MVHR Calculations

[john0wingnut]

Hi all

 

I have attached a spreadsheet with my current calculations, and just wanted to run them past the forum to make sure I am on the right track.

 

The current Bungalow floor area is 168m2, so at 0.3l/s that would require a minimum of 50l/s or 180m3/h. High rate would be 45l/s or 162m3/h for kitchen and 3 bathrooms and utility)

 

We are planning on doing a 1st floor extension under the new PD rules, which would bring the total floor area to 243 m2, which would require 73l/s (263m3/h) minimum ventilation and high rate of 69l/s (248m3/h)

 

1) Have I worked those out correctly

2) I was looking at the Brink Flair 400 unit, which maxes out at 400m3/h. So in theory my background ventilation of 263m3/h would mean the unit is running at 65%, which I would assume is too high, so am I looking at needing a bigger unit, or getting say 2 units, one for upstairs and one for downstairs.

 

Many thanks in advance

 

John

 

MVHR Calculations.xlsx

[john0wingnut]

Ok, so no replies, I figured I've probably done something daft and no one wants to say anything......

 

So, I've had another go using the English Building Regs minimum Vs Passive House good practice guide. 

 

Via BR:

 

Via PH Good Practice Guide:

 

 

So via BR method the required boost value is lower than the minimum ventilation requirement, which doesnt make sense to me, and would mean I under spec the unit!

 

But via the PH method, I get a similar ventilation number @ 260m3/h and a boost of 340m3/h, which makes much more sense.

 

So the 400m3/h unit I was considering should be absolutely fine, so long as it is turned down to the minimum setting of 183m3/h, after signoff / commissioning etc, which would mean it was running at 45% of max capacity.

 

 

[CC45]

I've attached calcs for ours - done by BPC.

 

I had the impression that as long as you are there overall with a bias towards more ventilation in bathrooms & kitchens then its OK.  Kitchen is approx 0.5m3/hr with bathroom @ about 2m3/hr.  Despite the ensuites being a fair bit smaller they still seem to get the same extract rate.  I assume I've got it right... (all my notes are down the plot - not here).

 

 

[john0wingnut]

4 hours ago, CC45 said:

I've attached calcs for ours - done by BPC.

 

I had the impression that as long as you are there overall with a bias towards more ventilation in bathrooms & kitchens then its OK.  Kitchen is approx 0.5m3/hr with bathroom @ about 2m3/hr.  Despite the ensuites being a fair bit smaller they still seem to get the same extract rate.  I assume I've got it right... (all my notes are down the plot - not here).

 

 

Thanks.

What size unit did they spec you?

[CC45]

https://www.vent-axia.com/product/sentinel-kinetic-plus-b

[PeterW]

On 17/12/2020 at 15:43, CC45 said:

Despite the ensuites being a fair bit smaller they still seem to get the same extract rate.  I assume I've got it right... (all my notes are down the plot - not here).

 

Those convert to the boost rates for the minimum required for the Building Regs - nothing scientific about it. 

[john0wingnut]

On 20/12/2020 at 22:16, CC45 said:

https://www.vent-axia.com/product/sentinel-kinetic-plus-b

 

Many thanks. Looks like that doesn't have a Pre-Heater to stop frosting of the HE, but does have the humidity sensor. The Brink 400 does have a pre heater, but no humidity sensor, unless bought as an add on.

 

My other consideration is I want to be able to control it with my phone. Ive seen some of the Vent Axias can work this way - does the B plus have that function, or does it need an additional module to allow that? The Brink unit needs their e-module, which is another £300, humidity sensor another £200, so ends up being £2,100 rather than the base price of £1600.

 

[jack]

Why do you want to control it with your phone?

 

I had grand plans for connecting our Brink Excellent 400 into our home automation system, which would have allowed app-based control. However, after living with the system for a while before implementing this, there just didn't seem to be any point in doing so.

 

The humidity sensor was broken by clod-hopping painter (didn't realise until much later) before I had a chance to install it, so we don't even have that connected.

 

We run ours at 100m³/h in our 289m² (with very high ceilings downstairs) house, and that seems more than good enough. It doesn't get boosted when people shower. I manually boost it if I'm cooking something smoky or we have a lot of people over, but I wouldn't pay hundreds of quid to do this via an app when it's so easy (easier than opening an app, in fact) to just turn a dial the odd time I need to do it.

[JFDIY]

23 hours ago, john0wingnut said:

Ive seen some of the Vent Axias can work this way - does the B plus have that function

 

My Plus B does not, and unless things have changed in the last 12months I don't think there is a module to do so.

 

But you can get (and I have) a remote panel, with 15m of cable, this allows fill control of the unit (My unit is in the loft).

 

Like @jack mentions I can't see the need to be able to use an app. If it's set up reasonably well you'll find the automatic humidity control works very well and is proportional, so it varies the doped to maintain a set point rather than just boosting to a fixed setting.

 

i spent ages setting up boost switching from lights in our main bathroom to combine boost switching from a remote en-suite.

 

in reality the humidity control does the nearest bathroom better on its own, and I could have just boost switched the remote en-suite if needed.

