COP performance coefficient and EER energy efficiency in HVAC system

7 min readAug 31, 2021

What is the coefficient of performance? ( COP)

Coefficient of Performance or COP (sometimes CP or CoP) stands for Coefficient Of Performance. COP represents the index number to determine the optimal energy consumption in refrigeration and heating devices of refrigeration cycle such as air-cooled compression chiller , water-cooled compression chiller , roof top package, VRF system heat pump , gas cooler | Split and so on.

Higher COP equals higher efficiency, lower energy consumption and consequently lower operating costs.
The COP is usually more than 1, especially in heat pumps.

Most air conditioners have a COP of 2.3 to 3.5. Heat transfer requires less work than heat conversion, which is why heat pumps, air conditioners, and refrigeration systems can have a performance factor of more than one. However, this does not mean that they are more than 100% efficient; in other words, no heat engine can have a thermal efficiency of 100% or more. For complete systems, COP calculations must include the energy consumption of all power consuming aids. The COP is highly dependent on the operating conditions, especially the absolute temperature and the relative temperature between the sink and the system, and is usually plotted or averaged against the predicted conditions.

(How to determine the energy consumption label rating of the Governor of Iran, which is ranked according to the table above in electrical appliances.)

What is the productivity factor? (EER)

EER stands for Energy Efficiency Ratio, which means energy efficiency coefficient or energy efficiency coefficient. Simply put, this number represents the amount of cold produced as the amount of electricity consumed. The higher this number, the higher the energy efficiency of the device and the less power it consumes.

The energy efficiency ratio (EER) of an HVAC cooling device is equal to the ratio of the output cooling energy (in BTU) to the input electrical energy (in watts) at a specified operating point.

EER is usually calculated at 95 ° F and indoor temperature (return air) at 80 ° F and 50% relative humidity.

What is an HVAC system?

HVAC stands for Heating, Ventilating and Air Conditioning . H-Walkers are used indoors as well as in industrial processes. This energy consumption depends on the amount of load changes, seasonal changes, performance and maintenance status, environmental conditions and so on. HVAC systems are a turning point in building mechanical systems that provide thermal comfort to occupants with indoor air quality. HVAC systems can be classified into central and local systems according to different regions, locations and distributions. Basic HVAC equipment includes heating equipment, ventilation equipment, and cooling or air conditioning equipment. Central HVAC systems are located away from the building in a central equipment room and transmit air conditioning through a ductwork system. Small (home) HVAC systems can be located near the required location and do not require ducting.

In the following, the chiller gain coefficient, chiller energy consumption coefficient, chiller cooling tower capacity and compressor power in heating and air conditioning (HVAC) systems are discussed.

Significant amounts of energy are consumed by air conditioning and cooling systems, inside buildings as well as in industrial processes. This energy consumption depends on the amount of load changes, seasonal changes, performance and maintenance status, environmental conditions and so on. Therefore, in order to evaluate the performance of air conditioning systems, all of these factors should be considered as much as possible. In this article, how to calculate the chiller gain coefficient, chiller energy consumption coefficient, cooling tower capacity, compressor power, ….

COP and EER testing in the cooling system

The purpose of this test is to confirm the performance of a cooling system through field measurements. In this test, the cooling tower capacity (in terms of refrigeration tonnage) and the energy required will be measured under actual operating conditions. This test is performed with the aim of estimating the amount of energy consumption in terms of actual load in the design conditions.

Terms and definitions required to perform the test

Refrigeration Tone: (TR) One ton of refrigeration is the amount of heat required to melt one ton of zero degree ice per day, which is equivalent to: 3024 kcal / h or 12,000 BTU per hour. (Btu / h) or 3.516 kW of heat.

Determining the capacity of the cooling tower in the HVAC system

It is a quantity in which the evaporator water flow is multiplied by the enthalpy difference between the inlet and outlet water to the coolant, and is expressed in terms of kilocalories per hour and ton of refrigeration.
Ratio (kW / ton): This quantity is known as efficiency, but in reality, it is obtained by dividing the input power to the compressor motor by the cooling body or by the kilowatt body. The lower the kW / ton, the higher the efficiency of the device.
Chiller gain factor ( COP ): Chiller performance factor or chiller gain factor is the division of output power (cooling) on the input power to the compressor.
Energy Efficiency Ratio ( EER ):Often, the performance of smaller chillers and roof units is measured in terms of ERP instead of kilowatts per ton. ERP is calculated by dividing the cooling capacity of the chiller by (Btu / h) by its input power (in watts) at full load, and the higher the EER, the higher the efficiency.

