Correct ventilation is important for maintaining a healthy and comfortable building. Without adequate ventilation, humidity, CO2, dust, particulate, and other forms of air pollution can build up indoors leading to respiratory problems like asthma attacks, increased spread on respiratory infections, and deterioration of the building structure as conditions become conducive to the growth of black mould, and various forms of fungal rot. In addition, in summer conditions, well insulated but poorly ventilated buildings can become excessively hot.
Traditional buildings were strongly ventilated, had no damp proof course, were built of vapour permeable materials, and were poorly insulated – which works for the structure provided inappropriate modern materials are not used in any renovations, but can result in very high energy consumption if heated to typical modern standards. IF MODERNISING AN OLD BUILDING, ALWAYS CONSULT A SURVEYOR WITH SPECIFIC EXPERTISE IN RENOVATING SUCH BUILDINGS FOR ADVISE ON APPROPRIATE MATERIALS AND METHODS.
In more recent years, buildings have been constructed with a damp proof course using largely impermeable materials, high levels of insulation, and much more air tight construction methods. Whilst this greatly improves energy efficiency, such buildings need suitable active ventilation systems to ensure that air quality is maintained.
Using simple vents and extractor fans can adequately ventilate such a building, but at the cost of losing all the energy efficiency advantages of the more air tight construction methods, and on new buildings would be unlikely to meet the energy efficiency requirements of Part L of building control.
A much better approach is to use a Mechanical Heat Recovery Ventilation system (MHRV) in which incoming ventilation air is warmed in a heat exchanger by outgoing stale air. This type of system with good design can in optimum conditions recover around 80% of the heat in outgoing air whilst using a very modest amount of power to run the fans moving air through the system. This achieves the goal of adequately ventilating premises whilst retaining heat.
MHRV systems come in single room and whole building forms, can incorporate high quality hepa-filters to remove dust and bacteria, and can adjust their ventilation flow according to sensors detecting levels of humidity and CO2 in the rooms being ventilated, and in summer can be set to high air flow night ventilation bypassing the heat exchanger in order to cool the building on summer nights and so minimise or eliminate the need for air conditioning.
MHRV systems – (usually single room models) can also be retrofitted to older buildings, and are particularly useful in eliminating condensation related damp issues - so removing the conditions which lead to issues like the growth of black mould.
Look out for heat recovery efficiency and specific fan power on the data-sheets of any MHRV equipment you consider obtaining as well as checking that it incorporates a humidistat – to reduce air flow rate when the air is relatively dry, for the ability to incorporate air filters (especially in areas with high air pollution), and for the ability to run in summer bypass configuration – taking unwanted heat out of the building especially at night when ambient temperatures are lower.
When installing whole building systems, minimise pipe runs, incorporate soft curves rather than sharp right angle bends, and use adequate cross sectional area (To optimise specific fan power and minimise aerodynamic drag), also ensure air tight joints, and that pipe runs are insulated to prevent your ventilation and heat leaking away where you don't want it to go.