 

 

[CC45]

I bought the romote unit & cable so we have a control point in the kitchen (so we can boost it when cooking).  I just want to leave it do its thing.  less complexity = more reliability

[john0wingnut]

5 hours ago, jack said:

Why do you want to control it with your phone?

 

I had grand plans for connecting our Brink Excellent 400 into our home automation system, which would have allowed app-based control. However, after living with the system for a while before implementing this, there just didn't seem to be any point in doing so.

 

The humidity sensor was broken by clod-hopping painter (didn't realise until much later) before I had a chance to install it, so we don't even have that connected.

 

We run ours at 100m³/h in our 289m² (with very high ceilings downstairs) house, and that seems more than good enough. It doesn't get boosted when people shower. I manually boost it if I'm cooking something smoky or we have a lot of people over, but I wouldn't pay hundreds of quid to do this via an app when it's so easy (easier than opening an app, in fact) to just turn a dial the odd time I need to do it.

Fair point. Maybe I’m getting too techy on something that doesn’t need to be.

 

I think the kitchen boost and hall controller is a must, so I will do those.

 

I wasn’t going to worry about bathrooms / ensuites as figured the humidistat will take care of that.

 

Does the Brink Excellent have a pre heater as that is my other consideration; from what I’ve read in other threads it’s a good idea to have one.

 

My building will be 250m2 ish when upstairs extension is done, so I will go with a 400 sized unit then. 
 

I was looking at the Ducobox Energy400 which you can get with a day/night supply 2 zone setup. Seems quite a neat idea, but have not read about any others on here with one.

 

Brink Flair 400 may be a sound choice in my case then, if I don’t need the fancy bits.

[Bitpipe]

36 minutes ago, john0wingnut said:

Fair point. Maybe I’m getting too techy on something that doesn’t need to be.

 

I think the kitchen boost and hall controller is a must, so I will do those.

 

I wasn’t going to worry about bathrooms / ensuites as figured the humidistat will take care of that.

 

Does the Brink Excellent have a pre heater as that is my other consideration; from what I’ve read in other threads it’s a good idea to have one.

 

My building will be 250m2 ish when upstairs extension is done, so I will go with a 400 sized unit then. 
 

I was looking at the Ducobox Energy400 which you can get with a day/night supply 2 zone setup. Seems quite a neat idea, but have not read about any others on here with one.

 

Brink Flair 400 may be a sound choice in my case then, if I don’t need the fancy bits.

 

Our electrician wired up the neutrals of our bathroom lights, plus proximity sensors, so that when either is triggered the MVHR  goes into boost mode (via the light switch input on the main unit). This also triggers the pump for the DHW hot return.

 

I think there's a humidity sensor in the unit itself but this set up triggers everything automatically when required.

[tanneja]

On 23/12/2020 at 16:47, john0wingnut said:

Fair point. Maybe I’m getting too techy on something that doesn’t need to be.

 

I think the kitchen boost and hall controller is a must, so I will do those.

 

I wasn’t going to worry about bathrooms / ensuites as figured the humidistat will take care of that.

 

Does the Brink Excellent have a pre heater as that is my other consideration; from what I’ve read in other threads it’s a good idea to have one.

 

My building will be 250m2 ish when upstairs extension is done, so I will go with a 400 sized unit then. 
 

I was looking at the Ducobox Energy400 which you can get with a day/night supply 2 zone setup. Seems quite a neat idea, but have not read about any others on here with one.

 

Brink Flair 400 may be a sound choice in my case then, if I don’t need the fancy bits.

Speaking with Zehnder customer support, where my required trickle rate for building regs is around 200m3/hr, they said the Q350 would be fine for me, where it's maximum airflow is said to be 350m3/hr, so close to your % capacity of the unit you were looking at.  They explained that the unit has more capacity than stated, so could shift more air if asked when in boost function, probably at detriment to the heat recovered (that last part is my assumption).

 

I was considering upscaling to the Q450, however they confirmed that a harder working Q350 would be quieter based on their data.  I plan to double check all this with them again, but this conversation, along with personal accounts throughout the site of users electing for a lower ventilation rate relative to building regs, it feels like I would be fine with the smaller unit.  I also asked about using F7 filters with the unit, thinking that would demand a high capacity from the unit, but they still felt that would be ok, all this in consideration of the MVHR unit being in a hallway cupboard, rather than tucked away in a loft where noise is less of an issue.

 

Interestingly when speaking with PAUL heat recovery about buying a Q350, they offered to look at my calcs and confirmed my 200m3/hr based on part F regs.  However they said they usually recommend passive house level ventilation levels which would bring my trickle up to around 250m3/hr.  Given I am a refurb project unlikely to have a stellar ACH despite my best efforts, spec'ing for that level of ventilation would mean a bigger unit, more runs, and just a more complex task overall asking more of the living spaces to be claimed by MVHR infrastructure.  My instinct is to keep things as part F regs level and hope that will be comfortable in the house, further hopeful of being happy to reduce the flows to result in the unit and vents being as quiet as possible.

 

Any thoughts are welcomed of course.

Edited January 27, 2021 by tanneja