MVHR DiY install?

[MikeSharp01]

6 hours ago, JSHarris said:

 

I do wish that I'd run pipes from the downstairs UFH up to the bedrooms, along with condensate drains, as I could then have fitted a couple of fan coil units

Good idea - I will be running the ASHP connection pipework through and along inside the wall, suitably separated, insulation and bring them through the air tight membrian in the plant room I guess I could do the same with the feeds, and drains, upstairs. 

[Jeremy Harris]

42 minutes ago, PeterStarck said:

That wasn't the case for me. I had all the results ready to show him for building regs. compliance and he wasn't interested. So after setting it all up for SAP, which he wasn't interested in, I set it up again for PH rates which it's been running at for eighteen months without problems.

 

Same here, I wrote up a commissioning report, printed it off and had it lined up on the kitchen work top, ready to be checked and taken away by the inspector during our completion inspection and he wasn't at all interested in it.

[Bitpipe]

42 minutes ago, JSHarris said:

 

Same here, I wrote up a commissioning report, printed it off and had it lined up on the kitchen work top, ready to be checked and taken away by the inspector during our completion inspection and he wasn't at all interested in it.

 

Mine asked for it along with a bunch of other stuff (water usage calcs etc) so no idea if he ever really looked at it.

 

But your @PeterStarck 's experience makes the case for DIY commissioning even stronger

 

Did either of you notice any difference when balanced or, like me, was it more of a peace of mind exercise?

[Jeremy Harris]

10 minutes ago, Bitpipe said:

Did either of you notice any difference when balanced or, like me, was it more of a peace of mind exercise?

 

I didn't really get a chance to sense how well, or otherwise, ours ran before I balanced it, as I started to balance it pretty much as soon as I first turned it on.  It was out a fair bit (about 20%) in terms of the flow from all the fresh air feeds not equalling the flow from all the extracts, as most of our extract ducts are a fair bit shorter than the supply ducts.  I also had a fairly big imbalance from the kitchen extract, as I fitted two runs of ducting to it, anticipating that this would be needed to meet the 13l/s extract requirement, and this proved to be a bit much, so I had to throttle kitchen down a fair bit.

[Bitpipe]

I know a few of us had to crank up the main fan to hit the whole house ventilation requirement (40% for me) but then dialled it back down to 30% or so to reduce fan noise.

[ProDave]

I am still running mine "unballanced" and have been for a year.

 

The reason (very weak reason) is the utility and en-suite are not finished, utility not even plastered, so I have not put the proper ceiling cowls on those yet, and without those there is no control over flow rates from those rooms.

 

I set it up "intuitively" i.e ceiling vents at the opposite end of the house are pretty much wide open, and vents closer to the distribution plenum, are closed down a bit.

 

All I know is the system runs silently (at normal speed) and the air quality in the house is always good, nowhere seems stuffy and smells, e.g cooking, don't linger.  So it can't be far out.

 

It will be interesting when I do set it up properly and measure the flow rates how it measures up.  If I find I have to increase the fan speed to meet BR ventilation rates, then I will probably slow it down again afterwards if it is not totally inaudible as it is now.

[Jeremy Harris]

I think the primary advantages of balancing are getting the best heat exchanger performance (this will drop off a fair bit if the extract and fresh air flows don't match well) and getting the lowest energy consumption for an acceptable ventilation level.  Our MVHR seems to use about 60 W when running at the normal background ventilation rate, which seems to be pretty much in line with the specification.

 

As the fans and control board all run from 24 VDC it's a pity there isn't an easy way to just power it from DC, as it wouldn't be hard to make a small PV system that could keep a battery charged up and so run the MVHR for free.  I reckon a single standard solar panel would be enough to do this, coupled to a battery rated at maybe a couple of kWh capacity.

[Barney12]

am I being a complete dullard in terms of finding where the calc is for the minimum flow rates for the regs?

I've quickly read the part f document but its not jumping out at me! 

OK and I admit it I'm trying to avoid properly reading the document! Sorry  

 

[Jeremy Harris]

17 minutes ago, Barney12 said:

am I being a complete dullard in terms of finding where the calc is for the minimum flow rates for the regs?

