Ventilation in the stables

In practice, ventilation is mainly an issue in indoor stables. Most of the problems relating to ventilation are not issues in outdoor stables, except sometimes in summer.

In the case of new indoor stables, it is essential to give thought to ventilation right from the draft stage of the project to cater for the health of the horses. Ventilation is involved in all of the other environmental factors : temperature, hygrometry, contamination by germs, dust, and concentration of harmful gases. Respiratory conditions (equine asthma…) are a major cause for having to take horses out of service, and are essentially due to allergies or infections. The aim is therefore to reduce exposure of the horses to a potentially allergenic environment.

Good ventilation should immediately evacuate any emissions, without any stagnation or recirculation, whilst avoiding overly abrupt exchanges. In stables with a sufficient number of sheltered openings, the air will naturally flow towards the center of the building and upwards. Well ventilated stables are those with a high volume per horse (40m3) with side partitions which offer shelter from draughts. Good ventilation should ensure efficient air renewal : when the weather is cold, the velocity of air is quite low around the animals, but it accelerates when it is hot.

Bad ventilation is either insufficient or excessive (in winter) ventilation. Insufficient ventilation leads to considerable condensation. This makes the horse more sensitive to viral or bacterial contamiation, and also contributes to early deterioration of the buildings.

General considerations to remember

Air flow results from :

• The chimney effect : warm air rises (convection)
• The wind effect : the wind blowing on the stable sucks the air out on the leeward side.

In practice these two effects combine. However, the wind effect will dominate the chimney effect whenever the wind speed is greater than 1m per second.

Proper ventilation is situated between :
♦ A minimum rate which allows evacuation in cold weather :

• Of the humidity from the animal (respiration and excretions)
• Harmful gases encountered in stables (CO2, ammonia NH3...)
• Dust and infectious agents.

There is no standard established for horses, but it is usually considered that pollution factors are eliminated in sufficient proportion where the air renewal is sufficient to evacuate water vapour.

♦ A maximum rate to maintain a good temperature in winter and in summer. It is therefore necessary to implement a permanent ventilation system which airs without overcooling. The most efficient system is a continual flow of air upwards. In this way the ventilation can vary between a factor of 1 and 10, from cold weather to hot weather.

Extraction chimneys

Extraction chimneys are frequently fairly inefficient as there are often not enough of them. Air flow enters through lateral windows, and leaves through chimneys of which the base is at best 5m high, and where the size of the opening depends on the number of horses (0,1m2 /horse).

A temperature difference of 3 to 5°C between inside and outside temperature is required for this system, based on the fact that warm air rises, to be effective. The main aim of insulation in a stable is not to keep the horses warm, but to allow the ventilation system to function correctly and limit condensation.

Roofing on different levels is to be avoided as this is only efficient when the wind blows on the opposite side from the openings.

Open roof ridge

Open roof ridges are a very good solution. Air entry through them is due to poor layout : insufficient width, lack of windbreaker, lack of protection near the closed gables.

Ventilated roof lights or ridges are in fact open roof ridges protected by another element of roofing located over the roof ridge. They are quite efficient, and also contribute to lighting.

Breathable roofing, or openwork partitions (spacing of 1 to 2cms between the planks) are popular techniques in the UK. They are efficient in temperate climates, but do not cater for any adjustments and will let small amounts of rain or snow in, therefore they can only be used in sheltered locations.

When good natural ventilation is not possible (very wide stable buildings, or low ceilings) mechanical ventilation can be used. Being able to install mechanical ventilation should not however lead to neglecting natural ventilation.

Ventilators can be installed on air flow outlets, or on both inlets and outlets. It is not advisable to install them only on the inlets (ventilation by overpressure).

Three techniques

There are three different techniques :

• Direct extraction : ventilators are positioned on the openings of vertical walls.
• Extraction by means of chimneys : mostly used in smaller premises, and when the buildings have a ceiling.
• Extraction via ducts : ventilators are positioned in a distribution duct which will homogenise extraction of contaminated air and avoid creating preferential flows.

Any mechanical ventilation demands some maintenance : regular cleaning of the ventilator blades and ducts, frequent adjusting of the regulator depending on the outside temperature.

The goal to reach is complete air renewal 4 times an hour, when the doors are closed and there is no wind.

In winter , the air should flow very slowly, so that the horse’s coat retains its insulating properties (0,25m/s, i.e. air flow which is imperceptible to humans, but can be seen using a hazer) . In summer on the other hand, air velocity should be increased (up to 4 to 5m/s) to help the horses combat the heat.

The size of the openings is calculated taking into account the thermal properties of the building and the heat produced by the animals. In a poorly insulated building, openings should be larger to get the correct air renewal rate. Insulating the walls and partitions enables to reduce the size of the openings, thereby reducing draughts. The surfaces to be implemented should allow efficient ventilation, even when there is no wind.

The surface of the openings is related to the number of horses, or loose boxes, and in practice at least :

• Air inlet = 0,30 m2 per horse
• Air outlet = 0,10 to 0,12 m²/horse

In summer the surfaces should be multiplied by 2,5 to 3, so as to obtain evacuation through blowing out some of the heat and promoting the evapotranspiration from the horses’ skins.

Ratio inlet/outlet

It is important to respect not only the size of the openings, but also the ratio inlet/outlet : modular openings are therefore advisable. The layout and type of stables should also be considered.

Air flow circuits are complex and depend on the shape of the building, inside and outside obstacles, the direction of the wind… The environment can completely modify the air flow circuit from those foreseen.

Distribution of the openings is as important as their surface : homogeneity and air flow velocity depend on the distribution of the openings.

When there are a lot of openings this makes air inlet uniform. On the contrary, one large opening (door kept permanently open) is usually a source of draughts.

Air inlets and outlets are positioned in such a way that the air flow naturally goes over the horses without cold air falling onto their backs (deflectors can be installed if necessary). Wind breaker nets can be used to slow the speed of the air flowing in.

For an outdoor box with a single slope roof, there should be two openings in addition to the door, on the two sides which are not exposed to dominant winds and rains. When the roof has two slopes, an additional opening on the roof ridge is recommended.

For indoor stables, the surface of the openings should be increased, making sure that they allow fresh air to come in, therefore they should not open over the manure pit, or over a confined volume of air...