A live study of specific ventilation systems.
Background
Our passion is creating happy, warm, dry, well ventilated, resilient, healthy homes for all people to live in. We have a live study of simple negative pressure systems running in three adjoining St Albans.Townhouses.
https://www.healthyhome.kiwi/negative-positive-neither
Earlier in the year, a set of circumstances occurred that meant another two properties needed the ventilation to be improved.
– A 90m2 three bedroom, 1990 built Richmond property where the insulation was upgraded with 180mm of Terra Lana insulation. There were already moisture issues in this property, so upgrading the insulation, without upgrading the standard intermittent extraction would have been foolhardy.
– A 100m2 three bedroom, 1950’s Dallington property where an old HRV unit finally died. This house is often shut up for long periods and relative humidity can reach near 100% regularly, due to lack of manual ventilation. Basically, the occupants refuse to open the windows in winter.
What we decided to do was
– Install a Moisture master MVHR system into the Richmond Property. Moisture Master
– Install a Multi Vent Continuous Extract Ventilation system into the Dallington property. Multi Vent
Discussion
As we add insulation, we need to improve ventilation. A house is a system, so changing one thing has flow on effects to others. The discussion to roll back H1 is a classic case of shooting the messenger, rather than solving the (obvious or not-so-obvious) issue.
So, if we improve ventilation, which way should we go?
– Positive pressure is dead and buried – it’s not even allowed in the UK.
– Intermittent extraction doesn’t work with added insulation – that much should be obvious.
– Continuous negative pressure systems are being touted as the cheap and cheerful way forward.
– And then there is balanced systems like mechanical ventilation with heat recovery (MVHR). These systems are the minimum standard for high performance and passive houses.
But what should be retrofitted to an existing house and what works the best?
Aim
The aim is to compare two houses retrofitted with two different ventilation systems to see what difference they make to the temperature, relative humidity and CO2 levels in a real-world application.
Equipment
Richmond House
We installed a Moisture Master system to test a low-price entry-level ventilation system, to see how well it works. This system comes with a summer bypass and a preheating / tempering element.
The layout and design of the system is as below.
The site-based changes were that the main extraction shown yellow, utilises the old laundry extract vent to save adding additional holes in the soffit. Also, the unit sits on the other side of the hall to allow access past the ceiling hatch.
The system was designed and balanced on paper before installation, with the calculations provided for review.
It can be seen that a lot of care and attention went into the design and installation of this system to make sure it functions correctly.
Dallington House
Initially, I gave HRV the opportunity to install either their continuous extraction system or their MVHR system into the property. They declined this opportunity, preferring to try and hard sell me their positive pressure system, which I discovered only runs intermittently most of the time, in any case.
I’d been talking to Storm Harpham at Simx and we discussed the Homestar accredited Multi Vent system. This continuously extracts from up to three locations via the one fan box, which then vents outside.
We’ve decided to extract from the Kitchen, Laundry and Bathroom, being the moisture laden rooms in the house. The doors were checked and were already 20mm off the floor.
There is no makeup air – Being built in the 1950’s, this is a fairly draughty house.
Method
Both properties have had monitoring sensors installed for several years, so it will be easy to provide before and after data for temperature, humidity and CO2.
The Richmond property has temperature and humidity sensors in the bedrooms and temperature, humidity and C02 sensor in the lounge.
The Dallington property has temperature and humidity sensors in the occupied bedrooms only. Historically, it’s had a temperature, humidity and C02 sensor in the lounge. This has been recently replaced, to conclude this study.
Monitoring Results
Richmond
Additional insulation was installed on Sunday 12th May 2024, with the ventilation install taking place a month later on Friday 14th June 2024.
The vertical lines show the two milestone dates.
Temperature
Temperature monitoring over the monitored timespan has been included to show the background conditions before the MVHR unit was installed. It also shows that even with adding 180mm of R4 insulation to the ceiling, there was only a marginal improvement in temperature in the month following installation.
This backs up the Warmer Kiwi Homes studies in that adding additional ceiling insulation only warms the house by a couple of degrees.
We turned on the preheating element in the MVHR to try and temper the air and offset the cold air being sucked out of the bathroom.
