The Zehnder ComfoFond-L Q brine-earth heat exchanger has been developed for use in conjunction with the Zehnder ComfoAir Q350/450/600 comfort ventilation units. It combines the highest comfort with very high efficiency in a compact installation. In winter, when the outdoor temperatures are low, it pre-heats the outdoor air to prevent freezing. This ensures optimum operation of the ComfoAir Q ventilation unit, even at outdoor temperatures below freezing. In summer, the ComfoFond-L Q sub-soil heat exchanger lowers the temperature of the outdoor air, and helps to support a conventional air-conditioning system.