MarcelHoldinga Posted November 12, 2020 Share Posted November 12, 2020 Me again, this time I've got some basic questions about MVHR... We have an Airflow Adroit DV96 MVHR unit (one of the earlier units without onboard CO2 sensing), with radial distribution using Airflex Pro ducting. We have a CO2 monitor in the main bedroom (unfortunately, it's not a sender for the MVHR unit) and I know there are certain levels at which the unit will show a green, amber or red light, though I'm not quite sure at what levels it would change from one to the other... With the MVHR unit on the standard setting (running at 75% of max power), we were getting the of 1300+ PPM as the maximum. I've set the unit to run the boost profile a number of times during the night, to compensate for the fact it can't increase air flow automatically (lack of CO2 sensing capability), and we're still going up to around 1100 PPM... My question is: what sort of CO2 levels can you reasonably expect to see overnight in a bedroom with properly functioning MVHR? Link to comment Share on other sites More sharing options...
epsilonGreedy Posted November 12, 2020 Share Posted November 12, 2020 How far apart are the external MVHR intake and exhaust? Have you tried leaving the bedroom door open or ajar overnight? Have you tried placing the co2 monitor elsewhere in the house? Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 12, 2020 Author Share Posted November 12, 2020 15 minutes ago, epsilonGreedy said: How far apart are the external MVHR intake and exhaust? Have you tried leaving the bedroom door open or ajar overnight? Have you tried placing the co2 monitor elsewhere in the house? Intake and exhaust are around 2m (6'6") apart on the west face of the house (the high part of the mono-pitch) bedroom door is ajar, as is the door to the ensuite (extraction point) CO2 monitor is wall mounted and doesn't look like it can be removed... Link to comment Share on other sites More sharing options...
ProDave Posted November 12, 2020 Share Posted November 12, 2020 I am surprised you need to run it at 75% as the "standard" setting, that does not leave much extra for boost? Has it been set up properly with the flow rates at each terminal being measured? Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 12, 2020 Author Share Posted November 12, 2020 They have, but I'm not too sure that they were set up right. The guy doing it can't have spent more than about an hour and a half on the whole house (4x supply and 4x extract valves) - I;ve read on another blog that it could take the best part of a day to get it right... I suspect it was windy when they set it up, 'cos I've noticed that if it blows a hoolie, the levels stay low (in the 400s while we're asleep). I'm hopefully able to borrow an anemometer off the company who installed it, so I can double check the rates and (hopefully) adjust them. The installers only installed the system, they didn't supply or design it... Link to comment Share on other sites More sharing options...
SteamyTea Posted November 12, 2020 Share Posted November 12, 2020 5 hours ago, MarcelHoldinga said: We have a CO2 monitor in the main bedroom Have you calibrated the unit? Some need to be placed outside where PPM is about 420. Link to comment Share on other sites More sharing options...
joth Posted November 13, 2020 Share Posted November 13, 2020 12 hours ago, MarcelHoldinga said: I suspect it was windy when they set it up, 'cos I've noticed that if it blows a hoolie, the levels stay low (in the 400s while we're asleep). How airtight is the house? Our temporary home is incredibly drafty (no MVHR) and the co2 monitor behaves much like yours - high on a still night, low if it's windy Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 13, 2020 Author Share Posted November 13, 2020 1 hour ago, joth said: How airtight is the house? Our temporary home is incredibly drafty (no MVHR) and the co2 monitor behaves much like yours - high on a still night, low if it's windy Supposedly 1.75 cu m/h/sqm (from a specified target of 5), but from what you've just said, that might not necesarily the case. 9 hours ago, SteamyTea said: Have you calibrated the unit? Some need to be placed outside where PPM is about 420. the unit is a DETA wall mounted unit (pictured), it's mains powered, so I don't know how we'd go about calibrating it... I'll RTM and see whether that could be an issue. Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 13, 2020 Author Share Posted November 13, 2020 @ProDave re the high background ventilation rate, you're right - the boost profile would normally increase extraction by 30%, which means it should boost at 105%, so it's not extracting right. I've spoken to Airflow, who told me you should get 20% extra air flow at the terminals, but as it stands, we're measuring 13% extra on the boost profile in the bedroom. We've measured the flow rate there, it's 24.6 background and 28 boosted. The calculations for the spec of the system shows 30 background and 28 boosted... Link to comment Share on other sites More sharing options...
Gone West Posted November 13, 2020 Share Posted November 13, 2020 14 hours ago, MarcelHoldinga said: They have, but I'm not too sure that they were set up right. The guy doing it can't have spent more than about an hour and a half on the whole house (4x supply and 4x extract valves) - I;ve read on another blog that it could take the best part of a day to get it right... I suspect it was windy when they set it up, 'cos I've noticed that if it blows a hoolie, the levels stay low (in the 400s while we're asleep). I'm hopefully able to borrow an anemometer off the company who installed it, so I can double check the rates and (hopefully) adjust them. The installers only installed the system, they didn't supply or design it... It took us all day to set up our system. It isn't possible to set it up accurately if it's windy outside. I've never checked the CO2 levels but the humidity never increases for long before going back down to normal levels and our system has stayed at setting 2, out of four, for the last 2.5 years. 1 Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 13, 2020 Author Share Posted November 13, 2020 9 hours ago, MarcelHoldinga said: We've measured the flow rate there, it's 24.6 background and 28 boosted. The calculations for the spec of the system shows 30 background and 28 boosted... that second 28 boosted should have read 36 cu m/h boosted... missed the edit window - ? Link to comment Share on other sites More sharing options...
