Newbie

[DOIGAN]

Hello,

 

Hopefully ok to be on this forum as I am not in the building trade.

I am however a tradesman,( mechanical) so do not mind trying to do some DIY if I feel capable.

I do however believe that if you feel you cannot do something properly or safely get a professional.

 

I just moved to Orkney into a four year old so called energy efficient home with air to water heating and an MVHR air system and a biodisc sewage unit.

 

Trying to get my mechanical head around these systems as they don't appear to do what the manufacturers claim in my opinion.

 

Either that or my systems are not configured or working properly.

 

I plan to do work in the garden too so will no doubt be asking for lots of advice from members if that is ok.

 

Thanks in advance to anyone who posts to any ofy questions.

[Jeremy Harris]

Welcome.

 

It's far from unusual to find that MVHR systems, in particular, haven't been properly set up and commissioned.  They only work well when the house is pretty airtight, and when the flow rates have been adjusted at each extract/fresh air supply.  This is supposed to be done as a part of the commissioning process, but as it can be a fairly time consuming job, I get the feeling that lots of installers just don't bother to do it properly.  We've had examples here before where new builds have had pretty poor MVHR installations, and all of us here that have set up and balanced our own self-installed MVHR system know how time consuming it can be to get it right.

 

The BioDisc treatment plant isn't something I'd want to work on if it goes wrong!  I took a look at a cut away of one at the Swindon self build centre and my first thought was "how the heck do you service the motor and disc drive system?"  Both are down inside the unit, and looked to me to be something fairly unpleasant to work on if it ever went wrong.  I think the general consensus here is that the air blower systems are fairly easy and straightforward to install and service.  That's what we opted to fit, as it looked to be something that could be DIY fixed if it ever went wrong.

[DOIGAN]

2 minutes ago, Jeremy Harris said:

Welcome.

 

It's far from unusual to find that MVHR systems, in particular, haven't been properly set up and commissioned.  They only work well when the house is pretty airtight, and when the flow rates have been adjusted at each extract/fresh air supply.  This is supposed to be done as a part of the commissioning process, but as it can be a fairly time consuming job, I get the feeling that lots of installers just don't bother to do it properly.  We've had examples here before where new builds have had pretty poor MVHR installations, and all of us here that have set up and balanced our own self-installed MVHR system know how time consuming it can be to get it right.

 

The BioDisc treatment plant isn't something I'd want to work on if it goes wrong!  I took a look at a cut away of one at the Swindon self build centre and my first thought was "how the heck do you service the motor and disc drive system?"  Both are down inside the unit, and looked to me to be something fairly unpleasant to work on if it ever went wrong.  I think the general consensus here is that the air blower systems are fairly easy and straightforward to install and service.  That's what we opted to fit, as it looked to be something that could be DIY fixed if it ever went wrong.

Hello, thanks for responding, I have opened the biodisc cover and it is surprisingly not that smelly ?, my understanding is that as long as it does not flood the gearbox they are very reliable. I do need to check if mine is a chain or belt drive, I have been told belts can break, the problem I have in Orkney is no-one bothers to get things serviced, they wait until they stop working so I have been unable to get reliable costs etc.

The thing about my MVHR system is that the air it pumps into the dry rooms is cold? I believe that they are supposed to extract moist warm air from wet rooms and mix this with filters incoming air and pump into into the dry rooms. But most of the time the wet rooms do not create warm moist air. So what is the point of them pumping cold filtered air into rooms, we only feel cold.

 

This is why I feel that the unit is faulty/ not set up correctly or a waste of time and energy.

[ProDave]

I share Jeremy's concerns about the boidosc.  But as long as it works it does the job it's okay.  Just pray it does not go wrong, and when it does you can find a mechanic with no sense of smell.

 

Perhaps start a new topic regarding each of the systems that are not working as you expect.

 

But briefly the fresh air into rooms from mvhr will always be colder than the air in the rooms, but not as cold as it would be if it ws raw outside air coming straight in.

 

[DOIGAN]

Just now, ProDave said:

I share Jeremy's concerns about the boidosc.  But as long as it works it does the job it's okay.  Just pray it does not go wrong, and when it does you can find a mechanic with no sense of smell.

 

Perhaps start a new topic regarding each of the systems that are not working as you expect.

 

Cheers Prodave, good idea, will do.

[Jeremy Harris]

Just now, DOIGAN said:

Hello, thanks for responding, I have opened the biodisc cover and it is surprisingly not that smelly ?, my understanding is that as long as it does not flood the gearbox they are very reliable. I do need to check if mine is a chain or belt drive, I have been told belts can break, the problem I have in Orkney is no-one bothers to get things serviced, they wait until they stop working so I have been unable to get reliable costs etc.

