MEV & MVHR Retrofits and Why They Should Not Be the GoTo Strategies скачать в хорошем качестве

MEV & MVHR Retrofits and Why They Should Not Be the GoTo Strategies

There are around 28 million existing properties in the UK that must have insulation retrofits if we are to get anywhere close to achieving our Net Zero ambitions. We've known this ever since the 2050 carbon reduction deadlines were first committed to well over a decade ago. Whilst these insulation improvements are mandatory for each and every property so too is simultaneous ventilation performance improvement without which we will further compound the increasingly well recognised and understood problem of health and wellbeing issues caused by poor indoor air quality. So what is the best way to improve ventilation in an existing building ? Opening windows is the usual suggestion but it wastes energy and costs money and is often not effective. Install trickle vents or air bricks is another common one but this too wastes energy, is usually not effective and will make a condensation and mould problem worse. In fact any strategy that relies on natural background ventilation via opening windows, trickles or air bricks should be avoided in this context because it wastes energy without being very effective. So that leaves mechnical retrofits. As mentioned above we can forget System 1 Decentralised or System 3 Centralised Extraction (MEV) because the supply component of these is natural and wastes lots of energy without being very effective at all. How many times have you seen a property with extraction in the bathroom and kitchen but with condensation and/or mould in the bedrooms ? Now you know why .. The two other retrofit approaches are MVHR System 4 and PIV. Lets talk about MVHR first. Since the pandemic MVHR has been cited as the go to retrofit by certain membership bodies without any reference to the practical issues affecting its performance. MVHR was originally envisaged for whole building new builds as the ductwork infrastructure can be designed with the building taking into account run lengths, resistances etc. In a retrofit it may not be possible to route ductwork to be relevant spaces not to mention other key factors such as air permeability. Even with today's auto compensating MVHR units and semi rigid duct systems retrofits are usually not feasible and certainly offer less energy efficiency than PIV even with 95%+ heat recovery. In our experience, unless you have a loft space or sunken ceiling void with no obstructions and covering the entire building footprint then MVHR is never feasible. PIV is the only whole building strategy designed for retrofit. It is cheaper and easier to install than MVHR (yes even ducted flat units) and if done correctly it is equally or more energy efficient than MVHR. Many PIV installs are not done correctly due to lack of proper knowledge in the industry. Most unqualified specifers or installers think you just put it in a loft or on a wall and turn it on and thats it. There's a lot more to it than that. Perhaps the biggest issue with PIV understanding is the PAS2035 suggestion that trickle vents or air bricks should be used. Anyone with serious PIV installation experience will tell you that is nonsense and in fact reduces performance and (you guessed it) wastes energy. Another key aspect of a PIV solution is the importance of effective extraction which means energy loss compared to MVHR but this can be minimised with humidity tracking extraction or brought into similar line with MVHR with the use or SRHR units. In our experience PIV is always feasible in a retrofit and almost always preferable to MVHR for energy efficiency. PIV (and properly installed MVHR to be fair) means the entire building gets all the ventilation it needs regardless of occupancy size and habits without the need to open windows at all during the colder months of the year. No wasted energy, reduced heating bills and better health and well being. To sum up we must stop making the mistake of saving energy by improving insulation only to throw that energy away by opening a window, trickle vent or airbrick to ventilate. If we are to have any hope of hitting Net Zero without creating a health and wellbeing crisis we need to retrofit 28 million buildings primarily with PIV but without the PAS2035 trickle/airbrick recommendations.