Cooling a poultry house
How evaporative pads, fogging and sprinklers differ
The principle: the air’s heat evaporates water
All three methods below are evaporative cooling. Water evaporates using heat from the air, so the air temperature falls and its humidity rises [1]. Hence the main practical rule: cooling cannot be calculated separately from ventilation. Evaporative cooling works together with air movement [1], and excess humidity in the house makes it harder for the birds to shed heat: with lower humidity, birds tolerate a higher temperature [2].
The methods differ in where the water evaporates: in a pad at the air inlet, in the air inside the house, or on the surface of the birds.
Evaporative pads with tunnel ventilation
Tunnel-mode air passes through wetted porous pads and is cooled before it enters the house. The University of Kentucky describes evaporative pads as the most effective and efficient systems for cooling broiler houses [1].
What matters for pads, according to this source [1]:
- All incoming air must pass through the pads. That is why the building must be airtight: air leaking in around the pads reduces the effect.
- The pads need a pressure drop across them. So they do not work with natural ventilation through open curtains and are used mostly in tunnel-ventilated houses.
- Pad area. It is chosen so that the air velocity through the pad is not excessive.
- Even wetting. The pad must be wet over its entire area whenever cooling is needed.
- Water and care. Part of the water is bled off continuously, or the system is flushed periodically, to limit deposits; pads are dried daily; algae in the pads reduce efficiency.
The source gives an efficiency of 70–90 % for new or well-maintained pads [1]. Efficiency here is the share of the maximum possible temperature drop at the current air humidity [1]. The drier the outside air, the more cooling a pad produces and the more water it evaporates [2].
Fogging
Nozzles spray fine droplets of water directly into the indoor air [1]. Unlike pads, such systems can be used in both naturally and mechanically ventilated houses [1].
Limitations noted by the sources:
- the cooling potential of fogging is limited, so it is often installed as an auxiliary system to pads [2];
- if fogging runs after the pads, humidity in the house rises further and the birds find it harder to cool themselves [2];
- pads give more cooling without the risk of wetting the house interior [1].
Sprinkling the birds
The University of Kentucky notes that chickens are not usually wetted: feathers insulate them from the cooling, and wetting the birds also wets the litter and feed [1]. The University of Arkansas describes a different approach used in tunnel-ventilated houses. Low-pressure sprinklers spray coarse droplets onto the birds themselves: water evaporates from their surface, so the birds are cooled rather than the whole volume of air [2]. According to this source, sprinkling is most effective in dry air; it is therefore recommended to run sprinklers before the pads are wetted (for younger birds and in the morning hours) and to reduce sprinkling once the pads are wet [2]. In the source’s study, sprinkling used less water than pads in an adjacent house at similar daytime temperatures [2].
A combined option: pads wetted by nozzles
The source also describes an intermediate solution: evaporative pads kept wet by fogging nozzles instead of the usual water recirculation system [1].
Comparison
| Aspect | Evaporative pads | Fogging | Sprinkling the birds |
|---|---|---|---|
| Where water evaporates | In the pad at the air inlet | In the indoor air | On the birds’ surface |
| Ventilation type | Mostly tunnel, airtight building [1] | Natural or mechanical [1] | Tunnel, with adequate air flow [2] |
| Role according to the sources | Main method for broiler houses [1] | Often an auxiliary system [2] | Alternative to fogging; best in dry air [2] |
| What to watch | Area, wetting, water quality, care [1] | Rising humidity, risk of wetting [1, 2] | Order of operation together with pads [2] |
What this means for a project
Choosing a cooling method is a decision about the climate system as a whole, not a separate line in a specification. We calculate cooling together with tunnel-mode air exchange, taking into account the regional climate, the water source and quality, and how the controller will run the system. The specific solution for a site is decided after the calculation.
Sources
- University of Kentucky, Department of Animal and Food Sciences. Chapter 9 - Evaporative Cooling Systems. afs.mgcafe.uky.edu
- Liang Y., Tabler T. Water Use Patterns Differ Between Pad and Sprinkler Cooling (FSA1068). University of Arkansas System Division of Agriculture. uaex.uada.edu
