file-Convertito
08 Feb 17

PARTIAL OR TOTAL BY-PASS??

The EU Regulation nr. 1253/2016 makes it compulsory, from January 1, 2016, the presence of a device thermal bypass on VMC units. The by-pass can be automatic or manual, total or partial, or realized by the unbalance of the fans (Sent to the maximum speed set, and shooting at the minimum speed set).

With the opening of the bypass device (BP) the air does not pass through the exchanger and therefore does not occur the heat exchange between the external air flow introduced into the environment and the internal extract air flow. The objective of the BP is to take advantage of the outdoor air temperature conditions when they are energetically favorable compared to the internal air, in order to decrease the load of the heating / cooling primary; in summer / spring it will benefit from the so-called free cooling, while in winter from the free-heating.

Modern VMC units, provide temperature probes on the exchange pack: detecting the renewal T (outside air) and recovery T (inside air) control determines the automatic opening of the BP device when 1) the air conditions external / internal are energetically favorable and 2) do not create discomfort.

BP total, means that 100% of the external air flow by-passes the exchange pack and enter into the environment with external conditions (heating to the net due to the fan motor); the partial BP means that a part of the air (eg 70%) by-passing the heat exchange, with the advantages described above, and the remainder (30%) crosses the parcel exchanging energy with the 100% return air, undergoing a significant temperature rise. The union of the two flow before being placed on the environment (partial BP, 70% to the external conditions and heated 30%) will allow a limited energy benefit (estimated 50% compared to the total BP).

Consequently a total by-pass device allows to benefit fully from the energy of the outside air temperature, and it is very important requirement for VMC units for passive houses or high energy class.