Integrating an MVHR to our build

[Bitpipe]

16 hours ago, Rich123 said:

. If I was buying a house with no heating in the bedrooms , I would want to have supporting evidence that this is an engineered solution and not a guess.

 

I have a full PHPP analysis that clearly calculates the heating requirement per m2.  Also SAP A rated (91).

 

But my clincher for any buyer would be to show them my energy bill which averaged over the year s £1/day for gas and £1.50 for electricity. This is for a 6 bed 400m2 house, family of 4 and two adults who work from home (even pre -lockdown).

 

Note also that building this passive house was no more expensive (and possibly cheaper) than a traditional min BR standard.

 

I agree that if a developer / builder was throwing up a house (or more) for profit then I'd be very wary of poorly though through systems (such as ASHP, solar thermal, even MVHR etc) to get SAP points. We learned early on that a house is a system and all parts need to complement - fabric (insulation, airtightness, solar gain/shading) and the DHW, heating and ventilation system.

 

Our experience is that winter comfort heating is not an issue but spring/summer/autumn overheating is. Throwing an over specified heating system into a house with a low energy requirement is not a great idea. Cooling (or bettter, preventing overheating) strategies are every bit as important.

[DavidO]

47 minutes ago, Bitpipe said:

 

I have a full PHPP analysis that clearly calculates the heating requirement per m2.  Also SAP A rated (91).

 

But my clincher for any buyer would be to show them my energy bill which averaged over the year s £1/day for gas and £1.50 for electricity. This is for a 6 bed 400m2 house, family of 4 and two adults who work from home (even pre -lockdown).

 

Note also that building this passive house was no more expensive (and possibly cheaper) than a traditional min BR standard.

 

I agree that if a developer / builder was throwing up a house (or more) for profit then I'd be very wary of poorly though through systems (such as ASHP, solar thermal, even MVHR etc) to get SAP points. We learned early on that a house is a system and all parts need to complement - fabric (insulation, airtightness, solar gain/shading) and the DHW, heating and ventilation system.

 

Our experience is that winter comfort heating is not an issue but spring/summer/autumn overheating is. Throwing an over specified heating system into a house with a low energy requirement is not a great idea. Cooling (or bettter, preventing overheating) strategies are every bit as important.

Very sound advice! Agree 100%

[DavidO]

6 hours ago, Rich123 said:

I it won’t effect the SAP as it’s based on the system not individual room heating .

Most SAP assessors won’t be designers. 
 If you add electric heating points then that will effect the SAP so if you are going to I’d keep that quiet.

I think perhaps you might have missed the main point I was trying to make (for djcdan rather than you) which is to guard against the potential trap of losing sight of the big picture as a result of focusing on the minutiae of the calculations. Depending on where you start from, and what you’re aiming at, there are usually lots of alternative routes to achieving an acceptable SAP score. The important thing is to make sure that whichever of those routes you consider they work with what you are trying to achieve.

[Rich123]

18 hours ago, DavidO said:

I think perhaps you might have missed the main point I was trying to make (for djcdan rather than you) which is to guard against the potential trap of losing sight of the big picture as a result of focusing on the minutiae of the calculations. Depending on where you start from, and what you’re aiming at, there are usually lots of alternative routes to achieving an acceptable SAP score. The important thing is to make sure that whichever of those routes you consider they work with what you are trying to achieve.

Thanks , I was a registered SAP assessor for 10 years so I understand .

[DavidO]

44 minutes ago, Rich123 said:

Thanks , I was a registered SAP assessor for 10 years so I understand .

????

[Adsibob]

On 04/01/2021 at 20:14, DavidO said:

Rigid rather than flexible ducts are supposed to help with this, as well as trying to keep your duct runs as simple and free of bends as possible. 

Just to make things more confusing, I’m in discussion with a MVHR company that are recommending “semi rigid radial ducting”. 

[PeterW]

8 hours ago, Adsibob said:

Just to make things more confusing, I’m in discussion with a MVHR company that are recommending “semi rigid radial ducting”. 

 That just means the corrugated plastic ducting that is 65/75mm in diameter. Rigid is normally uPVC or galvanised steel, flexible is the nasty plastic film coated slinky spring wire stuff. 

[DavidO]

On 19/01/2021 at 23:51, Adsibob said:

Just to make things more confusing, I’m in discussion with a MVHR company that are recommending “semi rigid radial ducting”. 

Bin them....!!

[Iceverge]

On 19/01/2021 at 23:51, Adsibob said:

Just to make things more confusing, I’m in discussion with a MVHR company that are recommending “semi rigid radial ducting”. 

No issue so long as it's specced correctly. They are easy to DIY and eliminate cross talk. 

 

Just avoid this style of flexible ducting.

