Ok, one year less a day since my retrofitted MVHR was installed and comissioned.
So, how has the past year gone and has it achieved the objectives?
Objective:
To reduce/eliminate condensation within the property such as on windows and some internal walls.
Improve quality of air.
Why:
After undertaking various renovations (most significantly replacing an open fireplace with an room sealed WBS), we were suffering severe condensation on some windows, some areas of the house with little passing air (inside fitted cupboard and toilet - ok there was some air passing in the latter
) and a small area of the underside of the roof felt to the point that I was getting concerned about our well being, items within these areas suffering from mould, and the construction of parts of the house.
Concerns:
As this was being retrospectively fitted to a property, relatively well insulated and mostly double glazed, but not built to highest air flow standards, not even modern construction, and some rooms (specifically two of the extract rooms and the utility) had little or no heating, I was concerned that our heating bill would rocket and that we would suffer drafts/cold spots.
What was fitted:
Vent-axia Sentinel Kinetic Plus with humidistat and summer bypass, supply pollen filter, wired remote, a radial system consisting of two Airflow chambers, 75mm (?) Ubbink semi rigid round ducting, 3 extract (kitchen, bathroom, toilet), 7 supply (4 x bedroom/office/spare, 1 x lounge, 1 x dining, 1 x utility). The system is fully balanced, so, except in antifrost mode (supply measured at <= 0C), supply airflow equals extract airflow. During the day, the system runs at building regs flows (IIRC theoretically full air change every 2-3 hours), during the late evening and night, this automatically reduces to about half that.
So...
Well in past year, we have had the slightest (you had to go looking for it) bead of condensation on the two bedroom windows - coincidentally? when outside temp around approx 4C. No evidence of condensation/mould in any of the places of issue, especially fitted wardrobe which was making clothes a bit musty - I must admit that I was surprised to find condensation on the inside of the roof felt above the bathroom prior to fitting (which may have been caused by a fault in the old bathroom extractor/pipe work) and there is no evidence of that now. Bathroom still suffers condensation on window when a shower is had, but this clears much quicker than when using previous bathroom fan and tbh, if we manually triggered boost rather than relying on the humidstat this would probably be minimal. The kitchen is similar when cooking with steaming dishes, but again, clears very quickly and certainly not major condensation on the windows.
99% success.
As for improvement in air quality. I am sure that air quality has improved, at very least mould will not be floating around and moisture levels largely kept to very comfortable levels. But its not like sitting outside in fresh air, and the odd odur will still linger - that said, my son who sleeps in a bunk bed is much more comfortable as heat buildup at ceiling height is much reduced. In summer, we tried to run without opening windows, and was largely effective, but there is nothing like a nice breeze blowing through the house - but on hot days with still air, the MVHR provides a little respite where conditions that would probably have led to unpleasant still/stale hot air - so whilst the air movement is not noticable unless you put your hand within a few inches of a vent, or close a door almost shut and feel the flow with back of your hand through the gap, there is enough of an air change to reduce the stifling associated with hot still weather. The pollen filter meant that there were no issues that may have been associated with hayfever as would sometimes happen at certain times of year when windows were open.
Difficult to quantify the success with this. Im not disapointed as its performance, but its not the fresh air feeling that some may have you believe.
Concerns.
Well my concerns were largely unfoundered, especially after reading some peoples reports that MVHR's need particularly airtight buildings. Yes, we are well insulated, but certainly not air tight. I keep meter readings, typically on a week by week basis, and whilst I know that the MVHR will have been consuming 17W during night, 28W during the day (often powered by solar PV), its not distinguishable on the electricity bill over and above what would also have been down to lower Solar generation last year - I once calculated it to be roughly £20-30/year extra and I am sure that is in the similar ball park. As for gas heating, an average indistinguisable from last years not taking in to accound weather, and probably a little less as peak weekly reading since MVHR is less than peak non MVHR readings. However, a couple of rooms at certain times of the day feel slightly less warm. I put this down to a number of factors - first the temparature of the incoming air when very cold outside can be 3C or so less than room temperature - largely due to the extract rooms that heat the incoming air may be at 16-17C - this is bound to make the room slightly harder to heat. Second, the airflow movement distributes the warmth around the room and the house. So we have a couple of rooms, largely unused, where the TRV turns the rad on slightly, where previously this was probably not the case. The up side to this is that those rooms are getting a little heat in them. Finally, our boiler is on its way out and its supply pressure has been reduced to minimum by the service guys. This means that the boiler output is reduced, so when its having to run at higher capacity, ie cold and windy outside and everything is heating up from 'cold' at the same time, not all the rads get as hot as I would expect. Putting this in perspective, when temp outside is sub 0, a bedroom unheated between 9:30pm and 5:30am gets at worse mid 16C overnight and typically 17C something where 18C would have been the bedroom temp setpoint on the runup to bedtime.
The unexpected:
I certainly was not expecting to hear the unit at the far end of the house. I was initially concerned that it would cause problems sleeping in summer when on summer boost modes, but it turns out that I am the only person in the house (including the piano tuner) that can hear it, I got use to it, and it doesn't cause problem in the summer. Sometimes, when outside of 80-90% humidity and inside is hovering at 70% I hear the humidity stat boost cut in, but its not a problem. However, can I suggest, for the sake of £60 or so quid, that anyone else having one fitted gets a couple of inline attenuators fitted.
Second, I sleep quite close to a supply vent - its about 18" from foot of bed on my side, and I think I feel the temperature difference of cooler air being supplied. Its not a draft, just that my shoulders (which I typically have outside duvet) are probably a little cooler than they once were. This of course is a bonus in the summer... The vents come supplied with little baffles that can be fitted to block airflow at some angles - so these can stop any drafts,
I was also concerned that the supply to the main bedroom was not capable of reaching the design spec. It looks like the distance of the vent from the main chamber is far enough to reduce the flow - a second supply pipe would have cured this, but the suppliers were 'reluctant' to fit this without extra cost and coming back and convinced me that the flow achieved was adequate. Seems like they were right as condensation in that ropom is all but gone, but its upset the balance a little.
Which is my final say on the matter. Having lived with the unit for a year now, I am convinced that the balance and room size between source and extracts plays a more significant role than air tightness. In my case, I have 7 supply and 3 extract, which means that the extracts are having to work much harder than the supply. So, especially in case of mine, the extract rooms play a significant part in determining the recovered supply temperature, so if you have a large extract room (ie my kitchen) the temperature of that room will be the major factor in what the supply temperatures will be, ie my kitchen temperature at 16/17C or so is probably influencing 60% of the supply temperature. But airflow at 14C from a room supply vent, when its <0C outside, is not the big deal that some may think, especially when the alternative would be a window open to the outisde at <0C.
Finally:
Installation was about £2k more than I felt comfortable with. Much of this was VAT as it was a retrofit. Not cheap, buts its done its job.
Running costs, Gas immeasurable, electricity probably £20-30/year. Plus 2 x filters, one of these pollen, about £45/year.
Maintenance costs - I cleaned the heat exchanger myself.
Question:
I am after some insulation for the semi rigid ducting. I think it is 75mm outside diameter. I remember seeing some last year on internet, for iirc 10m length specifically for this type of ducting, but cannot find it again. Can anyone help me find the supplier.
