Although the recent trend in the UK has been towards embracing mechanical heat recovery ventilation, there is a school of thought in favour of demand controlled ventilation (DCV), commonly used in Europe and Scandinavia in social housing, as a superior solution for ventilating air-tight buildings.
A 2008 study by the Fraunhofer Institut Bauphysik in Germany shows that DCV is a more cost-effective and reliable method of delivering the optimum indoor environment. The study calculated the energy needed for a supply and extract fan with heat recovery in comparison with a demand-controlled mechanical extract fan.
The Institut found that a demand-controlled MEV system generated only 1,070 kWh extra consumption per heating period than an 80% heat recovery system - and for half the cost.
This was equivalent to only 47 euros (£40) in the conditions of the study, which was carried out on a 75 m2 flat occupied by three people (indoor temperature = 21 deg C; U-Value = 0.25 W/m2.K). This represents much less than the cost of the annual filter change.
In the long run, the initial extra cost of the heat recovery system (supply and fit) in comparison with DCV is never paid back - and that is without taking the required filter change into account. This study also shows that a DCV system offers a method of staying below 1,200 ppm CO2, which guarantees optimal indoor air quality.
In France, two large-scale monitoring projects, Performance and HR-VENT, have allowed testing in-situ of mechanical and hybrid ventilation systems.
The Performance project spent two years monitoring demand controlled MEV in on two air-tight apartment blocks (n50 = 1.51 and 0.94 ACH @ 50 Pa). The project concentrated on two buildings erected in 2007 and the efficiency of humidity controlled MEV in general and the DCV system in particular.
Thirty occupied dwellings were monitored for two years to measure representative parameters for energy consumption and indoor air quality. Measurements show that indoor air quality is ensured in both low- and high occupancy bedrooms.
The peak of CO2 concentration shifts from 700 ppm in the low-occupancy bedroom to 950 ppm in the latter, with the 1,500 ppm level only exceeded for a few hours in the heating season.
The Performance project found that the DCV systems reached high levels of indoor air quality compared with fixed ventilation systems; condensation risks are negligible; the monitored systems enabled 30 per cent (and more); and fan consumption was decreased between 35 per cent and 50 per cent.
With more than two million homes on the Continent operating successfully with DCV, is it time for the UK to consider adopting this highly effective system as a standard for both new build and refurbishment?
Colin Hone is sales director for Aereco