Nice. I've been meaning to use my RPi to monitor the heating system but there just never seems to be enough hours in the day. But it's on the list . . .
I also have things on my list, which serves as my up-front apology for the fact that my rain gauge and anenometer (force only) have all stopped working. The rain gauge I put down to spiders and/or failure of the reed switch (I have 3 on my desk waiting to be fitted) and the anenometer is 3 storeys up on a very elastic pole and SWMBO won't allow me to shimmy up to fix it (I suffer from epilepsy but haven't had a fit in 25+years!), so I have to make do with temperatures and the wind direction.
Well, it's all installed and working. I stress that the purpose here is 100% to remove moisture from the air in the house while minimising heat loss, not to provide ventilation. The unit is an Airflow DV72 which has 3-speed control operable by relays in addition to a manual 3-speed selector.
I still have some work to do on making the controller a bit cleverer. I had thought that setting %RH triggers for fan speed would suffice, but I see now that temperature difference is a huge factor to consider. When I have time, I will change to base the fan speed setting on Absolute Humidity difference between air leaving and air entering as well as responding to rapid changes in RH.
The live performance graphs are here: http://www.greenbank.duckdns.org:9999/index.html (to make things clearer you can click on the labels to selectively remove and reinstate lines from the graphs). The house is unoccupied at present, hence the low indoor temperatures (and nil need for MHRV). That all changes late December.
When I've got some time on my hands, I'll add graphs for % heat recovery efficiency and water removal though the heat recovery figure can only refer to heat recovery within the system as any additional air leakage induced elsewhere in the house is undetectable. So far, the assessment that "it's working" is purely qualitative: from the graphs and from the lack of condensation on my bedroom window in the morning after the system had been switched on, though I would have appreciated some colder weather to really put it to the test.
The total cost of the system was about £1600 and it took me a week to install.
The performance graphs are fun. Looks like nearly 10% reduction in humidity when the fans are switched on (if anyone is interested select a start date near the bottom of the page to avoid just getting the current day). I note it has been raining and blowing a gale almost constantly up there since you installed the system - I am going to visit Glasgow at the weekend and have been keeping an eye on the weather.
I see you are still fiddling but how do you feel about it at the moment? The great advantage must be that it introduces slightly warm air into the house rather than a extraction fan which sucks in really cold air through the door and window gaps. Does the heat exchanger have a drain for water that falls out of the cold air after it has been warmed up? It would be interesting after the winter to know if your heating bills are much different from previous years.
It's still to early to tell whether or not it does the job, though it certainly extracts moisture to some extent. When the house gets occupied and there is a big temperature difference between inside and out: that's when we used to get horrendous condensation.
Yes, there's a condensate drain, 21.5mm overflow pipe which has a trap near the unit and is connected to the waste plumbing on the floor below.
I don't expect any difference to the heating bills and if there was a difference it would be masked by the differences in occupancy between one year and another. If anything, it should slightly increase the heating cost as it recovers less than 100% of the heat. On the other hand, occupants should feel a little warmer with drier air.
It's been running for a year now and I'm moderately pleased with the result: the paintwork around the windows is no longer getting covered in mould. We still get condensation on the bedroom windows, but not measured in gallons any more!
Each of the upstairs rooms has an inlet and and extract air valve, so the overall leakiness of the house doesn't have too much impact on efficiency.
The performance graph has moved to: http:/scotland-cottage.com/data/mhrvgraph.html
The temperature graph indicates heat recovery efficiency as closeness of the outside and outgoing temperatures and closeness the incoming and room temperatures (at times when the fan is running - see bottom graph).
The indication of moisture extraction is a bit more tricky because the humidity figures are relative humidity and therefore vastly affected by temperature. However, just the outgoing air at 100%RH shows that water is getting extracted and the incoming is generally the lowest line on the graph by some margin so it is replacing indoor air with drier air.
On that graph, if temperatures in the house are below 15, then you can be pretty certain that it's unoccupied, so the ventilation system has little to do.
Monitoring and controlling it has not been straightforward: the sensors are little devices called DHT22. These have good accuracy for temperature but should ideally be calibrated for humidity as they tend to vary by up to 5% RH. And that's when they are new. Some deteriorate quickly so that I've had to replace 1 already and another one is highly suspect and will get replaced next week.
In agreement with a few other voices on here I would try a dehumidifier first. Recently bought a Meaco Zambezi, has rave reviews, and must admit am pleasantly surprised how efficient it is in extracting moisure out of the air. It is at the more expensive end of the dehumidifier chain but I think worth every penny. You could always get one from Amazon and if not happy send it back so really nothing to lose.
Ben_f, very interesting project, and very much what I am thinking of in our farmhouse.
We do have doubleglazing, but the walls and the windows can get wet when there are lots of people in the house. Part is often used as self catering holiday accommodation when no family visiting. Part is not used for weeks or months. I'm thinking a number of small units to keep the ducting limited and use not when needed.
Your graphs are great and still working!
My main concern is to keep it operating quietly when not boosted, but I'm struggling to decide on the unit and air velocity in the ducting to achieve that.
Might put in the first in the next couple of months as decorating (= also partial replastering in our case!) the coldest nedroom at the north east end of the house.
Interested if you are still happy after nearly 10 years
I hadn't seen this thread before. Roybridge is a lovely spot.
I think full blown MVHR is overkill for traditional properties for the reasons given in this thread. There are too many other ways for air to leak in and out for the heat recovery part to be effective so you'll be paying a premium for no benefit.
Continuous extract or positive input is still however a very good idea. Anything that gets air moving through the building, including opening the windows... The practicality of running ducts to a central unit and putting terminals through the walls is the tricky part.
I have a Vent-Axia central extract unit that extracts from the kitchen and one bathroom (other bathroom is still planned...). It runs continuously on trickle and is boosted either by a short term increase in humidity (but that is pretty unreliable), or by a flow switch in the shower pipework. I was fortunate I was able to route the ducting from the kitchen across a false ceiling and then up the back of the shower in the bathroom above, both rooms were torn apart for refurbishment at the time. The extract terminal goes through the roof to a rather ugly plastic "periscope" but its at the back of the house so acceptable.
There hasn't been a single spot of black mould in the bathroom since I installed it and in general the windows in all rooms have much less condensation in early winter than they used to. Its rare now for me to get out the window vac. Big day to night termperature swings will still cause condensation though and with climate change we seem to be getting more of those. I'm hoping that once I get the front shower room hooked up that will draw air out of the master bedroom during the night to help with that.
There is a slight background noise in the bathroom on trickle, but the fan unit is directly above the ceiling and the duct run is very short so that's probably why. There is no noise in the kitchen on trickle and only a slight hum on boost. From outside its actually quite noisy when its on boost. Bigger ducts equals less noise but also equals more spend and more practical problems fitting. I think mine are 5" diameter or the rectangular equivalent.
I have a single room unit in the utility room which is just a timber framed porch on the side of the house, and on trickle the noise is quite noticeable. Its also quite rubbish at clearing condensation when the dryer is running so personally I don't think I'd go with single room units, certainly not for habitable rooms.