DundeeDancer Posted November 14, 2020 Share Posted November 14, 2020 (edited) On 12/11/2020 at 17:36, MarcelHoldinga said: My question is: what sort of CO2 levels can you reasonably expect to see overnight in a bedroom with properly functioning MVHR? Hello Marcel, I have stayed in a few nice guest houses that have had MVHR installed (new builds and retro-fits) and when staying at these places I tend to take my trusty CO2 monitor just to see how things preform. With me and the wife sleeping in these rooms we have found that at the start of the night when we haven't been in the room for ages the ppm start off at about 500. Then pretty soon once we have nodded off to sleep the ppm raise up to just under the 1,000 ppm mark and hover around there till breakfast time. When I spoke to the owners though they did say they ran their systems at 20% or even at 10% capacity overnight to keep the noise levels down when sleeping, which I did furrow my brows a little at ? I've just fitted a single-room MVHR fan into our main bathroom as an interim measure until the time is right to do a deep refurb on my own place. I'm not too impressed with the single-room MVHR so far but it's only been 5 nights and maybe I'm expecting to much for a £300 fan but I feel my own thread brewing ? Best of luck with it all, DD. Edited November 14, 2020 by DundeeDancer 1 Link to comment Share on other sites More sharing options...
Gone West Posted November 15, 2020 Share Posted November 15, 2020 14 hours ago, DundeeDancer said: When I spoke to the owners though they did say they ran their systems at 20% or even at 10% capacity overnight to keep the noise levels down when sleeping, which I did furrow my brows a little at ? That's something I just do not understand. Our system supply runs at 30% all the time and is not audible even with my ear next to the vent. The extract runs at 45% all the time and is audible but only in those rooms with an extract vent. I fitted an attenuator to the supply side but didn't to the extract side as I didn't think it was worth it, but with hindsight I might have fitted one. I wouldn't dream of reducing the ventilation at night. 1 Link to comment Share on other sites More sharing options...
Oz07 Posted November 15, 2020 Share Posted November 15, 2020 Does that not make it unbalanced @PeterStarck? Likewise my unit is quite close to bedroom and no noise bothers me. There is almost a white noise from the vents but nothing that disturbs anyone's sleep. I've asked a couple of guests and they slept fine just said bit like a hotel Link to comment Share on other sites More sharing options...
Gone West Posted November 15, 2020 Share Posted November 15, 2020 2 minutes ago, Oz07 said: Does that not make it unbalanced @PeterStarck? No the fan speeds are adjusted in order to help balance the system. Link to comment Share on other sites More sharing options...
MarcelHoldinga Posted November 15, 2020 Author Share Posted November 15, 2020 (edited) Thanks for that information, @DundeeDancer and @PeterStarck. I've been able to borrow an airflow meter off the installers. I did some measurements on Friday night and got the figures in the attached image. These are values at on the background extraction level (called At Home on our unit), with supply and extract fans both running 75%. The Specified column shows what was specified by Airflow at the design stage of the system, Actual is what I measured on Friday night. From reading @Jeremy Harris's post in Balancing MVHR - how to? by @readiescards (below), I noticed that the levels we have set as background extraction are quite close to the extraction levels you would expect at on boost... No wonder that the guy who installed it had remarked that he had to put the fans up to 75% to get the right flow rates... I'm beginning to suspec that we're working out unit too hard... Speaking to Airflow themselves, I learned that the boost supply and extract levels should be around 20% more at the valves than you would have on At Home.... Would it be right to assume that the system's been set up the wrong way around? From Jeremy's post, you start from Boost, and then work your way down to background levels, but the manual to our unit tells you to set the background level, and the unit then automatically increases the fans' output by 30% (e.g. At Home is set to 50%, the unit would automatically set Boost to 80%) Edited November 15, 2020 by MarcelHoldinga pressed post again before I was done... Link to comment Share on other sites More sharing options...
Gone West Posted November 15, 2020 Share Posted November 15, 2020 50 minutes ago, MarcelHoldinga said: Would it be right to assume that the system's been set up the wrong way around? I wouldn't say so. I set up ours starting with the level 2, which is 'at home', and getting it all balanced for that and then there is boost, level 4, which is 100%. Level three is set halfway between 2 and 4 and level 1, which is unoccupied, is set halfway between zero and level 2. Our system has run automatically, without a humidistat, for 2.5 years 24/7 on level 2. Our system has a built in EASHP which warms the air if required and, if running, that increases the speed to level 4 for around 15 seconds and then modulates down and varies the speed to what is required to provide the desired volume of air to maintain house temperature. Link to comment Share on other sites More sharing options...
readiescards Posted November 28, 2020 Share Posted November 28, 2020 My experience, 3 years on is the unit runs in Normal mode in the daytime (with Boost just for manual boost post shower/bath) and at night I run it at 3% tickover (so minimal noise) - with the bedroom windows open. So balance it for Normal/At Home. Boost I set at a happy medium of being functional and not too noisy. Footnote: if you have a (sealed) log burner as I do I would encourage you to have a positive pressure in the space around the log burner as when opening the log burner door you don't want to suck the fumes out. Ours could do with a tweak, as we have to slowly open and shut the door to not create a stink. Link to comment Share on other sites More sharing options...
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