Analysis of the Advisability of Using an Air-Source Heat Pump in a Single Family House in Poland and Spain ^†

Abstract

In recent years, modern and energy-saving solutions, such as heat pumps or solar collectors, have enjoyed great popularity in the heating and cooling sector, which is conditioned by political and environmental factors. The aim of this paper was to analyze the advisability of the employment of renewable energy sources, such as a heat pump, for heating and cooling in single-family buildings in Poland and Spain. Based on the calculations made for a traditional house, located in two cities with different climatic conditions—Wroclaw and Cordoba, the heat losses and gains were determined. On that basis, the heating and cooling demand for these locations were calculated and next—taking into account the obtained results—reversible air–water heat pumps were selected. In addition, the investment expenditures for purchase and assembly of the heat pumps were estimated, as well as the operating costs of the installation. After a deep analysis, it was found that the total cost of using an air-source heat pump, is almost 44% lower for Cordoba, than for Wroclaw.

1. Introduction

According to the European Commission [1], the heating and cooling of buildings accounts for almost half of the total energy consumption in the European Union, ahead of sectors such as transport and electricity. To avoid energy waste and environmental pollution caused by inefficient heating and cooling systems, renewable energy sources such as heat pumps are increasingly used. The principal area of application for these devices is currently the energy supply of low-temperature installations, which are used in new and modernized buildings. The main system powered by heat pumps is the central heating system, however, by a reverse operation cycle, nowadays they are also able to lower the temperature in the rooms [2,3]. Examples of heat pump applications in different types of buildings and systems are described in [4]. Unfortunately, heat pumps are frequently considered to be an unprofitable solution, because of their supply by expensive electrical energy. In practice most of the used energy is renewable—gained from the ground, air, water etc. Energy-economic analysis, containing the comparison of heating and cooling systems with heat pumps, in terms of energy consumption, thermal comfort and environmental impact, was presented in [5]. Because the efficiency of heat pumps depends on the outdoor air temperature, they are more efficient in warmer climates—such as Spain, than colder climates—such as Poland. However, due to the implementation of support programs, grants, credit subsidies etc., an increase in the use of heat pumps can be observed also in Poland recently. A review of heat pump systems in many different climatic regions (including cold climates) was presented in [6,7,8], while the coefficient of performance of a heating and cooling system with heat pumps was determined in [9].

2. Methodology

The analysis was conducted for a single-family house, made by traditional technology, which consists of two residential floors and a non-usable attic. The building is characterized by simple and uniform construction. It is intended for the living of 4–5 people. The materials it was made of meet all applicable technical requirements and quality standards. The usable area of the building is 165.4 m², while its cubic capacity is 474.3 m³. The plan of the house is presented in Figure 1.

The calculations were made for two variants of the building location—Wroclaw, which is located in the II climatic zone in Poland and Cordoba, placed in the B4 climatic zone in Spain. The design’s outdoor temperature was adopted as −18 °C and −0.3 °C in the heating season, as well as 26.3 °C and 36.8 °C in the cooling season in Wroclaw and Cordoba, respectively. The indoor temperature was set as the thermal comfort temperature: 20 °C in Poland, 22 °C in Spain (for heating season) and 22 °C in Poland, 24 °C in Spain (for cooling season). The division into climatic zones of the analyzed countries and the parameters of outdoor air in Poland and Spain, as well as design parameters of the indoor air, were established based on [10,11,12,13,14]. The calculations were performed using the computer program Purmo OZC 6.7, the special engineering tools prepared under the Vipskills project [15] and the other calculation formulas.

3. Results and Discussion

The results of the heat losses and gains calculations for Wroclaw and Cordoba are presented in

Table 1. Heat losses for the single-family building depending on the location [16].

Location	Transmission Heat Loss [W]	Ventilation Heat Loss [W]	Total Heat Loss [W]
Wroclaw	8396	3445	11,841
Cordoba	4782	2008	6790

below.

The total value of the heat losses in Wroclaw was almost 43% higher than in Cordoba. The difference between the amount of heat losses is due to the fact that the buildings are located in different climate zones, with different parameters of external and internal air. That indirectly translates into the value of the design temperature difference, which in turn, has a significant impact on the calculation results.

Figure 2 shows the amount of heat gains in the analyzed room, divided into their main sources. The total heat gains in Cordoba are 7802 W, which is only 3.5% higher value than in Wroclaw. The amount of individual heat gains depend primarily on the geographical latitude of the analyzed cities, the angle of incidence of sunlight and the degree of its absorption, as well as the regulations in force in a given country (determining unit heat gains per person) and the total power of the electrical devices.

Based on the summary results of heat losses and gains in Poland and Spain, the heating and cooling loads for the analyzed cities were determined (Figure 3).

In the case of Wroclaw, the total heating load for the building reached 26,943 kWh/year, while for Cordoba it was 16,245 kWh/year—about 40% less. The energy demand for cooling the house in Cordoba obtained 8541 kWh/year, while for Wroclaw it was 31% lower. The differences in the presented results mainly depended on the amount of heat losses and gains, as well as the number of degree days of the heating or cooling season. On the basis of the obtained results, reversible air–water heat pumps type LAK 9IMR from the Dimplex company were selected.

In order to handle the heating and cooling needs of the building, two air–water heat pumps were necessary for Wroclaw and only one for Spain. The total investment outlays for purchase and installation of heat pumps, as well as preparation of project documentation, were determined on the basis of the Dimplex price list and its own calculations. The operating costs of the system were also estimated based on [17].

Figure 4 presents a comparison of the total costs of the heat pumps system implementation in a single-family house, located in two climate zones. The use of an air–water heat pump in a single-family house is much more profitable (in economic terms) in Spain than in Poland. In the case of Wroclaw, the total cost of the implementation of heat pumps is as much as 67,854 PLN, while for Cordoba it is only 38,202 PLN—almost 44% less.

What is more, analyzing only the total energy demand for heating and cooling the building, the use of the heat pump in Spain is also more beneficial than in Poland. However, it should be noticed, that, regardless of the location, heat pumps are an ecological source of energy—it does not cause the emission of pollutants into the atmosphere and does not harmfully affect the environment or human health, which nowadays is an invaluable thing.