Building Reg Ventilation Rates (a paste)

[Fallingditch]

 

 

#1NeilW

Posted 02 June 2014 - 06:57 AM

Looking at the Building Regs rules for ventilation it looks like the minimum air flow rate is governed by the floor area of a building.

So that seems to suggest that if I go to a warm roof design, even if that area is essentially storage, then I increase my ventilation requirements substantially over the equivalent 'cold roof' design. 

And there doesn't even seem to be any reduction for ceiling height. 

I want the MVHR to operate in the loft space, since it is likely to become a bit of a heat well and it'd be useful to be able to purge that, or recycle it as required, however 20.2l/s seems like a lot. 

So I have the ludicrous situation now where the volume of air at Passivhaus ventilation rates (0.3ach * volume) gives me a ventilation requirement of about 35 l/s, and the Building Regs ventilation rate (0.3l/s * floor area) giving me a requirement of 62 l/s

Is there a way around this? Can you offset your air-tightness test result for example. 

#2DamonHD

Posted 02 June 2014 - 07:14 AM

As has been suggested here before don't you simply have to make sure that the Regs rate is achievable but then (say) with automatic CO2/RH%-driven modulation of flow rate actually have an average much more like PH requirements?

Rgds

Damon 

#3NeilW

Posted 02 June 2014 - 07:57 AM

That's what I had in mind before the loft came into it. Now it appears I need a 77% uplift in ventilation just to pass building regs which seems like overkill 

#4jsharris

Posted 02 June 2014 - 05:42 PM

You need to read and interpret the regs carefully, and remember that they only apply for the ventilation system test; there is no requirement to use these rates once the house has been tested.

Take our house, for example, which has a warm roof and vaulted ceilings, so has a much greater volume than a typical cold roof house, and has a floor area of 130m². We have to meet two building regs requirements. The first is the minimum whole house low rate from the 0.3 l/S/m² floor area requirement at the base of table 5.1b, which gives 39 l/S, or 140.4 m³/h. As the house volume is 342 m³, this equates to a ventilation rate in ACH of about 0.41, below our design ventilation rate of 0.43 ACH. This rate has to be achieved with the MVHR on its normal occupied house minimum speed setting (more on this later).

The second building regs requirement relates to the maximum ventilation rate in some rooms. In our case we have a kitchen, two bathrooms, a utility room and a downstairs WC. The flow rate from these room with the MVHR on maximum needs to be:

KItchen = 13 l/S
Bathroom 1 = 8 l/S
Bathroom 2 = 8 l/S
Utility room = 8 l/S
WC = 6 l/S

Giving a total with the MVHR on max boost of 43 l/S, or 154.8 m³/h. This is still only an ACH of 154.8 / 342 = 0.45 ACH, so even on max boost we're still not overly high.

It's worth noting that for many MVHR units with multiple speeds, the lowest speed isn't the official continuous rate for an occupied house. For example, ours has four speeds, with speed 2 being the occupied house continuous rate and speed 1 being reserved for airing the house when its unoccupied. Speeds 3 and 4 are the boost speeds and the building regs max rates are tested at speed 4.

I'm finding that running at speed 1 is fine and easily exceeds the building regs requirement for the floor area, and ventilates adequately even though the volume of our house is large relative to the floor area (a conventional house of 130m² would have a volume of around 312 m³, whereas ours is around 10% more because of the warm roof and vaulted ceilings.

Another point is that some MVHR units (like ours) have fully programmable speeds. I can set the fan speed for speeds 1 to 4 to anything between 0 and 100%, independently for extract and supply, so I can tweak the speeds to those we feel comfortable with. What you do with the system after the building regs ventilation test is really just up to you, there's nothing to stop you winding the speeds down. 

Edited by jsharris, 02 June 2014 - 05:45 PM.

