Exergetic Analysis of a Vertical Ground-Source Heat Pump System with Wall Heating/Cooling

Abstract

The present study deals with an exergetic analysis and assessment of a Vertical Ground-Source Heat Pump System (VGSHP) combined with a Wall Heating System (WHCS) in a building. This study is an experimental investigation of a real building’s heating system. The system is located at Yildiz Renewable Energy House (YREH) in Yildiz Technical University and fulfills the heating demand of YREH and a living room of the neighboring dormitory. In order to validate an exergetic model, the system is divided into three subsystems: (1) the ground coupling circuit, (2) the refrigerant circuit, and (3) the WHS circuit. The schematic diagram of the constructed experimental system is given in Fig. 26.1. Exergetic model is obtained by applying mass, energy, and exergy equations for each system component. YREH has four rooms, each has 8 m² floor area, and the neighboring dormitory has a 50 m² living room. In this study three rooms of YREH and the living room have been heated during heating season. The heating season was assumed to be between 1 January and 31 March. As average results on the heating season, 6.509 kW heat energy was extracted from ground and 5.799 kW was used in the WHS. In this process electrical energy consumption of system components are as follows: compressor 1.711 kW, ground heat exchanger pump 0.092 kW, accumulator tank circulation pump 0.114 kW, and WHS circulation pump 0.108 kW. For heating season, calculated overall system efficiency was 67.36 % while GSHP unit’s efficiency was 85 %. In addition, overall system COP was 2.76, while GSHP unit’s COP was 4.13. Total exergy destruction was found 1.759 kW and largest exergy destruction has occurred in the compressor as 0.714 kW. The exergy efficiency values for the individual components of the system have been found ranging from 58.3 to 98.4 % according to P/F concept. It is expected that the model would be beneficial for evaluating low exergy heating systems which use ground source as a renewable energy.

Nomenclature

COP:

Coefficient of performance, dimensionless

$\dot{ Ex}$ :

Exergy rate, kW

h:

Specific enthalpy, kJ/kg

$\dot{m}$ :

Mass flow rate, kg/s

P:

Pressure, kPa

$\dot{Q}$ :

Heat transfer rate, kW

T:

Temperature, K

$\dot{W}$ :

Rate of work or power, kW

s:

Specific entropy, kJ/kgK

$\dot{S}$ :

Entropy rate, kJ/K

ε :

Exergy (second law) efficiency, dimensionless

η :

Energy (first law) efficiency, dimensionless

ψ :

Specific exergy, kJ/kg

0:

Reference (dead) state

C:

Cooling

c/p:

Compressor or pump

dest:

Destroyed

expv:

Expansion valve

F:

Fuel

gr:

Ground

H:

Heating

HE:

Heat exchanger

in:

Input

k:

kth element

P:

Product

ref:

Refrigerant

out:

Output

whsc:

Wall heating cooling system