An electronic HEMD determines the optimum balance between gas cooling and heat exchanger pressure loss, for any given operating condition, and adjusts the gas flow rate through the exchanger accordingly, to yield the maximum net power savings afforded by the exchanger. If the lottery entry is not a winning entry in the first lottery drawing the lottery entry is eligible automatically for a second lottery drawing subsequent to the first lottery drawing. Onto said layer can be applied a functional covering, for example of rubber.