ollie Posted November 2, 2021 Share Posted November 2, 2021 Hi all, I have balanced mvhr unit in our closed panel timber house that is around 195 m squared and received an air permeability score of 1.14 Currently the MVHR system is delivering 60 l/s on its default setting Can i safely turn this down to its lower setting that delivers 40 l/s (worried about co2 and oxygen levels, i have 2 young kids which makes me paranoid!) whilst i know there is a heat exchanger i still don't want to be over ventilating the house with cooler than internal air if not required particularly in the colder months ps it has an auto function that kicks if it detects higher levels of moisture thanks in advance Oliver Link to comment Share on other sites More sharing options...
DamonHD Posted November 2, 2021 Share Posted November 2, 2021 10l per second per person seems a reasonable goal, including for covid! We are managing (though with humdity somewhat too high) on about 10l/s/p for *four* of us. You should defintiely NOT be worried about Oxygen levels I suspect! https://www.earth.org.uk/MHRV-mechanical-heat-recovery-ventilation.html Rgds Damon Link to comment Share on other sites More sharing options...
Marvin Posted February 3, 2022 Share Posted February 3, 2022 (edited) Although ten litres per second per person is a great idea I'm not sure how you would regulate this when the amount of occupants can vary. I am not sure that it's just breathing that would be the problem either... cooking and human odors for example. I think you can get ( the best I can describe it) chemical vapor from some house materials and contents which I understand can also build up in a property. It may be that this is less of a problem now. I'm sure someone will clarify.... We keep our MVHR at 30 litres a second for our 100m2 bungalow. Our humidity is removed from the room it is detected in by automatically shutting the other extracts off for 10 mins and not turning on the boost function. Admittedly this was a labour of love, I did it myself, and it will probably never pay for its self. However, in my humble opinion, the bigger the property the bigger the potential saving of heat (or cooling in the summer). M Edited February 3, 2022 by Marvin Add info Link to comment Share on other sites More sharing options...
JohnMo Posted February 3, 2022 Share Posted February 3, 2022 I would look up passivhaus recommended flow rates and use that as the minimum. Oxygen levels will never be the issue. You need to worry about CO2. CO2 in bedrooms can be the worst. Get a monitor, tweek flows, monitor bedrooms, somewhere around 1000ppm or below should be the target. Once you have that move monitor to living room and check that also. I have our living space at below 800ppm. So if we have guests CO2 levels don't get too high. Link to comment Share on other sites More sharing options...
Mike Posted February 3, 2022 Share Posted February 3, 2022 (edited) On 02/11/2021 at 09:52, ollie said: worried about co2 and oxygen levels Lack of oxygen isn't a problem, other than that it will be displaced by carbon monoxide in the blood if you have a carbon monoxide problem - possible if you cook with gas or have a fire. CO2, however, is a significant; research has shown that brain function & sleep quality decline as CO2 levels rise. Less than 700ppm is generally regarded as acceptable*, based on current knowledge. It's possible to control MVHR ventilation rate using a CO2 sensor, and that would be advisable rather than cutting the rate manually. Volatile Organic Compounds (VOCs) are also a concern. VOC levels are likely to be high for around the first 3 years of use, so better not to rely on CO2-based control during those first years - unless you have consciously built & furnished your home with low-VOC materials (see my post here) BTW, if you're in an urban area you may also need to filter your air to to remove outdoor pollution (particularly PM2.5 and NOx). *The recommended level for schools is 800ppm; it's concerning that many schools with monitors show CO2 levels >1500ppm - see https://www.nasuwt.org.uk/article-listing/survey-shows-government-failing-ventilation.html Edited February 3, 2022 by Mike Link to comment Share on other sites More sharing options...
MikeSharp01 Posted February 3, 2022 Share Posted February 3, 2022 8 hours ago, JohnMo said: 1000ppm or below should be the target As Mike says this is a bit high we target 660 as a safe level in our lecture rooms if teaching students face to face. You can get the definitive answer (with associated caveats) here: https://www.hse.gov.uk/coronavirus/equipment-and-machinery/air-conditioning-and-ventilation/identifying-poorly-ventilated-areas.htm#:~:text=A consistent CO2 value below,talking Link to comment Share on other sites More sharing options...
Ajn Posted February 3, 2022 Share Posted February 3, 2022 A snapshot of ours running at 16 l/s for two people and 95sqm Link to comment Share on other sites More sharing options...
