Is DCV an alternative to MVHR?

[Zoo]

Afternoon all

 

I'm a new member and I'm planning to build a timber frame home with a target fabric air tightness of 1 ACH and the u-values of the home will be 0.14 w/m2.

 

On the good advice of others, I had only ever considered MVHR as an option for our ventilation solution. Though the cost makes me shudder a little.

 

However, I recently spoke to a consultant who spoke about ventilation strategies and suggested many options I hadn't even heard of. Some not appropriate for my build e.g passive stack, but one that caught my attention - Demand Controlled Ventilation. .

 

It's an occupancy and humidity controlled system that uses CO2 sensors and humidity sensitive extract grilles and air inlets that react to occupation in rooms whereas MVHR runs at the the same rate whether the house is occupied or empty.

 

There were points that made it sound like a credible alternative to MVHR. However, it is not a heat recovery system and doesn't temper the air that goes back into the room.

 

The eyebrow raiser for me is that I don't know of ANY private residential project in the UK that has heard of it let alone installed it! Commercial yes, student accommodation, apartments yes. Ireland and mainland Europe yes. 

 

I have scoured this site high and low and not a mention of DCV within the most clued-up, switched-on self build community.

 

Anyone know anything about it - good, bad, ugly?

 

 

[jack]

8 minutes ago, Zoo said:

It's an occupancy and humidity controlled system that uses CO2 sensors and humidity sensitive extract grilles and air inlets that react to occupation in rooms whereas MVHR runs at the the same rate whether the house is occupied or empty.

 

Interesting idea, but won't all these sensors and (active) grills be costly too? You'll also lose heat recovery, which over several years will more than pay for any difference between MVHR and DCT.

 

MVHR needn't be expensive. Several of us have installed most or all of the components on our own.

 

Another thing: if no-one's installed one yet, it's probably worth thinking about whether building control will be happy with you being the first!

[K78]

This is a really good forum, but I find many people take the same approach as many of the main contributors have finished their builds. If it’s timber frame it’s usuall Mbc, with a insulated slab, underfloor heating and MVHR.

 

I’m taking the sip route and that isn’t so popular on here. So there is not so much information regarding them on this forum. 

 

MVHR doesn’t have to be expensive. It’s quite simple in principle. My house will have a industrial feel with exposed ducting, conduit etc and concrete walls. This has the added benefit of making things easier to DIY. 

Edited May 9, 2018 by K78

[ProDave]

Why is the cost of mvhr frightening you?  I paid about £500 for my mvhr unit and all the ducting and terminals was about £1000

 

I am not sure if English building regs demand an air tightness test yet. Watch out if they do, a local build near me was just installing mechanical extract ventilation, but his air test came out too good, and building control insisted he rip that out and fit mvhr.

 

By the way mvhr does not run at the same speed all the time. It's on 24/7 on trickle rate and can increase speed when cooking or showering. Some use a manual boost, some use humidistats to select boost speed..

[SteamyTea]

I like the idea of DCV, but is it really just a poshed up single room ventilation system?

 

Some people have fitted CO₂ and RH sensors to their MVHR, so this amounts to the same thing.

 

Seems to me that when fitting MVHR, the initial design/layout is important as it makes fitting easier.

[ragg987]

I looked at DCV briefly before settling on MVHR. I saw DCV as similar to leaving a window open all the time, you throw heat out, the only part you control is how wide your window is open based on air monitoring. DCV would be a benefit compared to a ventilation system that ran at a constant speed. As you are aiming for a low energy build, it seems pointless.

 

Agree that as a forum there are quite a few similarities, and some of us have taken very similar approaches. "Tried and tested".

[Zoo]

9 minutes ago, jack said:

Another thing: if no-one's installed one yet, it's probably worth thinking about whether building control will be happy with you being the first!

Right! I actually don't mind being a maverick, but i do want to be armed with as much information asIi can before taking a leap into the unknown!

 

 A building control engineer I know has confirmed that it does meet Part F ventilation and part L low energy of the English B Regs.

[jack]

1 minute ago, K78 said:

This is a really good forum, but I find many people take the same approach as many of the main contributors have finished their builds.

 

And why do you think that is? 

 

That said, there are plenty of people doing brick and/or block, as well as ICF.  We have suspended floors (wood and concrete) and insulated slabs. We don't have a lot of SIPs, but there are good (in some cases historic) reasons for that as set out in the relevant sub-forum. 

 

There are good reasons why such a large proportion of people on this forum have used MVHR, including air quality and reduced energy consumption.

[joe90]

I bought my MVHR unit for £350 on Ebay, yes the duct can be a bit pricey but I made my own manifold/silencer from ply and my own room vents from cheap bits available at half the MVHR price. I also wanted my MVHR to be run like central heating ( sensors to measure RH and CO and only run when required) but the cost annually is so low and gives permenantly heat recovery, add to that the CO sensors are expensive . There is a reason why most people instal it in “ good” new builds. ( p.s. mine is block and brick as will be very airtight ?with no expensive membranes or tapes ).

Edited May 9, 2018 by joe90
Edit

[Declan52]

If you get your build down to 1 ACH then you will have done a lot of work putting in lots of insulation to keep the house at a nice constant temp and have used a lot of tape and membranes to stop the leakage. So why would you install a system that gets rid of the heat. A mhrv will recover some of the heat going out but it also filters the air coming in which in my view is it's best selling point.

There's maybe a good reason it's not used widespread. Have a look at bpc as they do full kits for less than £2k depending on the size of your house.

https://www.bpcventilation.com/heat-recovery/full-diy

[K78]

1 hour ago, jack said:

 

And why do you think that is? 

