Cycle of an air conditioner and power consumed

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Discussion Overview

The discussion revolves around the power consumption and thermodynamic principles related to a 9,000 BTU air conditioner. Participants explore the relationship between BTU ratings, electrical power consumption, and the thermodynamic cycle involved in air conditioning systems.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the stated power of 1.2 kW accurately reflects real power consumption due to the inductive nature of air conditioner motors and their power factor.
  • Another participant seeks clarification on the meaning of BTU in relation to thermodynamic cycles, specifically asking how it relates to heat transfer in the system.
  • Some participants assert that BTU is a measure of heat, not electrical energy, and inquire if 9,000 BTU corresponds to approximately 2.637 kWh of electrical energy consumed in one hour of operation.
  • There is a suggestion that the 1.2 kW rating may refer to volt-amperes rather than true power, and participants discuss the importance of checking the nameplate for actual current draw during normal operation.
  • One participant mentions the coefficient of performance (COP) of the air conditioner, suggesting that it can provide more cooling output than the electrical input due to its function of moving heat rather than generating it.
  • Another participant raises the question of applying the first law of thermodynamics to relate the cooling effect to the mechanical work done by the compressor, although they acknowledge the complexity of this relationship.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of BTU and its implications for power consumption. There is no consensus on the exact relationship between the cooling output and the input power, as well as the application of thermodynamic principles to the air conditioning cycle.

Contextual Notes

Participants note that the BTU rating may represent an ideal condition and that actual performance can vary based on several factors, including the age of the unit and its operational efficiency. The discussion highlights the complexity of relating mechanical work to heat transfer in air conditioning systems.

Delta2
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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.
 
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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.
 
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Google is your friend:

1624968000962.png


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.
 
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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?
 
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).
 
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...
 
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Lnewqban said:
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
russ_watters said:
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?
 
Delta2 said:
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.
 

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