It’s taken nine months from start on site to moving back into my not-quite-finished house. Despite the long build period, it’s only looked like a ‘special’ house for a short time. Before long, the insulation and airtight taping were covered up. The ventilation ducts were concealed in the ceiling void. There are some subtle hints that this isn’t a standard house: the triple glazed windows, the ceiling vents and the way opening the front door feels like you’re entering an airlock.
But, open the utility room door, and ….. well, WOW! It’s packed full of technology, pipework and switches. There’s just enough room for a neat laundry area with a sink for washing my muddy boots, a washing machine and a Sheila Maid ceiling clothes airer.
So what are the various different bits?
I’ve only lived with this technology for a few weeks and haven’t yet fully got to grips with it all. This Blog Post provides first impressions of the MVHR, with initial views on heating and hot water in the next one.
Air tightness and ventilation: The EcoBungalow is an extraordinarily airtight building. The interim airtightness test was 0.2 Air Changes per Hour (ACH) – better than a new build Passive House! Air tightness is a really important part of creating a Passive House – it goes hand-in-hand with high levels of insulation to create a building that doesn’t lose heat.
Ventilation is still required, of course. But this is done in a controlled way rather than the standard, rather haphazard approach of relying on trickle vents, extractor fans and holes in the building fabric (think gaps around the kitchen sink waste pipe). Mechanical Ventilation with Heat Recovery (MVHR) provides fresh filtered air into my house whilst retaining the energy used in heating.
The Zehnder MVHR unit extracts air from the kitchen, bathrooms and utility room (all of which create heat and moisture) and supplies fresh filtered air to the living area, gym and bedrooms. The extracted air is taken through a heat exchanger, where it warms the incoming air, so that very little heat is lost. There’s an automatic ‘summer bypass’ where the warming of the incoming air is switched off once the inside of the house has reached the temperature I’ve set.
So what’s MVHR like? The bottom line is I don’t notice it. No noise, no air movement. I have to stand on a chair and put my hand next to an input vent to feel any air movement. I have, however, noticed that:
there are no lingering smells of last night’s dinner when I get up in the morning;
the mirror in the shower room doesn’t steam up when I have a hot shower; and
clothes hung on the airer in the utility room dry really quickly overnight.
It’s fantastic!
Ah, but what does it cost to run? The MVHR unit runs continuously. It’s a Zehnder Q350 ComfoAir, which has an annual electricity consumption of between 135 kWh and 258 kWh for an average climate. At a current rate (June 2024) of 24.5 pence per kWh, this works out as £33 to £63 per year. With heat recovery during the colder months of the year, the saving on heating bills will far exceed the cost of running the MVHR.
How do you know it’s working properly? The system has to undergo a thorough commissioning process by a qualified person to (i) make sure it’s working properly; and (ii) provide evidence to submit to Building Control to obtain a completion certificate at the end of the building works. Diane Hubbard from Green Footsteps undertook the commissioning, which included checking air flow rates to the different parts of the house. These were adjusted through the vents – opening them right up in the bedrooms to increase air flow, and closing them down to a minimum for the gym.
Is it noisy? MVHR is not like a traditional kitchen or bathroom extractor fan. It’s pretty much silent. The only noise is from the external vents, which can be heard if you stand outside right next to them. Even then, it’s hard to hear the gentle, continuous noise above everyday sounds of birds singing, lawnmowers going, and cars passing.
Can you open windows? MVHR works best with the windows shut. However, it’s sometimes nice to open the windows. I’m sitting here typing this with the living room window open so I can hear bird song from my garden. Not a problem for the MVHR, although it may reduce efficiency by a small amount.
What if there’s a power cut? Is it’s stuffy, open the windows until the electricity comes back on! It’s an interesting experience opening a door or window for ventilation in a very airtight house. Unless it’s windy, nothing happens. There’s nowhere for the air to go, so there’s no draught. You need to also open a window opposite to create cross-ventilation.
What maintenance is needed? There are two filters in the unit that I have to check periodically and replace when required, at least annually. These cost around £30. I also need to keep a close eye on the grease filter in the extract from the kitchen area. This prevents grease entering the ducts, and it will need cleaning and/or replacement from time to time. Other than that, it’s a simple system that I don’t need to touch.
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