The health benefits of Mechanical Ventilation with heat recover
In this article, our team member Dave considers the health benefits of mechanical ventilation and heat recovery (MVHR) that he’s experienced in his own home.
Background ventilation is a requirement of Building Regulations – Approved Document Part F identifies four basic systems for providing background ventilation to a residential property
- System 1 trickle ventilation the most basic ventilation which is a small ventilator, normally set into the window frame with a hit or miss cover to “control” the ventilation – which relies on air leakage in an uncontrolled way. Also, if you are spending a lot of money on good quality windows with triple glazing and good seals around the openings why have a vent in the frame which you cannot control?
- System 2 PSV passive stack ventilation – relies on the “natural” air leakage of the house and vents through an exhaust duct through the roof, as hot air rises through the stack effect it produces ventilation and still requires trickle vents in the windows.
- System 3 MEV continuous mechanical extract ventilation – mechanical extract from wet rooms still requires trickle vents.
- System 4 MVHR this is a better system as it does away with the trickle vents but has a supply and extract ducts through the external walls. First just a quick reminder of how the system works – fresh air is drawn in from the outside and warm, moist air from the wet rooms, kitchens and bathrooms is extracted. Ducts cross one another at a heat exchanger so that the fresh incoming air is warmed by the outgoing stale air, but do not mix. Air is circulated within the dwelling through open doors and a gap under the door leaf.
The health benefits of mechanical ventilation with heat recovery, are that the ventilation of the dwelling is continuously refreshed with filtered clean air, 24 hours a day, 7 days a week. Air is pre-warmed by a heat exchanger so there are no cold drafts.
At first you wonder that there is a waste of energy continuously operating a fan all the time, but with a properly installed and commissioned system you will not feel any drafts, and the heat energy saved by the heat exchange unit can be 8 to 15 times the electrical energy consumed by the ventilation unit. The heat exchanged is “by passed“ during the summer months so that the incoming fresh air is not pre- warmed. I have measured the temperature of the air coming out of the supply ducts (during the winter) and the temperature can be 12oC whilst the ambient temperature is 5oC, if I was relying on trickle vents I would be getting a draught of 5oC!
As an owner of a house with MVHR system, it is really staggering to see the difference in the filters as they are changed as you can see from the image the filter is black from extracting pollutants from the air, which we would have otherwise breathed in. The filters minimizing impurities coming in from the outside, such as dust, pollen and diesel particulates, which helps if you have an allergic reaction to these things.
As there is a continuous supply of fresh filtered air there will be better control over the moisture content, which will control the moisture content in the house reducing damp, and mould which is obviously beneficial to health.