1. Introduction
Poultry production is a major sector of the U.S. agricultural industry, with chicken leading the per capita meat availability [
1]. In South Carolina alone, roughly 235 million broilers are produced each year [
2]. Energy costs for operating broiler barns (electricity and gas) represent the largest variable production cost at about 57% of total cash expenses [
3], and have also been estimated to be about 25% of gross farm income [
4]. The majority of the energy used in broiler barns is dedicated to environmental modification, which includes ventilation, space heating, and lighting [
5]. Better quantification of how and when energy is used in broiler barns is critical for evaluating energy-saving facility improvements. However, there has been little work to evaluate the farm-scale effects of these upgrades or to benchmark overall energy used in poultry housing.
Broiler chicken production occurs in three types of buildings (breeder barns, broiler barns, and pullet barns) that correspond to the three phases of production [
6]. The first phase is the production of fertilized eggs in breeder barns that are designed to provide feeding, breeding, roosting, and nesting areas for hens and roosters. Here, the main uses of energy are mechanical ventilation, lighting, feed handling, and egg conveyance to the egg sorting area. A small amount of energy is also needed to control the temperature and humidity in the room where fertilized eggs are held before being transported to the hatchery. When chicks are about one day old, they are placed in a broiler barn that has been designed to provide the environmental modification needed for the brooding stage followed by the grow-out stage. During brooding, ventilation and heating systems are needed to provide air temperatures as high as 32 °C when the chicks are first placed [
7]. As the birds grow and are better able to maintain body temperature, the temperature requirement decreases gradually to about 21 °C once the chicks are around 4–6 weeks old. The birds remain in the barn until they grow to market weight, which ranges from 1.8 to 4.5 kg per bird, depending on market requirements. The total time required to raise a flock of broiler chickens can range from 38 to 84 days depending on target market weight [
3]. As the birds increase in body mass, the amount of energy needed for supplemental heating decreases to zero and the energy required for ventilation increases by a factor of 10 or more. Lighting requirements also change as the birds grow, with the highest light levels required during brooding. The number of flocks produced in a broiler barn each year can range from approximately four flocks for heavy birds (3.6 to 4.5 kg/bird) to six flocks for small birds (2.3 kg/bird).
The third type of broiler barn used in a commercial operation is the pullet barn, which is used to raise replacement hens and roosters for the brooder barns. These barns are designed to provide the same types of indoor environmental modifications as broiler barns and, as a result, are equipped with similar heating, ventilation, and lighting equipment. The main difference is that fewer birds are grown per unit of floor area and generally only two flocks are brooded per year with 4–6 weeks between flocks [
6,
8], resulting in less energy used for heating. The lighting programs (intensity and daylength) in pullet barns are more rigorously controlled compared with broiler barns. Light traps are used on fans and inlets to practically eliminate natural light from entering the barns. The use of light traps increases the static pressure drop that the ventilation fans must work against, resulting in an increase in electrical use for ventilation as compared to broiler or breeder barns.
The previously mentioned details of how production occurs in these barns is germane to energy use because the size of the bird grown impacts both environmental control and the energy consumption of broiler barns. Bird size determines the number of brooding periods per year and the number of months for which high ventilation rates are needed. For example, growing larger birds results in greater total metabolic heat production, which requires higher ventilation rates for more days a year, resulting in more electrical energy consumption. Conversely, producing larger birds results in fewer flocks per year, which translates to fewer weeks of brooding and reduced gas use for space heating.
The timing of flock placement also plays a crucial role in seasonal fluctuations in energy use. In much of the USA, and especially in the warm southern states, most of the electrical energy is used by the ventilation fans during the late spring, summer, and early fall. In general, hot weather ventilation rates are 10 times greater than the ventilation rates needed during cold winter weather, and periods when barns are left empty might coincide with the hottest part of summer, naturally reducing ventilation needs and associated energy consumption. Similarly, a flock placed during the coldest portion of the year would require extra energy for supplemental heat for the first few weeks. Therefore, something as simple as variations in the flock placement schedule can result in differences in energy consumption between broiler barns with similar types of equipment for ventilation, heating, and lighting.
