Use of heat pumps in HVAC systems for precise environment control in broiler houses: System’s modeling and calculation of the basic design parameters

Highlights

• Thermal modeling of broiler houses.

• Defining heat pump-HVAC design parameters.

• Precise environment control of broiler houses through heat pump-HVAC systems.

Abstract

Environment control in broiler houses aims at achieving optimal growth rate and welfare conditions through ventilation, heating and cooling and is currently realized by using conventional techniques such as Liquefied Petroleum Gas (LPG) heaters, fans and evaporative panels. These systems use electricity or fossil fuels as energy sources and they are neither efficient nor renewable, thus further contribute on the increase of Greenhouse Gases (GHG) from livestock operations. They are technologies not always capable to establish optimal comfort conditions, in terms of indoor temperature and relative humidity, within the broiler house. Heat pump, on the other hand, is fully aligned with EU directive for energy efficiency and nearly Zero Energy Buildings (nZEBs) as a Renewable Energy Source (RES). The application of heat pumps as heating technology in Heating, Ventilation and Air Conditioning (HVAC) systems are capable for precise control the environment of broiler houses assuring comfortable conditions that maximize animals’ welfare and productivity. This study presents a time series model to simulate in hourly step the behavior of a broiler house equipped with HVAC system with heat pump that finally concludes to the calculation of the basic design parameters of the system. The model was developed in Engineering Equation Solver (EES) model and applied for a 10,000 broilers’ house at the area of Kavala in Northern Greece. Maximum grand total cooling and heating loads were estimated at 390 kW and 47 kW, respectively. The size of cooling unit should be 8 times larger than that for heating, pointing-out the major problem of high temperatures in Southeast Mediterranean. In terms of heat consumption, a year-round simulation of the broiler house reveals that sensible cooling loads account for 189 MWh while heating for 24 MWh. Sensible cooling is mostly accompanied with dehumidification and reheating, an expected finding for such dense population buildings. The model results for heating were very similar with those available from energy audits, but unfortunately no cooling data were found for comparison.

Introduction

Environmental management in broiler houses aims at maximizing flock performance and to achieve optimal growth rate for the animals, ensuring at the same time health and welfare conditions for the broilers housed. In this framework, among others, heating and cooling play an important role. It is well documented (Da Silva and Maia, 2013, Yahav and Scanes, 2015) that broilers are homeothermic animals and need to maintain their body temperature at constant levels. Broilers subjected to cold temperatures have (Lee et al., 2003) impaired immune and digestive systems, resulting in reduced growth and increased susceptibility to diseases. Similarly, high ambient temperatures characteristically reduce feed intake, growth rates and feed efficiency in growing broilers (Reece and Lott, 1983). Too-high and too-low ambient temperatures have a negative effect on broiler performance rate by reducing body weight gain, feed efficiency, health and mortality (Heier et al., 2002, Baarendse et al., 2006, Blahova et al., 2007, Akşit et al., 2008). Broilers should be housed under comfortable conditions in terms of air temperature and relative humidity (De Oliveira et al., 2006) as these two thermal factors directly affect the homeothermic regulation of broilers. Achieving this using ventilation, heaters and mixing fans (Okelo et al., 2003, Han et al., 2013), tunnel ventilation and evaporative cooling, results (Bokkers et al., 2009) in high energy use because of the use, in most cases, of fossil fuels, which in turn increases emissions of the greenhouse gases (GHG).

The same conclusion was reached (Costantino et al., 2016) with regards to high energy use for environment control in broiler houses when reviewing European data. More specifically, it was reported that total thermal energy consumption and total electrical energy in broiler houses range from 86 kWh/m² year to 137 kWh/m² year and 7 kWh/m² year to 16 kWh/m² year, respectively. However, consumption calculation is a complicated task since it depends strongly on the site in terms of climatic data, the building’s materials, the heating cooling technology and the automations applied. A simulation model presented (Costantino et al., 2018) for the estimation of energy consumption for environment control in broiler houses could estimate the thermal energy consumption due to heating and the electrical energy consumption due to ventilation, but not due to cooling. Simulation was run during an entire production cycle for a broiler house having a useful floor area of 1200 m², a useful volume of about 3900 m³ and a mean U-value of walls equal to 0.81 W/m² K. The total energy consumption for space heating was calculated to be 3551 kWh and was simulated to be 3184 kWh (about 10% difference) and the recorded electrical energy consumption was 5061 kWh with the estimated being 5463 kWh (an overestimation of 7.9%). Other relative literature studies indicated that the energy consumption in poultry houses is expected to vary between 12 and 16 MJ/bird or 60–80 kWh/m²/year depending on the location of the poultry farm and on the level of the used technology (de Vries and de Boer, 2010). For Greek conditions and for poultry farms in different altitude and different technology adoption level it was found that the average final energy consumption varies from 46.38 kWh/m², in lowland farms with “new technology”, to 89.37 kWh/m² for “old technology” mountainous farms (Baxevanou et al., 2017). The characterization of technology “new” or “old” is related with the insulation and automation level. Thus, a well-insulated and equipped with the appropriate automations for environment control of broiler house is classified as a new technology one, while a poorly insulated without automations as an old technology one.

This study presents a time series model to simulate in hourly step the behavior of a broiler house equipped with HVAC system with heat pump, that finally concludes to the calculation of the basic design parameters of the system, for heating and cooling purposes, as an alternative technology for precise environment control in broiler houses. The term “precise control” stands for the capability of the heat pump-HVAC technology to keep the indoor environment conditions continuously within the desired set-point limits, as these are determined by the optimal growth curves of broilers, namely values or ranges of indoor dry-bulb temperature and relative humidity as a function of broiler mass. This is achieved by appropriately combining the operation modes of heating, cooling, humidification, dehumidification and reheating. Design parameters include the maximum sensible and latent heating and cooling loads and their sum, the ventilation air flow rate as well as apparatus characteristics such as the dew point and the bypass factor (BF). Currently, conventional technologies (i.e. heaters, fans, evaporative cooling panels) are used to regulate the environment in broiler houses, supplied either by fossil fuels (e.g. LPG) for heating, or electricity to run the ventilation and evaporative cooling systems. HVAC-heat pump systems have the capacity of precisely controlling the buildings’ environment, whereas on the contrary limitations (i.e. not effective control of temperature and relative humidity) are acknowledged for the conventional ones. Additionally, heat pumps as a RES technology closely follows the EC priorities on energy efficiency (European Commission, 2012) and is fully in-line with the new strict EU directives for energy performance in buildings (European Commission, 2010) requiring to reach nearly zero energy buildings (nZEBs) in the short-term.

The integration to broiler houses therefore, is challenging in terms of sustainable environmental control and mitigation of carbon footprint. Heat pump has been considered as an expensive technology for environmental control in animal housing compared to the conventional technologies, a fact that constitutes a major constraint towards their wide expansion in the sector. Nevertheless, recent advancements in heat pump’s technology have led to radical improvement of COPs, making the technology worthy to investigate.