I've quickly read the part f document but its not jumping out at me! 

OK and I admit it I'm trying to avoid properly reading the document! Sorry  

 

 

 

No, not your fault, as the regs are just a wee bit obscure.

 

There are two different requirements, the most significant one (in terms of sizing the unit) is the background whole house ventilation rate.  This is no less than 0.3l/s per m² of floor area, and refers to either the fresh air supply flow rate, or the extract flow rate, for the whole house (extract should be equal to supply).  So, using our 130m² house as an example, the whole house ventilation rate should be no lower than 0.3 x 130 = 39l/s

 

The other criteria that have to be met are the minimum extract flow rates from the kitchen (13l/s), bathrooms (8l/s), utility room (8l/s) and WC (6l/s).  In our case we have a kitchen, two bathrooms, a utility room and a downstairs WC, so the sum of the extract rates from these rooms needs to be 13 + 8 + 8 + 8 + 6 = 43l/s.

 

However, it's allowable to have the MVHR on boost to meet the extract flow rates, (whole house rate has to be at the background fan speed), so if you can't quite meet the minimum extract rates at the normal background fan speed it is acceptable to boost the unit to show compliance.  In practice I found that we got around nearly 46l/s when running at the background fan speed, after I'd balanced the system, and this exceeded the figures required for the rooms with an extract.

 

Balancing has two aims, to match the fresh air flow rate for the whole house to the extract rate for the whole house (ideally within about 5% or better), and to set the extract flow rates in order to obtain the building reg minimums for each extract room.  I found the latter the hardest part, as I needed to throttle our kitchen extract down a lot, as well as the downstairs WC and utility room, in order to get enough extraction from the bathrooms.

[Gone West]

1 hour ago, Bitpipe said:

Did either of you notice any difference when balanced or, like me, was it more of a peace of mind exercise?

The instructions for our MVHR came with a crude setup to get started, which we ran for a couple of months before we moved into the house. We then set up the system for the BCOs final visit which we ran for about a month and then changed it to PH rates. It worked with each of the setups but it is quieter with the current setup but without measuring the CO2, power consumption etc I don't know how much difference it really makes.

[Barney12]

19 minutes ago, JSHarris said:

 

 

No, not your fault, as the regs are just a wee bit obscure.

 

There are two different requirements, the most significant one (in terms of sizing the unit) is the background whole house ventilation rate.  This is no less than 0.3l/s per m² of floor area, and refers to either the fresh air supply flow rate, or the extract flow rate, for the whole house (extract should be equal to supply).  So, using our house as an example, the whole house ventilation rate should be no lower than 0.3 x 130 = 39l/s

 

The other criteria that have to be met are the minimum extract flow rates from the kitchen (13l/s), bathrooms (8l/s), utility room (8l/s) and WC (6l/s).  In our case we have a kitchen, two bathrooms, a utility room and a downstairs WC, so the sum of the extract rates from these rooms needs to be 13 + 8 + 8 + 8 + 6 = 43l/s.

 

However, it's allowable to have the MVHR on boost to meet the extract flow rates, (whole house rate has to be at the background fan speed), so if you can't quite meet the minimum extract rates at the normal background fan speed it is acceptable to boost the unit to show compliance.  In practice I found that we got around nearly 46l/s when running at the background fan speed, after I'd balanced the system, and this exceeded the figures required for the rooms with an extract.

 

Balancing has two aims, to match the fresh air flow rate for the whole house to the extract rate for the whole house (ideally within about 5% or better), and to set the extract flow rates in order to obtain the building reg minimums for each extract room.  I found the latter the hardest part, as I needed to throttle our kitchen extract down a lot, as well as the downstairs WC and utility room, in order to get enough extraction from the bathrooms.

 

Thanks, understood.

 

I've just found the table by supplier (BPC) supplied with my system design. Their assumptions don't seem to meet the regs as what they describe as "WC1" and "WC2" are actually bathrooms. The table also seems to provide the same results for continuous flow and boost?  

