Best Practice Makes Perfect - May 2011

This article appeared in Energy @ Home, May 2011

Paul Rainbird, Operations Manager, at Titon, offers some tips for getting Whole house ventilation right first time.

Competent Person’s Schemes, like the Gas Safe Register, are well known. However, it is only in the last few months, following the updates to the Building Regulations that the industry is focusing on domestic ventilation.

The new regulations mean that whichever ventilation strategy is chosen, it needs to be installed properly, commissioned appropriately and the system “handed over” to the end user to ensure correct and effective use.

And although training is important (which is why Titon has recently launched a BPEC Certified Training Course), there are some simple things that can be done to make an installation successful.  Always following the advice given in the Domestic Ventilation Compliance Guide, which accompanies Part F, should be a prerequisite of any installation.

Fully mechanical whole house systems such as Extract and Supply with Heat Recovery (MVHR) have vastly increased in popularity due to the energy saving benefits they offer. Installed well, such a ventilation system will perform as designed, keep the occupants healthy and the air clean, as well as eliminating condensation and mould growth. However, installed badly or shoddily it won’t work as it was meant to, it will use far too much energy and won’t deliver the benefits of decent ventilation.

The first element in getting the installation of a whole house MVHR ventilation system correct – and in many ways the most important – is to use rigid or semi-rigid ducting for the majority of the installation.  By using rigid duct (either rectangular or round) you’re ensuring that the air will meet the least resistance to flow and maintain efficiency. Flexible duct is a useful tool, but should only be used where absolutely necessary – and that’s the second element.  Keep flexible duct use to a minimum – ideally only in very short straight lengths, for example to aid connection between solid duct and terminals. Inappropriate use of flexible duct for long runs will cause problems such as being more resistant to flow and undermining system efficiency, it can sag or easily be crushed and result in excessive noise or insufficient ventilation.

Make sure you use the correct duct size – the cross sectional area of the duct should be equivalent to the manufacturer’s recommendations and, where a SAP Q product is being used, ensure the duct size is as stated in the test documentation – this will ensure full efficiency of the system and a performance that equates to the SAP Q Certification. Here at Titon we’re introducing new semi-rigid ducting – which makes installation quick, easy and SAP Q compliant – along with specially designed joists with pre-made apertures in to make duct runs really simple. With the click-lock joint system, you don’t need to tape and silicone seal the joints either – saving you time!

To ensure the air moves with the least resistance you need to make the smallest number of bends possible in the installation.  It’s a case of taking the most economical route between the terminal in the room or wall and the central unit.  This holds true for both central mechanical extract systems and whole house ventilation systems – with or without heat recovery.  If you end up creating a duct run which has more bends and curves in it than a Formula 1 race track, you’ll have a system that performs inefficiently and won’t comply with the Building Regulations. Additionally, make sure all the joints are well sealed and as tightly as possible.  That means silicone sealing and using a good quality sealing tape, or mechanically fixing with a worm-drive clip.

Always ensure you use insulated duct for the runs to and from the outside air and wherever ducts pass through cold spaces, otherwise condensation will form on the inside or the outside of the duct. Condensation can damage the system or surrounding areas and you will lose much of the benefit of using heat recovery - you don’t want the heat you’ve paid for to be lost!

Consider the terminals.  Room terminals (air valves) should be sited to encourage movement of air through the room, for example, away from the doors; otherwise you’ll end up with a stagnant area and also note that there is often a difference between supply and extract terminals. Always ensure the external terminals, such as roof cowls or air bricks, are designed to meet the system performance requirements by following the MVHR unit supplier’s recommendations. Many products are not suitable and can seriously impair system performance due to excessive airflow resistance or cause the formation of excessive moisture.  With central mechanical and whole house systems, you need to ensure the measured air flow at the room terminal (both extract and supply air) complies with Part F of the Building Regulations.

Of course, it may be obvious, but you should always read the manufacturer’s instructions.  You’ll need to pay particular attention to the wiring details because it will differ for each type of unit – even from the same manufacturer.  Some units will require one-way booster switches, others will need two-way switches, and you don’t want to set about rewiring for switches when the house has been freshly plastered!

Finally a word about commissioning – a requirement of all systems and now included in Part F of the regulations.  A good commissioning process would be to check the installation against the design drawing, check the manufacturer’s instructions are available, make sure the installation matches the design, and that the correct controls are installed. You’ll also need to check that any condensate pipes are fitted correctly and that the airflows are adjusted to meet the requirements of Part F for that dwelling room by room.  You should also note any alterations to the original design and make sure they are not impeding the efficiency of the system.  The commissioning should be completed so that the controls are left in working order and once a proper system handover is complete, the home occupier can rest safe in the knowledge that their ventilation system will be doing its job.

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