Understanding part F for MVHR and recomendations for suitable units.

[dnb]

I am currently checking all the calculations I did 18 months ago for the heating and MVHR and updating where things are different to the original design. I happened to read through part F to verify the architect's initial figures and I am a little confused as to what the document is getting at. It seems I am required to ventilate at a rate of 0.3l/s per sqm of floor area as a minimum. This works out at 96l/s for my house and feels a little on the high side. But whatever happens I need to be able to demonstrate compliance with document F. Now we come to the boost requirement. It seems I now need to supply 53 l/s (4 bath, 1 kitchen, 1 utility) as a minimum - so less than normal. I consider this more than a little nonsensical so have made up my own requirement of a 15% increase over the minimum. I guess this bit of silliness is a function of the house not being average sized. What other interpretations have people made for these rules? (No doubt I will turn the whole thing down when I have a completion certificate.)

 

Now on to the MVHR unit. I would like a few recomendations as to which units perform well and aren't silly expensive and are actually available to buy. I would prefer to have one unit that will need to be able to provide somewhere in the region of 125l/s as opposed to trying to run smaller units in parallel. It would be an advantage if the unit were to have horizontal duct connections. I've not found one of these that is big enough yet.

[IanR]

5 hours ago, dnb said:

Now on to the MVHR unit. I would like a few recomendations as to which units perform well and aren't silly expensive and are actually available to buy. 

 

I have the Airflow Flexi DV1100. On paper it would be over-sized for your needs (as it is for mine), but that allows it to run at a gentle pace and well within its PH Certified range, and, with scope for a good boost above the required rate.

 

Airflow will do your design free of charge and provide a bill of materials with a target price to take around to their distributors. I found you can do a lot better than their target price, and also that some distributors had much better terms with Airflow than others. For me TP was the best price, although they had no idea what they were supplying, just a bunch of part numbers to them.

 

Airflow keep the unit in stock (in normal times), so delivery is reasonably quick.

[Conor]

Did you use the MVHR design spread sheet? That's what I used. 

 

I worked out the total volume of the house, multiplied by the Part F 0.3AC/hr and that gave me a "standard" ventilation rate of 260m3/hr (72lps). I then populated the sheet with this as a target rate for the minimum. I then went room by room and added individual flow rates using the passive house guide (Kitchen 60 m3 /h Bathroom, utility room 40 m3 /h WC 20 m3 /h). And added 33% for boosting. After all that, it showed I needed a system that would be maintaining a standard ventilation rate of 260m3/hr, and a boost capacity of 345m3/hr. Doubling that to get combined flow means a 700m3/hr unit. There aren't many. There is the Airflow Ardoit which meets this, and the Zehnder Q600 which is a little short. My design only roughly calculated pressure drop, so to be safe I've gone with two 400m3/hr Salda Smarty units. Two units does mean a lot more ducting, which adds significantly to the cost and complexity of installation. Either way, definitely oversepc your unit so fan speed and noise are minimised. 

Edited October 7, 2021 by Conor

[dnb]

5 hours ago, IanR said:

I have the Airflow Flexi DV1100. On paper it would be over-sized for your needs

 

Thanks. I was looking at various Airflow products and a recomendation that they do what they say is good. Very happy with the concept of having something too "big" and running it with capacity to spare.

 

2 hours ago, Conor said:

Did you use the MVHR design spread sheet?

 

Not quite. I rolled my own out of an air conditioning spreadsheet and some easy (OK, not exactly easy, but far from difficult) equations. The house is to be fully air conditioned so it made sense to reuse the pressure drop calculations and duct flow speed equations. All things being equal, I suspect we end up at similar operating points.

 

2 hours ago, Conor said:

And added 33% for boosting.

 

Did this come from the Passive House guide? The guidance in ADF is obviously absent here.

 

2 hours ago, Conor said:

Doubling that to get combined flow means a 700m3/hr unit.

My understanding from the specs I have seen was that a 700m^3/hr unit would extract AND supply that (after all, this is the air flow that results from doing both the extract and supply jobs). Is this not the case for all of them or do I have to divide the spec figures by 2 to select a unit? Probably not a bad plan either way because we are all saying that the units should not generally be run near rated capacity.

[Nickfromwales]

10 hours ago, dnb said:

Now on to the MVHR unit. I would like a few recommendations as to which units perform well and aren't silly expensive and are actually available to buy. I would prefer to have one unit that will need to be able to provide somewhere in the region of 125l/s as opposed to trying to run smaller units in parallel.

I have been installing Brink Flair 325's and 400's via CVC Ventilation and am super happy, as are my clients who are now living with these systems and report near inaudible operation when on trickle. Boost still very much acceptable with mitigatory provision such as inline sound attenuators at the unit ( before the manifolds ) to further reduce any nuisance noise in the rooms. Very effective combination when combining a good unit with such additional measures.

Nicholas Vaisey ( PH designer ) will happily look after you re designs / flow rates / specification etc, great service to date, and you could also inquire about the Brink Comfort units I am now routinely installing for 'cooling' as I've found them very cost effective (where an ASHP is being reversed for cooled water only ) to manage unwanted summer ambient uplift, but also to drip feed a tiny amount of 'heated' air into upstairs rooms where full on heating isn't justified. 