One of the frustrating issues with live trials involving people is “human nature.” The occupant changed in Bedroom 3 from a small child, to a teenage boy. The house is now too hot for him and he insists in sleeping with the window open! Sometimes he forgets to close it, too.
The intermittent heating is obvious, but with all the media coverage about saving power, rather than being warm, you’re ventilating the tide, trying to change to continuous heating, unless you can somehow “lose” the heat pump controller.
However, overall, there has been an improvement in temperature, with the house being in the optimum range for much greater proportion of the time.
Humidity Levels
Relative Humidity is the amount of water vapour in the air, relative to the temperature outside. To get a better understanding of relative humidity, there is a short clip near the bottom of the Mātauranga page on this website.
Before the installation of the MVHR it can be seen that the relative humidity levels are very high. Much higher than optimum as shown by the green band.
Remember, we are measuring relative humidity, so the colder the temperature the higher the relative humidity, as warm air holds more water vapour.
There was a period of “drying out” of the building, before results started to stabilise.
Ignoring the spiky issues with teenage boys that most families have, it can be clearly seen that relative humidity has dropped significantly. In fact, there are actually times in the Living room where it is too low.
Carbon Dioxide Levels
CO2 levels are used as a trigger proxy for indoor air quality. Low CO2 levels indicate fresher air or better airflow through a home.
Indoor CO2 concentration has an impact on comfort, health and wellbeing. CO2 concentration levels around 1500 ppm can cause discomfort and above this limit can start to have health impacts such as headaches or tiredness. Even higher levels can cause dizziness, sleepiness or even trigger attacks for people with asthma.
It is quite noticeable, when you are aware of what is causing your drowsiness in the evening or when you are not feeling refreshed upon waking.
Perhaps this is the reason for the growing popularity of the coffee café culture in Aotearoa?
It’s clear to see that there was a massive issue with CO2 levels in this house.
That’s a massive improvement. There are still spikes and it’s slightly higher than ideal, but there can be a lot of people in this living area at any one time, so this change is super successful.
Healthy Home Score
The software for the monitoring devices has a dashboard where at a glance you can get an overall impression of the health of the house.
Dallington
The trigger for improving ventilation was the failure of the HRV system, which had been there since 2007. Even though it wasn’t doing the job it was supposed to, it was an occupant favourite, due to their advertising and marketing campaigns.
The other trigger was the occupants installing a dryer than vented back into the laundry, despite years of education that this was a bad idea. It wasn’t even because the drier was cheap! Humans don’t help themselves!
An insulation upgrade was improved by Community Energy Action in 2015.
No specific makeup air has been provided. It’s unlikely to be necessary given the era of the house.
The ventilation install took place on the 26th June and this is shown by the vertical line in the below graphs, which are recorded over the same period.
Temperature
Temperature monitoring over the monitored timespan has been included to show the background conditions before the Multi Vent unit was installed. It shows how cold some people are prepared to live. There is a log burner in the lounge of this house and a heat pump in the hallway, but the occupant insists on sleeping with the Bedroom 1 door closed. I’ve recorded the lounge hitting 30 degrees, with the adjacent bedroom at 9 degrees by morning.
Initially the temperature dropped after installation and the occupants complained about having to turn up the heat and add a separate heater in Bedroom 3. They have also complained about the increase in power bill, but that has still to be analysed.
The intermittent heating is obvious, but with all the media coverage about saving power, rather than being warm, you’re ventilating the tide, trying to change to continuous heating, unless you can somehow “loose” the heat pump controller, and remove doors from bedrooms.
Humidity Levels
Relative Humidity is the amount of water vapour in the air, relative to the temperature outside. To get a better understanding of relative humidity, there is a short clip near the bottom of the Mātauranga page on this website.
Before the installation of the Multi Vent it can be seen that the relative humidity levels are extremely high. Often at or approaching 100% in the cold Bedroom 1.
Remember, we are measuring relative humidity, so the colder the temperature the higher the relative humidity, as warm air holds more water vapour.
There was a period of “drying out” of the building, before results started to stabilise. To accelerate that, the Multi Vent settings have been set to boost mode.
