Entry posted by Stones
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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.
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
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