#5Calvinmiddle

Posted 02 June 2014 - 09:18 PM

So for our house of 120m2 the minimum whole house low rate ventilation is 120*0.3 = 36l/s

And the maximum ventilation rate will be:
Kitchen 13l/s
Utility 8l/s
Bathroom 8l/s

Which totals 29l/s. But how does that work with the boost being less that the normal mode?? Especially as only these three rooms have extract vents so the min whole house rate of 36l/s will be coming out of these rooms. Do I just need to make sure each rooms extract rate is more than the rates above? 

#6jsharris

Posted 02 June 2014 - 09:46 PM

The two issues are separate in building regs. The specified room extract rate for wet rooms and kitchens can be with the MVHR at max boost. The whole house minimum ventilation rate (from the floor area usually, but check the number of bedrooms rule in table 5.1b) is with the MVHR in normal ventilation mode (which may not be it's lowest setting).

You just need to meet both of these. The extract rate is measured at the extract terminals in each of the applicable rooms, with the MVHR at full boost. The whole house rate is measured at the external ventilation terminals, after the system has been balanced so that extract and supply are more or less equal.

You only need to exceed the minimums in the regs, so if you find that your whole house rate at the normal continuous setting is 50% more than the regs require that's fine (but perhaps a bit wasteful of energy). The same goes for the room extract rates at full boost, these are the minimum fugures, so exceeding them still gets a pass. 

#7NeilW

Posted 03 June 2014 - 08:26 AM

The idea I have in mind is to put an extract and an inlet in the loft at opposite ends of the building and just have the extract in the loft balance the inlet for building regs purposes. The MVHR is going to be in the loft, so adding an extract to it near the device doesn't seem that onerous. 

If the rate is measured externally, then that should do the trick. 

The rest of the house can then be balanced more normally. 

In volume terms the loft adds 33m3/hr at a 0.4ACH value, but the area adds 73m3/hr at the 0.3l/s building regs minimum. 

#8NeilW

Posted 03 June 2014 - 08:27 AM

jsharris, on 02 June 2014 - 05:42 PM, said:

se of table 5.1b, which gives 39 l/S, or 140.4 m³/h. As the house volume is 342 m³, this equates to a ventilation rate in ACH of about 0.41, below our design ventilation rate of 0.43 ACH. 

How did you get to 0.43ACH as the design rate for the ventilation? 

#9jsharris

Posted 03 June 2014 - 04:45 PM

If the loft isn't habitable space then its floor area doesn't need to be included in the overall area used to get the minimum continuous ventilation rate. The same goes for my eaves storage areas, they are inside the heated envelope but aren't habitable spaces, so aren't included in the Part F calcs.

The 0.43 ACH is a figure selected because it seemed a reasonable compromise. 0.45 ACH is about the target figure that organisations like BRE say you should aim for (in effect, as they don't express it in quite the same way) and the max allowable for PH is 0.6 ACH, so, as the volume of our house is large for the number of occupants, I chose a figure that was slightly lower than the generally accepted rate. 

#10stones

Posted 03 June 2014 - 05:25 PM

Jeremy,

Out of interest, did BC demand a ventilation system test by an independent body / company. When we built, we specified in the warrant plans the system we would use and the ventilation capacity it had. No test required. 

#11jsharris

Posted 03 June 2014 - 05:51 PM

I did my own testing and submitted my test report to my BCO. Not heard back as to whether it was unacceptable, so I'm assuming it's OK. I just bought a Testo airflow meter and made up a conical hood to measure flow velocity through a 100mm diameter section of duct. Fairly easy to do, but quite tedious, as every time you adjust the flow in one terminal you upset the flow rates in all the other terminals. All told I spent around half a day running around adjusting the flow rates to get them both compliant and relatively quiet.

There's no requirement in Part F for any independent body to do the compliance testing, just a suggested format for the way that it's presented and the need for the air flow meter to be calibrated to the appropriate standard (mine was bought second hand, but was still in calibration when I did the tests). I didn't follow the suggested report format exactly, but did include some photos of the test method used and the instrumentation. 