The thing about my MVHR system is that the air it pumps into the dry rooms is cold? I believe that they are supposed to extract moist warm air from wet rooms and mix this with filters incoming air and pump into into the dry rooms. But most of the time the wet rooms do not create warm moist air. So what is the point of them pumping cold filtered air into rooms, we only feel cold.

 

This is why I feel that the unit is faulty/ not set up correctly or a waste of time and energy.

 

 

Fingers crossed that the Biodisc keeps working!  If it's not smelly then that's a good sign that it's working OK.

 

The way that MVHR works is to extract some of the heat from the air pulled from rooms like the kitchen, bathroom and toilet, and use that to pre-heat the incoming fresh ventilation air via a heat exchanger.  There's no mixing of fresh intake air with exhaust air, the two are kept separate.

 

The air that comes out of the fresh air vents will always be colder than room temperature, but not as cold as the fresh air that would otherwise be needed to ventilate the house, so the heat loss is a lot less.

[DOIGAN]

Hmmm, my system is a vent axia, from the information I have on it it is purely a mechanical heat exchanger. So the air pumped into the rooms always feels cold, it feels like a draught from an open window. Do so-called air tight houses like mine really need them? If you consider how often outside doors are opened surely the air inside would be replaced often enough. I have frequently thought about just switching it off.

[ProDave]

I like many on here have mvhr.  At normal trickle rates you don't need much air, and certainly not enough that you feel a draught from the vents unless you are really right up next to them. 

 

They are VERY necessary in an air tight house because you need air to breathe.  the alternative is uncontrolled trickle ventilation that will allow more heat out of the building to go to waste.

 

If you are feeling cold draughts all the time I suggest your system is not set up properly.  do you have any form of speed control panel or boost switches?

[Jeremy Harris]

Our house is much like @ProDave's, and as he says, you can't really feel the air coming in through the fresh air terminals.  Our system is set up to change all the air in the house about once every 2 1/2 hours, which seems to be about right.  If you can feel cool air blowing out of the fresh air terminals then it sounds as if it's not set up properly.

 

MVHR is just mechanical, in that it's just two networks of ducts connected to a plate heat exchanger and a couple of fans.  There are usually filters either side of the plate heat exchanger, to prevent dust from clogging it up (and these need cleaning/replacing every 6 months or so) plus some controls to vary the flow rate, so that it can be boosted when cooking, or when a shower or bath is run, then go back to the normal trickle ventilation rate.  Sometimes the boost function is manual, and sometimes it is via a humidistat that sense when the extract air is humid.  Worth having a good look at your system to try and see what you're dealing with.  Perhaps start a thread here and post some photos of your set up, and with luck someone here will recognise it and be able to offer first-hand suggestions as to how to get it working properly.

[DOIGAN]

Hi,

 

The system was set to run at 30% all the time which then boosts up to 50% when showers on etc, the only trouble with this is that I could not sleep due to the air noise coming out of the vents, I tried it down at 20% but still the same. I now have the system running at 5% all the time and the boost at 50%. i appreciate that this is probably too low but it drives me nuts.

[DOIGAN]

3 minutes ago, Jeremy Harris said:

Our house is much like @ProDave's, and as he says, you can't really feel the air coming in through the fresh air terminals.  Our system is set up to change all the air in the house about once every 2 1/2 hours, which seems to be about right.  If you can feel cool air blowing out of the fresh air terminals then it sounds as if it's not set up properly.

 

MVHR is just mechanical, in that it's just two networks of ducts connected to a plate heat exchanger and a couple of fans.  There are usually filters either side of the plate heat exchanger, to prevent dust from clogging it up (and these need cleaning/replacing every 6 months or so) plus some controls to vary the flow rate, so that it can be boosted when cooking, or when a shower or bath is run, then go back to the normal trickle ventilation rate.  Sometimes the boost function is manual, and sometimes it is via a humidistat that sense when the extract air is humid.  Worth having a good look at your system to try and see what you're dealing with.  Perhaps start a thread here and post some photos of your set up, and with luck someone here will recognise it and be able to offer first-hand suggestions as to how to get it working properly.

Yes this sounds like mine, from what you state can Ii presume that it doesn't run constantly? It only switches on every couple of hours? I know that I can set up timers etc, I just assumed that as Vent Axia states that these units are designed to be on  365/24/7 I have not bothered setting timers.

[ProDave]

My mvhr runs constantly and at the slow trickle speed is inaudible.  I have set mine up with manual boost timers. the upstirs boost for showering runs it at the fastest speed which is indeed noisy. downstairs I have a slower boost rate for when cooking which is not as noisy.

[Jeremy Harris]

Again, just as @ProDave says above.  Ours is on 24/7, and 99% of the time it runs at the trickle ventilation rate.  If we run a shower, or are cooking, the humidistat in the extract side automatically switches the unit to boost ventilation for maybe 15 minutes or so, to extract the additional moist air.

