|Positive ventilation system diagramatic|
Many of our houses are getting sealed up all in the name of energy efficiency. Draughts around doors are being sealed, windows are being replaced (often without trickle vents), chimneys are being blocked up, lofts insulated, vented suspended floors replaced by solid concrete slabs. We have also brought more humidity into our homes by installing indoor toilets and bathrooms (this could be for the better though!)
All this extra moisture needs to go somewhere. In a fully breathable structure the walls, floors and roof do all of this for us, but many of our homes now have cement renders, conventional painted walls, non breathable insulations etc. The moisture therefore is trapped in the home and on its internal surfaces. This if course can lead to condensation issues and the associated troubles of damp and mould.
So this gives us two choices – reinstate breathable structures, or manage the humidity in another way. Given that the former can require lots of work and disruption I thought that it was worth looking at the alternatives.
One solution to reduce damp on internal surfaces is to have greater ventilation. Here’s the rub. How to get warm air into your home to provide you with greater drying capacity without introducing a stream of cold air. Afterall we are trying to reduce carbon emissions etc by making our homes more airtight and by reducing consumption of energy.
There are three main solutions, but each has issues.
Positive pressure – this is the easiest solution. Basically the concept is to pump fresh air from the attic space into the rest of the house. Air in the attic is generally a couple of degrees warmer than outside ambient temperature, however it still represents a source of cold air. Other issues are that because you are using one point of entry for the fresh air its effectiveness is reduced when doors are closed and also where most of the damp problems are downstairs (unless you provide ducts to a lower level for the main air input). Ceilings also need to be airtight so that the pressurised air does not just go straight back into the attic! So care needs to be taken when thinking about how you live and whether you are prepared to accept cooler air as a means of getting fresh air.
Whole House Heat Recovery Ventilation – this is probably the most complicated (but probably the best solution). Here you have a heat recovery system (again normally in the loft space) that takes ‘stale’ and moist air from some rooms (kitchen, bathroom, living room) and uses it to pre-heat the incoming air from outside. Many of these are around 90-95% efficient at transferring the heat. The fresh air is now pre-heated and pumped to the rooms where it is required. This really does get to the root of the ventilation problem, however it requires ducting to be installed through the house. This is fairly instrusive and disrupting, but it might be the solution that you desire.
|Whole house system|
Solar air ventilation – this is a compromise between the two solutions. What happens here is effectively a positive pressure system with pre-heating and control elements added to it. Air is preheated using roof based solar collectors (just like the solar thermal systems that you see around) but rather than water, they heat air. The pre-warmed air is then pumped into the house as per positive pressure (so the same issues still remain), but this time the system is designed to give you control over how much air is delivered and at what temperature. The fan units have inputs from three sources normally (the solar collectors, the loft and the eaves). This means that they can cool the house as well as warming it. This system needs you to have an accessible roof that is preferably facing south. This solution is more expensive than the simple positive pressure system, but cheaper than a whole house system.
|Nuaire sunwarm system showing solar air panels, fan and vent input|
Hope that this give you an overview of what is available, in an add-on technological sense, for getting ventilation into sealed older homes that minimises carbon emissions and running costs.