AIR CONDITIONING, COOLING & VENTILATION


Whole house ventilation: common mistakes and how to avoid them


As ventilation systems become more complex, the more opportunity there is for errors to creep in. Here, Paul Williams, Domus Ventilation product manager identifies the four most common mistakes we regularly see when it comes to whole house ventilation systems


Mistake 1: Using the wrong size MVHR unit


Mechanical Ventilation with Heat Recovery (MVHR) systems, such as our own HRXE range, come in different sizes to meet different sized properties. Choose the wrong MVHR size and either it’s too big and therefore not energy efficient, or it’s too small and not going to deliver the ventilation required under Building Regulations, but will deliver excess noise as the fan within the unit works overtime to meet demand. Incorrect unit specification often results from a


failure to take into account the resistance in the ductwork. Avoid this by ensuring the ductwork drawing is done prior to unit specification and prior to other services going in. Domus Ventilation offers a free drawing service so this issue can be entirely – and easily! – avoided.


Mistake 2: Not following the ventilation drawing on site


Even if you have the best ducting drawing for that building, if it’s not adhered to on site the entire ventilation system can be compromised and will be noisy. Trying to make duct runs simpler, to save time and money, is a false economy if you have to rip out the system at your expense as it doesn’t comply with Building Regulations.


Also, avoid the temptation to replace rigid ducting with flexible duct work as this causes a lot more air resistance and can be crushed easily.


Mistake 3: Inadequate ducting insulation


Another key issue relating to ducting is the incorrect use – or total absence – of ducting insulation. Ducting insulation is required under Building Regulations where the ducting passes through unheated areas and voids, such as loft spaces. The minimum duct insulation standard is the equivalent of at least 25mm of a material having a thermal conductivity of ≤0.04W/(m.K). Specialist duct insulation is essential to meet


this requirement. A common mistake that is made is using insufficient insulation, using standard building insulation materials that are unsuitable or not using any insulation at all. Furthermore, we often see insulation missing from the intake and the exhaust. The problem with poor insulation is that condensation forms, which drops down onto the ceiling and becomes an ugly visible stain. In the worst cases, this can lead to mould which is not only unsightly but can be hazardous to health.


Mistake 4: Incorrect MVHR system commissioning


Commissioning an MVHR system accurately is one of the most vital parts of getting the ventilation system signed off correctly. Any mistakes at the commissioning stage will result in over or under ventilating. There are two common errors we see here, the first relating to anemometers used to measure airflow from the air valves in wet


rooms and the kitchen. Be sure to use a calibrated powered hood anemometer that meets the ±5% accuracy required by Approved Document F1 (2022). The second problem area is


when it comes to adjusting the potentiometers on the front of the MVHR unit to ensure the correct trickle and boost rate. In apartment blocks, it’s tempting to assume that each apartment of the same size will require the same setting. However, the commissioning engineer can’t see ‘behind the scenes’; the ductwork may be run slightly different in the next apartment, for example, which will mean the settings need to be different.


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Read the latest at: www.bsee.co.uk


Carlo Gavazzi UK Ltd. - 4.4 Frimley Business Park, Frimley, Camberley, Surrey GU16 7SG - Tel: 01 276 854 110 - www.gavazziautomation.com Carlo Gavazzi hp BSEE May23.indd 1


, and internet protocols such as


17/4/23 09:44 BUILDING SERVICES & ENVIRONMENTAL ENGINEER MAY 2023 15


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