The amount of energy used on a breeder, broiler, or pullet farm can also vary greatly between farms due to differences in the total airflow capacity of ventilation fans, fan efficiency, number of motors used for feed handling, the number and efficiency of the lamps used for lighting, insulation levels in the building envelop, the efficiency of the heating equipment, and the number of barns located on a single farm. Additional sources of variability in energy consumption between farms include weather, differences in control of the ventilation and heating systems, and variation in lighting programs. Most broiler producers grow under contract for companies that have ventilation and lighting requirements that often vary between companies, also increasing farm-to-farm variability.
Limited data are available to provide insight concerning the energy used to produce broiler chickens in general and specifically in the southeastern U.S. Some international works have reported energy consumption for poultry production in Turkey [
9], Iran [
10,
11], and Nigeria [
12]. The scope of what is included in these studies varies and often includes not only building energy but other energy inputs needed to grow the birds (human, machinery, feed, etc.), making it difficult to use them to assess building performance. Costantino et al. [
13] reviewed several studies from Europe and reported a wide range of energy uses from 7 to 16 kWh m
−2 yr
−1 for electrical energy use and 86 to 137 kWh m
−2 yr
−1 for thermal energy use. The University of Georgia Cooperative Extension Service conducted a survey to gain information concerning energy use on broiler farms in the mid-2000s and found electrical costs ranged from USD 1.36 to USD 1.60 m
−2 of broiler barn floor area per year, and gas use was approximately 165–225 MJ m
−2 per year, depending on the insulation provided in the house sidewalls [
14]. Baxevanou et al. [
5] found the total energy used in broiler houses averaged 77.2 kWh m
−2 in Greece, and a study in Poland concluded that 0.149 kWh were used per bird per year on the average [
15].
Several equipment upgrades can be made to broiler barns to improve energy efficiency, including installation of energy efficient fans, changing from incandescent or fluorescent lamps to LED lamps, and adding additional building insulation [
16,
17]. Traditional incandescent bulbs have largely been phased out for more energy efficient LED bulbs, which can reduce lighting energy use by as much as 80% [
17]. Replacing low-efficiency fans with high-efficiency fans can reduce ventilation energy requirements by 20% to 30% [
18]. Fan accessories have a varying impact on efficiency, with discharge cones increasing efficiency by 15% on average and shutters and light traps potentially decreasing system efficiency by 2% to 25%, depending on design and maintenance [
19]. Additionally, management practices influence energy (such as operating fans at higher static pressure), and fan maintenance has been shown to result in differences in performance of up to 24% [
20].
Evaluating proposed changes and upgrades to a facility requires an assessment using the baseline energy consumption, system configuration, and comparison between the current system performance with the recommended standard of performance. It must also be recognized that the installation of new energy efficient equipment provides an opportunity to greatly improve the building environment for the animals. The realized improvement depends on the entire system where new equipment is installed, and some recommended improvements in building performance may not lower the seasonal or annual energy costs. For example, if old low-efficiency fans in a broiler barn are also shown to be deficient in the airflow needed for hot weather ventilation, the recommendation will be to increase the maximum ventilation rate as well as the energy efficiency of the fans. The new system may require more or larger high-efficiency fans to meet performance standards, and the additional airflow provided by the more energy efficient equipment can at least partially negate any energy savings compared with pre-retrofit conditions. In such cases, rather than focusing on energy savings, the value of the improvements could be better viewed through the lens of improved animal health and performance.
In recent years, several state and federal programs have been developed to provide cost sharing and incentive programs for producers to install energy efficient ventilation, lighting, and heating equipment. These programs often require an energy assessment to evaluate energy savings of potential upgrades. This study presents baseline assessment information for 17 broiler farms and 4 pullet farms that the authors were able to obtain from one of these programs. Because assessments were only provided by request, this population of farms was biased toward barns that needed efficiency and performance improvements in at least one of the three systems known to use the majority of energy on broiler farms, namely ventilation, lighting, and heating. Therefore, the information collected from these farms is best viewed as providing baseline energy use for broiler barns that could benefit from retrofitting one or more systems to improve energy efficiency. The objective of this study was to quantify annual electrical and gas consumption in broiler production. Differences in annual energy use between production types were evaluated, as was the influence of equipment characteristics on energy consumption. Additionally, the relationship between temperature and month on electrical energy use was explored.
