A ventilation unit with heat recovery, comprising a first block having an air interconnection to the interior of the building, a third block having an air interconnection to the exterior of the building and a second block located between them, in which the heat recovery exchanger is located, with at least one first channel and at least one second channel. The second block is insertable between the first block and the third block in such manner that the first channels are airtightly connectable to the first block and to the third block. The second channels are airtightly connectable to the first block, different from the air duct to which the first channels are connectable, and the second channels are also airtightly connectable to one of the air ducts of the third block, different from the air duct to which the first channels are connectable.

Embodiments are directed to obtaining a specification comprising at least one requirement associated with a heating, ventilation, and air-conditioning (HVAC) system, and based on the specification, configuring a control system to control a movement of fluid back and forth across at least one regenerator device of the HVAC system and a mixing of the fluid with ambient air.

A low temperature cooling and dehumidification system uses a reverse airflow arrangement to defrost a frosted cooling coil while not interrupting operation. Automatic air dampers are used to reverse the airflow at the proper time to initiate defrost of that section of frosted cooling coil. This system is useful for low temperature cooling and dehumidification in situations where the inlet air is above freezing, however exiting air below freezing can be supplied if desired. It is advantageous for operation if the coolant flow and temperature internal to the cooling coil are regulated to create the conditions for frost formation to begin closer to the air leaving side of the active cooling coil. The dehumidified generated condensate can be collected and used as grey water and/or potable water.