The Conductive Heat Loss calculator computes the heat loss (HL) based on the surface area (A), temperature variance (vT) and the U factor of the surface material of a greenhouse.
INSTRUCTIONS: Choose units and enter the following:
Conductive Heat Loss (HL): The calculator returns the heat loss in BTUs per hour. However this can be automatic converted to compatible units via the pull-down menu.
Insulating Coefficient
U | Material | |
0.15 | triple pained glass | |
0.4 | double pained glass | |
0.7 | double layered plastic | |
1.22 | single pane glass |
Conductive heat loss is the transfer of heat through a membrane. For application in spaces such as greenhouses, the transfer of concern is typically warmth from within the greenhouse that is lost through the skin of the greenhouse into the outside environment. The equation for the conductive heat loss is relatively simple:
CHL=A⋅vT⋅U
Where:
The U value is published for many material. Consult your product supplier for the actual U value of the material planned to be used. However, some common U values are as follows:
Note: U factor is the reciprocal of R factor which is used to rate insulation materials (e.g. fiberglass batting)
Consider the extreme cases in your area for the maximum temperature variance. For example, if your plants require a minimum of 57^{o}F, and the possible low temperature outside is -14^{o}F, the variance is 71^{o}F.
The result of the equation is BTU/hour required to compensate for the conductive heat loss.
Greenhouses and high tunnels come in different shapes. The following diagrams shows several of the common shapes.
The following calculators help compute the surface area needed when computing Conductive Heat Loss (CHL).
Greenhouse or High-tunnel Calculators