MVHR

[Mike Steel]

Hi all,

 

We've recently self built and fitted MVHR for the first time, enjoying the constant fresh air! Like many other components with self building, the learning curve is steep and now we in the house we are reflecting on some of the many decisions we made and if given the time again, we would do some things a little differently. MVHR is a good example. The system we chose certainly appear to flood the house with fresh air but is perhaps fairly basic by comparison to some others on here in it's controls. Our system is either on or off with an additional boost function if required. Having read on here about other systems where you can effectively reduce the volume of exchanged air depending on occupancy, holiday mode etc I'm wondering if we should have gone for something more sophisticated.

 

There's no doubt our system brings in plenty of fresh air, but we cannot help thinking its almost over preforming. Just wondered if anyone else has found the same and what they did aside from installing a new unit.

 

Regards, Mike.

 

 

[Conor]

Does it have a service menu you can access via laptop etc? A lot of systems have a service menu for commissioning etc, Vs the owner menu / interface which can be limited 

 

My mvhr had four different modes that correspond to different fixed fan speeds. Default is 3, then when humidity goes over a threshold, it goes to full boost. In this cold weather I've changed it to mode 2, and on a timer as despite the heat exchanger, incoming air was only 15c and noticeable in bedrooms. Also, air was far too dry. Dry skin and static shocks all the time. Much better now and only runs at certain times of the day.

[ProDave]

Some of us (cough) run the MVHR at a slightly lower rate than building regs require, based on the fact the house has fewer occupants than building regs would count for the number of bedrooms.  This makes it totally silent in all rooms and we still get lovely fresh air and no condensation or mould.

 

Mine is also a basic unit and the only user controls we have are a timed boost activated with a button on the landing that we use when showering, that puts it into fastest speed for your chosen time period when showering. and another timed boost button in the kitchen that runs it at an intermediate speed while cooking.

[jack]

10 minutes ago, Mike Steel said:

Just wondered if anyone else has found the same and what they did aside from installing a new unit.

 

Welcome to BuildHub.

 

Do you know the make and model of your MVHR unit? 

[Simon Brooke]

My Ventaxia has a silent running mode which I have assumed means that the fans are running at minimum rates. The time period is adjustable via the touch screen.

[Mike Steel]

11 hours ago, Conor said:

Does it have a service menu you can access via laptop etc? A lot of systems have a service menu for commissioning etc, Vs the owner menu / interface which can be limited 

 

My mvhr had four different modes that correspond to different fixed fan speeds. Default is 3, then when humidity goes over a threshold, it goes to full boost. In this cold weather I've changed it to mode 2, and on a timer as despite the heat exchanger, incoming air was only 15c and noticeable in bedrooms. Also, air was far too dry. Dry skin and static shocks all the time. Much better now and only runs at certain times of the day.

No, as far as I know it has nothing like that. The user options are to have it switched on, or off, or boost mode. All via traditional 240v switches. It does have a summer bypass function which is controlled by thermostats on top of the unit.

[Mike Steel]

10 hours ago, jack said:

 

Welcome to BuildHub.

 

Do you know the make and model of your MVHR unit? 

Thanks !

 

It's a Rega unit.

[Mike Steel]

11 hours ago, ProDave said:

Some of us (cough) run the MVHR at a slightly lower rate than building regs require, based on the fact the house has fewer occupants than building regs would count for the number of bedrooms.  This makes it totally silent in all rooms and we still get lovely fresh air and no condensation or mould.

 

Mine is also a basic unit and the only user controls we have are a timed boost activated with a button on the landing that we use when showering, that puts it into fastest speed for your chosen time period when showering. and another timed boost button in the kitchen that runs it at an intermediate speed while cooking.

Out of interest how long have you run your system slightly lower?

 

I was looking at what building regs document F stipulate the other day in terms of minimum ventilation rates. One of the things that occurred to me was if the MVHR has been set up and balanced to meet building regs, should the MVHR ventilation levels take into account the level of air tightness achieved in that particular building? Presumably if a house is not as air tight as the next one, surely it will be providing some of the required ventilation naturally through fabric leakage, without the MVHR needing to be set to deliver 100% of what building regs stipulate. 

Edited December 16, 2022 by Mike Steel

[jfb]

I would ignore building reg minimum rates and just see how it goes by reducing the basic rate. You’ll probably find you can keep it comfortable at a much lower rate.

