**E**ff**ect of a Sustainable Air Heat Pump System on Energy E**ffi**ciency, Housing Environment, and Productivity Traits in a Pig Farm**

### **Myeong Gil Jeong 1,**† **, Dhanushka Rathnayake 1,**† **, Hong Seok Mun <sup>1</sup> , Muhammad Ammar Dilawar <sup>1</sup> , Kwang Woo Park <sup>2</sup> , Sang Ro Lee <sup>2</sup> and Chul Ju Yang 1,\***


Received: 14 October 2020; Accepted: 21 November 2020; Published: 23 November 2020

**Abstract:** High electricity consumption, carbon dioxide (CO2), and elevated noxious gas emission in the global livestock sector have a negative influence on environmental sustainability. This study examined the effects of a heating system using an air heat pump (AHP) on the energy saving, housing environment, and productivity traits of pigs. During the experimental period of 16 weeks, the internal temperature was found to be higher (*p* < 0.05) in the AHP house than in the conventional house. Moreover, the average electricity consumption and CO<sup>2</sup> emission decreased by approximately 40 kWh and 19.32 kg, respectively, in the AHP house compared to the house with the conventional heating system. The average NH<sup>3</sup> and H2S emissions were significantly lower in the AHP house (*p* < 0.05) during the growth stages. The AHP and conventional heating systems did not have a significant influence (*p* > 0.05) on the average ultra-fine dust (PM2.5) and formaldehyde level fluctuations. Furthermore, both heating systems did not show a significant difference in the average growth performance of pigs (*p* > 0.05), but the weight gain tended to increase in the AHP house. In conclusion, the AHP system has great potential to reduce energy consumption, greenhouse gas (GHG) emissions, and noxious gas emissions by providing economic benefits and an eco-friendly renewable energy source.

**Keywords:** air heat pump; carbon dioxide; formaldehyde; electricity consumption; ultra-fine dust

## **1. Introduction**

Various energy problems have been identified in the global agriculture sector not only for economic reasons, but also for sustainable ecological persistence [1–3]. This is due to the diminishing fossil fuel reserves and increasing energy prices worldwide [4,5]. In addition, excessive greenhouse gas emissions affect biodiversity degradation through global warming [6]. Furthermore, the increase of global CO<sup>2</sup> emissions into the atmosphere is expected to lead to a temperature increase from 1.1 to 6.4 ◦C by the end of the 21st century [7]. Fossil-fuel burning is the major contributor of CO<sup>2</sup> emissions, and the atmospheric CO<sup>2</sup> concentration has been enhanced by 31% since 1750, with an average annual increase by 1.5 ppm over the past decades [8]. Beside deforestation and excessive arable land utilization, fossil-fuel combustion is responsible for 90% of CO<sup>2</sup> emissions into the environment [9].

In the global livestock sector, pigs have an inefficient thermoregulation process for dissipating heat from their bodies. Their maximum voluntary feed intake (VFI) ranges from 19 to 25 ◦C and tends to decrease above 25 ◦C [10]. NH<sup>3</sup> and methane byproducts released by pigs, together with dust, affect the air quality and are considered important parameters in pig houses [11]. The emission of noxious gas from the livestock sector is one of the major problems; it exerts negative impacts on the environment and accounts for approximately 75–80% of NH<sup>3</sup> emissions in developed nations in the world [12]. Moreover, a combination of both NH<sup>3</sup> and H2S adversely affects the pig industry [13,14] owing to the direct harmful impact on both animals' and workers' welfare [15]. Dust can penetrate the respiratory organs easily owing to its smaller particle size. Super-fine dust particles less than <1 µm are the most harmful and cause pulmonary diseases [16]. Therefore, essential steps are needed to improve the housing environment by reducing noxious gas emissions, dust concentration, and environmental pollution. Moreover, due to the presence of an abundant renewable resource capacity, South Korea has the potential of utilizing them efficiently to mitigate the problems arising through high energy consumption, thus finding effective solutions for those challenges and the energy distribution process across the various geographical areas [17].

The air heat source pump system has the potential to conserve high-grade energy and allow the effective use of low-grade energy, as well as to provide energy savings and storage [18]. Other than the energy savings, it can reduce CO<sup>2</sup> emissions and is consistent with efficient structural compaction [19].The theoretical and experimental performance and effectiveness of the air heat pump were investigated by previous studies [20–23]. However, there are no publications available on the effects of utilization of air heat pump systems on energy efficiency, housing environments, and productivity traits in livestock sectors. Owing to the environmentally friendly and sustainable source, an air heat pump system can be introduced as an alternative energy system for conventional methods. Therefore, this study compared a conventional electric heating system and an air heat pump (AHP) system for the energy savings, housing environment (NH3, H2S, fine dust, formaldehyde), and productivity traits of pigs.

## **2. Materials and Methods**

### *2.1. Experimental Period and House*

The performance of the air pump heating system in a pig house was evaluated for 16 weeks (weaning period, four weeks; growing period, six weeks; finishing period, six weeks) in winter from 2 December 2019 to 2 April 2020 at the Sunchon National University Experimental Farm, South Korea. The pig house consisted of two separate rooms (3 m × 8 m) that were subdivided into 10 pens for individual replication. Two east-facing rooms were contained in the pig house. The room on the south side was considered the control house, which was connected to a conventional electric heating system. The air pump heating system was connected to the other north-facing room (Figure 1). An outdoor unit draws heat in from outside, and thereafter, blows it over a heat exchanger coil. The heat thus generated from the compressor is then transferred through an internal plastic tube with small pores that enable the uniform distribution of the heating pattern inside the house. Finally, the cold liquid vapor coolant mixture enters back into the outdoor unit to be heated once again. The conventional pig house was connected with heating lamps; the heights of these were maintained according to the growth phase of the pigs. The outside walls of the pig house were made from brick plastered on both sides. The floor was installed with a plastic slat, and the slurry was removed daily. The environmentally controlled pig houses' inside temperature ventilation processes were controlled automatically. Moreover, we maintained similar internal temperature settings according to each growing phase, covering both the conventional electric heating house and the AHP installed house to compare the inside temperature fluctuations, energy efficiency, noxious gas emission, ultra-fine dust, and formaldehyde concentration between the two experimental houses. Throughout the experiment, all animals received a commercial basal diet and had access to water ad libitum.

**Figure 1.** Schematic diagram of the air heat pump (AHP) system for the pig house.