 

 

[Gone West]

2 hours ago, Bitpipe said:

Mine asked for it along with a bunch of other stuff (water usage calcs etc) so no idea if he ever really looked at it.

Our BCO wasn't interested in the water usage either. I just told him all the taps and showers were aerating and water usage would be low. I guess we were lucky as I never did any calculations nor worried about bath sizes etc.

[Jeremy Harris]

22 minutes ago, Barney12 said:

 

Thanks, understood.

 

I've just found the table by supplier (BPC) supplied with my system design. Their assumptions don't seem to meet the regs as what they describe as "WC1" and "WC2" are actually bathrooms. The table also seems to provide the same results for continuous flow and boost?  

 

 

 

 

Looks like they misunderstood that WC1 and WC2 are really bathrooms, so those need to be a minimum of 8l/s.  I'm guessing they've just not bothered to work out boost flow rates, perhaps because they have tried to show that the minimum required extract rates can be met at the normal background ventilation level.

 

The design figures are generally a bit "finger in the air", IMHO, as there are so many installation-related variables that I doubt any initial design calcs can be accurate at the room level.  I found there was a bit of interaction between room terminals, in that when I throttled back our kitchen extract rate, just to get it within the sort of range needed, the extract rates on all the other terminals increased.  I found this almost the most tedious bit of balancing the system, alongside dealing with the fairly big variations created by gusts of wind.

[dnb]

13 hours ago, gc100 said:

I did read with interest your thread here and was looking at your design - is this the final one?

 

Not quite the final design. It's evolved a bit since then to simplify controlling the systems and I've done the maths to size everything now I have heat loss calculations I can trust.

 

The A/C will draw air (recirculating) from the entrance hallway on the ground floor, and also from the MVHR fresh output. This will be cooled/heated as required and distributed to the living rooms. Air will be drawn from the wet rooms by MVHR and passed through the heat exchanger (or not when in bypass mode - it only used under certain limited conditions) and out of the building. This shouldn't (in theory) provide unfair loads to either system and I should have sufficient points to monitor temperature and flow rate to maintain control without too many air dampers.

[gc100]

On 24/08/2019 at 00:17, dnb said:

 

Not quite the final design. It's evolved a bit since then to simplify controlling the systems and I've done the maths to size everything now I have heat loss calculations I can trust.

 

The A/C will draw air (recirculating) from the entrance hallway on the ground floor, and also from the MVHR fresh output. This will be cooled/heated as required and distributed to the living rooms. Air will be drawn from the wet rooms by MVHR and passed through the heat exchanger (or not when in bypass mode - it only used under certain limited conditions) and out of the building. This shouldn't (in theory) provide unfair loads to either system and I should have sufficient points to monitor temperature and flow rate to maintain control without too many air dampers.

 

How are you controlling the A/C temp? One supplier I spoke so said I'd really need separate controls in each room otherwise one or 2 rooms could get too cold, I said I wasn't too worried as the A/C was a course grained effort to bring the whole house temp down.

 

[ProDave]

When I install mine, I will have a fan coil unit in each bedroom and each bedroom will have it's own cooling thermostat, so if a room did start to get too cold, it would just switch off that room.

[Jeremy Harris]

4 hours ago, gc100 said:

 

How are you controlling the A/C temp? One supplier I spoke so said I'd really need separate controls in each room otherwise one or 2 rooms could get too cold, I said I wasn't too worried as the A/C was a course grained effort to bring the whole house temp down.

 

 

 

I can throw a practical data point into this mix.  A few weeks ago I installed a (recirculating) air con unit in our bedroom.  It tries to maintain 20°C at its air intake, using its thermostatic control.  We leave the bedroom door open all day (it opens to a landing above a 6m high, 5m long, 2m wide entrance hall in the centre of the house).  The MVHR temperature sensing and control is on the landing, the floor heating/cooling thermostats are on the ground floor in the hall.

 

In practice the air con holds the bedroom at close to 20°C all the time, the landing is very slightly warmer most of the time (perhaps 21°C) and the same with the ground floor.  Both the floor cooling and the MVHR cooling tend to come on a bit later as a consequence of the effect of the air con cooling, but this seems to work very well indeed, as we end up with the ground floor rooms around 1°C to 2°C warmer than the bedroom, which we find about right.