There has been an improvement in humidity readings, over the proceeding two months, which should be expected with three outlets extracting continuously. However, it is not as significant as expected, even in boost mode, we would have expected that the relative humidity would always been within the healthy range.
Carbon Dioxide Levels
CO2 levels are used as a trigger proxy for indoor air quality. Low CO2 levels indicate fresher air or better airflow through a home.
Indoor CO2 concentration has an impact on comfort, health and wellbeing. CO2 concentration levels around 1500 ppm can cause discomfort and above this limit can start to have health impacts such as headaches or tiredness. Even higher levels can cause dizziness, sleepiness or even trigger attacks for people with asthma.
It is quite noticeable, when you are aware of what is causing your drowsiness in the evening or when you are not feeling refreshed upon waking.
This house often smells stale and stuffy inside, due to lack of ventilation. However, due to infiltration, the CO2 levels, while far from ideal are not too bad. A CO2 sensor in Bedroom 1, would have been interesting, but it was beyond budget when these sensors were installed.
The CO2 sensor was removed to be utilised elsewhere, so there is no monitoring over the same period as the other results. I have realised this and reinstalled the monitor on the 8th September 2024. This means the data period is from the 8th September to the 21st September 2024.
It appears that the CO2 levels in the lounge are now under control, so in the lounge at least, this has been successful.
Healthy Home Score
The software for the monitoring devices has a dashboard where at a glance you can get an overall impression of the health of the house.
As you can clearly see, the improvement is far from dramatic. Should be healthier to almost healthy is like insulating to raise the temperature by 2 degrees.
Conclusions
– There is a lot more design, installation and commissioning required to install a MVHR unit. There is more technology and more care and attention needed.
– The Richmond house went from 6 Stars “almost healthy” to 8 Stars “This is now a healthy building.”
– The MVHR seems to be working well within the confines of the vagrancies of human behaviour.
– What could be improved; continuous heating would help a whole lot. Some sort of boost function in the living room would help when there are larger numbers. This would need to be automated via sensors.
– The Dallington House went from 6 Stars “Acceptable, should be Healthier”, to 7 Stars “Almost healthy”. This is still not a healthy home.
– The Smart Vent system has reduced the humidity in the house, but considering that there are three ducts extracting moist air continuously from the house at the maximum rate the system will allow, We would have expected the humidity to be lower. We would have expected the relative humidity to be within the healthy range the majority of the time.
– Again, continuous heating would help a whole lot.
– The three point extraction has successfully reduced the CO2 levels in the lounge, but this is unlikely to have flowed through into the bedrooms.
– The occupants complaints about the increase in power bills is a concerning issue, but that is anecdotal, and still to be confirmed by figures.
– With both properties, consistent, continuous heating would help, both in this monitoring exercise, but also in providing more comfortable living conditions for the occupants, but try as we might, they don’t believe this is the way to go.
– It’s fairly obvious which system performs best. In the battle between Moisture Master and Multi Vent, there is a clear medallist; that is Moisture Master and MVHR.
Recommendations
– The first response we expect to get to this study, is that the Moisture Master MVHR system is more expensive that the Multi Vent system and the Multi Vent system works fine for what it is.
– This is like buying a pair of shoes that don’t fit properly just because they’re cheaper.
– Despite what is being advertised, the Smart Vent system is not 6-8 Stars best practice at all. I really wish it was. It would make life so much easier.
– However, you cannot change the laws of physics.
– The demonstrated outcome from this study is that for a best practice ventilation solution, balanced mechanical ventilation is the only way to go. Recovering whatever heat you can from the system is a bonus for the average retrofit situation, where infiltration will dominate over airtightness.
– The heat recovered will be more than that lost by opening windows for ventilation.
– We have proven to ourselves that a basic MVHR system works fine. Or at least much better than a continuous negative pressure system.
– Our recommendation is to always go for what works best. There is no point throwing good money after bad.
HEALTHY HOME COOPERATION
Healthy Homes for all Kiwis. Housing is about people. People working together in cooperation to provide Healthy Homes for people to live in.
Damien McGill: Engineering Happy Healthy Homes for People & Planet