Introduction to data measurement

At least three sets of data are taken every five minutes after stable conditions are created. In order to minimize the effects of transient conditions, the test should be read almost simultaneously.

calculation method

This test involves measuring the net heat taken from the water as it passes through the evaporator by determining the following:
A: Cold water flow
B: The temperature difference between the inlet and outlet
water of the cold water heat is equal to the product of the flow rate Cold water, the difference between water temperature and specific heat of water, which is defined as follows.

Cooling tower capacity calculation formula in tons (TR)

Description of the formula for calculating the tower capacity of the H-Walk system

In this equation:
m: Cold water flow (kg / hr)
(kcal / kg˚C) Specific water heat 〖: c〗 _p
: t_in Cold water temperature at the evaporator inlet (˚C)
: t_out Cold water temperature at the evaporator outlet (˚C)

Accurate temperature measurement is critical in air conditioning and cooling systems, and calculations must be based on at least one decimal place.

Measurement of cold water flow in HVAC system

If the online flow meter is not available, the cold water flow can be measured by the following methods:
• If a hot and cold tank is available, by turning off the secondary pump, the flow can be reduced or increased by the tank level. Measured.
The non-invasive method requires a fully calibrated ultrasonic flowmeter that can be used to easily measure the flow rate in the system.
• If the pressure drop is close to the design values, the pump water flow can be assumed to be the nominal design flow.

HVAC compressor power measurement formula

Using a portable power analyzer, the power of the compressor can be measured, which directly shows it in kilowatts. Otherwise, an ammeter or tong tester should be used to measure the current. Power can then be calculated assuming a power factor of 0.9.

Power in kilowatts

Calculation formula (COP) and (EER) of HVAC ventilation systems

Chiller energy efficiency is usually expressed in one of the following ratios:

1- Chiller interest rate formula (COP)

2- Chiller energy consumption coefficient (EER) formula

3- Formula for calculating power per ton (KW)

First, we calculate the ratio of kilowatts per ton from the measured parameters.

Use this data in the following equations to calculate other energy efficiency parameters:

Chiller interest rate

Energy efficiency ratio

Evaluate the performance of the HVAC air conditioning system

For centralized air conditioning systems, airflow in air conditioners (AHUs) can be measured with the help of a barometer. The data can be used to determine the enthalpy (air heat content at the inlet and outlet of the AHU) along with the psychometric diagram in the figure below.

Thermal load

m: Cold water flow (kg / hr)
: t_in Enthal air enthalpy at AHU (kJ / kg)
: t_out Exhaust air enthalpy at AHU (kJ / kg) The
thermal load can be theoretically sensed by estimating different heat loads. And imperceptibly, calculated in the air conditioning room (see standard air conditioning manuals). The difference between the two shows leakage losses, unwanted loads, heat ingress, and so on.

Values and sizes to be recorded during testing

To measure the following parameters, all instruments used, including gauges and thermometers, must be tested in the reading range.
Evaporator
A: Inlet water temperature to evaporator
B: Outlet water temperature to evaporator
C: Cold water flow
D: Evaporator water pressure drop (inlet to outlet)
Compressor
T: Inlet power to compressor electrical power (kW)

Example

For example, in the brewery’s cooling system, ethylene glycol uses a secondary refrigerant.40 TR The cooling tower capacity is designed. An experiment was performed to obtain the performance capacity and energy performance ratios. The amount of flow in the hot tank was measured by turning off the secondary pump and measuring the difference in tank level.

Quantities and measurement data

= (-) 1 ° C Enthalpy temperature of ethylene glycol entering the evaporator

= (-) 4 ° C Enthalpy temperature of ethylene glycol output to the evaporator

= 13200 kg / hr Ethylene glycol flow rate

= 0.7 kg / cm2 pressure drop of ethylene glycol evaporator (inlet and outlet)

= 39.5 kW Input power to compressor electrical power ( kW )

= 2.34 kCal / kg ˚ C Specific heat capacity of ethylene glycol

Cooling tower capacity

30.65 TR=