Greenhouse floor heating system optimization using long-term thermal performance design curves

Abstract

Steady-state design curves suitable for the determination of long-term thermal performance of the floor heating system are presented in the paper. The dominant design variables considered in the system synthesis are: pipe diameter and spacing, floor depth, greenhouse main air mass temperature, hot water temperature, water flow rate and plant canopy density. The design curves are generated for a wide range of these parameter values. The nomograms are presented in terms of the greenhouse heat gain per unit floor area as a function of the floor depth, with other variables as parameters. The set of design curves also includes the values of the rate of change of heat flux with the floor depth. This facilitates in design optimization by reducing the three dimensional search in geometric parameter, namely, pipe diameter and spacing, and floor depth, to a two dimensional search. The utility of nomograms is illustrated through a design example for a floor heated greenhouse located in the midwest region of the United States. The optimum parameter values for the floor heating system are estimated using the classical calculus technique.