[vivienz]

FWIW, someone came out to supposedly commission my MVHR at the beginning of the month.  He made a complete balls up of it, didn't notice that the inlet and outlet on the MVHR unit itself (or some other mucho importanto pipework) was the wrong way around and there was no fresh air being circulated at all.  I'm currently considering doing this myself given the lack of support for it as my faith in the 'professionals' is lacking at the moment on many fronts.

[Declan52]

It's not a hard job to do. Much easier to wrestle with all the pipe work of you can get an extra set of hands. Plenty here have done it and saved a few grand which is always needed come the end. 

[joe90]

I DIYed mine (including making my own manifold and silencer), when the BCO visited to sign the building off he simply said “no window vents because you have MVHR”. I copied @JSHarris balancing sheet in case he wanted it but he didn’t ask fir anything. Funnily it’s been switched off all summer as my wife opens all the windows ?.

[Barney12]

1 hour ago, joe90 said:

I DIYed mine (including making my own manifold and silencer), when the BCO visited to sign the building off he simply said “no window vents because you have MVHR”. I copied @JSHarris balancing sheet in case he wanted it but he didn’t ask fir anything. Funnily it’s been switched off all summer as my wife opens all the windows ?.

 

Don't feel bad. Mine is always switched on WITH the windows open  

[dnb]

18 hours ago, gc100 said:

How are you controlling the A/C temp?

 

I have a cunning plan... The A/C will monitor the temperature of the recirculating air at the point where the ducting blends the air directly from the house and the outside air drawn in from the MVHR. This should be a reasonable average house temperature so set a bulk heating/cooling requirement that accounts for the effective losses (or gains in some cases) induced by the MVHR.

 

In a perfect world where everything is balanced all the time, this will be enough. Unfortunately we're not there so I will be allowing for fitting dampers controlled by the building management system to provide balancing based on air temperature and probably quality within rooms. The algorithms to do this don't look too bad on the back of the envelope on my desk right now. There will also be a damper to isolate the A/C recirc so that the MHVR can run stand alone - reversionary modes are important. The idea is of course to keep things as simple as possible. Otherwise you can start worrying about such things as having to detect open windows and closed doors in order to isolate rooms from the system.

[gc100]

12 hours ago, dnb said:

 

I have a cunning plan... The A/C will monitor the temperature of the recirculating air at the point where the ducting blends the air directly from the house and the outside air drawn in from the MVHR. This should be a reasonable average house temperature so set a bulk heating/cooling requirement that accounts for the effective losses (or gains in some cases) induced by the MVHR.

 

In a perfect world where everything is balanced all the time, this will be enough. Unfortunately we're not there so I will be allowing for fitting dampers controlled by the building management system to provide balancing based on air temperature and probably quality within rooms. The algorithms to do this don't look too bad on the back of the envelope on my desk right now. There will also be a damper to isolate the A/C recirc so that the MHVR can run stand alone - reversionary modes are important. The idea is of course to keep things as simple as possible. Otherwise you can start worrying about such things as having to detect open windows and closed doors in order to isolate rooms from the system.

 

So are you doing this all yourself (design) or do you have an A/C company helping? I cannot find anyone local yet who can help me on this. What system/software/box are you using to control air dampers (could you provide me a link to such an item as well please?)  ?

 

Any information I would really appreciate it. Thanks

 

[Bitpipe]

On 28/08/2019 at 15:12, Barney12 said:

 

Don't feel bad. Mine is always switched on WITH the windows open  

 

Mine too - like to have the bathrooms extracted (no opening windows there) and the basement ventilated.

[dnb]

On 29/08/2019 at 16:06, gc100 said:

So are you doing this all yourself (design) or do you have an A/C company helping?

 

I am working with a local A/C business, but their input only goes as far as supply, technical advice and supply of an FGAS installer. I am taking responsibility for the system working as intended.

I haven't settled on a damper control solution yet. None of them do everything I want, so it may well be a case of something that does just enough for buidling control, then work on a home brew solution later.