[Greenbuilding] Exhaust Only Passive Inlet Ventilation

[John Straube]

Sorry Nick, I did mean "INcorrectly"
Your solution is the one I would use.
In the past I have used, with resistance from code officials and designers, exhaust fans in bath rooms (operating continuously or 20 minutes of each hour) and air inlets (from Panasonic or Aldes) in each room in numerous houses (one storey houses so that stack effect does not cause air to flow in on the lower floor and out the top floor vents) and a few wood frame apartments (with airtight  separations between units) and one muliti-storey concrete building (my own, with tight floor seperation). 
These all worked acceptably well as far as I know.
In every case, I used this approach because I was using hydronic heating, did not require cooling, and the required ventilation rates were so low (like 15-30 cfm per suite) that HRV did not make sense.
The RH control does not work, although has been tried by many. In the winter, ventilation is very important to lower indoor RH, and people naturally try to button up their homes and close windows for comfort. Setting the humidistat at 60% will mean no ventilation occurs in a cold climate until it there is so much moisture that water is running down the windows and rotting walls and roofs. You could set it at a safer 35% in Ottawa or 40% in Boston, but then it would over ventilate during the spring. Then in nice weather when people leave the windows open and ventilation is not needed the fan would run like made trying to het the RH down to 60% by bringing in lots of 65% air :) Someone would have to know how to adjust it.  
Hence, other than fixed ventilation, the two controls that seem to work are timing controls and CO2 controls. The latter is the best. Occupancy controls can be used to boost base level ventilations but not in exclusion because there are pollutants in a space that are not occupancy related that need some ventilation.

I have had to repeatedly do the calculation to show that a 15-30 cfm ventilation requirement requires less energy if I use a 10W Panasonic exhaust fan (or 17W in the past) plus heating the air up versus a  70% efficient HRV that draws 250W. It is non obvious, but the numbers dont lie. Panasonic has recently released a small ERV that isquite a bit better: it uses a bit over 20W, offers 65% efficiency and moves 20 to 40 cfm of air. Alas, it is a bit expensive but likely is worth it for some applications.
 I have not been able to measure it or talk to someone who has used it yet so this is just based on their promises.

 


Nick Pine wrote:
> Rob wrote:
> 
>> If by "simpler exhaust fan" you mean exhaust-only, passive-inlet 
>> ventilation strategies (EOPIVS) ... testing done about 10 or 15 years 
>> ago here in Canada showed that EOPIVS do not work in all but the most 
>> mild Banana Belt locations in Canada, do not work in multi-storey 
>> homes and do not work in homes over ~1600 sf.
> 
> John wrote:
> 
>> The IRC and CMHC have done a number of studies on this. You can do the 
>> work to look these up.
> 
> Right... :-) "Prove me wrong!"
> 
>> The exhaust only passive inlet system can work even in cold climates, 
>> BUT, requires more careful design and does not usually offer mixing of 
>> the supply air and the interior air. I have this system in my 5 storey 
>> apartment building and it works well. Requires a specially designed 
>> air inlet in each room that does not have an exhaust fan.
> 
> Sounds like each unit should have an exhaust fan, eg a small fan in the 
> kitchen or bathroom that runs when the owners turn on a switch or the RH 
> exceeds 60%.
> 
>> This is still acceptable in code, but that does not mean it is the 
>> best system and many code approved things may not work if they are 
>> done correctly.
> 
> If done INcorrectly?
> 
>> HRVs often cost more electric fan energy and do no better for air 
>> quality than the return side air inlet with controller but they cost a 
>> lot more and demand better maintainance.
> 
> At 15 cfm per occupant, the energy penalty seems small, compared to the 
> cost of an HRV.
> 
> Nick
> 
> 
> 
> 
> 

-- 
Dr John Straube, P.Eng.
Associate Professor
Dept of Civil Engineering & School of Architecture
University of Waterloo
Waterloo, ON Canada