Types of MVHR System
Mechanical Ventilation with Heat Recovery systems come in a variety of shapes and sizes.
Thermal Wheel Heat Recovery
This is the largest of the different ventilation systems, not only in physical size but also in the air recovery efficiency. The systems are made up of 2 large wheels with a honeycomb design; one half takes in stale air from inside the room, the other half takes in fresh air from outside. The wheels rotate in opposite directions and simultaneously the energy from the stale air is transferred to the fresh air, and this heats it up to match the original temperature.
The heat exchanger wheels can be constructed from a wide range of materials including paper and plastic, however, most typically they are made from aluminium. The temperature of the air being fed back into the building can be controlled by changing the speed of rotation of the wheels and thus the amount of energy transferred. The thermal wheel system has some very key benefits, including its high efficiency (up to 80%) compared to other systems, and its quicker return on investment (if properly set up).
Plate Heat or Recuperator Technology
This type of system tends to be more common than thermal wheel heat recovery because it can be used on a smaller scale. It is made up of parallel plates built from plastic or metal that allow the air that has been extracted from inside the building to pass over the air coming in from outside, transferring the energy and heating it up. One of the key factors in the efficiency of this system is how conductive and slim the individual plates are. Plate heat recovery systems have an efficiency of maximum 70%.
Run Around Coil or Closed Loop Technology
This type of system can be added to an existing air ventilation system and is made up of two coils that are connected by a circuit of pipes. The circuit is charged using water which picks up heat from the exhaust pipe and transfers it to the supply air coil. These types of systems tend to be used where the two air streams are not close together. The maximum efficiency is around 50%.
Heat Pipe Technology
This type of system can only be used where the air handling is processed through one system. They are also, out of all the heat recovery systems, the lowest maintenance. The system involves a tube system including a refrigerant to take the heat from the extracted air and transfer it to the incoming air. Vertical arrays have a maximum of 75% efficiency and the process uses evaporation of the refrigerant to transfer heat. Alternatively, horizontal arrays have a maximum efficiency of only 50%, and the system incorporates wicks in the pipework that allow the transfer of the refrigerant.
Boiler Flue Economisers
These systems can be fitted on new boilers, or they can be retro fitted to older models. The systems capture the heated vapour which is then used to increase the boiler efficiency. Generally, an efficiency of 5 to 15% can be achieved by condensing or non-condensing gas-to-water systems.