Mechanical ventilation systems are those which incorporate a fan or similar device to assist air movement. An important subset of this main category is mechanical ventilation with heat recovery (MVHR). These systems extract heat from exhaust air and transfer it to incoming fresh air, greatly reducing the heat energy which would otherwise be lost from a building. Energy is transferred via a heat exchanger, of which there are several designs on the market. Contraflow heat exchangers are amongst the most efficient.
In contrast, natural ventilation does not incorporate heat recovery and is thus inherently wasteful of energy. For example, a classroom block in the Home Counties using natural ventilation is estimated to use around 12 times the energy for space heating that would be used by a similarly rated heat recovery ventilation system.
Heat transfer efficiency is adversely affected by build-up of deposits on the heat exchange surfaces. This can be prevented by effective filtration of supply and extract air flows. In each AirMaster heat recovery ventilation unit, the efficiency of heat exchange is maintained by the use of M5 (previously known as F5) filters as standard on both the supply and extract pathways. M class filters have rigid frames, enabling them to keep close control of bypass leakage. Given regular replacement, they ensure that the fine spaces between heat exchange surfaces remain clear at all times, making it possible for AirMaster units to maintain a high level of thermal performance during the whole of their 15 year lifespan.
SAV AirMaster units use high efficiency aluminium contraflow heat exchangers with a thermal efficiency of 84% at dry bulb conditions. However, with normal humidity levels of say 70% RH, heat exchange takes place much more readily, producing thermal efficiencies of up to 91%. Therefore when making comparative evaluation of thermal performance between different types of exchanger, it is important to establish the assumed level of relative humidity. Aluminium exchangers have excellent thermal conductivity, allowing a relatively wide pitch to be selected between heat exchange elements. This ensures the prompt evacuation of condensate, even when external temperatures fall to single figures. This is in stark contrast to plastic exchangers, where condensate build up at low temperature is often sufficient to restrict extract air flow, and thus impair the efficiency of heat exchange.
AirMaster units have a number of temperature control mechanisms, which enable them to keep room temperature remarkably steady. That being said, it is not possible to rely on such units for complete temperature control on very cold days. It will always be necessary to have some independent form of heating available to bring the occupied space up to temperature on cold mornings, before the occupants arrive. However, once the working day commences, AirMaster units are able to use heat recovery, bypass dampers and differential fan speeds to keep room temperature at set point. These processes are completely automatic with no manual intervention being necessary.