We realise that you might not have heard of a Mechanical Ventilation and Heat Recovery system (MVHR) before, so we thought it would be a good idea to write a blog on what it is, how it works, and why we use them in a Citu Home.
Let’s start with the why
Our goal as an organisation is to tackle climate change by helping you to reduce your carbon footprint while going about your daily life. A big part of that will come from making it as easy as possible for you to reduce your consumption of fossil fuels. In the home, it’s gas, and for transport it’s oil and petrol. We’ll cover transport in another blog, as that’s a whole other story to tell. For now, we’ll focus on the home.
Removing fossil fuels from the home
The Citu Home uses an airtight thermal envelope and incredible standards of insulation to create a home that’s so efficient that a traditional central heating system with a gas boiler will no longer be required.
This doesn’t mean that your energy bills will be cheaper, but it does mean that you’ve immediately reduced your carbon footprint because all the energy supplied to your home is 100% renewable. We know, it would make sense for your energy bills to be cheaper, but electricity at this moment in time costs more than gas. And then, it all depends on your energy consumption during the day and at night. Take our Head of Digital & Marketing, he’s a big gamer. He likes nothing more than to lock himself away with his Xbox One and game for hours on end. He’s not going to see much difference in the cost of his energy bills, but at least he knows that his gaming no longer contributes to climate change. He now goes around telling people that he’s an “Ethical Gamer”.
How do we heat our home without a traditional heating system?
Because the Citu Home is 10x more airtight than what’s required by current UK building regulations, the heat generated from you and your appliances in the house can’t escape. It also means that no cold air can get into your house either.
Okay, no fresh air getting in, and no stale air getting out. That doesn’t sound appealing, but that’s where the MVHR system comes in to play as you’re going to need a ventilation system to keep everything box fresh. Especially if you’re an “Ethical Gamer.
And that’s part of what your MVHR system does. It’s a ventilation system that brings a flow of fresh air into every room of the Citu Home, while removing the moist stale air.
The MVHR unit has a quiet fan that blows fresh air through the whole home and sucks out the stale air via a network of pipes, which ensures your Citu Home will never get damp. The air-tight fabric of your Citu Home also acts like Gore-Tex but in reverse – it keeps the air locked in but let’s moisture out.
The really clever part is that your MVHR system has a built-in air-humidity detector, that will mean when the humidity rises because you're taking a bath, drying clothes or cooking food, the MVHR unit will power up to remove all the humidity, and then power back down into its normal mode again once the humidity level is back down to a low level.
So, it doesn’t matter how long you like to spend in your hot, steamy shower, your Citu Home isn’t ever going to get damp.
Air as fresh as the Welsh hills
The constant flow of fresh air means combined with the outflow means low levels of humidity and indoor pollutants. This is because the MVHR unit has a filter that removes particles from the air as they’re entering the home.
Studies of houses with MVHR units versus those that don’t show that houses with MVHR systems have levels of particulates (PM 10 & PM 2.5) that are up to 4X lower than conventionally build houses, & three times lower than the air outside the house. The study of air-tight houses with MVHR systems showed indoor particulate levels in the houses were equal to or lower than average outdoor air in the rural Welsh hills.
The filtration of all fresh air entering the house combined with the houses high degree of air-tightness is also great news for allergy suffers – levels of hay-fever inducing pollen particles will be many times lower in a Citu House thanks to the MVHR unit’s filter.
You can see all the pipes that take in fresh air and remove stale air from every room in a Citu Home in our interactive model.
How MVHR will make your home more efficient
Your MVHR system doesn’t just ventilate your home. It also makes it more efficient, because it’s a heat recovery system. This means the MVHR unit will strip heat from the exiting warm stale air, and transfer it to the fresh cool air that’s coming in.
The MVHR units we are putting into Citu Homes will transfer 90% or more of the heat of the exiting stale air onto the incoming cooler fresh air. That means your heating requirements are just a small fraction of what would be required in a traditionally built home. Once your house has warmed up to what-ever temperature you find comfortable, you’ll find it doesn’t take very much heating at all to keep it at that comfy temperature.
In fact, on all but the coldest days, you’ll find just the heat given off by the people living your home and the appliances you have on will be enough to keep your home warm. The small amount of heating you’ll require to top this up will vary from plot to plot, because it depends on how many exterior walls you have and how much your house is being warmed by sunlight. You can see a full breakdown of the heating requirements of each plot in the Climate Innovation District on our Masterplan page.
When it does get really chilly, your MVHR system will still work at full efficiency, but you’ll need a bit of extra heating to keep your house nice and toasty. Don’t worry, there’s no need to buy any of those naff electric radiators that’ll ruin your Scandi-minimalist look- the Citu Home has additional heating systems built in, that will run on 100% renewable zero-carbon energy.
We hope this explainer helps you to understand how the MVHR system in your new Citu Home works. If you have any more questions, feel free to get in touch with the Citu Team who’ll answer any questions you may have.
We’ve also created a little FAQ below for you that goes into a little more detail on how to maintain and look after your MVHR system.
What if it is too hot?
When the MVHR is transferring all the heat from the exiting air onto the fresh incoming air, you might think it would get too hot in summer.
That’s why the MVHR system has a summer mode, which by-passes the heat exchanger, so the MVHR unit still brings in fresh air and removes stale air, but doesn’t transfer heat so your home doesn’t over-heat.
To prevent over-heating, we’ve also designed the Citu Home with openable roof-lights at the top of the triple height void space, and an openable ventilation panel on the ground floor, so on the hot days all the heat in your house can escape from the top, drawing in a cooling breeze through the ventilation panel.
Does the MVHR provide heating?
The MVHR isn’t a heating system. What it does is help your home retain heat. It doesn’t generate the warmth, it just means it is kept in your home and not lost to the outside.
The Citu home also has in-built heating systems powered by renewable energy to keep you nice and toasty. You control this through our actuate app – so you can set the temperature from your phone, laptop or tablet.
Does the MVHR work as air-conditioning?
The MVHR unit can’t work in reverse. It has no moving parts other than the fan, which means it’s extremely durable and very unlikely to break down. Really important point to note about MVHR, it doesn’t act as air-conditioning. But luckily, the Citu Home’s passive cooling features will keep you cool in summer.
If you are the kind of cool cat who really doesn’t like the heat, you can opt to have solar shading installed on your Citu Home as an optional extra, this will ensure your house will never over-heat without requiring an energy intensive and expensive air conditioning system.
Is it expensive to fix if it breaks?
An MVHR system just has one moving part – the fan. This means they’re very reliable and extremely unlikely to break. We’ve never had one break at any of our properties, and they'll keep working for decades with very minimal upkeep.
They’re easy to maintain – you can clean the filters just by hoovering them or putting them through the wash.
If you ever need to replace your MVHR unit, they cost £1,200, so are no more expensive than a typical gas boiler that you’d have in a traditional property.
How often do I need to clean or replace the filters?
The MVHR unit’s filters scrub particles from the air entering your home, improving the air quality, and helping allergy sufferers. To keep the filters at tip-top condition, we recommend washing or hoovering them to get rid of built-up dust once every 2 months during the construction phase when it’s likely to be dustier than usual. Once the development is complete, you’ll just need to give them a clean every 6 months. The filters are cheap & easy to replace. You just slot them in. It’s recommended you replace them every 2 years. They cost £10-£12.
When you move into your Citu Home you’ll get a detailed guide to how all the Smart Home technology, heating and MVHR works, so you’ll know how everything works.