 

That said, there are plenty of people doing brick and/or block, as well as ICF.  We have suspended floors (wood and concrete) and insulated slabs. We don't have a lot of SIPs, but there are good (in some cases historic) reasons for that as set out in the relevant sub-forum. 

 

There are good reasons why such a large proportion of people on this forum have used MVHR, including air quality and reduced energy consumption.

 

 

I suppose because it reassures them that more knowledgeable people have taken that route? I will be using MVHR myself.

 

i was just making the point that things outside the usual don’t get a big response on here sometimes. 

 

I was put off sips due to valid foundation concerns raised on ebuild. After doing a bit of research, for me they are better than a timber-frame.

 

i appreciate there have been problems, just like there have been with timber frame. 

 

I’d never use OSB skinned sips but cement fibre board or mgo make a lot of sense to me. Waterproof, no need for membranes, can be rendered or plastered on to directly.

 

The one approach I don’t understand is a 140mm standard timber frame. By the time it’s insulated, lined and clad they’re expensive. I like the mbc closed panel system but I find it expensive for what it is.

 

Im on a tight budget as I’m doing this without a mortgage. 250mm thick mgo or cement fibreboard sips make a lot of sense for me. I appreciate others have a different take. 

 

I’ve learnt a lot from this forum and had good advice which I appreciate. It wasn’t a criticism. 

[Zoo]

I have the utmost respect for both tried and tested and for forging a different route. There are merits and pitfalls to each.

 

I am interested in something a little less explored in this particular instance because i like the idea of DCV and it warrants further exploration. It is not enough for me to go with what's tried and tested for its own sake if there is a possibility of something else out there that is equivalent or even superior when matched up.

 

BTW I too considered the SIPS route very seriously, but decided in the end to go with none other than MBC!

[K78]

7 minutes ago, Zoo said:

I have the utmost respect for both tried and tested and for forging a different route. There are merits and pitfalls to each.

 

I am interested in something a little less explored in this particular instance because i like the idea of DCV and it warrants further exploration. It is not enough for me to go with what's tried and tested for its own sake if there is a possibility of something else out there that is equivalent or even superior when matched up.

 

BTW I too considered the SIPS route very seriously, but decided in the end to go with none other than MBC!

 

Is this forum the main reason behind your choice. Or were you already aware of MBC?

 

[Zoo]

This forum made me aware of MBC and also Touchwood Homes then I met two other self builders independently of this forum who were very happy with choosing MBC.

All ticks in the right box but not enough for the final sway.

 

Sat down with the final three contending quotes, MBC, JML (SIPs) and Bentley (SIPs) all pretty much the same price. Came down to thinness of external walls (our plot is not that big) and craneage included in the price or not.

[gravelld]

DCV is essentially "smart" MEV. It's less installation work (ducts only to wet rooms). It looks ideal for retrofit to me, but I think for newbuild you might as well go with MVHR which is tried, tested and has a more competitive landscape.

[Zoo]

37 minutes ago, Declan52 said:

filters the air coming in which in my view is it's best selling point.

My concern with DCV has always been thermal comfort.

 

The answer I've received from that is the volume of air entering is quite low so the energy required to maintain the temperature isn't significant in a modern, well-constructed air tight building with very modest space heating demands.

[joe90]

2 minutes ago, Zoo said:

My concern with DCV has always been thermal comfort.

 

The answer I've received from that is the volume of air entering is quite low so the energy required to maintain the temperature isn't significant in a modern, well-constructed air tight building with very modest space heating demands.

 

Have you had a quote for DCV ?

[Construction Channel]

I'm slightly confused about how this will become cheaper?

 

from what im reading, you would still need ducts to every room as the entire house would be relatively airtight and you would still need the fan to move the air through the ducts, 

so essentially you are swapping the heat recovery part for a bunch of sensors?

 

or am i missing something?

 

also how much does it roughly cost to run MVHR / yr?

[jack]

1 hour ago, K78 said:

It wasn’t a criticism. 

 

None taken! 

[Zoo]

I do have a quote for the DCV. Design and supply only. To cover 4 wet rooms and 5 rooms with air inlets. Doesn't include ducting which is bog standard 204x60mm or 125Ømm ducting. The claim is that the installed cost of DCV is usually approx. 60% the installed cost of an MVHR system

[Zoo]

It's also a slight issue for me that I've only found one company (possibly two) that supply DCV in the UK.

[Declan52]

6 minutes ago, Zoo said:

I do have a quote for the DCV. Design and supply only. To cover 4 wet rooms and 5 rooms with air inlets. Doesn't include ducting which is bog standard 204x60mm or 125Ømm ducting. The claim is that the installed cost of DCV is usually approx. 60% the installed cost of an MVHR system

There is cheaper full mhrv kits on that link above.

[Zoo]

My quote from BPC was £1200 for the unit (Vent Axia) and £1k for the ducting. I would also need to get it installed as sadly I don't have the skills.

 

I've had quotes from the usual guys - CVC Airflow, Total home ranging from £3-5k which I was expecting.

 

Then the DCV was brought up which I'm exploring on the basis of capital cost, running cost, maintenance, IAQ, control and commissioning as it seems to have something in it, but I don't yet have enough information to confirm any claims or merits.

[ProDave]

installing an mvhr really is simple, especially if using the radial ducting system from BPC.  It took me a weekend

 

It starts as 2 manifolds next to the mvhr

 

 

 

And 2 ducts in parallel run to each vent terminal

 

 

Posi joists do make it somewhat easier.

 

If you have quotes for £3K or more to install it, that will be your best "paid" weekends work ever.

[Zoo]

ProDave you have made it look beautifully simple and if I do end up going this route, I will be coming to you for support! 

 

What system do you purchase from BPC and how many wetrooms and outlet rooms did you have to lay ducting to?

 

My other concern is a poorly installled MVHR system not perform well.