[Mike Steel]

23 minutes ago, jfb said:

I would ignore building reg minimum rates and just see how it goes by reducing the basic rate. You’ll probably find you can keep it comfortable at a much lower rate.

The thought had crossed my mind. We'd have to establish a way of controlling the air flow.

 

When you describe keeping it comfortable, how do you measure that? Currently we can hear and feel the incoming air. The heat recovery is fairly good, but the volume is high so it's noticeable. What would be the signs there is insufficient fresh air entering the house?

[ProDave]

1 hour ago, Mike Steel said:

Out of interest how long have you run your system slightly lower?

About 4 years with no issues.

 

The problem was my MVHR unit only has 4 speeds (it actually has a fine +/- adjustment on each speed) and I needed speed 2 to get the BR rates in all rooms.  At that speed it was just audible in some rooms.  So now it runs at speed 1 with the + adjustment on.  It's not much below regs levels but dead silent.

[NSS]

Five years in we've experimented with different settings and settled for a summer programme and a winter programme. In summer it runs on speed 2 (of 4) from 7pm to 7am and speed 1 from 7am to 7pm. In winter we reverse that. If we have a particularly hot spell, as earlier this year, then we up the night time speed to 3. Summer bypass is programmed to avoid heat recovery when outside temp exceeds 20C.

 

Speed 4 (boost) is reserved for the likes, for example, of when cooking fish and runs for 60 minutes unless manually stopped. In all bar boost mode there is no perceptible noise in the house. We never open windows, and doors are seldom open for more than a few seconds.

[Mike Steel]

10 hours ago, NSS said:

Five years in we've experimented with different settings and settled for a summer programme and a winter programme. In summer it runs on speed 2 (of 4) from 7pm to 7am and speed 1 from 7am to 7pm. In winter we reverse that. If we have a particularly hot spell, as earlier this year, then we up the night time speed to 3. Summer bypass is programmed to avoid heat recovery when outside temp exceeds 20C.

 

Speed 4 (boost) is reserved for the likes, for example, of when cooking fish and runs for 60 minutes unless manually stopped. In all bar boost mode there is no perceptible noise in the house. We never open windows, and doors are seldom open for more than a few seconds.

Thanks NSS, that's useful intel. How do your described settings compare to how it was set up or instructed to be set up by the manufacturers info/building regs. And how did you determine what was right for you? Apart from the obvious such as cooking smells, did you have some kind of air quality monitoring to find a happy balance?

 

I might be missing something but I'm not aware of how our fan speeds can be adjusted as you and others have described. As far as I know, they are fixed.

 

Which MVHR system do you have out of interest?

[Mike Steel]

11 hours ago, ProDave said:

About 4 years with no issues.

 

The problem was my MVHR unit only has 4 speeds (it actually has a fine +/- adjustment on each speed) and I needed speed 2 to get the BR rates in all rooms.  At that speed it was just audible in some rooms.  So now it runs at speed 1 with the + adjustment on.  It's not much below regs levels but dead silent.

Thanks for that additional info ProDave.

 

The 4 speeds you have on your system, are they intended to be adjustable by the user, as we don't appear to have any adjustment on ours. Unless there is something deep inside the unit which I assume we should be leaving well alone.

[ProDave]

2 minutes ago, Mike Steel said:

Thanks for that additional info ProDave.

 

The 4 speeds you have on your system, are they intended to be adjustable by the user, as we don't appear to have any adjustment on ours. Unless there is something deep inside the unit which I assume we should be leaving well alone.

the 4 speeds are selected by 4 volt free contacts.  You could buy a switch that could be mounted anywhere in the house that was simply a rotary switch labelled 1,2,3,4  but I chose to do my own thing.

 

I used this sort of time switch

 

 

But because that has a switched 240V output I use that to switch on a small relay, that then provides the volt free contact to connect to the ASHP

[JohnMo]

It surprises how much over thinking that goes into a ventilation system, which designed to run at a constant rate, except when on boost.

 

Set to building regs or passivhaus flow rates, or somewhere in-between. Push the boost button as you go for a shower, job done.  Manage the filters as deemed by the manufacturer.

[NSS]

34 minutes ago, Mike Steel said:

Thanks NSS, that's useful intel. How do your described settings compare to how it was set up or instructed to be set up by the manufacturers info/building regs. And how did you determine what was right for you? Apart from the obvious such as cooking smells, did you have some kind of air quality monitoring to find a happy balance?

