The analysis of the temperature in the case of the utilization of ducts to heating of the plastic house by the warm wind heater

Abstract

1. Two observations to analyse the air temperature in the plastic house were carried out. The one is the air temperature in the tunnel in the plastic house, and the other is the air temperature in the curtain in the plastic house. On both cases, a warm wind heater equipped with ducts is utilized.
2. When the air in the duct laid in the tunnel is discharged out of the tunnel, the longer the distance from the heater, the lower the air temperature in the tunnel.
The next notation was set up:
heat transmission rate of the tunnel; h₁kcal/m² h°C
heat transmisson rate of the duct; h₂kcal/m² h°C
heat transmission rate of the soil surface; h₃kcal/ m² h°C
radius of the tunnel; r₁ m
radius of the duct; r₂ m
wind velocity in the duct; v m/h
specific gravity of the air; w kg/m³
specific heat of the air; c_P kcal/kg°C
then, the condition to minimize the air temperature lowering near the tunnel end is
2h₂r₁/r₂vwc_P•(πh₁+2h₃)/(πr₁h₁+2πr₂h₂+2r₁h₃)=1
3. When the air in the duct laid in the tunnel is released into the tunnel (the length of the duct is a little shorter than the tunnel) the air temperature in the tunnel is too high near the end of the duct. The larger the blast amount of the heater, the more uniform the air temperature in the tunnel.
4. On the two cases, that the duct is laid in the tunnel, the data measured in the large vinyl house at Hanyu Shi, Saitama Ken have good fitted the theory.
5. When the tunnel is removed and the duct is laid in the curtain, the analysis of the air temperature in the curtain is similar with the one in the tunnel in which the air in the duct is discharged.
6. On the air temperature in the curtain, by the data measured in the fylon house at the Saitama Ken Horticultural Experimental Station, we have decided the constant of the function which is obtained by the theory.
7. The results calculated the air temperature in the curtain were as follows: 1) To get the even distribution of the air temperature in the curtain, large radius of many ducts and high speed of the air in the duct are effective. 2) A considerable difference in maximum air temperature and a smaller one in minimum air temperature were observed between two heaters which had heating power of 3×10⁴ kcal/h and 2×10⁴ kcal/h respectively.
The air temperature inside the curtain dropped by 3.4°C and 6.6°C, when the air temperature out of the house and the soil surface temperature fell down by 10°C.