right. This point also indicates the heat content (46 kJ/kg) *. From here, trace the sloping heat content line upwards to the left until this line crosses the horizontal temperature line (dry bulb). The corresponding climate state can again be found at the intersection of these (red) lines. From this point, can find the moisture content by tracing vertically upwards (11 g/kg) and the RH by following the RH curve upwards to the right (85%).
* To determine the heat content you only need the wet bulb, so the wet bulb is also a measure of the heat content!
Summary basic parameters Mollier diagram Temperature (dry bulb) Wet bulb RH (relative humidity) AH (absolute humidity / moisture content) Moisture defi cit Enthalpy (heat content)
The three examples above should serve to clarify the essence of the entire Mollier diagram!
Which parameters (apart from temperature and RH) are important for mushroom growing? • If the outside AH is lower than the growing room AH, the outside air is suitable for drying.
• If the outside enthalpy is lower than that in the growing room, the outside air is suitable for cooling.
Example 2.
Moisture defi cit (example 3) As well as temperature, RH, heat and moisture content, the very latest climate controllers also provide an option to regulate the moisture deficit. Moisture deficit is nothing more than the difference between the moisture content (AH) and the saturation humidity (SH) at 100% RH. In the example below, at a temperature of 18 °C and an RH of 85%, the moisture content is 11 g/kg and the saturation humidity at 100 % RH is 12.9 g/kg. This means a moisture difference - or moisture deficit- of 1.9 g/kg. The moisture deficit therefore indicates the amount of moisture the air can still absorb until it is saturated.
• If the AH of the inlet air is lower than the growing room AH, moisture will be extracted from the growing room.
• If the enthalpy of the inlet air is lower than that in the growing room, heat will be extracted from the growing room.
• As the moisture deficit increases, the growing room air can absorb more moisture from evaporation.
Note: the parameters above also apply in reverse.
Example 3.
Air pressure and altitude As the examples show, the Mollier diagram indicates a number of the parameters per kilo of air (weight) and not per m3 air (volume). The relationship between volume and weight concerns the air density. This depends on the air pressure or altitude. As a rule of thumb, at an altitude of 0 metres an average air pressure of 101.325 kPa is assumed with an air density of 1.2 kg/m3 at a temperature of 20 °C. So, at 0 m altitude (sea level) 1 m3 air of 20 °C weighs 1.2 kg. At higher altitudes, the air pressure is lower, therefore the air has a lower density (thinner). Farms situated at higher altitudes should install a greater fan capacity in m3/h in order to have the availability of the same number of kg/h. Generally, about 10% extra fan capacity is required per 1000 m of altitude. This information also makes clear that you should use a different Mollier diagram if there are significant differences in altitude – i.e. air pressure!
Symbol Unit T of Td °C Tn φ x dx h °C % g/kg g/kg kJ/kg
MUSHROOM BUSINESS 27
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