[Adsibob]

12 minutes ago, Iceverge said:

No issue so long as it's specced correctly. They are easy to DIY and eliminate cross talk. 

 

Just avoid this style of flexible ducting.

Thanks @Iceverge. Just to clarify, are you saying avoid the example pictured in white, but go for the example pictured in blue, or avoid both?

[Iceverge]

Avoid the white one. 

 

The blue one is fine but beware of the low flow rates of smaller sizes.  (Noise) 

 

In essence a duct should be non collapsible.

 

This includes the ducts on the intake exhaust (Outside) side of the MVHR. 

 

[Jason L]

7 minutes ago, Iceverge said:

Avoid the white one. 

 

The blue one is fine but beware of the low flow rates of smaller sizes.  (Noise) 

 

In essence a duct should be non collapsible.

 

This includes the ducts on the intake exhaust (Outside) side of the MVHR. 

 

Can you get & use 90 degree bends for the blue ducts for say when it is running in the first floor zone and needs to turn to go vertically? 

[Roundtuit]

40 minutes ago, Jason L said:

Can you get & use 90 degree bends for the blue ducts for say when it is running in the first floor zone and needs to turn to go vertically? 

You can just bend it to 90 degrees within the joist depth, no need for joints.  Best to try and avoid too many sharp bends though.

[Russdl]

41 minutes ago, Jason L said:

Can you get & use 90 degree bends for the blue ducts for say when it is running in the first floor zone and needs to turn to go vertically

Yes you can, and if needed you can also get a flatter version if there isn’t room for the round.
 

The more 90 degree bends the more the flow is restricted though. 

[Jason L]

10 minutes ago, Roundtuit said:

You can just bend it to 90 degrees within the joist depth, no need for joints.  Best to try and avoid too many sharp bends though.

Great thanks ?

[Jason L]

9 minutes ago, Russdl said:

Yes you can, and if needed you can also get a flatter version if there isn’t room for the round.
 

The more 90 degree bends the more the flow is restricted though. 

Ok cheers there won’t be many ?

[DavidO]

11 hours ago, Adsibob said:

Thanks @Iceverge. Just to clarify, are you saying avoid the example pictured in white, but go for the example pictured in blue, or avoid both?

 

The problem with both the blue and white versions is that the “ribbed” structure creates turbulence within the air-flow which results in increased noise problems and a higher power consumption to move the volume of air you need to achieve satisfactory ventilation + both of those problems will be compounded if the pipes have a smaller bore. The other longer term issue is that the ribbing tends to result in the accumulation of dust/debris within the pipes increasing the risk of mould/bacterial growth. Basically the smoother the internal surface of your ducting the better. The only advantages I can see for flexible ductwork are ease of installation, which I think is only marginal in reality, and a price differential, which is probably also marginal when weighed against the whole system and long term running/maintenance costs.

[joe90]

With my DIY installed MVHR I used a red version of the blue stuff posted earlier. The internal bore is smooth and sooo much easier to instal compared to large diameter metal. Sweeping bends create much less resistance than 90’ bends. The air speed is so slow that noise is not an issue with mine. I created my own terminals, manifold/silencer and it all works great.

[dpmiller]

12 hours ago, DavidO said:

 

The problem with both the blue and white versions is that the “ribbed” structure creates turbulence within the air-flow which results in increased noise problems and a higher power consumption to move the volume of air you need to achieve satisfactory ventilation + both of those problems will be compounded if the pipes have a smaller bore. The other longer term issue is that the ribbing tends to result in the accumulation of dust/debris within the pipes increasing the risk of mould/bacterial growth. Basically the smoother the internal surface of your ducting the better. The only advantages I can see for flexible ductwork are ease of installation, which I think is only marginal in reality, and a price differential, which is probably also marginal when weighed against the whole system and long term running/maintenance costs.

 The semi-rigid ducts are smooth-bore.

[Haylingbilly]

On 04/01/2021 at 20:14, DavidO said:

 

We'll be having UFH on the ground floor and previously had specified radiators to the upstairs. By installing MVHR, could the upstairs be heated by i) rising heat from downstairs and ii) the MVHR to replace the needs to install rads?

 

- By installing MVHR, this replaces the need for other forms of ventilation to kitchen and bathroom areas, which would typically be extractor fans? I assume this is correct since any additional ventilation system would reduce the airtight seal on the property and decline the efficiency of MVHR.

We did exactly what you are describing in 2013 in a 195msq timber frame build. Our architect said it was “brave” and his energy consultant said we were “bonkers”. Both were wrong; it has worked perfectly and 7 years on we have no regrets whatsoever. Omitting the heating, other than heated towel rails in the bathrooms upstairs, saved £1,100 which was a significant contribution to the £2,600 cost of the MVHR system. We also negotiated a £600 discount from our window suppliers as we didn’t need trickle vents and saved another £800 or so as we didn’t need a cooker hood or any bathroom extractor fans, so the “net” cost of the MVHR was pretty minimal.