#12mishad

Posted 30 September 2015 - 06:52 PM

Blatant thread necro but anyway:

Looking at Part F Appx A it appears to say that the 0.3 l/'s is based not on moisture but VOC discharge rates. Which suggests that it's related to chipboatd, carpets and soft furnishings and the like, rather than occupancy. And thus that it should drive the minimum (trickle) ventilation rate, not just the maximum possible rate. 

Is this (VOC exposure) a real concern? Is anyone aware of any other research in this area - are PV-style designs really exposing the occupants to increased VOC levels? 

#13jsharris

Posted 30 September 2015 - 07:22 PM

VOC emissions depend wholly on what you choose to put inside the airtight barrier (which is often also the VCL), so is usually pretty much nothing to do with the main fabric of the house. My guess is that 90% plus of the VOCs will come from paint, furniture, fixtures and appliances, with the majority of those dissipating pretty quickly over the first few weeks post-build/purchase.

The "new" smell associated with many things is just VOCs outgassing, but few of those will either be harmful, or at levels likely to cause any impact on health. 

There is an awful lot of BS associated with volatile emissions. People obsess about stuff like formaldehyde (which is so volatile that it evaporates away very quickly indeed) so won't have chipboard etc in the house, and yet those same people will happily have a woodstove and generate high concentrations of far more harmful carcinogens which they and their neighbours then breathe in....................... 

#14mishad

Posted 30 September 2015 - 07:40 PM

Yes, it did seem a bit excessive to require 90 l/s for a 300 sqm 4/5 bed house!

Treating that as a "boost" rate is much more reasonable (and "only double" the min high continuous rate of 13+8+8+8+6=43 for kitchen+utility+2bath+wc). 

#15gravelld

Posted 30 September 2015 - 08:37 PM

I've got the same problem mishad, same numbers too. I ran it past BC but they didn't really appear to understand the regs themselves (this is all under new dwellings in the regs but my case is retrofit). They said that's the continuous rate required. Seems excessive. 

#16notnickclegg

Posted 01 October 2015 - 08:11 AM

stones, on 03 June 2014 - 05:25 PM, said:

Out of interest, did BC demand a ventilation system test by an independent body / company. When we built, we specified in the warrant plans the system we would use and the ventilation capacity it had. No test required.

According to our MVHR supplier, the calculations they've provided will be sufficient to satisfy building control. We'll see...

Jack 

#17jsharris

Posted 01 October 2015 - 08:34 AM

My BCO accepted a report, with measurements, that I did. Not hard, really, as I had to measure all the flow rates at the terminals anyway to set up and balance the system, so it was just a matter of writing them down, taking a few photos and writing up a test report. There's no requirement in the regs for this report to be written by a competent person (as in someone who has some form of accreditation), so it's a pretty easy DIY job if you have access to a flow meter. 

#18notnickclegg

Posted 01 October 2015 - 09:08 AM

jsharris, on 01 October 2015 - 08:34 AM, said:

There's no requirement in the regs for this report to be written by a competent person (as in someone who has some form of accreditation), so it's a pretty easy DIY job if you have access to a flow meter.

Our electrician has a flow meter and a bit of experience with such measurements, so that's our fallback plan.

Jack 

#19jsharris

Posted 01 October 2015 - 09:17 AM

notnickclegg, on 01 October 2015 - 09:08 AM, said:

Our electrician has a flow meter and a bit of experience with such measurements, so that's our fallback plan.

Jack

The MVHR will need to be measured during balancing and commissioning anyway, so just use those figures. You can't install one properly without measuring the flow rates at the terminals and adjusting the flow to get both the intake and exhaust rates the same overall (essential for performance) and you need to measure the flow rates from the key extract rooms to ensure you meet the BR rates and also to get the balance right from room to room. 

#20notnickclegg

Posted 01 October 2015 - 09:24 AM

Our MVHR unit is self-balancing (you can actually define a slight positive or negative pressure if desired) so that's one less thing to worry about.

