Modelling ventilation rate, balance temperature and supplemental heat need in alternative vs. conventional laying-hen housing systems

Abstract

An Excel-based spreadsheet model has been developed to delineate ventilation rate (VR), supplemental heat need ( H s ), balance temperature ( t bal , outdoor temperature below which H s is required to maintain the desired indoor temperature), energy use and cost for H s in alternative (aviary and enriched colony) vs. conventional cage laying-hen houses. The model was applied to the Midwestern U.S. housing characteristics (same land footprint) and winter weather conditions (−30 °C to 5 °C ambient temperature, and a constant relative humidity or RH of 70%). Effects of hen stocking density, target indoor temperature and RH ( t i , RH i ), building insulation, and light period vs. dark period on VR, t bal and H s were examined. For the housing characteristics considered and target indoor condition of 25 °C and 60% RH, t bal for the alternative housing systems was found to be 2.0–2.6 °C higher than that for the conventional cage counterpart. The supplemental heater capacity would need to be 20.5–22.0 kW per 10,000 hens for the aviary houses (107,000-hen capacity) and 17.6 kW per 10,000 hens for the enriched colony house (124,000-hen capacity). Annual H s was estimated to be 0.09 and 0.12 MJ [kg egg] −1 for the enriched and aviary houses, respectively. The corresponding H s cost (in US dollars) would be, respectively, 0.11 and 0.15 US cent [kg egg] −1 at a wholesale liquid propane (LP) fuel price of $0.32 l −1 ($1.21 gal −1 ) or 0.26 and 0.35 US cent [kg egg] −1 at a retail LP fuel price of $0.75 l −1 ($2.84 gal −1 ). Among all the influencing factors considered, t i and RH i setpoints had more pronounced impacts on t bal and H s . The analysis indicated that H s energy cost for the alternative housing systems in the Midwestern USA is less than 0.3% of the total production cost. The simulation model was validated with measured heating energy use by a commercial aviary house in northern Iowa and the difference between the predicted and field-measured H s values was less than 5%. This interactive model can be readily used for analysis of other laying-hen housing, climatic conditions, and/or management scenarios.