BIALYSTOK UNIVERSITY OF TECHNOLOGY

Faculty of Civil Engineering and Environmental Sciences

Department of HVAC Engineering

Lab manual

Determination of the Coefficient of Performance COP of

the heat pump

Experiment #10

Laboratory in the subject

Heat exchange

Code: 19284202H

Written by:
Cezary Pieńkowski, DSc, Eng.

Bialystok, September 2022

1. Objective
The aim of the experiment is to determine the Coefficient of Performance COP of the heat
pump.

2. Theory of heat pumps

2.1. Definition
A heat pump is a device that can heat water and the interior of buildings by transferring heat
energy from the outside using the refrigeration cycle. Many heat pumps can also operate in the
opposite direction, cooling the building by removing heat from the enclosed space and rejecting it
outside. Units that only provide cooling are referred to as air conditioners.

2.2. Principle of operation

Heat will flow spontaneously from a region of higher temperature to a region of lower
temperature. Heat will not flow spontaneously from lower temperature to higher, but it can be made
to flow in this direction if work is performed. The work required to transfer a given amount of heat
is usually much less than the amount of heat.
The transfer of heat from a low-temperature region to a high-temperature one requires
special devices called heat pumps and refrigerators. Heat pumps and refrigerators are essentially
the same devices; they differ in their objectives only.

Fig. 1. The objectives of refrigerators and heat pumps [1]

The above figure shows the objectives of refrigerators and heat pumps. The purpose of
a refrigerator is the removal of heat (QL), called the cooling load, from a low-temperature medium.
The purpose of a heat pump is the transfer of heat (QH) to a high-temperature medium, called
the heating load. When we are interested in the heat energy removed from a low-temperature space,
the device is called a refrigerator. When we are interested in the heat energy supplied to the high-
temperature space, the device is called a heat pump.

2.3. Operation – refrigeration cycle

The transfer of heat from lower temperature regions to higher temperature ones is called
refrigeration. Devices that produce refrigeration are called refrigerators, and the cycles on which
they operate are called refrigeration cycles. The working fluids used in refrigerators are called
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refrigerants. Refrigerators used for the purpose of heating a space by transferring heat from a cooler
medium are called heat pumps.
The most widely used refrigeration cycle is the vapor-compression refrigeration cycle.
The vapor-compression refrigeration cycle is a common method for transferring heat from a low
temperature to a high temperature. The vapor-compression refrigeration system has four
components: evaporator, compressor, condenser, and expansion (or throttle) valve (Fig. 2a). In an
ideal vapor-compression refrigeration cycle, the refrigerant enters the compressor as a saturated
vapor and is cooled from a superheated vapor to the saturated liquid state in the condenser. It is then
throttled to the evaporator pressure and vaporizes as it absorbs heat from the refrigerated space
(transition from a liquid-vapor mixture to the saturated vapor state).

Fig. 2 (a) Schematic diagram of a compressor heat pump (or a refrigerator)

(b) T-s diagram for the ideal vapor-compression refrigeration cycle [1]

The ideal vapor-compression refrigeration cycle consists of four processes (Fig. 2b):
1-2 isentropic compression in a compressor (s = constant)
2-3 isobaric heat rejection in a condenser (P = constant)
3-4 isenthalpic throttling in an expansion valve (h = constant)
4-1 isobaric heat absorption in an evaporator (P = constant)
The P-h diagram (Fig. 3) is another convenient diagram often used to illustrate the
refrigeration cycle.

Fig. 3. The P-h diagram of an ideal vapor-compression refrigeration cycle [1]

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2.4. Types
Many possible sources are available for heat transfer to the refrigerant passing through
the evaporator. These include the outside air, the ground, and lake, river, or well water. So common
types are air source heat pumps, ground source heat pumps, water source heat pumps and exhaust
air heat pumps. In the most common type of vapor-compression heat pump for space heating,
the evaporator communicates thermally with the outside air. Such air-source heat pumps also can be
used to provide cooling in the summer with the use of a reversing valve. In the cooling mode,
the outside heat exchanger becomes the condenser, and the inside heat exchanger becomes
the evaporator. Although heat pumps can be more costly to install and operate than other direct
heating systems, they can be competitive when the potential for dual use is considered.

2.5. Refrigerants
Until the 1990s, heat pumps, along with fridges and other related products used
chlorofluorocarbons (CFCs) as refrigerants that caused major damage to the ozone layer when
released into the atmosphere. Use of these chemicals was banned or severely restricted by the
Montreal Protocol of August 1987.
Replacements, including R-134a and R-410A, are hydrofluorocarbons (HFC) with similar
thermodynamic properties with insignificant ozone depletion potential but had problematic global
warming potential (GWP). HFC is a powerful greenhouse gas which contributes to climate change.
By 2023, devices using refrigerants with a very low global warming potential still have
a small market share but are expected to play an increasing role due to enforced regulations.
Isobutane (R600A) and propane (R290) are far less harmful to the environment than conventional
hydrofluorocarbons (HFC) and already being used in air-source heat pumps. Ammonia (R717)
and carbon dioxide (R744) also have a low GWP.

2.6. The Coefficient of Performance COP

The energy balance of a heat pump and a refrigerator can be written as:

where:
QL – the heat transferred to the refrigerant in the evaporators, J,
Win – the compressor work input, J,
QH – the heat transferred from the refrigerant in the condensers, J.

The efficiency of heat pumps and refrigerators is expressed in terms of coefficient of

performance COP, defined as

where:

– the heat transfer rate from the refrigerant to the water in the condensers, calculated from
Formula 4, W,

– the compressor power input, W,

– the refrigeration capacity, W.