[DOIGAN]

Hi Guys , sounds like I probably have it set up just fine going by both of your comments, my system is set this this too.The only gripe is the cold air feeling I even covered the ducting with more insulation to try and increase the air temp from the intake duct, can't say I notice any difference though.

[Gone West]

1 hour ago, DOIGAN said:

I believe that they are supposed to extract moist warm air from wet rooms and mix this with filters incoming air and pump into into the dry rooms. But most of the time the wet rooms do not create warm moist air. So what is the point of them pumping cold filtered air into rooms, we only feel cold.

Hi, welcome to the forum. You could try having the heating on in the wet rooms all the time which would also create a more comfortable environment in those rooms. We heat the whole of our house to 23C with just the towel rails in the bathrooms.

[DOIGAN]

2 minutes ago, PeterStarck said:

Hi, welcome to the forum. You could try having the heating on in the wet rooms all the time which would also create a more comfortable environment in those rooms. We heat the whole of our house to 23C with just the towel rails in the bathrooms.

Hi Peter,

 

Thanks for this, to be honest the bathrooms are usually fine, the main one is the warmest room in the house, I think it is the open loop in the system as it has no thermostat and is always warm the en-suite heats up via the bedroom stat and you can feel it through the flooring, it is really just the lounge that is the problem, I am not sure if it is because the ceiling is vaulted and teh calculations have not taking this into consideration with regards to the floor area for the heating loops.

[Jeremy Harris]

17 minutes ago, DOIGAN said:

Hi Guys , sounds like I probably have it set up just fine going by both of your comments, my system is set this this too.The only gripe is the cold air feeling I even covered the ducting with more insulation to try and increase the air temp from the intake duct, can't say I notice any difference though.

 

 

To set the system up is a fiddle, TBH, as you have to go around measuring the air flow rate at every terminal and then adjusting them to both get the right flow rate for each room, and, more importantly, to ensure that the total extract flow rate equals the fresh air flow rate.  If this is out of balance the heat exchanger won't work as efficiently, and as a consequence the ventilation heat loss will be higher.  The forum has a couple of sets of MVHR flow metering equipment that's been donated and is available via the tool loan scheme here, specifically so that people can DIY set up and balance their MVHR systems.  There's often a waiting list for this, though, as it can be a time consuming task.

[DOIGAN]

8 minutes ago, Jeremy Harris said:

 

 

To set the system up is a fiddle, TBH, as you have to go around measuring the air flow rate at every terminal and then adjusting them to both get the right flow rate for each room, and, more importantly, to ensure that the total extract flow rate equals the fresh air flow rate.  If this is out of balance the heat exchanger won't work as efficiently, and as a consequence the ventilation heat loss will be higher.  The forum has a couple of sets of MVHR flow metering equipment that's been donated and is available via the tool loan scheme here, specifically so that people can DIY set up and balance their MVHR systems.  There's often a waiting list for this, though, as it can be a time consuming task.

Cheers for the info, might add my name to the list, Orkney might be too far north though

[Jeremy Harris]

7 minutes ago, DOIGAN said:

Cheers for the info, might add my name to the list, Orkney might be too far north though

 

 

Not sure if the forum kit has already been up to Orkney yet, but it may have, as we have another self-builder here from the islands.

[Gone West]

21 minutes ago, DOIGAN said:

it is really just the lounge that is the problem, I am not sure if it is because the ceiling is vaulted and teh calculations have not taking this into consideration with regards to the floor area for the heating loops.

Do you know what type and thickness of insulation you have under the UFH pipework.

[DOIGAN]

35 minutes ago, PeterStarck said:

Do you know what type and thickness of insulation you have under the UFH pipework.

Sorry no, as I stated it wasbuilt for the previous owners but was a Scotframe Valu therm kit

[newhome]

50 minutes ago, DOIGAN said:

Sorry no, as I stated it wasbuilt for the previous owners but was a Scotframe Valu therm kit

 

You should be able to look up the plans containing this sort of detail from the council website? Building control should also have air test results, SAP etc. Maybe they will email you those if you ask? 

 

 

[Stones]

Hi @DOIGAN, welcome to the forum. Good to have someone else from Orkney here.  Where are you located?

[Stones]

In respect of your MVHR, we have a Vent Axia as well, and generally it seems to be performing at round 90% efficiency.  I know you say its cold air coming from the supply vents.  Have you measured the temperature of that incoming air (it will be below whatever the room temperature is and will feel cool, think of the effect of wind chill - feels colder than it is)

[Gone West]

15 hours ago, DOIGAN said:

Sorry no, as I stated it wasbuilt for the previous owners but was a Scotframe Valu therm kit

Looking at their website they don't seem to mention ground floor U values, just wall values for different stud sizes.

 

U Value Options
(Brick & Block Cladding)

Stud Size	V-U-T	Std Kit
140mm	0.15	0.25
184mm	0.13	0.21
235mm	0.11	0.18