Temp Posted February 3, 2022 Share Posted February 3, 2022 On 02/11/2021 at 09:52, ollie said: I have balanced mvhr unit in our closed panel timber house that is around 195 m squared and received an air permeability score of 1.14 Currently the MVHR system is delivering 60 l/s on its default setting If we assume 2.4m ceiling height that's a volume of about 468 m^3. 60L/S is about 216 m^3 per hour. So the ACH works out at around 216/468 = 0.5 ACH. https://www.epa.gov/indoor-air-quality-iaq/how-much-ventilation-do-i-need-my-home-improve-indoor-air-quality The rate at which outdoor air replaces indoor air is described as the air exchange rate. ASHRAE (formerly called the American Society of Heating, Refrigerating and Air-Conditioning Engineers) recommends (in its Standard 62.2-2016, "Ventilation and Acceptable Indoor Air Quality in Residential Buildings") that homes receive 0.35 air changes per hour but not less than 15 cubic feet of air per minute (cfm) per person. To achieve 0.35 ACH you could reduce the flow rate to 60*0.35/0.5 = 40L/S 15 cubic feet per min is about 7 L/S. So 40L/S would be ok for 5-6 people. On 02/11/2021 at 09:52, ollie said: Can i safely turn this down to its lower setting that delivers 40 l/s It would seem that's OK. Link to comment Share on other sites More sharing options...
JohnMo Posted February 3, 2022 Share Posted February 3, 2022 Schools and COVID precautions are not really appropriate settings to aim for in a living or sleeping space. My recommendations are taken from. https://www.paulheatrecovery.co.uk/air-tightness-standards-testing/ Link to comment Share on other sites More sharing options...
MikeSharp01 Posted February 3, 2022 Share Posted February 3, 2022 4 hours ago, JohnMo said: Schools and COVID precautions are not really appropriate settings to aim for in a living or sleeping space. They tend to use open windows to achieve it but the people density is much higher. @Ajn Looks to be doing even better that those levels. 4 hours ago, JohnMo said: https://www.paulheatrecovery.co.uk/air-tightness-standards-testing/ Great link Link to comment Share on other sites More sharing options...
Simplysimon Posted February 3, 2022 Share Posted February 3, 2022 4 hours ago, JohnMo said: Schools and COVID precautions and our glorious leader is intending to spend £300,000 cutting the bottom from school doors (2-4%) to improve ventilation and a few million on fans and filters. two years after start of pandemic, ahh timing, perfect. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted February 3, 2022 Share Posted February 3, 2022 14 minutes ago, Simplysimon said: glorious leader Don't worry another one will be along shortly. There is plenty of evidence that good ventilation aids concentration so it might be a good idea, but as you say 2 years too late. (see link above) Link to comment Share on other sites More sharing options...
Mike Posted February 4, 2022 Share Posted February 4, 2022 7 hours ago, JohnMo said: Schools and COVID precautions are not really appropriate settings to aim for in a living or sleeping space. My recommendations are taken from. https://www.paulheatrecovery.co.uk/air-tightness-standards-testing/ For deeper information, these may be of interest: The effects of bedroom air quality on sleep and next-day performance; Strøm-Tejsen, Peter ; Zukowska-Tejsen, Daria; Wargocki, Pawel; Wyon, David Peter Associations of Cognitive Function Scores with Carbon Dioxide, Ventilation, and Volatile Organic Compound Exposures in Office Workers: Allen, Joseph G., Piers MacNaughton, Usha Satish, Suresh Santanam, Jose Vallarino, and John D. Spengler. Link to comment Share on other sites More sharing options...
Ajn Posted February 4, 2022 Share Posted February 4, 2022 12 hours ago, MikeSharp01 said: Ajn Looks to be doing even better that those levels That is a snapshot at the time. CO2 is monitored in the extract and it will increase to the standard .35 ACH if CO2 gets to 1000ppm and above. Thing is, with doors opening due to dog or grandkids in and out etc etc there isn't a need for higher flows. Bathroom and Kitchen RH is monitored to control the boost which is set at standard levels. Boost is loud but the unit is not boxed in yet. At night 2230 - 0700 it always runs in bypass mode and it does give the feeling of slightly nicer air. This is done as we don't have windows I can open. Link to comment Share on other sites More sharing options...
SteamyTea Posted February 4, 2022 Share Posted February 4, 2022 Use relative humidity as a gauge. Find a level you are comfortable with, i.e. 60%, then reduce your flows until you get to that. Worrying about O, CO, CO2, NOXs, bacteria and viruses in the air is not going to make you more or less 'healthy'. I work in a place with air extraction so huge, it makes for a 20 MPH wind by an open door. I still feel tired after a nights work. It is normal. Link to comment Share on other sites More sharing options...
