ACR Journal

CM YK / .ai CMYK / .ai CMYK / .ai acrjournal.uk 29 VENTILATION mitigate COVID19 Regarding noise from increasing the fan speed, the best modern ventilation systems generally include more e cient fan motors which mean higher performance with lower power consumption, and lower noise. Modern ventilation units (such as our own Lossnay range) can also benefit from a wider air volume range, generally with variable fan speeds of the rated air volume of each unit. Units can be quickly and easily switched from full fan speed (at times when spaces are unoccupied) to 75% or 50%, if noise is likely to be more of an issue for occupants. Noise wise, these modern systems oƒer fan speed noise levels from 17dBA (for the lowest fan speed in the smallest unit) to 40dBA (for the largest model on high fan speed). A study room or library is considered to be at a level of about 20dBA, whilst a whispered conversation is recorded at anywhere between 25 and 35dBA. Overall a suburban area at night registers at 40dBA, so even with an increased fan speed, the units can still provide the quietness of operation that will deliver significantly increased air flow into the space, without disturbing the occupants. At the moment, the current consultation on Part-F is calling for changes in the way buildings are designed so that we can increase ventilation by an extra 50%. Hopefully this article helps to highlight that for many buildings, the systems are already in place, and with a tweak of the control or the fan speed, they can increase the amount of fresh air, without compromising on comfort. And if your building or budget doesn’t allow for a complete upgrade in your ventilation system, then there are individual wall-mounted MVHR systems that can be easily retro-fitted to immediately increase air flow. These require an outside wall and electrical connection to oƒer a quick and cost- eƒective remedy. How does MVHR work? Mechanical ventilation with Heat Recovery allows the stale air in a room to be removed but captures heat energy from the outgoing air to reduce the amount of energy needed to heat up the incoming air. The best systems can recover between 80-90% of the heat energy and they do this without the two air flows (exhaust and supply) touching each other. In the case of the Lossnay system, a specially designed paper core ensures the maximum crossover of heat energy from one air flow to the other. The use of paper also allows both latent heat and sensible heat, meaning the moisture levels in the room are maintained and the air doesn’t become too dry and static. In the case of Lossnay’s paper core, this has also been tested using the E-Coli bacteria, which is significantly smaller that the SARS (COVID-2) virus. Not only can MVHR therefore increase the amount of fresh air inside our buildings, it can also safeguard the occupants by filtering out harmful or toxic things in the air. In conjunction with BESA, Mitsubishi Electric has produced a free Guide to Indoor Air Quality which can be downloaded here. https://library.mitsubishielectric. co.uk/pdf/book/Indoor_Air_Quality_ Guide#page-1 Crossflow heat exchanger – energy exchange without mixing air streams.

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