Allegedly our design takes into account run lengths, hard bends (basically preformed rigid bends that the flexible ducts fit into) and terminal types, so I currently plan to just do some basic tests to make sure everything seems to be within the expected range. I anticipate making adjustments based on our experience with the house after we've moved in.

Jack 

#21jsharris

Posted 01 October 2015 - 09:35 AM

There's no such thing as a system that doesn't need setting up. The fans may well self-balance for overall intake/exhaust, but there is no way of knowing what the flow rates actually are at the terminals unless you measure them. They will be way off the calcs, that I can say for sure, as I calculated ours carefully, taking account of all the duct runs and bends and some of the terminals were 50% or more out. 

#22notnickclegg

Posted 01 October 2015 - 09:41 AM

I hadn't really planned to do any measurements other than the bare minimum to make sure that the relative rates at the terminals were in the expected ballpark. Might have to spend a bit more time on it.

Jack 

#23djh99

Posted 01 October 2015 - 10:15 AM

I think I've got the same system as you, Jack. I just plugged it in and it worked. Job done. 

#24notnickclegg

Posted 01 October 2015 - 10:24 AM

It's a Brink Excellent 400 Plus. 

Jack 

#25jsharris

Posted 01 October 2015 - 10:35 AM

Sorry, but having spent a lot of time measuring the TRUE flow rates I think you will find that the system isn't anywhere near optimised. All the Brink does is balance the external intake flow rate with the external exhaust flow rate. It cannot, and does not, establish the flow rates to each room, and there is absolutely no way of knowing if a particular terminal, by a quirk of layout, is "hogging" all the flow. Add in that as soon as you make a minute adjustment to the flow in one terminal you change the flow in every other terminal (because of the slight pressure change this causes) and then add in the fact that if the Brink is set to self-balance when trying to do these adjustments it will change the overall flow rates in response to changes in resistance, and you have a recipe for a badly balanced and inefficient system.

There is a set order to make adjustments, and this is to get the individual terminal flow rates right, with the same fan speed on the intake and exhaust (so any auto balancing turned off) and then measure the overall intake and exhaust and see how far out of balance it is. If it's out by more than about 5% or so, then re-adjust the terminals equally to get the whole house rates close to being in balance. Only then do you fine tune the balance by allowing the auto balance to adjust the fans speeds, or manually adjust the fan speeds to do the same thing.

Setting up the system   makes a big difference to efficiency and reduces overall energy use, and is essential, in my view. 

#26djh99

Posted 01 October 2015 - 11:53 AM

We'll just have to agree to differ then, Jeremy, we're quite happy with ours. Mine's a 300, Jack, and FWIW I should have got a Plus too. 

#27jsharris

Posted 01 October 2015 - 01:02 PM

Sure, no problem with differences, but this isn't a difference of opinion, it's choosing to ignore the way MVHR systems should be commissioned, according to building regs.

  domestic_ventilation_compliance_guide_2010.pdf   1.75MB   6 downloads

If you don't at least check the terminal flow rates at two different fan speed settings (because some flow effects are velocity dependent) then you have no way of knowing if you've got your system running efficiently. You could easily be way off the spec SFP, for example, just because the auto adjust is running the fans at a high differential rate in order to try and balance the whole house intake and exhaust.

My system runs with one fan on 25% and one on 28% for balance at the normal background rate, for example, just to fine tune the whole house balance so that the flow rates are the same at the intake and exhaust. The Brink does this automatically, but how big is the differential? If you've not set the terminal flow rates to balance the rooms and then balance the whole house, the auto balance system may well be trying to make up for the gross errors by running at higher than efficient differential fan speeds.

My experience is that calculating duct and terminal flow rates gets you to within around 50% of the true flow rates after installation. That's a big error margin, but is mainly a consequence of some of the quirks of incompressible flow in ducting, particularly where you may have a any bends leading up to the manifold that creates a velocity profile across the duct that then favours some of the radial connections over others (this is a significant reason for semi-rigid duct measured rates to differ from calculated rates).

