Healthy Homes Deserve Designed Detailed Ventilation

Every Kiwi deserves a healthy, well ventilated home!

Especially if you have health issues relating to sensitivity to mould or pollen. In this situation mechanical ventilation with heat recovery #mvhr is an ideal solution as the filters in the air handling unit, remove contaminants such as pollen and dust particles.

However, the system has to be designed, installed and commissioned correctly to achieve the desired results.

Matariki found me in the southern seaside town of Oamaru, visiting a 1907 Victorian Villa with charm, character and a challenge.

The lovely owners had spent a great deal of time and money modernising the inside of this old girl, to make it much more healthy including installing a MVHR system, but something wasn't quite right.

The owner is particularly sensitive to pollen particulates and had done many of the right things, but in her words "something was still off."

At my behest, she procured some sensors to monitor internal air quality, mainly humidity and CO2 levels to see if monitoring could measure the issue.

The months monitoring came back with good CO2 levels but quite low humidity readings.

The optimal relative humidity range is 40-60%. Many people say that nothing lower than 50% is appropriate. In this house, occasionally readings we under 30%, with some variability in maximum and minimums, considering that the home is now constantly centrally heated and ventilated.

Low humidity can be unhealthy too. Symptoms include, dry skin, cracked and chapped lips, itchy eyes and throat, and even asthma flare-ups, so it's important to get the ventilation balance right!

The likely cause of this issue is over ventilation. Too much airflow through the MVHR. Air coming in at low temperature from outdoors will have much lower relative humidity when heated to 20 degrees than internal air, absorbing cooking, showering and breathing, water vapour.

The possible reason for this over ventilation is that there is only one extract vent in the whole house and that is trying to balance the five supply nozzles. Now, the supplier's website states "The warm, moist, stale air is extracted from a central point in the home, such as the hallway or wet rooms." That kind of sounds like a single point?

In reality, warm, moist, stale air should be extracted from the kitchen, laundry, bathroom, toilet and ensuite, not just one source. This will also help with balancing the airflow around the house, so that extraction and supply areas are closer together and there is less pressure for air to be forced around the home under doorways and across transfer areas like hallways.

Also, not having a single sucking source will likely reduce the risk of dust being drawn in from outside the thermal envelope, especially in an older style home like this villa.

There are a few other things that are not ideal; the type of ducting used (smooth bore rigid is preferred), that fact that all the ducting wasn't fully insulated, and the air handling unit wasn't firmly fixed down, but in general, as shown by the CO2 readings, it is working. Perhaps, a little too hard, hampered by human hands. It just needs refining. This should be part of the commissioning process. But the design philosophy needed to be right first.

Given that this is a villa, and even with the significant work done, it's probably still pretty leaky, (I have suggested a blower door test, to find any more major leaks), I was thinking that rather than the airflow in being totally balanced by the airflow out, slightly more airflow in might create a slight positive pressure environment and help reduce the daily dust accumulation? At least we remove the risk of sucking in dust from outside. It's probably worth a trial, since the monitoring equipment is there.

So, I've made some recommendations on airflow rates to target and a positive balance to achieve, now we'll see what happens next.

This is not about pointing fingers, more lessons learnt. The main thing is the health and welfare of the owner and getting this house feeling "right", instead of "off" for her. Hopefully, we're on the way to achieving that, now.

As an aside, the Steam Punk museum is well worth a visit, if you're ever down that way! I didn't see a steam punk MVHR system, I must ask next time...