Principles, recommendatins for ventilation

What is ventilation?
? The objective is to provide fresh air to the horse
? Openings must be sufficient so fresh air can enter and stale air can exit
? Ventilation removes heat in hot weather and provides a cooling breeze over the horse
? In winter, ventilation controls moisture, odor and ammonia that have built up in the stable
? Proper ventilation distributes fresh air throughout the horse stalls
? Improper ventilation is using fans to simply move stale air around a closed facility
What are comfortable conditions?
? A horse’s most comfortable temperature range is between 45°F and 75°F
? In hot weather stable temperatures are within a few degrees of outdoors, but more comfortable due to shading from the sun
? In winter the stable is almost as cold as outdoors but comfortably dry with no condensation
? Cold and humid conditions are uncomfortable for both horses and humans
? Stables in winter are no more than 5-10 degrees warmer than the outside temperature
? If conditioned to cold weather, horses with long-hair coats and adequate nutrition can withstand temperatures below 0 degrees
? Even show horses with a short-hair coat can be maintained in a cold but dry indoor facility when provided with blankets and hoods
? Within a box stall, horses have the freedom to move away from uncomfortable conditions
? What humans consider drafty is not necessarily uncomfortable to the horse
? Owners who want warm conditions for horse care activities may provide a heated grooming and tacking area, rather than heating the whole barn or cutting off ventilation
What about distribution of air within the stable?
? Moisture, odor and ammonia are generated primarily in the stalls
? Fresh air is needed for horse respiration and to dilute air contaminants
? Since most dust and ammonia are down near the bedding and manure, check air quality near the floor as well as at horse-head height
? An open, unobstructed interior helps move air around the stable

How much ventilation should be provided?
? Natural ventilation is often expressed in air changes per hour
? An air change is when the total volume of air in the stable is replaced
? Provide 4-8 air changes per hour
? By contrast, modern homes have 1-air change per hour

How is ventilation provided to the structure?
? Wind and thermal buoyancy (hot air rises) are the natural forces that drive ventilation
? Use openings located along the sidewall and ridge (roof peak) to accommodate these forces
? Wind pushes air into the stable through openings on the windward side of the building while drawing air out of the stable on the leeward side
? Variability in wind speed and direction allows stable openings to alternate between letting fresh air in and stale air out
? Thermal buoyancy occurs as horses’ body heat slightly warms their surroundings, creating temperature differences with cooler outside conditions
? Ridge openings allow warm and moist air, which accumulates near the roof peak, to escape
? These openings aid wind-driven air exchange since wind moves faster higher off the ground
? Once wind speed exceeds about 1 mph, wind-driven ventilation dissipates effects of thermal buoyancy in horse stables
? Mechanical ventilation is typical in livestock housing for poultry and swine, but not for horses and cattle that tolerate a wide range of temperature conditions
? Proper stable ventilation design should virtually eliminate the need for circulation fans

Permanent openings
? Furnish stalls with some sidewall openings that are permanently open year-round
? The best location for this permanent opening is at the eave, where sidewall meets roof
? A slot opening along the eave, that runs the entire length of the stable, provides every stall with fresh air since air is equally distributed down the length and on both sides of the stable
? Since a slot opening at the eave is 10-12 feet above the floor, incoming cold air is mixed and tempered with stable air before reaching the horse
? During cold weather a long slot opening admits a thin sheet of cold fresh air, rather than the large drafty mass of cold air admitted by an open window or door
? A minimum guideline for cold climates is to provide at least 1 inch of continuous-slot, permanent opening for each 10 feet of building width
? Supply each stabled horse the equivalent of at least 1 square foot of opening into its stall
? For a 12-foot-wide stall, a 1-inch-wide continuous slot will supply 1 square foot (144 square inches) of permanent opening
? Openings which are slightly above the minimum recommendation can help ensure good ventilation during cold and cool conditions when other stable openings are often kept closed
? If ridge venting is insufficient, double the eave vent opening sizes
? Eave openings ideally should be left completely open; covering them with insect screening or metal soffit treatments severely restricts airflow and will soon clog with dust and chaff
? In double-aisle stables where central stalls are not near a fresh-air opening (or when stables share a common sidewall with an indoor riding arena), the stable interior must have an open design with no ceiling and with grillwork on stall walls

Seasonal openings
? In stables with interior central aisles, large endwall doors can be opened to allow cooling breezes during warmer weather
? When horses are kept indoors during warm weather, allow breezes to enter the horse stall with windows or doors that open from the stall to the outside
? Provide openings equivalent to at least 5 to 10 percent of the floor area in each stall
? For a 12×12-foot box stall, a 3×2½ window provides a 5 percent opening and a 4×3½ window (or top of Dutch door) provides a 10 percent opening

Ridge vent
? The ridge opening area should match the eave opening area with a minimum of 1 square foot of opening per horse
? As with eave openings, ridge openings should provide at least 1 inch of continuous slot opening per 10 feet of building width
? If no ridge opening is provided, double the minimum recommended eave opening
? The simplest and most effective ridge vent is an unprotected opening, where trusses or rafters are protected from precipitation and the stable interior can tolerate occasional rain entry
? The ridge vent can be a continuous opening or a series of uniformly spaced vent assemblies
? During winter a portion of the vents can be closed to provide only the recommended permanent opening area, and then opened during hot weather when more air exchange is needed
? Do not cover ridge openings with insect screens, and avoid residential and commercial ridge vent assemblies that are overly restrictive to air movement
? Ridge vent assemblies made for agricultural buildings offer relatively unrestricted airflow with modest protection from precipitation
? Since warm moist air flows up and is not inclined to move down to exit a ridge vent assembly, avoid designs that prevent natural upward flow when no wind is blowing; trapped air blocks ventilation and may condense in cold weather
? The actual ridge opening is measured at the most restrictive part of the ridge vent assembly, so that the key measurement for air movement is where the airflow path is narrowest
? Cupolas can be used as ridge openings but provide no way for stable air to move through them, while louvers commonly block 50 percent of the open area they are protecting
The breathable wall
? Traditional barn board siding provides a “breathable wall” with miles of small cracks between the boards that allow bits of air movement at each juncture
? Air coming in the cracks is nicely uniform throughout the structure, while the tiny air jets are quickly dissipated without becoming drafty
? This effect is reduced when battens added to the wall, and eliminated when tongue-and-
groove siding or modern 4×8 (or larger) construction panels are used
? Stables can be built with a breathable wall concept by spacing vertical barn boards ¼” to 1” from each other, or using roughcut green lumber siding that leaves gaps once it dries

Three ways to improve  ventilation
? Open grillwork on the top portion of front and side stall partitions is highly recommended versus solid stall partitions
? When the interior has no ceiling and is open to the ridge vent, more air exchange and distribution can occur
? Do not incorporate overhead hay and bedding storage in the stable, or at least construct the storage over the work aisle so that horse stalls have no ceiling

Measuring ventilation rates
? Measure the velocity of air entering or leaving the stable through ventilation openings and multiply this by the opening size
? Air velocity is measured with an anemometer (in feet per minute) and multiplied by the opening area (in square feet) to get the ventilation rate in cubic feet per minute
? To calculate air changes per hour, divide the ventilation rate by the building air volume
? The stable volume is the floor square footage multiplied by the average roof or ceiling height
? Measure the incoming ventilation air speed at several openings and at several locations on large openings, then average the velocities and multiply by the open area of airflow
? The primary difficulty in accurately estimating natural wind-blown ventilation rates is the frequent change of air speed and direction at each ventilation opening as measurements are made.

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