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Ventilation

How you ventilate a house depends very much on the level of energy efficiency you are aiming for. At the lower end the Building Regulations provide a “better than nothing” standard

The building regulations

cover the ways that houses should be ventilated –

England & Wales   Approved document F  (and see the Domestic Services Compliance Guide)

Northern Ireland   Technical Booklet K

Scotland  Domestic handbook

Taking the example of the English and Welsh regulations –

Although the performance based regulations are quite detailed and require careful reading they basically ask that a house should have 3 types of ventilation – extract , whole house and purge .

The extract and whole house combinations can be seen on page 12 diag. 1

Another way of showing the permutations is –

  • Extract ventilation in places that have damp air or smells – kitchen, bathroom, toilet, utility room via –
    • passive stack ventilation – to outside or
    • extract fans which take air –
      • straight out or
      • out through ducting, either
        • to outside or
        • to heat exchanger unit and then out
  • Whole house ventilation– this is background ventilation
    • trickle vents (in habitable rooms) in all cases unless you use –
    • continuous extract and supply with heat recovery
  • Purge ventilation – this is basically the ability to leave the window open for a bit to clear smells, smoke etc.

There are options for controls for energy saving if mechanical ventilation is used. There are also special conditions for basement rooms and rooms off other rooms.

There are two interesting green options here for energy saving –

  • passive ventilation which uses no electrical energy and is extremely reliable
  • mechanical ventilation with heat recovery

Passive stack ventilation

(not to be confused with Passivhaus ventilation) utilises the natural convection effect (stack effect) of hot air rising so that warm damp air from kichen and bathrooms simply goes up a flue and out through a terminal in the roof. The flue has an automatic closer in it so that it only opens when it detects moist air. This prevents warm air leaking out when not necessary. There is no power used, no noise and nothing to break down. The air is replaced by fresh outside air coming in through trickle ventilators. The Building Regulations part F – Ventilation have lots of references to passive ventilation and it pays to do a local search when in the pdf. See also Passivent

Heat recovery ventilation (MVHR)

–  is ventilation incorporating a heat exchanger. When it is installed as a whole house system it extracts air from all the main rooms including kitchen, bathrooms and toilets and replaces it with fresh air from outside which is then ducted back to the various rooms. There is a central fan/heat exchanger unit where the cool incoming air picks up heat from the warmer outgoing air by means of the heat exchanger. This saves a considerable amount of energy in terms of heat but does require a fan to be running most of the time. This consumes energy, will create a (very small) amount of background noise and may need repairing every 15 to 20 years. The heat exchanger and parts of the ductwork (especially close to a cooker) will need regular cleaning

In the case of highly insulated houses such as Passivhauses there is often a case for a summer bypass mode so that overheating does not occur in summer.

It is worth considering incorporating a service duct where all the services such as MVHR, boiler, pipes, cables etc. can be housed. See Service Ducts

There have been considerable problems in the UK with MVHR.  These are mainly to do with poor design or installation rather than the concept itself and they follow the same pattern as has occurred with other technologies new to the UK such as Ground Source Heat Pumps, – often to do with new companies rushing into the field with poorly trained staff.

A recent study,  Characteristics and performance of MVHR systems  highlights the importance of competent design, installation, commissioning and handover.

Decentral ventilation

Fairly new on the market is the fresh-r by the Dutch company VAVENTIS. This is a balanced heat exchanger fitted to an outside wall and works by transferring heat through huge lengths of very fine copper wires rather than through the interleaved plates of the more traditional type of heat exchanger. It needs no filters. Typically two units would serve a medium sized house. Viking House, who are very committed to Passivhaus construction are very enthusiastic about their future. See also the Breathing Window.

Other through-the-wall systems are coming on the market: A German one, Lunos, is claiming up to 90% efficiency for heat recovery with very low running costs.

What needs remembering about all MVHR systems is that their efficiency is dependent on how clean they are kept. If they are venting a kitchen, for instance, particles of cooking oil can coat the internal heat exchanger surfaces, which then clog up with dust. This reduces not only the exchanger efficiency but also the flow of air. So the way in which the heat exchanger surfaces can be cleaned becomes important along with what type of filter is incorporated.

Passivhaus Ventilation

At the most advanced end of ventilation technology has been Passivhaus ventilation . This system balances several factors –

  • sealing the house extremely tightly to limit any wasteful effects of draftyness
  • introducing the minimum amount of fresh air needed to keep a house healthy and pleasant
  • the ability to heat the house via the ventilation air (thus avoiding the need for a central heating system) This is done by an electrcal heater or sometimes a ground source heat pump.
  • efficiently recovering heat from the extract air (over 75% efficiency – sometimes even over 90%)
  • careful ducting of the air so that
    • the air circulation is effective but slow enough that air movement is not noticeable
    • the air is extracted from the damper areas such as kitchen and bathroom
  • the ability to throw your windows open in summer

Ventilation for heating appliances

The Building Regulations have a good deal to say about permanent ventillation required by heating appliances such as open fires and wood burning stoves. These appliances require a certain amount of air to keep them burning properly and to avoid carbon monoxide (which is poisonous) escaping into the house. The requirements are laid out in the Approved Documents, part J.

 


see also Air tightness because this has a bearing on infiltration rates used in ventilation calculations.

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