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where:

– the mass flow rate of water through the condenser, calculated from Formula 5, kg/s,
Cp – the specific heat of water at constant pressure [at temperature Tave = (T1 + T2)/2], J/kg·ºC,
T2 – the water temperature at the outlet of the condenser, ºC,
T1 – the water temperature at the inlet of the condensers, ºC.

where:
ρ – the water density at the inlet of the condensers at temperature T1, kg/m3,

– the volume flow rate of water through the condenser, l/min.

To determine the heat transfer rate from the refrigerant to the water in the condensers you
must first calculate from Formula 4 the heat transfer rate from the refrigerant to the water in the
condenser no. 1, then calculate from Formula 4 the heat transfer rate from the refrigerant to the
water in the condenser no. 2, finally add these two values to each other and insert the resulting value
into Formula 2.

3. Methodology of the experiment

3.1. Equipment description

Fig. 4. Main elements of the laboratory station: 1 – heat pump with water-water, air-water, air-air,
water-air exchangers, 2 – control unit, 3 – data acquisition board, 4 – software, 5 – computer [3]

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 Fig. 5. Heat pump diagram [3]

Designations

1) Pressure measurement
SP-1 refrigerant pressure sensor at the outlet of the compressor
SP-2 refrigerant pressure sensor at the inlet of the compressor
M-1 pressure gauge at the outlet of the compressor
M-2 pressure gauge at the outlet of the condenser
M-3 pressure gauge downstream of the expansion valve
M-4 pressure gauge at the inlet of the compressor

2) Flow measurement
SC-1 refrigerant flow sensor
SC-2 water flow sensor through the first water evaporator
SC-3 water flow sensor through the second water evaporator
SC-4 water flow sensor through the first water condenser
SC-5 water flow sensor through the second water condenser

3) Temperature measurement
ST-1 temperature sensor, J type (compressor outlet)
ST-2 temperature sensor, J type (compressor outlet/evaporator inlet)

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ST-3 temperature sensor, J type (evaporator inlet/condenser outlet)
ST-4 temperature sensor, J type (compressor inlet)
ST-5 temperature sensor, J type (water inlet)
ST-6 temperature sensor, J type (condenser outlet/evaporator)
ST-7 temperature sensor, J type (condenser outlet/evaporator)
ST-8 temperature sensor, J type (evaporator outlet/condenser)
ST-9 temperature sensor, J type (evaporator outlet/condenser)
ST-10 temperature sensor, J type (room air)
ST-11 temperature sensor, J type (condenser outlet/evaporator)
ST-12 temperature sensor, J type (condenser outlet/evaporator)
ST-13 temperature sensor, J type (evaporator outlet/condenser)
ST-14 temperature sensor, J type (evaporator outlet/condenser)

4) Regulating valves
AEAI-1 valve at the inlet to the air evaporator used to regulate the air stream through the evaporator
(knob on the operating panel in the computer application)
ACAI-1 valve at the inlet to the air condenser used to regulate the air stream through the condenser
(knob on the operating panel in the computer application)
AEA-1 valve to regulate the water flow through the water evaporator
ACA-1 valve to regulate the water flow through the water condenser

3.2. Experimental procedure

1) Turn on the computer and the control unit.
2) Click "Thibar44C" icon on the computer monitor.
3) Start recording by clicking "START" icon on the work panel.
4) Open the water supply to the laboratory station from the building water supply system.
5) Set the water flow rates in the evaporators at the level set by the laboratory instructor.
6) Set the water flow rates in the condensers at the level set by the laboratory instructor.
7) Start the compressor by pressing the AC-1 button on the work panel.
8) Let the system to stabilize. Note the readings ST-8 and ST-9 every 5 minutes until
the temperature does not rise.
9) After stabilizing the system, write down the measured values indicated in Table 1.
10) When the readings are complete, turn off the compressor and recording by clicking "STOP"
icon on the work panel.
11) Close the water supply to the laboratory station from the building water supply system.
12) Click "QUIT" icon on the work panel.
13) Turn off the computer and the control unit.

3.3. Presentation and analysis of the obtained results

Table 1. Obtained experimental values
Parameter Obtained value Unit
Electric energy used by the compressor (SW-1) W
Water temperature at the inlet of the condensers (ST-5) ºC
Water temperature at the outlet of the condenser no. 1 (ST-8) ºC
Water temperature at the outlet of the condenser no. 2 (ST-9) ºC
Volume flow rate of water through the condenser no. 1 (SC-4) l/min
Volume flow rate of water through the condenser no. 2 (SC-5) l/min

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Name and surname: Date:
1.
2.
3.

On the basis of the performed measurements, calculate the COP of the heat pump from
Formula 2.

4. Laboratory safety rules

a) Observe the safety regulations in the laboratory room.
b) Do not turn on the devices without the consent of the teacher.
c) Before starting the experiment, carefully read the lab manual.
d) It is forbidden to perform the experiment without the supervision of the teacher.
e) In the event of noticing damage or improper operation of the device, immediately turn it off
(stop performing the experiment) and notify the teacher.
f) Students are not entitled to make any kind of repairs or alterations at individual laboratory
stations.
g) The devices should be used in accordance with their intended purpose.
h) Performing the experiment must be careful not to obstruct the work of others who perform
the experiment.

5. Students’ report
The content of the students’ report:
1. Composition of the group, name of the field of study and laboratory, title of the experiment, date
when the experiment was performed.
2. Objective and scope of the laboratory experiment.
3. Equipment description.
4. Experimental procedure.
5. Performing the necessary calculations.
6. Summary of the obtained results in the form of conclusions.

6. References
1. Cengel Y.A., Boles M.A. Thermodynamics: An Engineering Approach. McGraw-Hill Education,
New York, 2015.
2. Borgnakke C., Sonntag R.E. Fundamentals of Thermodynamics.Wiley J., Hoboken, 2013.
3. Edibon materials.