 

Unlike others our experience is that there is an element of heat redistribution from the MVHR, you can feel slightly warm air coming in through the vents. It’s difficult to quantify, but our bedrooms maintain a pretty constant 19 degrees in winter from the combined contributions from the ventilation system and the “migration” of heat which you mention from the ground floor, probably enhanced by an open plan layout downstairs which is also open to the stairwell. 
 

As regards your noise questions, our experience is yes you can hear it when it’s on boost, but not if the TV or radio is on, and in reality the boost level is so infrequently required it just isn’t an issue. We’ve also found that we can run the fans at much lower speeds than recommended by the manufacturers so in reality the system is virtually silent most of the time. Rigid rather than flexible ducts are supposed to help with this, as well as trying to keep your duct runs as simple and free of bends as possible. 
 

We located the intake/exhaust ducts on a north facing gable wall rather than through the roof in order to benefit from shaded/cooler air in summer. It’s amazing how hot a dark coloured slate/tiled roof can get with the sun on it, and the thought of sucking any of that heat into the house in July/August was unbearable, even in Northumberland. We also sited the exhaust duct downwind from the intake, which was a no cost option which which we thought might have (unquantifiable) benefits for both air quality and intake temperature in summer.

 

Good luck. Hope it works well for you!

 

 

Hi DavidO, this is really interesting. Please can you tell me what uValues you had on your wall and did you have double or triple glazing?

Thanks!

Andy

[Haylingbilly]

On 07/01/2021 at 13:51, Bitpipe said:

 

I would respectfully disagree on that last point.

 

In a near passive house (and I have lived in mine coming up on 5 years) it is really not needed.

 

We have a 110m2 passive basement, no heating whatsoever and is always 22^oC. Ground floor (same foot print) has low temp wet UFH which is active year round and set to 22^oC but only comes on Nov-Feb and even then only on the really cold days. First floor bedrooms have no heating and are always comfortable (21 usually) due to solar gain, convected heat from the rest of the house and occupancy.

 

Bathrooms have electric UFH as tiles will feel cold even at an acceptable room temp and wet ufh towel rails. Rooms in roof have no heating but always warm due to solar gain (roof-lights) and convection.

 

If there was heating installed where it is not, it would never be on so the invested cost would be wasted until such times as the house needed sold (which is no time soon). 

 

If I really wanted heat in bedrooms, I'd just plug panel heaters into the wall.

 

I don;t have much time for NHBC to be honest, especially looking at the appalling design and quality of the builders boxes churned out annually that all meet NHBC standards.

Hi Bitpipe

A very interesting post - please can you tell me what uValue you had for your walls and did you go double or triple glazed. Can you remember your airtightness result too?

Thanks!
 

Andy

[DavidO]

14 hours ago, Andy brown said:

Hi DavidO, this is really interesting. Please can you tell me what uValues you had on your wall and did you have double or triple glazing?

Thanks!

Andy

Hi Andy

The wall uValue was 0.14 and the windows are double glazed (though quite well specced for the time, we do have uValues for them somewhere if you’re interested). The big win for us had been airtightness, which tested at 0.296 from memory.

[Bitpipe]

16 hours ago, Andy brown said:

Hi Bitpipe

A very interesting post - please can you tell me what uValue you had for your walls and did you go double or triple glazed. Can you remember your airtightness result too?

Thanks!
 

Andy

 

It was passive standard so airtightness of 0.56 ACH, triple glazed passive certified glazing from Gaulhofer. Walls were 0.12, roof 0.1 and basement 0.1 also.

 

https://www.mbctimberframe.co.uk/passive-house/passive-house-technical-detail/

[Andrew Sharratt]

A number of people commented in this thread about putting PV panels in trays as its cheaper than roof tiles. I am not sure about this argument. The mounting trays alone cost the equivalent of over £60/m without fitting. That's a lot more than roof tiles. In fact a mounting tray is now only slightly cheaper than the PV panel that it holds. I was planning to fit the trays now and then add the panels at a later date but I cant justify the cost of the trays. Its cheaper to fit tiles and then use mounting brackets. Of course the trays look nicer! Has anyone else done the calculations?

[Bitpipe]

23 hours ago, Andrew Sharratt said:

 I was planning to fit the trays now and then add the panels at a later date but I cant justify the cost of the trays. Its cheaper to fit tiles and then use mounting brackets. Of course the trays look nicer! 

 

You can't do that as the panels need to be in the trays to make your roof watertight.

 

Theres another active thread with pricing for trays & panels, look at that for some lower pricing suggestions.