In my case, for example, it so happens that the two very short bathroom extracts were originally running at around 30 to 50% below the calculated flow rate, and the kitchen extract (which is the longest run by far and has a double duct connection) was running at nearly double the calculated rate. It turned out that the manifold doesn't distribute air evenly, and tends to pull more from the point where the kitchen ducts are connected. Just simply adding restrictors to the kitchen extract got that to around the right rate and this then caused the pressure in the manifold to drop which in turn increased the extract rates from the bathrooms.

It's not arduous to check and adjust the flow rates, it's required by building regs (there is a written procedure for demonstrating compliance if you have a whole house mechanical ventilation system) and you have the assurance that the MVHR is running as close to the spec SFP and efficiency as you can get. I chose to set our system up so it is running most efficiently at the low speed background ventilation rate, and have accepted that it is nowhere near as efficient when running at boost rate. This is because at boost rate the flow velocity in some parts of the system starts to upset the individual room balance, the most notable effect being one fresh air room terminal that increases flow rate by around 80% for a 50% change in fan speed. The cause is a shift in the velocity profile across the manifold, something I am sure all radial systems have to some degree. 

Edited by jsharris, 01 October 2015 - 04:33 PM.

#28Calvinmiddle

Posted 20 October 2015 - 01:20 PM

Just trying to work out my Ventilation rates

Got that we need 0.3L/S per m2 of floor for the reg, and also that we need a min of 13l/S for kitchen, 8l/S for bathroom and 6l/S for utility on the boost

Put this spreadsheet together and I'm concerned that the ACH of 0.39 is on the low side, over half the house has vaulted ceilings up to 3.6m in height so our volumn is pretty high. I'm wondering do I need to increase the ventilation rate a bit to get the ACH up.

  Ventilation Rates.pdf   8.64K   3 downloads
edited to add attachment and typo 

Edited by Calvinmiddle, 20 October 2015 - 03:12 PM.

#29jsharris

Posted 20 October 2015 - 03:01 PM

I'm pretty sure that 0.39 ACH is OK, we run at about 0.43 ACH and that seems fine. You can always tweak the rate up a bit by altering the fan speeds slightly if you find it's too low after installation. Practically, it's the occupants that need ventilation anyway, so a lower ACH on a larger than normal house with the same number of occupants should be fine. I doubt that any house without a ventilation system, one that relies on trickle vents for example, would get anywhere near this sort of ventilation rate.

My experience with measuring CO₂ , humidity and temperature in a bedroom with an open window showed that there was a very low ventilation rate, less than about 0.1 ACH at a guess, as the CO₂ build up was pretty much that in a sealed room. I think that the building regs are a bit unfair on MVHR, really, as the ventilation requirements are, I believe, very much more demanding than those from a house with no MVHR and just trickle vents 

Edited by jsharris, 20 October 2015 - 03:02 PM.

#30Calvinmiddle

Posted 20 October 2015 - 04:00 PM

jsharris, on 11 March 2015 - 08:15 AM, said:

Don't run 75mm ducting at 2.5m/S if you can help it. It's best run at around 1.5 to 2 m/S in my experience. Double up ducting to high volume flow areas (the terminals allow two pipes to be fitted in parallel).

Note on another thread you mention running ducting at 1.5 - 2 m/S. Trying to work out what this is in terms of m3/h to see if I can increase the ventilation rates a bit more.

75mm ducting has an internal radius 63mm which gives an area of 0.0031m2

So running at 2m/S gives 0.0031*2*3600 = 22.32m3/h

Or at 1.5m/S = 0.0031*1.5*3600 = 16.74m3/h

Am I working this out right?

Also for the boost setting it is clear that the min rates are in excess of the building regs max rates, so what have people done for the boost setting on their MVHR, we have an internal humidistat, and 2 time delay switches, one in kitchen and one near bathrrom with the idea that the boost would be hit if cooking or having a shower or if the humdity reached to high a point.

