Jump to content
  • entries
    26
  • comments
    247
  • views
    71086

Part 19 - MVHR


Stones

8815 views

One of the final significant jobs I had to do before we moved in was connect up and commission the MVHR.  All the radial ductwork and individual plenums had been fitted at first fix, however I had left installing and connecting the actual unit until the loft has been insulated, as I didn't want to risk pipe connections being damaged.

 

The day before we were due to move in, the insulation contractor having laid all the loft insulation, I spent a couple of hours in the loft space above our vestibule connecting ducts for the air intake, air exhaust, and the supply and extract ducts to the distribution boxes.

 

I decided to locate the MVHR in our (cold) loft space, primarily to free up space in my service cupboard which houses our DHW cylinder, UFH manifold and CU.  The installation manual advises that where the MVHR unit is located in a cold rather than warm part of the envelope it should be insulated.  I initially considered lining the whole of the relevant loft area with insulation, but having worked out the cost, and then being able to salvage a number of sheet insulation offcuts from the skip, I ended up forming an insulated box around the MVHR unit.

 

P2020064.thumb.JPG.bce8bb567caf841e1e8b0cb90f9541fd.JPG

 

As you can see in the picture, it's a very simple box, the relevant supply and extract ducts simply cored through the insulation.

 

Our MVHR unit is a Vent-Axia Kinetic Sentinel Plus.  These can be supplied in either left hand or right hand format to suit your installation.  My plans had originally shown the air intake and exhaust on the Southeast roof of the house, but as the house was being built it became clear it would be more convenient for those vents to be located on the northwest side of the house.  Making that change left me with a problem of having an MVHR unit with the duct spigots for the internal supply and extract on the wrong side of the unit.  Fortunately the Vent Axia units can be reconfigured by taking off the front and back of the unit, disconnecting and removing the control panel, rotating the unit chassis through 180 degrees, then reassembling so that the back is now the front.

 

Having connected all the ductwork, the final thing to do was connect the condensate pipe I had fitted during first fix (which discharges to a rainwater trap outside) to the flexible condensate pipe on the base of the MVHR unit.

 

Having switched the MVHR on, I then went about balancing the system using an Air Flow meter borrowed from my builder.  This was a relatively straightforward process and just required minor adjustments to individual diffusers in each room.  

 

Our system is currently operating at a normal supply rate of 32% which equates to 150m3/hr. Having measured efficiency during cold and windy weather, it operates at 90% efficiency in terms of temperature differential (room temperature to supply air temperature).

 

In warmer weather, the Summer Bypass, which I have set to come on when internal air temperatures exceed 22C and ambient air is above 10C, automatically activates.  If ambient air temperature exceeds internal house temperatures, as was the case last week, the summer bypass remains inactive so that outgoing stale air can cool incoming fresh air (albeit the effect is negligible).  As others have found, whilst summer bypass does provide limited cooling of incoming air, it is not on its own enough to cool the house. Cross ventilation by opening windows remains the most effective way of providing such cooling (in the absence of any active or UFH cooling).

 

The final feature worth mentioning is the humidity sensor, which variably boosts the ventilation rate to ensure RH does not exceed the level set in the controller.  This also seems to be working well, auto boosting ventilation when showers are used.  When cooking, if we deem it necessary, we can manually boost ventilation to assist in the extraction of cooking odours.

 

Overall I pleased with how the system is operating. The one thing I have noticed compared to other MVHR systems we have lived with is the noise of the fans which you can hear through the ductwork.  This is the first house where we have used a radial system rather than 150mm main ducts with branches off, so it may be the duct choice, as I can't recall hearing fan noise on previous installations.  To combat this issue, I've ordered some self adhesive acoustic foam sheet, and plan to construct a silencer out of scrap MDF and timber, line with foam and externally insulate, to fit between the MVHR unit and distribution boxes.  I'll report back in due course how effective this is.

 

The final tweak to the system that I'm considering is fitting a CO2 sensor so that the unit can auto boost ventilation rates as required. Vent Axia want £350 for their sensor which is a non starter, but looking around, the following may be an option as it seems suited to the parameters of the Vent Axia:

 

https://www.digikey.co.uk/products/en?keywords=235-1413-ND

 

Again I'll report back when I've looked into this some more.

 

Next entry - 2nd fix plumbing

 

 

  • Like 1

30 Comments


Recommended Comments



Out of interest: how much of a bend can you put on the insulated flexible ducting before it loses its shape?

Ive read somewhere (although I can't remember where!) that you shouldn't put a bend radius on it as it reduces the flow but equally I've seen a few pictures online that seem to show it turning 90 degrees out of the top of the MHRV without issue. Or is it perhaps that there is metal/plastic pipe inside it?

Link to comment

I think for sharp turns, you really need to use a rigid bend as the flexi stuff ends up deforming if you try bending it too much. I've just posted an new blog entry about the silencer, where to make final connections to the MVHR unit and supply manifold, I used a combination of rigid bends and flexi. I think large radius curves are preferable to sharp bends, but sometimes that's just not possible.

Link to comment

Hi Stones, 

 

Sorry for the bit of a delay, my back ground is I am a chartered building services engineer, so design heating, vent, cooling etc in homes and commercial buildings. 

 

What i am not 100% sure is what are you trying to do. are you trying to reduce room noise? building a box around the MVHR tends to deal with the break out noise but what deals with room site is inline duct attenuators. 

 

Ryan

 

Link to comment
8 hours ago, Ryan4Healthy Home Movement said:

Hi Stones, 

 

Sorry for the bit of a delay, my back ground is I am chartered building services engineer, so design heating, vent, cooling etc in homes and commercial buildings. 

 

What i am not 100% sure is what are you trying to do. are you trying to reduce room noise? building a box around the MVHR tends to deal with the break out noise but what deals with room site is inline duct attenuators. 

 

Ryan

 

 

Ryan, there is a lot of history here on this forum about duct silencers that is relevant.  I take the blame for starting it a couple of years ago, when installing our Genvex active MVHR unit, and making an error in not fitting the recommended silencers, because a late change to the services room layout in our build, and a change of MVHR unit, left insufficient room to fit off-the-shelf absorption silencers.

 

As a consequence, I made units very like the ones that @Stones has made, and found they were very effective.  Others have done much the same.  I made ours because I needed a custom shape to fit in the available space, originally.

 

There is a requirement to build an insulation box around an MVHR fitted outside the heated envelope, both in the MIs and Part F (or the Scottish equivalent in this case).  The access requirement in Part F (or it's equivalent) still has to be complied with, but generally everyone on here that's fitted MVHR (that's a lot of us now) seem to have found that building control are fairly relaxed about demonstrating compliance.

Link to comment

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
×
×
  • Create New...