Heat pumps with internal combustion engines using natural gas as an alternative to electric heat pum

Abstract

Keywords: Heat pump; renewable energy; efficiency; consumption

Introduction

Increasing energy consumption and rising energy prices force us to think and constantly develop new energy facilities that are more efficient and more environmentally friendly. In the light of declining fossil fuel reserves are brought into awareness of renewable energy sources. In order to realize the ambitious targets for reducing the consumption of fossil fuels and reducing greenhouse gas 141 countries signed the Kyoto Protocol. Also, the European Parliament adopted a directive on the use of renewable energy sources. This Directive aims at determining share of energy from renewable 814

Energy Efficiency Of HEAT Pumps

Heat pumps are among the alternative sources of energy and using energy from the low-potential source (air, water, ground) for their function. The heat pump consists of four basic components (compressor, condenser, expansion valve and evaporator) interconnected to the circuit in which circulates the working fluid - refrigerant. Gas heat pumps are identical constructionally with electric heat pumps, the difference is that the electric motor to drive the compressor is replaced by a gas combustion engine with its own cooling circuit and the exhaust system as show in figure 1 and 2. GHP work only in system air - water, but obtained heat not only from renewable energy sources, but also the engine cooling and exhaust system are participating of the total production of heat. Based on current analysis, it appears that transformation of primary energy into heat more effective in GHP.

Energy efficiency heat pump can be determined on the basis of two factors COP and PER. The COP (Coefficient of Performance) compares the ratio of the generated heat (supplied to the heating) and the energy required to drive a heat pump which can be either an electric or energy produced by combustion of gas.

where QOUT [kW] is heating power at temperature TOUT, G HP ,drive [kW] is energy supplied to the heat pump (electric

power or energy contained in natural gas). For systems rated coefficient of performance is valid, higher COP achieve energy-efficient. To compare the energy efficiency on the basis of the COP factor is important that the systems were compared with the same type of primary energy. It is therefore not appropriate to compare GHP and EHP on the basis of the factor of primary energy rate. Primary Energy Rate (PER) compares the efficiency of energy systems with different types of fuel and energy productivity. PER is generally the ratio of all the available energy in the system of the useful energy produced. The system, which has a lower value PER thus consume a smaller amount of primary energy per unit of useful energy and thus the system is more energy efficient.

where GHP is the energy of gas supplied to the heat pump (kWh), EHP is the electricity supplied to the heat pump (kWh), ηel is the efficiency of electricity production (35%), QOUT is heating power produced by heat pump (kWh).

Characteristic Of Experimental Device

Heat pumps are installed at the area of University of Žilina in Slovakia. Measuring of the energy efficiency of GHP and also EHP was realized in time from 02/19/2013 02/24/2013. Because heat pumps work in system air - water, it was necessary to measure the weather data by the meteorological station (Fig. 3) at the time. The greatest impact on performance of HP air - water has outside temperature of low potential heat source.

Fig. 4 Schematic diagram of gas heat pump air – water Table 1 Basic data on the performance of experimental heat pumps

Experimental

device Model Rated heating capacity (kW) Rated cooling capacity (kW)

Aisin 10HP

In Table 1 are presented models of experimental equipment - electric heat pump and gas heat pumps and their performances. Figure 4 shows the connection diagram of the gas heat pump, and the figure 5 and 6 show the outdoor unit and indoor unit of GHP. In Figure 7 and 8 show the actual electric heat pump connected. The outdoor unit consists of a heat exchanger air / coolant, a compressor, a combustion engine and a heat exchanger for preheating the coolant, included in the cooling circuit of the engine. Orange color shows the refrigerant circuit GHP, using R410A refrigerant. The inner side is called technology unit AWS (from the English Air - Water System), consisting of a plate heat exchanger is used to transfer heat from the refrigerant circuit to the water serving for heating, hot water, respectively, in reversible mode for cooling. Part of heat pump is a so-called. HOTKIT (from the English Hot Water kit) consisting of plate heat exchanger water - water added to the cooling circuit of the engine. Water from the AWS and the HOTKIT distributes into a distributor is used to heat or cool a laboratory.

Results And Discussion

Throughout the measurement period were measured to determine the necessary parameters COP and PER experimental facilities, while also the meteorological data measured at one-minute intervals. Average daily temperatures were in the range -6.1 to 4.9 ˚C. The outlet water temperature of the heat pump was set at 45 degrees Celsius. After evaluation of all parameters were determined PER of both heat pumps shown in Figure 9. The number of COP electric heat pumps are reached 3-5, for gas heat pump COP is in the range of 1.2 to 2.4. Electric heat pump achieved during measurements of performance figures COP = 2.61 to 3.13, gas heat pump but does not exceed a value of 1 (Fig. 10). The graph indicated the course of daily average temperatures in the measured period. Since the comparison of the COP is not objectively because heat pumps are of a different power and the type of fuel to be recognized that electricity as primary energy, but is made with effect 0.35 to 0.4%. Therefore, to properly compare the two systems, the value PER, which

Technical Note incorporates the efficiency of primary electricity. In our case, was used for electricity generation efficiency of 0.35%. The higher the value the lower the PER system is more efficient and produce the required heat output using less primary energy. It is important to note that the gas heat pump is burnt in order to drive natural gas compressors. The ratio of 1 kW fuel prices between natural gas and electricity in the long term holds in the ratio 1: 4 in favor of natural gas in Slovakia. By investing in PTČ as the sole source of heat and cold are reduced investment costs for creating the heating system in comparison with the building of two sources (heating - gas cooling - electricity).

Conclusion

Measurement to obtain the relevant data on the gas heat pump in real conditions. The experimental measurements showed that the electric heat pump is more energy efficient under the same climatic conditions as compared to gas heat pump, the outdoor air temperature from - 6 ˚C to 5 ˚C. However, gas heat pump worked in a range of about 47 to 63% power, which was due to insufficient heat demand on the secondary side. Electric heat pump worked between 70-90% of the power. This meant that for low heat consumption on the secondary side of the gas heat pump to the total production of heat is not used heat from the engine cooling and exhaust.

Acknowledgments

This paper is supported by the following project: University Science Park of the University of Zilina (ITMS: 26220220184) supported by the Research&Development Operational Program funded by the European Regional Development Fund.

Nomenclature

COP (Coefficient of performance), PER (Primary Energy Rate), GHP (Gas heat pump), EHP (Electric heat pump), QOUT [kW] is heating power at temperature T OUT, G HP ,drive [kW] is energy supplied to the heat pump (electric

power or energy contained in natural gas), GHP [kWh] is the energy of gas supplied to the heat pump, EHP [kWh]is the electricity supplied to the heat pump, ηel is the efficiency of electricity production (35%).

References

1. E. Bakker at al. Gas heat pumps. Efficient heating and cooling with natural gas. GasTerra/Castel international Publishers, Netherlands, 2010.
2. M. Malcho, A. Kapjor, J. Hužvár. Measurement of heat pumps air - water, Ventilation and Air Conditioning, Bratislava. 2011
3. B. Langeley. Heat pump technology. Publisher Prentice Hall. 2001.
4. A. Hepbasli at al. A review of gas engine driven heat pumps (GEHPs) for residential and industrial applications. Elsevier. 2009. Fig. 10 Coefficient of performance of GHP and EHP 818 Technical Note
5. M. Janovcová, R. Kiš, J. Jandačka. Transformation of heat by gas heat pump depending on primary energy sources. Žilina. 2012.

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