3. Space and zone heating for housed livestock and poultry

2.2.2. The hybrid natural/mechanical HLPP system

of improper alignment relative to predominant summer winds.

4 HVAC System

2.2.3. The mechanically ventilated HLPP system

often used (see Figure 1b) with a heavily insulated attic space.

are becoming more popular, which are discussed in a later section.

The NV method of HLPP building ventilation, although once the predominant method of ventilating HLPP systems, has given way in many cases to NMV or MV approaches where tighter control of the thermal environment is desired. The NMV method uses exhaust fan ventilation in cold-to-mild conditions with sidewall curtains and wind potential handling warm weather ventilation (see Figure 1a). The NMV method was developed to replace the NV action during cold weather in an attempt to better control the thermal environment. Warm and hot weather ventilation is handled with sidewall curtain opening action and wind, requiring the same basic orientation requirements of an NV building. The NMV method does not require cold weather ridge vents and therefore in the NMV method a flat interior ceiling is

Figure 3. Typical (a) wind rose pattern evaluated when planning for a naturally ventilated building and (b) the influence

The vast majority of modern intensive HLPP systems use a negative pressure MV system with exhaust fans connected in parallel and fresh inlet air drawn in through ceiling diffusers (Figure 4) in cold-to-mild conditions and sidewall and/or endwall curtains (Figure 1a, b) in warm-to-hot conditions. In modern HLPP systems, the ceiling diffusers are cable controlled to stage inlet action with fan staging, using static pressure differential as feedback. Typical operating static pressures range from 10 to 30 Pascals (Poutside-Pinside). The MV system will typically incorporate at least one sidewall 'drop' curtain opening for emergency power loss events. The negative pressure MV arrangement has become a popular choice, preventing moisture and gas-laden air from exfiltrating through uncontrolled locations where condensation and building deterioration could be an issue. Specialty-designed positive pressure systems Space and/or zone heating are integral components of modern HLPP systems. Space heating has been traditionally accomplished with unvented forced air furnaces. Heated air distribution is handled primarily with a single diffuser attached to the heater outlet, providing minimal distribution and thus uniformity. Ducting of heated air to targeted locations is traditionally not employed in the HLPP systems. Zone heating has traditionally been handled with radiant spot (Figure 5a), radiant tube, or heat lamps (Figure 5b). In some of the colder regions of the USA (e.g., Minnesota), additional microclimate enclosures with heat lamps are provided for immature animals in the coldest weather (Figure 5b). Cold climate ventilation rates are designed to control moisture, gases, and temperature, with moisture control almost always governing the cold weather ventilation rates. Many HLPP ventilation control platforms available today allow the producer to control for building temperature, with relative humidity sensing as a backup for assessing moisture control. Gases such as ammonia, carbon dioxide, hydrogen sulfide, and methane can be an issue in many HLPP systems. In most cold weather situations, and during

Figure 5. (a) Radiant spot heater with shielded radiant sensor for feedback control and (b) microclimate with heat lamps.

normal operating conditions, ventilating for moisture control will also control targeted gases below occupational standards such as those provided by ACGIH or OSHA [4, 5].
