Mechanical Ventilation System Vent distances

mugwumpjism

Hi All,

I am installing a small MVHR system for a bedroom (vent axia 100R...small one room system). I have two vent slates installed. I am just wondering on the recommended distances from each other and pollution sources. The vent slates are aprox 1.2 m apart and are on the roof above the exhaust from the combi boiler (which is on the wall under the gable) which is aprox 2.5 m away diagonally. I haven't hooked it up yet but do these distances seem ok for clearance? The manual say 1m apart....but I have seen ranges from 30cm to 2.5m, what are the chances of the exhaust getting sucked into the intake or from the boiler flue? Thanks

BryanF

I thought the 100 was discontinued

I fail to see the issue with extract vent v slate vents (assuming slate vents are just venting roof void/cavity)

mugwumpjism

Hi Byran,

Sorry I prob wasn't clear...I have 2 roof vents on the slope just installed with a 100mm adapter on the back which will take an intake on one and an extract on the other. They are a meter apart (which is what it said in the manual). I have done further reading and the recommended distance between vents ranges from 60cm to 2.5m. I am just wondering the chances of the exhaust air from one being sucked into the intake on the other? The unit is max 29W and max 18l/s so it is not that powerful. Thanks

Outkast_IRE

I can tell you on commercial projects 10m is good practice.

Domestically as you won't be expelling anything too smelly or with very high co2 levels just get them as far apart as feasible and ensure the fan is capable

mugwumpjism

Here is what the manual says

13. The external grilles for intake and exhaust
air should be positioned so that the exhaust air
is not drawn in again.
14. If the grilles are fitted in the same gable at
the same height, a minimum of 1m between
grilles is recommended.
15. If the grilles are positioned above one
another the distance apart should be at least
1m with the exhaust grille at the top.
16. Roof ventilators placed on the same roof
surface should be positioned at the same
distances as the grilles.

BryanF

A greater distance would be better. I’m sure if you read the en bs standards associated with part F compliance a distance will be recommended

mugwumpjism

So just for anyone interested, I installed the Vent Axia 100R into a double bedroom that has one passive wall vent but very poor circulation (we need to keep the door closed). I have an monitor which I ran for a few nights pre installation and recorded a high of 4040ppm CO2....average prob >3500ppm. There are 2 settings on the MHRV boost (18l/s) and trickle (13l/s). Over a few nights on boost the average comes down to 1050ppm and on trickle 1250ppm. The air is noticeably fresher in the morning and we are not as drowsy or 'polluted' feeling as we were (of course there is prob some element of placebo here too). I am going to do more investigation to see if there is any cross contamination between the in and out grilles ( 1.5m apart on the ceiling) and the vent slates (1.2m apart on the roof) and whether the vent slate is big enough (10,000mm2 vent area)

Any observations or advice welcome

Dardania

mugwumpjism wrote: »

So just for anyone interested, I installed the Vent Axia 100R into a double bedroom that has one passive wall vent but very poor circulation (we need to keep the door closed). I have an monitor which I ran for a few nights pre installation and recorded a high of 4040ppm CO2....average prob >3500ppm. There are 2 settings on the MHRV boost (18l/s) and trickle (13l/s). Over a few nights on boost the average comes down to 1050ppm and on trickle 1250ppm. The air is noticeably fresher in the morning and we are not as drowsy or 'polluted' feeling as we were (of course there is prob some element of placebo here too). I am going to do more investigation to see if there is any cross contamination between the in and out grilles ( 1.5m apart on the ceiling) and the vent slates (1.2m apart on the roof) and whether the vent slate is big enough (10,000mm2 vent area)

Any observations or advice welcome

Great & gratifying result - interesting to compare against this: https://www.kane.co.uk/knowledge-centre/what-are-safe-levels-of-co-and-co2-in-rooms

mugwumpjism

The background levels with a window wide open are about 500ppm and with everything closed and the MHRV running with no one in the room is about 650ppm. I'd love to get it down below 1000ppm to have 'excellent' air quality but 1000-1250ppm is acceptable indoor air quality and a vast improvement...but being a bloke I'll be looking for any tweeks I can do

Calahonda52

mugwumpjism wrote: »

The background levels with a window wide open are about 500ppm and with everything closed and the MHRV running with no one in the room is about 650ppm. I'd love to get it down below 1000ppm to have 'excellent' air quality but 1000-1250ppm is acceptable indoor air quality and a vast improvement...but being a bloke I'll be looking for any tweeks I can do

May not be practical but best idea would be to introduce the fresh air as low down as possible in the room, as far away as possible from the extract;
perhaps a rectangular duct in the corner..
How big is the room so what ACH number are you seeing?

mugwumpjism

Cheers for that. Both grilles are on the ceiling 1.5m apart ( the manual said 1m minimum to stop draw in). I will look at putting the fresh air lower down but it is prob not possible as all the walls are solid and it is coming from the attic. I wonder are the vents on the roof a problem at all (cross contamination), the are 1.2m apart and the extract is downwind from the inlet. I think because it's 2 people in a room for 8 hours maybe 1250ppm or 1050ppm is the best I will get, short of getting an industrial machine!

Any other tips very welcome!

Calahonda52

a retangular duct in the corner could be boxed in and painted up to blend in

Could you put one of the vents on another part of the roof

mugwumpjism

I have the roofer out again soon to fix a few things so I might get him to move the slate vent to 2m and maybe above the fresh inlet. The grilles in the room ceiling I haven't much scope to move them. I could put them farther apart on the ceiling. With a double bedroom with one passive vent which has not got good draw, then maybe 13l/s (or 18l/s) on boost I am not going to get to under 1000ppm? I can't seem to find any calculations on room measurements, occupancy and MHRV air change rates for CO2.

Calahonda52

What do you mean by passive vent: have you an open wall vent if you have then .....whats the airflow path.

say room is 2.4m high and 4m square so m cubed is 38.4

18l/s is 18 by 60 by 60/1000= 64.8 m3/h

This is a theoretical number, you must allow for pipe/filter losses so say 90% off = 58m3/h
so one air change every 40 minutes
[38.4/58 by 60 for minutes]


I haven't time to access Part L but its a start

serox_21

@mugwumpjism I'm considering installing same HRV unit myself.
As it passed over 1 year since you have it running can you give a short update?

1. How noisy is it? Can you hear it from your bedroom?
2. Have you checked the efficiency? Is it as claimed?
3. How does it work in winter time? What is the temperature difference from exhaust and incoming air in the bedroom?
4. How often do you change(clean) filters and exchanger. Where do you buy new ones(filters)?
5. Would you recommend it?
6. What was the total cost of installing it? Unit plus all fittings?
7. What's the crossflow air exchanger made of?

Calahonda52

serox_21 wrote: »

@mugwumpjism I'm considering installing same HRV unit myself.
As it passed over 1 year since you have it running can you give a short update?

1. How noisy is it? Can you hear it from your bedroom?
2. Have you checked the efficiency? Is it as claimed?
3. How does it work in winter time? What is the temperature difference from exhaust and incoming air in the bedroom?
4. How often do you change(clean) filters and exchanger. Where do you buy new ones(filters)?
5. Would you recommend it?
6. What was the total cost of installing it? Unit plus all fittings?
7. What's the crossflow air exchanger made of?

Are you a señor counsel:(

serox_21

Just looking for more info about this unit from someone who has it in use for a while.
Not much reviews online about it.