RobLe Posted February 4, 2022 Share Posted February 4, 2022 We have a Vent Axia Sentinel Kinetic Plus BH, and like many units it comes with a few 0-10V analogue inputs for external controls, it even has a handy +24V supply output. One of them I've connected up to a CO2->0-10V sensor powered from that 24V, and the vent axia can be told it's a CO2 input where 10V=2000ppm, and told over a certain ppm to proportionally increase fan speed. Here's the sensor I used: https://www.digikey.co.uk/en/products/detail/amphenol-telaire/T8031/5774483 We've had this add-on for ~5years, It boosts when needed, or it all slows right down if nobody is home. If the humidity is high the MVHR increases, or if CO2 is high it increases. I generally set the desired speed quite low, and let it just get on with things, depending on CO2 and humidity. MVHR units should just come with this built in I think, rather than expecting people to adjust up or down. We left our MVHR on it's factory settings initially, and ended up with a very low humidity house full of itchy people with dry skin! Link to comment Share on other sites More sharing options...
hb1982 Posted February 4, 2022 Share Posted February 4, 2022 Objectives of ventilation are - provide clean outdoor air - maintain CO2 level to acceptable level - remove humidity - remove other harmful pollutant CO2 is the metric used normally for occupied space. 1,000ppm was the gold standard but modern building design target a range around 800ppm. 660ppm (suggested by another poster) is very hard to achieve as the atmosphere CO2 level is around 430 ppm (it was 370ppm when I was in my first year degree 20 years ago). to achieve 1,000ppm, you need 10 l/s per person. to achieve 800ppm, you need 15 l/s per person. Both are based on steady state model, no matter how big your space volume is. Figure 2 here illustrates it. https://www.cibsejournal.com/cpd/modules/2014-10/ Do typical MVHR installations provide sufficient ventilation in an air tight house under "work from home ; 24/7 stay at home" scenario? I very doubt it. Open windows if you have a chance! Link to comment Share on other sites More sharing options...
Adrian Walker Posted February 4, 2022 Share Posted February 4, 2022 (edited) You needs to get yourself a CO2 sensor/logger. This is where I get mine from https://www.gasdetectorsdirect.com/products/air-quality-guardian-aqg Edited February 4, 2022 by Adrian Walker Link to comment Share on other sites More sharing options...
tonyshouse Posted February 4, 2022 Share Posted February 4, 2022 I have measured CO2 in a school, UGH - I carry a CO2 monitor to meetings and walk out at 600 at home we are 450 or there abouts. and an Omicron story We now have my son, his wife and our youngest grandson T staying with us, T came home from school with Covid last week. All the rest of us did a test and all showed negative. We had rules, T spends a lot of time in his room or in my office with the MVHR inlet blocked and the outlet in the anteroom opened up. I turned the MVHR up to full time 65% when we usually use a programme varying the flow between 35%, 45% or 60% and 15% overnight. T eats separately and we minimise contact with him. He wears a mask if he comes in the lounge with us and that is limited to 15mins, he washes his hands a lot. Three days into this regime none of us were positive, it is worrying though and I was certain that we would all get it. Upstairs we have three bedrooms all with MVHR inlets, landing and bathrooms have extract so bedrooms are under slight positive pressure and any aerosols can’t float into other bedrooms, they are extracted from the landing and bathroom. I estimate that we are on over one air change per hour. My son says that following the rules is all that you need to do, I like the ventilation system as it ensures that we breathe pre-warmed fresh air nearly all the time and that T’s aerosols go to outside without us breathing them in. Happy to be able to report that after six days none of us caught it and T is now clear too Link to comment Share on other sites More sharing options...
Simplysimon Posted February 4, 2022 Share Posted February 4, 2022 19 hours ago, MikeSharp01 said: Don't worry another one will be along shortly. have you looked at the (zealots) sorry, scottish political party running this country Link to comment Share on other sites More sharing options...
SteamyTea Posted February 4, 2022 Share Posted February 4, 2022 4 hours ago, Adrian Walker said: You needs to get yourself a CO2 sensor/logger. This is where I get mine from https://www.gasdetectorsdirect.com/products/air-quality-guardian-aqg Can you get the logged data out of it and onto a PC? Link to comment Share on other sites More sharing options...
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