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Heat loss through open door

I found this on a website about pig rearing! Does anyone know of a more definitive source?

Ventilating through the door is not very helpful

By Nick Bird, FarmEx - One interesting point to emerge from our energy monitoring project on British pig farms is the effect of leaving the door open.

Sometimes it’s accidental, other times it’s intentional – leaving the door open and the fan switched off for young pigs. Where intentional, it’s not clear whether it’s to save money (ie. electricity for the fan) or whether it’s believed that ventilation is in some way ‘better’ with the door open than with the fan running.

Whichever, the result tends to be higher costs rather than lower, since leaving the door open loses a lot of heat. This is illustrated in Chart 1. Heat loss depends on the size of door and inside and outside temperature. The chart shows the calculated heat loss based on stack effect alone (thermal buoyancy) for a range of outside temperatures, at two inside temperatures, for a regular sized door (1.98m high by 0.79m wide aperture).

The amount of heat loss may seem surprising – 6kW of heat lost through the door at a relatively mild 10ºC outside. At 0ºC outside, it’s a massive 13kW! This huge heat loss is, of course, useful when power fails and the only ventilation is by leaving the door open. But somewhat less handy when it’s from fragile weaners, or electrical heating. It’s worth noting that – though calculated on an overall inside temperature of 25ºC – temperatures will be far lower at floor level where the pigs are.