2. Materials and Methods
The energy records and production characteristics utilized in this study were collected as part of a South Carolina program focused on providing cost share for energy-efficient upgrades for broiler production. An in-person assessment was completed to inventory lighting, heating, and ventilation equipment and to collect other pertinent production characteristics such as number, size, and age of the broiler barns, average bird size, and number of flocks produced in a year. The size, quantity, and location of each type of fan was recorded, as well as the primary use of the fan (tunnel or conventional ventilation). In the best-case scenario, specific make and model numbers were recorded, along with pictures of the equipment. However, in many cases, specific details were only recorded for systems that were of interest for upgrade, and, for older equipment, the specific model was often unintelligible, and general characteristics such as size, manufacturer, and style were collected. The location, rating, type, and quantity of lighting was similarly recorded. General observations concerning the adequacy and quality of building construction (e.g., insulation, ventilation inlets, and evaporative cooling pads) were also made, but improvements to the building envelope were ineligible for cost-share, so, in most cases, this information was limited and not used in this study.
2.1. Energy and Weather Data
The amount of electrical energy purchased per month and the amount of gas purchased per year were obtained from farm records. For electrical records, the exact format varied slightly by utility provider but generally included meter read dates, energy used (kWh), bill amount, bill dates, and days of service. In cases where multiple meters were present, they were aggregated to determine the total for the farm. Producers generally provided at least 2 years of records and annual totals were determined for each year (based on 12 consecutive months), along with an average for the operation. These values were normalized per unit floor area to compare different operations. A minority of operations only provided one year’s worth of energy data or only provided an annual total. These operations still met the minimum suggested in ANSI/ASABE S612 [
21], and were noted in the results.
Most electrical bills were based on meter readings taken at specific intervals, not necessarily aligning with the calendar month. This created a discrepancy between billing and monthly energy use. In this study, monthly energy use was determined from read dates and adjusted for the number of days in the billing period. This was again normalized by floor area, and the percentage of annual electrical energy used in each month was determined. In instances where meter dates were not reported, energy use was assigned to the corresponding billing month. To examine the relationship between energy use and temperature, daily ambient air temperatures were obtained for each farm using the closest weather station available from the Midwestern Regional Climate Center database [
22]. These daily temperatures were then aggregated into monthly averages that corresponded to the electrical billing period.
Annual gas use for heating was estimated utilizing producer-provided energy bills, similar to annual electrical use. For barns utilizing natural gas as a fuel source, the procedure for estimating annual use was the same as previously described, with annual usage based on 12 continuous months of data. For LP users, annual gas consumption was estimated by aggregating all billing records for a given calendar year, acknowledging that when the fuel was delivered did not precisely reflect actual usage. In both cases, energy use was converted to MJ equivalent and again normalized by floor area.
2.2. Analysis
This study quantified energy use for broiler production and evaluated how energy use varied between production systems and over the course of the year. The relationship between normalized monthly electrical use and mean monthly air temperature was investigated using Pearson’s correlation (Proc CORR in SAS (SAS 9.3, SAS Institute Inc., Cary, NC, USA)). Trends in monthly electrical use were further explored by using Tukey’s honest significant difference (HSD) test to evaluate whether normalized monthly energy use could be categorized into distinct seasons. This portion of the analysis was performed separately for each production group, and the number of observations was based on producer/month combinations. Differences in annual electric and gas use between production groups were evaluated using PROC GLM, and, in this portion of the analysis, the number of observations was based on producer/year combinations. Throughout this manuscript, all mentions of significance indicate statistical significance using p < 0.05.
Farms were grouped based on two characteristics: the size of the birds grown (small or large) for broilers, and, for large broilers, the relative efficiency of the equipment (high or low efficiency). Pullet barns have some differences in equipment (e.g., light traps) and how they are utilized relative to broiler barns, so they were analyzed as a separate category. A description of the groups evaluated and the number of farms included in each portion of the analysis is given in
Table 1. Limited availability of exact performance specifications for older equipment (ex. VER of fans) and sparse details regarding the building envelope made quantitatively classifying the large broiler farms based on exact efficiency impractical; however, three farms were segregated into a “high-efficiency” group because their major electrical systems generally indicated higher efficiency relative to the other farms included in this study (e.g., cones on all tunnel and conventional ventilation fans, newer buildings, LED lighting). For LB-LE and SB, there was some variation in which farms were included in various portions of the analysis based on the data provided.