How Much Moisture Do Brooders Add to Poultry Houses?

The vast majority of poultry growers use unvented heating units, i.e. brooders or space furnaces, to heat their poultry houses, using propane or natural gas as fuel sources. Record high propane/natural gas prices over the last two years have led a number of producers to explore the possibility of using biomass furnaces to provide heat in their poultry houses. A number of alternative heating systems exist with a price range of less than $10,000 to over $60,000 (Czarick, et al., 2008). Generally alternative heating systems are considered profitable if they are able to replace approximately 85% of the propane use, but conventional brooder/space heating systems must still supply heat during peak demand (Wimberly, 2008).

While the main benefit of biomass furnaces lies in its potential fuel saving, an overall improvement in air quality in the house as a result of introducing "dry heat" is an additional benefit reported by furnace vendors and some growers. This claim is based on the fact that unvented heating units such as brooders or space heaters release water vapor as they generate heat, while vented systems leave the combustion byproducts outside and introduce heat into the houses by heat exchangers. Unvented propane heaters are estimated to add 0.000078 pounds of water vapor for each BTU heat generated (ASHRAE, 1985). Natural gas releases slightly more water vapor than propane per unit of heat generated. If "dry heat" releases less water vapor into the poultry house, this is likely to lower in-house ammonia and ventilation requirements because of drier litter conditions. However, water vapor from unvented conventional heaters is only a portion of the moisture load added to the house, and this portion varies both within a flock and among flocks in a year. It may represent a high proportion of the moisture load during the brooding stage in cold weather when feed and water consumption are low, but much less of the load as birds get older. We decided to study the relative contribution of moisture to housing environment and potential significance of the "dry heat" benefit based on available scientific data so that growers are equipped to make wise investment decisions with respect to the relative importance of "dry heat."

This analysis was conducted based on weekly propane usage, feed consumption and water intake data collected from 18 winter flocks (flocks placed in November, December and January) raised at the Applied Broiler Research Farm (ABRF). When we did this study we assumed that, when relatively low levels of heating were required during mild weather, because of convenience and system efficiency, propane heating systems would be favored over biomass furnaces.

Moisture loads in poultry houses consist of moisture generated by birds and water vapor generated by propane heaters. Moisture generation by birds included water intake from drinkers, water in the feed (assume feed moisture content of 13%) and metabolic water generated through the digestion of feed. Yet some of the water in poultry houses is retained in the bodies of the birds. Therefore, the amount of water retained by the birds (water retention) was calculated.

Several assumptions were made to conduct the analysis:

Further analysis was made on daily propane use during the first two weeks of the most recent five winter flocks raised in 2006, 2007 and 2008, and compared to daily moisture loads added by birds.

On average, birds drank between 1.5 to 2.1 pounds of water for every pound of feed consumed. Water consumption from drinkers was found to represent a majority of water added to the house. An average of 19% of the water in the house was retained by the birds. This means that 81% (range of 75 to 85%) of the water that entered houses was released back into the house environment, by respiration and excretion (Figure 1).

If unvented propane heaters account for a large portion of the moisture added to poultry houses, it seems logical to assume that moisture addition problems would be worst in the winter months. Yet, analysis of propane consumption data from winter flocks revealed that unvented burning of propane generated an average of 23% of total moisture loads in the first week of brooding, 11% of the moisture in the second week, and 5% or less in the remaining weeks (Table 1, Figure 2). Still, a major portion of the fuel combusted over the life of the flock is expended maintaining house temperatures of 85 to 90°F during these early weeks. In addition, the overall growth rate and settlement status may well be determined during these early weeks (Tabler, 2000; Tabler, 2003). Therefore, daily propane usage data from the five most recent winter flocks was analyzed to get a better picture of moisture loads within the first two weeks of chick placement.

Figure 1. Weekly Water Released and Retained (reflected as weight gain) per 1000 Birds as a Result of Feed and Water Intake. 

Figure 3 shows that moisture generated by propane burning represented 84 and 41% of the total load on days 1 and 2, respectively. The percentage of moisture from burning propane decreased as birds grew, and stabilized at around 11% during the second week of age. The dry heat from vented furnaces is clearly beneficial during the early days after bird placement when propane consumption is very high. Calculations show that on average the moisture load could be reduced by 20% during the first week. While this reduction in moisture load would translate to drier litter conditions, and may allow the grower to reduce ventilation rates, it is important to remember that total moisture loads increase dramatically as birds grow, and moisture generated by birds remains the main reason for ventilation. While the benefits of dry heat from biomass furnaces become smaller as birds grow, it is also important to recognize that energy efficiency is also related to litter preparation between flocks. Growers that skip or short cut may save time, but those who take the extra time to do the job right will likely find dividends in the settlement check (Tabler et al., 2008).

Figure 2. Weekly Moisture Addition from Water Released by Birds and Generated by Propane Heaters (analyzed for 18 winter flocks, per house basis) 

 

Several potential environmental and economic benefits have been reported for biomass furnace systems. While these benefits are often valid, it is important to see the whole picture. Vented furnaces produce dry heat that is reported to reduce in-house ammonia levels, decrease ventilation rates, improve litter quality and produce a healthier environment within the house (Wimberly, 2008). Moisture load calculations based on propane usage data collected at the Applied Broiler Research Farm indicate that when using vented biomass furnace, about 23% less moisture can be added to the indoor environment during the first week of brooding, when birds are very sensitive to house conditions and maintaining elevated temperatures requires the combustion of large amounts of propane. However, as birds grow bigger, more moisture is added by feeding and drinking, which represent more than 90% of in-house water inputs from second week on.

Authors: Y. Liang¹ and G.T. Tabler^2
1 Department of Biological and Agricultural Engineering and
² Department of Poultry Science, University of Arkansas Division of Agriculture