## 4 The Central Role of Climate Control
### Climate Control and Energy Use  
A strong mutual relation exists between climate control and energy use. In many cases, the adoption of only passive strategies, such as natural ventilation and envelope thermal insulation, would not be enough to guarantee adequate indoor climate conditions, especially in certain periods of the year and at certain latitudes. Consequently, mechanical climate control systems--such as fans and air heaters--are adopted in livestock houses. The use of mechanical equipment entails a considerable consumption of thermal and electrical energy. Very poor information about this energy consumption is present in literature and its quantification could be a complex task as several variables should be considered. In broiler houses, for example, 96% of the total on-farm thermal energy is for supplemental heating (up to 140 kWh m\({}^{-2}\) y\({}^{-1}\)), while 76% of the total on-farm electrical energy is for mechanical ventilation (up to 16 kWh m\({}^{-2}\) y\({}^{-1}\)). In laying hen houses, around 60% of the total on-farm electrical energy is for ventilation (up to 40 kWh m\({}^{-2}\) y\({}^{-1}\)). In pig houses, the thermal and electrical energy consumption for climate control--supplemental heating and ventilation--represents around 70% and 50% of the total on-farm energy consumption, respectively [70]. Currently, the energy used on farms is mainly from non-renewable energy sources, a negative aspect for the environmental, social and economic sustainability of the livestock sector. In addition, the energy performance of agricultural buildings is usually low. According to the Organization for Economic Co-operation and Development (OECD) [82], the current energy performance of agricultural buildings in OECD countries is still similar to those of 1990s or 2000s because no substantial improvements have occurred in the last years. Consequently, an energy-efficient climate control of livestock houses is of the foremost importance to move towards a more sustainable agriculture. This is especially true considering the expected rise of food demand and the consequent increase of the energy consumption due to food production [67]. In this context, energy simulation models could represent powerful tools to decrease the energy consumption for climate control of livestock houses. These models enhance the evaluation of the energy performance of these buildings in standardized conditions, considering different climate change scenarios, different technologies and solutions. Nevertheless, few authors have focused on this specific topic and few ad hoc energy models developed for the estimation of the energy consumption of livestock houses are present in literature [74]. The strength of ad hoc energy simulation models developed for livestock houses is the integration of the main peculiarities of these buildings and their climate control systems. Furthermore, these models are specifically fine-tuned for the purposes of the analyses and adopt the most updated energy simulation method in compliance with the normative framework [83]. In literature, models that were developed ad hoc for the energy simulation of duck houses [76], pig houses [75] and broiler houses [73] are present. Other energy simulation models for livestock houses [68; 69; 72] were developed using building energy simulation (BES) tools, such as EnergyPlus (U.S. Department of Energy's Building Technologies Office, Washington, DC, USA) and TRNSYS (University of Wisconsin, Madison, WI, USA). BES tools were not specifically developed for simulating intensive livestock houses and, consequently, they cannot consider all the boundary conditions in detail that are specific to this building type, as reported by [PERSON] et al. [71]. Despite the differences that exist between customized energy simulation models and BES models, all these models can be used to improve the energy performance for climate control of livestock houses.