Figure 1 Lair for 100 calves in South-Western part of Romania

For standard buildings in stock raising (see Figure 1), heat per time for temperature maintenance in a lair for 100 calves at Tin=160C is Qx = 5070W, [1]. The flow rate of warm air is m = 715kg/h. Warm air is supplied by air flat plane solar collectors and the temperature of the air entering the solar collectors is equal to the outdoor temperature (t1=te ).In this way the possibility of indoor air spoiling is eliminated. Warm air at the temperature to is introduced into the lair. The solar collecting surface area could be calculated [2] by:

In equation (1) the meaning of the quantities is:

— K is coefficient of thermal losses

— Cp is isobar specific heat for air

— 0 is equivalent air temperature related to solar radiation and is calculated [3], [4], [5] by:

в = {тОя /K + te (2)

In equation (2) (Ta)e is the effective value of the absorption-transmission product.

For the values GR=385W/m2, K=4.73W/(m2K), to=40oC, te=11.6oC, (та)=0.74, the obtained area is A=32m2. The surface of 32m2 is made up of n=8 solar collectors, each with an area of a=4m2, that means A=na.

The average specific power of the passive wall (Trombe) at delayed heating is roughly qT=52W/m2, [6]. The Trombe wall with an area AT=100m2 can heat the indoor air for four hours after sunset.

Water heating

The water quantity consumed daily in a lair for 100 calves is m=480kg. The required thermal energy for water heating by 15°C is Q2=30.2MJ. For this purpose are used five solar collectors with warm water storage, each supplying 90kg/day heated water.

Air ventilation

The air circulating through the lair towards the outside has to evacuate CO2, biological heat and water vapours. The air flow rate (m3/h) is calculated after the criteria: maximum admitted concentration of CO2, humidity and heat excess. The sanitary norms for stock raising are satisfied if the ventilated air flow rate in warm seasons is V1=9000m3/h and in cold seasons is V2=1500m3/h, [1]. For spring and autumn, the average velocity of the evacuated air is v=0.56m/s, but in summer it could reach 2 to 3m/s. The total area of the transversal surface of ventilation shafts (in m2)

A’=V/(3600v) (3)

For spring and autumn, there results A’=0.74m2.

Ventilation could be ensured by using sections of Trombe walls with a height of h=2.5m arranged on the South wall of the building. Along the Trombe wall the temperature gradient causes a hydrostatic depression which stimulates the air absorption from the inside through the lower skylight and its evacuation through the upper skylight towards the outside. There are eight sections and each section has squared area of side l=0.3m.

In the summer air solar collectors from the roof could fulfil the role of ventilation shafts. The hourly flow rate of the air ventilated through them is V3=4050m3/h.

It is shown that in the warm season 1m2 of solar wall ensures the evacuation from the lair of 400m3 of air per hour, [1]. It means that 10m2 of Trombe wall covered with metallized reflective foil evacuates 4000m3 air per hour.