Tuesday, February 4, 2014

Smells, Moisture, CO2 and Indoor Air Quality in Tight Houses

In past blog posts, I've noted various areas in which we are in a technological revolution - including lighting, renewable energy, energy storage, not to mention high performance buildings and windows..

But smells!  The science of smelling/sniffing is definitely in its infancy, but the potential for advancement to yield results is huge.  I looked into this just today because I've been working on our ventilation system, and we happened to install the PAUL Novus 300 HRV (probably the most efficient machine on the market).  But effective and efficient ventilation goes well beyond the heat recovery efficiency.  The energy demands of the ventilation strategy have a lot to do with sensing and control.  (And this was the main reason we chose the Novus. It allows up to 4 channels of control.  )

The ventilator should slow down when users are not occupying the house, or windows are open, should ramp up when users are having vigorous activity in the house, or there are a lot of people in the house, and should operate with a big imbalance if there is a vented dryer in operation or a vented kitchen range hood.  What if 6 people took a crap nearly at the same time?  The indoor air quality could be very poor for a while.
So, to minimize energy demands and maximize effective provision of fresh air to house, I would consider sensing the following, in order of importance with first items most important;

  1. CO2
  2. moisture
  3. Pressures inside and out
  4. windows and doors
  5. smells (!)
(this listing is not including the CO sensor - which could be important if you have gas appliances).

Using CO2 sensing, one could minimize the delivery of fresh air to the house and not over-ventilate.  It would also take into account the presence of more or less people and plants, and probably even fires.  CO2 sensors on the market for HVAC applications (there are also lots for greenhouse applications) are about $300 with NDIR (recommended) sensing systems).  Companies like Honeywell, GE, Senseair all make them).  You can get desktop CO2 monitors on Amazon for about $150.

Moisture sensing is important to protect the building contents, but more importantly to protect the structure, and prevent mould formation, etc.  But don't forget to protect houses from dry conditions also - moulds wont' grow, but anything made of wood will shrink and crack - very low humidity is just as bad as high humidity.

Pressure sensing would compensate for any other exhaust fans as well as open and closed windows.

Smells! - what if someone were to be using a harsh paint, or a cleaner, or indeed, the washrooms.  The science of gas analysis (all smells are due to gases in the local atmosphere) applied to smells has incredible implications.  For example, this company http://www.enose.nl/ says they can make electronic sniffers that can detect pathogens in the air - this means one could potentially detect a virus in the air in one's house, and record that event in a log.  By smell detection, the house could 'know' when the washroom was being used, or when cooking was being done, or when there was a fire, or when laundry is being done, or when mould was growing in the walls (!), when animals have nested inside the attic, perhaps, or when the outdoor air is more polluted than the indoor air.
There is much to read online regarding electronic noses.  The process of technological smelling involves 3 steps:  acquiring a standardized sample, detecting the chemicals in the sample, and analyzing what was detected.  This last part involves a fair bit of software, including databases - because various odor events are logged as a certain configuration of results form the gas chromatography or whatever detection method was used. - the device needs to learn and grow its knowledge to be effective.

All the above is another way for me to feel good about all the low voltage wiring we've been putting into our house - we'll have the built-in ability to employ sensors all over the house because of this, and things are telling me the future of buildings will have a lot to do with sensing.


  1. I like the ideas expressed, but I wonder how wise it would be to entrust health and safety to such devices? Air supply is critical and accordingly risk of failure can't be tolerated.

    Perhaps a code-defined minimal air exchange rate (for safety) to be supplemented when the sensors indicate the need. But the mechanism should be fail safe so that the minimum is provided even in the event the sensor system fails.

    1. This comment has been removed by the author.

    2. An insightful comment. One of the great advantages of a high-performance building envelope is that it is just there, all the time, and does what it is supposed to do, without any gadgets - why go and mess it all up with technology? I get that.
      There are a wide range of needs among occupants, however. Some have signficant fragrance sensitivities, for example.
      I was recently involved in an assembly hall project. We were building a new one, to replace the old. The new mechanical system was all controlled by CO2 levels. Upon finishing, the occupants definitely noticed a significant improvement over the older system, which was heated and cooled kind of like a house, with no measurement of how fresh the indoor air was.

  2. This comment has been removed by a blog administrator.

  3. Very interesting article, I have a humidity sensor at hoe which measures the temperature and humidity. I can recommend it!