Lubing House Pads

The Relationship Between Temperature and Humidity

The relationship between temperature and humidity and related physical parameters with regard to evaporative cooling of poultry houses are corelated in a psychometric chart:-. 

The critical parameters of concern are: -

• Dry bulb temperature – This is measured using either a conventional or electronic thermometer. Dry bulb temperature is shown on the bottom horizontal axis of the chart and increases from left to right.
• Wet-bulb temperature is determined by immersing the bulb of a thermometer in a wick saturated with water using a sling psychrometer or alternatively an electronic hygrometer.  Wet bulb temperatures are depicted along the relative humidity curve representing saturation on the left side of the chart. The difference between dry bulb and wet bulb temperature is a function of the quantity of water in a given volume of air.
• Relative humidity – This is a measure of the quantity of water that air can hold at a given temperature.  Relative humidity is expressed as a percentage of the maximum level of water contained in a volume of air at a given temperature. On the chart relative humidity values are shown as a series of sequential curves extending from right to left with 100 percent humidity, or saturated air on the extreme left.
• Humidity ratio is the weight of water contained in a unit of air, expressed as a fraction of a pound of moisture per pound of dry air.  Humidity ratio values are indicated along the vertical axis on the extreme right of the psychrometric chart.
• Enthalpy is the heat energy contained in air expressed as Btu per pound of dry air. Values are shown along a diagonal scale on the left of the chart.

The principle of evaporative cooling can be illustrated using the definitions provided and with reference to the psychrometric chart, guided by the following simplified diagram:-

• Select 100 F dry bulb temperature on the horizontal scale at the bottom of the chart. Assume wet bulb temperature to be 65 F.  The curved line from 65 F downward to the intersection point with the 100 F dry bulb temperature indicates a relative humidity of 20 percent.  This state point indicates that the air in the house would contain 0.008 pounds of moisture per pound of dry air, a situation that would be encountered in incoming air in a layer house in Arizona or California.

• If moisture is introduced into the incoming air by an evaporative cooling system, the change in state from liquid to vapor will have a cooling effect but will increase relative humidity in the treated air to 50 percent.  This would reduce the dry bulb temperature of the incoming air into the house to 82 F. The reduction in temperature would require the addition of water by the evaporative cooling system with the humidity ratio  increasing from 0.008 to 0.012 pounds of moisture per pound of dry air.
• Theoretically to achieve saturation, dry bulb temperature could be reduced to slightly under 70 F.  Due to inherent restrictions, saturation is neither achievable nor recommended since the flock would be compromised by relative humidity values in excess of 50 percent.  This is due to the fact that feathered birds are insulated and rely on evaporative cooling from the respiratory and oropharyngeal mucosal surfaces to maintain core body temperature at or above 104 F. 

The psychrometric chart can be used to predict the effect of changes in dry and wet bulb temperature and corresponding changes in state points reflecting relative humidity and quantity of moisture to be added to incoming air for a variety of weather conditions.

• It may be necessary to add moisture to air to increase the relative humidity to at least 40 percent during brooding to protect the respiratory surfaces of chicks and poults.
• Adding heat to incoming air using a heat source or heat exchanger module will decrease the relative humidity of incoming air and facilitate removal of moisture from litter.  Litter serves as a moisture-sink accumulating urinary and fecal excretion and water spillage from drinkers. High moisture content of litter compromises flock welfare and health and affects three body systems:-

                 The respiratory tract is adversely affected by the release of ammonia,

                 The intestinal tract is impacted by ulcerative and necrotic enteritis and parasitism

                       including coccidiosis and other protozoal pathogens,

                       The integument is predisposed to footpad lesions and gangrenous dermatitis. 

The efficiency of evaporative cooling systems is dependent on adequate volumes of water passing over the pads and their ability to convert water to vapor.  The unique design of optiCOOL plastic pads contributes to cooling the incoming air without introducing water into the airstream, contributing to saturated litter in the floor area adjacent to inefficient pads.