Edited October 7, 2021 by Nickfromwales

[BenP]

4 hours ago, Conor said:

MVHR design spread sheet

 

Hi - I'd be interested in having a look at this? Is it on BH?

[dnb]

11 hours ago, Nickfromwales said:

Brink Flair 325's and 400'

They are a good call. Not seen that particular brand before.

 

Thanks also for the design recomendation. I don't believe there's a need to revisit my design at the moment since the overall requirements are still close enough to the initial design.

[Nickfromwales]

14 minutes ago, dnb said:

They are a good call. Not seen that particular brand before.

 

Thanks also for the design recomendation. I don't believe there's a need to revisit my design at the moment since the overall requirements are still close enough to the initial design.

Purely if you needed a sense-check   “Measure twice” and all that jazz……

[dnb]

8 hours ago, Nickfromwales said:

“Measure twice”

With you there! I made friends with the people at work that do the air cooling designs for some of our equipment a while ago. ?

[Adam2]

On 07/10/2021 at 13:01, Nickfromwales said:

now routinely installing for 'cooling' as I've found them very cost effective (where an ASHP is being reversed for cooled water only ) to manage unwanted summer ambient uplift, but also to drip feed a tiny amount of 'heated' air into upstairs

 

What duct coolers have you found that work well with ashp? I was thinking of these and have in my bpc quote but wasn't really sure if would help that much

[hendriQ]

On 07/10/2021 at 13:01, Nickfromwales said:

I have been installing Brink Flair 325's and 400's via CVC Ventilation and am super happy, as are my clients who are now living with these systems and report near inaudible operation when on trickle. Boost still very much acceptable with mitigatory provision such as inline sound attenuators at the unit ( before the manifolds ) to further reduce any nuisance noise in the rooms. Very effective combination when combining a good unit with such additional measures.

Nicholas Vaisey ( PH designer ) will happily look after you re designs / flow rates / specification etc, great service to date, and you could also inquire about the Brink Comfort units I am now routinely installing for 'cooling' as I've found them very cost effective (where an ASHP is being reversed for cooled water only ) to manage unwanted summer ambient uplift, but also to drip feed a tiny amount of 'heated' air into upstairs rooms where full on heating isn't justified. 

@Nickfromwales as you're familiar with these machines, I wonder if you would do me a MASSIVE favour and let me know what is the minimum space required in front of a flair brink 400 to change filters and service it? The filters sold on ventilation land are 510mm long so is it just that ones needs enough space to open the door and pull out the filter, as shown in the space image or are there other servicing that need to be done which would need more space than that 510mm depth in front of the machine?

 

  

[Nickfromwales]

I’ll be working on one on Tuesday. If you can hang on I’ll measure it for the minimum requirements?

[hendriQ]

46 minutes ago, Nickfromwales said:

I’ll be working on one on Tuesday. If you can hang on I’ll measure it for the minimum requirements?

That would be great, thank you! I have checked and I have enough space to remove the 510mm filter, but i pretty much don't have a mm more than that. Given the unit is 560mm deep in total, I'm just concerned that if a large part inside the unit ever needs to be removed for a service or replacement, I won't be able to. Presumably eventually the motor or heat exchanger needs servicing/replacing.

[Nickfromwales]

4 minutes ago, hendriQ said:

That would be great, thank you! I have checked and I have enough space to remove the 510mm filter, but i pretty much don't have a mm more than that. Given the unit is 560mm deep in total, I'm just concerned that if a large part inside the unit ever needs to be removed for a service or replacement, I won't be able to. Presumably eventually the motor or heat exchanger needs servicing/replacing.

I’ll get answers on all the above from my go-to guy at CVC Direct. 

[Nickfromwales]

4 hours ago, hendriQ said:

That would be great, thank you! I have checked and I have enough space to remove the 510mm filter, but i pretty much don't have a mm more than that. Given the unit is 560mm deep in total, I'm just concerned that if a large part inside the unit ever needs to be removed for a service or replacement, I won't be able to. Presumably eventually the motor or heat exchanger needs servicing/replacing.

Ok, had a reply. 
510mm for filter AND the heat exchanger is plenty. Fan is small so no issues with that. Door is 440mm projection when open. 
If you speak to Nick or Will at CVC and mention my username and the forum he will give you a discount off the Brink unit ( if you’ve not purchased already ). I organised the same thing for BH members wanting unvented cylinders and buffer tanks with Trevor at www.Cylinders2go.co.uk That offer still stands. 

“Every little helps” etc etc. ?

[hendriQ]

1 hour ago, Nickfromwales said:

Ok, had a reply. 
510mm for filter AND the heat exchanger is plenty. Fan is small so no issues with that. Door is 440mm projection when open. 
If you speak to Nick or Will at CVC and mention my username and the forum he will give you a discount off the Brink unit ( if you’ve not purchased already ). I organised the same thing for BH members wanting unvented cylinders and buffer tanks with Trevor at www.Cylinders2go.co.uk That offer still stands. 

“Every little helps” etc etc. ?

That's very reassuring, thank you. It's amazing that you have a faster line of communication to CVC than I do, even though I'm a paying customer! 

[Nickfromwales]

1 minute ago, hendriQ said:

That's very reassuring, thank you. It's amazing that you have a faster line of communication to CVC than I do, even though I'm a paying customer! 

They are very, very busy atm.

If you have trouble getting through just pm me.