[Stoves] Air exchange RDP Homes

[Kevin Chisholm]

Dear Kobus

Firstly, what is a "RDP Home?"

I would suggest that the approach "someone" gave you is perhaps 
theoretically correct, but that it is not very good on a practical basis.

Consider, for example, a room that was perfectly sealed, like a very large 
Bell Jar. Simply making a hole of say 1 M^2 in the door at floor level would 
not result in the living space being ventilated. Air could enter, but it 
could not leave. If there was a 0.1 M^2 hole in the door, and a 0.1 M^2 hole 
in the roof, then with a temperature differential, there could be excellent 
air change. It does not suffice to make provision for ventilating air to 
ENTER a room; there must also be provision for air to EXIT a room.

Similarly, there may be provision for air to enter and exit a room, but 
there may be a pocket in the room with poor circulation, so that the 
ventilating air does not flush away the pollutants as intended.

The equation "someone" gave you assumes perfect backmixing of pollutants 
with the air in the living space. This is seldom the case. Fugitive 
emissions from the stove are hotter than the room temperature, and tend to 
rise vertically. A well designed exhaust hood directly above the stove can 
capture the stove emissions almost perfectly, and they would never enter the 
living space.

One should also ask "Why are there stove emissions into the living space in 
the first place??" One should not light a stove in a living space unless 
there is adequate provision to remove the products of combustion. In my 
opinion it is irresponsible to adopt the approach of "improved combustion" 
to improve indoor air quality, rather than ensuring that products of 
combustion are positively vented outside the living space. "Improved Stoves" 
being promoted as a way to reduce IAP, without adequate provision for 
outside venting of products of combustion are, in my opinion, as big a lie 
as Santa Clause and the Easter Bunny.

The mere specification of Inlet Air Area in no way positively ensures 
adequate ventilation of the living space. There must be provision for 
adequate "make-up air", and equally, there must be adequate provision for 
exhaust of contaminants.

There has been much talk about testing stoves and their emissions. The 
simplest way to test a stove is to operate it in the Living Room of a 1st 
World house for 8 hours before Important Visitors are to arrive. If the 
Important Visitors have no complaints after a 2 hour visit, then the stove 
passes. :-) An even simpler test of the indoor air quality attributes of an 
"Improved Cook Stove" is to ask "Would it sell in Middle Class Suburbia?"

Best wishes,

Kevin


----- Original Message ----- 
From: "Venter Forestry" <ventfory at iafrica.com>
To: <STOVES at LISTSERV.REPP.ORG>
Sent: Monday, December 04, 2006 6:53 AM
Subject: [Stoves] Air exchange RDP Homes


Dear David W and list,

Thank you for your insights, a hood definitely has potential then in these
areas when using good improved wood or charcoal stoves, but not so much
coal.  Improved stoves will no doubt be the way to go by venting cleaner
emissions in "smoke free zones".

But what about the replacement of oxygen used by non electric stoves, good
or poor?

Someone gave me the following equation to determine the air exchange in a
room (and CO buildup), but as of yet I have not been able to put it to use
as an example was not provided, and I am not well versed in these types of
things!  I would be grateful if anyone could assist.

He states:

mg/m³) from (t) = 0 to ti hr: ,

C (t) = [(E+O)/V][1/(a+k)][1-e-(a+k)t]

where E is your stove emission rate (mg/hr), O is the outdoor CO
contribution to indoors (mg/hr), V is the volume of your room (m³), a is the
air exchange rate (hr-1), k is the CO decay rate (hr-1), and t is time (hr).

Please note, you probably can assume O is 0, and k is 0 as well.

You may use the following equation to determine your indoor CO concentration
from the time you stop burning:

C (t) = [(O/V(a+k)][1-e-(a+k)(t-T)]+[Cmaxe-(a+k)(t-T)]

Cmax is the maximum CO concentration achieved.

Each habitable room and I quote the housing spec ..."must have an opening
not less than 5% of the floor area of the room, or 0.2 m2, whichever is
greater, comprising either of an opening or door in an external wall, or an
openable glazed window in an external wall or in a suitable position in the
roof"... The regulations also states that the floor space of each home is to
be 50m2. If windows and doors are shut (a scenario apparently not mentioned
by the writers) a ventilation opening of 140 x 140 mm in each room will
conform to these regulations. Are these openings sufficient to allow for the
use of non-electrical stoves indoors?

Regards

Kobus

>Dear Kobus,

>In my opinion, hoods placed directly over or stoves placed directly under
hoods, with incoming >ventilation is a better option than a chimney.

>With a hood over a fire, the operator can see the burn and adjust if smoke
occurs. With most chimney applications I've seen or heard about, the
operator pays less attention >to the burn and if smoke occurs it leaves the
home often to enter the windows of the >neighbors. My wife heard so many
tales of this woe when she was in Mexico training solar >cooking promoters.

>In Bolivia, we recommend using sticks or bamboo as a basic structure in a
corner, forming a triangle >from wall to wall, decreasing in width as it
increases in height, using mud or stucco to >plaster inside and out of the
structure of the hood and have an opening in the highest part directly >in
the corner if it is possible without harming the corner's structural
integrity. Then an open >door or open windows or shuttered hole low in the
opposite wall provides sufficient ventilation. >The top hole can have a
shutter or plug for when it is not in use, in the case of cold >climate.

>If good improved stoves are used, they should not smoke and the ventilation
will evacuate the >majority of harmful gases and particles, without causing
excessive outdoor pollution or bothering >neighbors.

>can discuss more off list if you wish.

>warm regards

>David Whitfield



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