COP calculation and monitoring in HVAC applications

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What is COP?

COP stands for Coefficient Of Performance and indicates the efficiency of heating and cooling machines.

The COP is defined by the ratio heat dissipation and electrical power intake. It’s like the efficiency of the machine, but higher than 100%. It could be less than 100% for a machine not working properly.

Why do we need to calculate and monitor COP?

Because in refrigeration cycles, measuring plant performance is important, the higher the COP, the more efficient the machine operates and low performance coefficient generally have negative impact on the machine’s operating cost. Continuous monitoring of results can give a complete picture of plant performance over time.

COP calculation allows:

1. Continuous improvement of the machine
2. React quickly when the COP is deteriorated

Three outside factors that can directly impact the consumption of a chiller or a cooling unit:

1. The load (depends on the usage, AC, cooling, etc…)
2. The outside temperature (and humidity sometimes)
3. The cooling temperature

To do energy savings with the regulation, we have to manage the machine when the outsides factors evolve to have the lower consumption of the machine.

How is COP calculated?

The COP calculation is based on the following formula:

COP = Thermal Power [kW]/Electrical Power [kW]

1.0 Thermal Power Calculation: The calculation of the thermal power of a hydraulic system is based on the mass flow rate, the heat capacity of the medium, and the temperature difference before and after heat dissipation.

For meters providing a volume flow, the mass flow is calculated according to:

Mentioned method is considered as a traditional one in which a flow meter is needed.

2.0 Electrical Power Calculation/Reading:

2.1 Direct: reading it directly from power/energy meter.

2.2 Indirect: calculating it base on: P=√3*V*I*Cosɸ in 3 phases applications

P: Active Power (W)

V: Line Voltage (Volts)

I: Load Current (Amps)

Cosɸ: Power Factor

Example:

If COP=3, 1kW electrical power will produce 3 kW of cooling at the evaporator and 4 kW of heating at the condenser.

Notes:

• COP indicates without any unit measurement.
• With 1 kW of electricity used, the cooling power produced is generally between 2 and 5 kW (in AC).
• An efficient machine could consume less than the half of a less efficient machine!
• The COP value depends primarily on the temperatures of the evaporator and the condenser, the closer the two temperatures are, the higher the COP.

Finally, by having both Thermal and Electrical Power values on board, instantaneous COP is calculate able, log able and also monitor able via graphical or text based Human Machine Interfaces in parallel with Web Visualization via Smart Phones or Tablets in all over the world.

Period related COP monitoring:

• Instant COP: Real time machine COP value.
• Short-term COP: Average COP over duration of 5 minutes.
• Seasonal COP: Average COP for a user-defined period.

Consequently, by continuous COP monitoring the idea of running an efficient machine comes true.

I recommend it not only because of no additional cost on the end user shoulders but it also helps them to detect malfunctions in the machine at once by reducing the level of performance and prevents wasting money, energy, time… or machine failure by setting preventive actions to reduce machine down time accordingly less CO2 emission/foot print.