Social Housing Passivhaus
As Leeds embarks on a massive project to build over 400 new houses to Passivhaus standard, some thoughts of how the ventilation might work.
Mechanical Ventilation Heat Recovery (MVHR) systems are potentially the Achilles heel in Passivhaus design, loved by purists of the PassivHaus and the believers in well designed systems that deliver silent constantly flowing fresh air for great indoor air quality. Though MHRV is often dismissed by breathing building and natural ventilation aficionados, and those who have had bad noisy uncontrollable systems. Fortunately PassivHaus can be both naturally ventilated in summer and mechanical heat recovery ventilated in winter (opening the windows on a cold day would simply result in a cold house and a long warm up period – householders will learn and adapt. MVHR can be designed properly – to be silent and provide correct levels of fresh air, but it still needs to be installed correctly. The key, I think, is simplicity of specification and layout, and getting integrated design done, without this the installers will always struggle. We designers need to help them.
Another problem cited is that these units get turned off, fail or the filters block and are then not fixed – especially in social housing schemes. Proper design and specification is key again here to ensure the units are easily accessed, but what about monitoring and maintenance? An annual check is all very well, but can be costly to perform and disruptive for tenants, and could also be six months too late to save the bathroom walls from black mould. With the cost of data loggers and controls becoming less, and the desire to smarten houses it should be possible to monitor these units. For a small extra cost (less than 5% of the total system cost) a multi input monitor device could be added to the MHRV units in social housing, this could have one simple input from the MVHR own inbuilt fault signal, and also a multi sensor input from the duct to measure temperature, and humidity and pressure to sense a range of problems. This monitor device would need to be connected back to the landlords FM centre, the beauty of modern controls and technology is that there are multiple ways of achieving this often from a single device. For example in a big block of flats a data-bus (BACnet Modbus, KNX, LON, etc) could be daisy chain wired to each device and a single data collector transmitter could then send fault signals back to the FM centre. In a block there is likely to be a networked heating controller that the MVHR monitors can connect directly to. In individual houses you may be looking at a data-bus wire brought into the house alongside the BT/Fibre cables, or perhaps radio transmitters to local collectors. These devices could even be GSM (mobile network) enabled monitors.
There is a danger of over complicating this and that the monitoring devices and sensors added on to the MVHR units go wrong themselves, I would suggest the most robust route is to use the inbuilt technology of these MVHR units, some already monitor many aspects of their own operation, and therefore if we select a unit with built-in data-bus connections and wire these direct back to a local broad band enabled data collector we can access this from the FM centre.
by Jim Wild