[hutchphd]

May I recommend the wikipedia article (which ends by talking about a Carnot Refrigerator):

https://en.wikipedia.org/wiki/Heat_pump_and_refrigeration_cycle