Do you set the boost flow rates at? Is it a fixed % of the normal - say 150% or something else? 

Edited by Calvinmiddle, 20 October 2015 - 04:01 PM.

#31jsharris

Posted 20 October 2015 - 04:13 PM

The calcs look OK to me. 

Our boost is controlled by a programmable humidistat (cost around £40, with a remote probe) and it senses the RH in the extract plenum. It has a programmable threshold, hysteresis and timer on period after the RH reduces below the off point.

Boost on our system is 75% of maximum fan speed, background continuous ventilation is around 25% fan speed. 100% fan speed on ours can be manually switched if needed, or I could programme the MVHR so that the humidistat boosted to 100% if we find we need to. Also, our MVHR has a programmer, rather like a central heating system, so can be programmed to run at different rates or target temperature (it has a built-in ASHP) if needed, plus a quick press "party button" that gives a set time boost if you have a lot of visitors. 

#32Calvinmiddle

Posted 20 October 2015 - 05:16 PM

So does that mean you go from 140m3/h on background ventilation to 420m3/h on the boost?

Or 0.41 ACH to 1.23 ACH

Or does the fan speed not have a linear relationship to the extract/supply rates?

Just worried about the speed of the air through the ducts on the boost, the restriction rings don't work with the Airflex distribution ducts, so using acoustical room values

http://www.bpc-direc...eq=133|9041168| 

Edited by Calvinmiddle, 20 October 2015 - 05:22 PM.

#33jsharris

Posted 20 October 2015 - 05:45 PM

Pretty much. The duct velocities are over the 2.5m/s normal limit for duct noise reasons when it's on boost, but not enough to be objectionable, especially as it doesn't spend long on boost anyway and it's still a lot quieter than either a bathroom or kitchen extractor. I don't have the figures immediately to hand, but seem to remember we had velocities of around 5m/s in some ducts on boost. 

Edited by jsharris, 20 October 2015 - 05:48 PM.

#34Calvinmiddle

Posted 23 October 2015 - 10:32 AM

Jeremy

Do you think these duct speeds look ok? Think I'm happy with the background rate, jsut thinking about the boost rates.


  MVHR Flow rates v2.pdf   9.87K   6 downloads 

#35jsharris

Posted 23 October 2015 - 12:27 PM

I think you'll find those flow velocities are OK in practice. My experience is that, although all the design guides say that you should keep flow velocity below 2.5m/S too keep noise levels down, you can exceed these velocities in a radial ducted system without creating any noticeable noise problems. It may be because isolation is better, or perhaps it's because there are no joints or sharp bends with radial ducting, but it does seem fine at higher speeds. 

When our system is on full boost I'm sure most of the noise (not that there's much) comes from the transmitted noise of the fans through the ducting, rather than flow noise in the ducts themselves. This is born out by the massive noise reduction we had when I fitted big silencers to the feeds to and from the manifolds. 

 

[Jeremy Harris]

The building regs relate to the habitable floor area, or are meant to. 

This means you should be able to argue that your loft space is not habitable floor area, does not need habitable space levels of ventilation, and therefore should not be included in the floor area calculation for Part F.  I excluded the area of the unventilated eaves storage areas from our house when doing the Part F compliance report and it was passed without question.

[PeterW]

From what I remember the BRegs also ignore any space in a sloping room under 1m high as it is not classed as habitable. 

 

I will find the spreadsheet I did and put it on here later 

[le-cerveau]

If you are prepared to take a stand you can challenge the BCO as the Building regulations are not enforceable only recommended, see my post:

The only enforceable bit is:

Means of ventilation
F1(1). There shall be adequate means of ventilation provided
for people in the building.
(2). Fixed systems for mechanical ventilation and any
associated controls must be commissioned by testing and
adjusting as necessary to secure that the objective referred to
in sub-paragraph (1) is met.

The rest is should so if you can provide adequate means of ventilation and prove it then do it yourself, however the Building Regs are a good guideline.