 

I might be missing something but I'm not aware of how our fan speeds can be adjusted as you and others have described. As far as I know, they are fixed.

 

Which MVHR system do you have out of interest?

Hi Mike, it was originally suggested that speed 2 was 'normal' but we've found, through trial and error, what works best for us. Air quality was the main objective for the house due to Mrs NSS's lung conditions, and so far as any monitoring is concerned, her lungs know when the intake filter is close to needing changing.

 

We have the Paul Novus 300. Pic of the control panel below.

 

[NSS]

24 minutes ago, JohnMo said:

It surprises how much over thinking that goes into a ventilation system, which designed to run at a constant rate, except when on boost.

 

Set to building regs or passivhaus flow rates, or somewhere in-between. Push the boost button as you go for a shower, job done.  Manage the filters as deemed by the manufacturer.

Maybe you need to think about it more 🤔 

Edited December 17, 2022 by NSS

[ProDave]

45 minutes ago, JohnMo said:

It surprises how much over thinking that goes into a ventilation system, which designed to run at a constant rate, except when on boost.

 

Set to building regs or passivhaus flow rates, or somewhere in-between. Push the boost button as you go for a shower, job done.  Manage the filters as deemed by the manufacturer.

That is exactly what we do.  I don't see the need for a fancy complicated control panel.

[Mike Steel]

20 minutes ago, NSS said:

Hi Mike, it was originally suggested that speed 2 was 'normal' but we've found, through trial and error, what works best for us. Air quality was the main objective for the house due to Mrs NSS's lung conditions, and so far as any monitoring is concerned, her lungs know when the intake filter is close to needing changing.

 

We have the Paul Novus 300. Pic of the control panel below.

 

All really useful info from people who have used MVHR for much longer than us. Having never lived in a house with it before, it's inevitably a little bit trial and error and hearing about how some have developed their own optimum settings is helpful.

 

We feel our heating and MVHR are working against each other and so the next step is to accurately measure the air exchanges to see if they are set to building regs. Still not sure how buildings regs vs house air tightness work together because if we were at Passivhaus standard (which we are not) it seems the system would still be set at the same flow rates. That seems odd to me.

 

I've bought a basic air monitoring device off Amazon to try and measure air quality with the MVHR on and after turning it off for a few hours during the day.

 

Needless to say we've never needed the boost function, far from it - we can feel and hear air entering through the vents. And the bathroom soon clears after a shower. If we find the rate of air exchanges is correct as per regs, then I guess we'd need to consider a way to reduce the fan speeds. Over ventilating the house would seem like a waste all of the hard work and money invested in insulation and air tightness.

 

Thanks again to all for sharing info on what you have found using your own MVHR systems. 

[ProDave]

48 minutes ago, Mike Steel said:

Needless to say we've never needed the boost function, far from it - we can feel and hear air entering through the vents. And the bathroom soon clears after a shower. If we find the rate of air exchanges is correct as per regs, then I guess we'd need to consider a way to reduce the fan speeds. Over ventilating the house would seem like a waste all of the hard work and money invested in insulation and air tightness.

We can only feel and hear the air from the vents when at boost speed. At normal speed, you would have to stand on something at get right up next to a vent to feel the gentle flow of air.

 

If it is running too fast, then it will be wasting heat.  Do you even know how to adjust the speed on yours?

[JohnMo]

1 hour ago, NSS said:

Maybe you need to think about it more

No don't think so, enough other jobs to think about.  MVHR is all sorted setup and running nice and quietly.

[Mike Steel]

35 minutes ago, ProDave said:

We can only feel and hear the air from the vents when at boost speed. At normal speed, you would have to stand on something at get right up next to a vent to feel the gentle flow of air.

 

If it is running too fast, then it will be wasting heat.  Do you even know how to adjust the speed on yours?

No there is nothing externally to control the air flow except boost, or turn it off completely.

[Mike Steel]

21 minutes ago, JohnMo said:

No don't think so, enough other jobs to think about.  MVHR is all sorted setup and running nice and quietly.

That's where we need to get to JohnMo, set up and running nicely. As you said in your previous post, perhaps we need to find the balance in flow rates. I don't think we are over thinking it, just not sure it's working at the optimum balance yet and listening to others who have years of experience with their systems, is much appreciated.

[JohnMo]

My take on flow rates is.

 

All bedrooms have people in them and bedrooms have the doors shut at night, go will building regs flow rates.

 

Anything else, passivhaus rates or above.