For residential houses, 6 air changes per hour should be ok.
Regards,
Believe it or not : A Neutrino is so mass less(and electrically neutral) that, a conservative estimate states, it can pass through a 50 light year thick lead block.
Suppose 4 to 6 persons in an house (200 m2 * heigth of 2.5 m = volume of 500 m3), and 35 m3/h,person of fresh air, according to ASHRAE.
It gives you 140 to 210 m3/h the fresh air requirements for the house, which means about o.5 change of air/h related to its volume. Plus three toillets, and kitchen 120 m3 and 8 to 10 extract of their volumes in an hour, gives you nearly 1000 m3. If you add this figure to the above 0.5 air changes of whole house: 1000 + 210 = 1210 m3.
Thus if we finally divide this last number by the the house volume, 1210/500 ~ 2.5 complete air changes. That's why, 6 air chances is excessive in my opinion. Besides that you will need a lot of power (electrical power/enthalpy) to cool/heat the house in the summer/winter.
I hope this be of some help for the discussion.
zzzo
6 AC/hour is definitely a high figure, if you are talking about taking outside air for air-conditioning a space.
6 AC/hour is normally applied for ventilation only. For normal residential Air-conditoning applications - 1 to 1.5 AC/hour or 10% of supply air should be a good figure. Alternatively, best bet would be take as per ASHRAE codes.
Hi sam42!
Some more information...
From the building code perspective,
adequate ventilation refers to that level of ventilation that protects the health and safety of its occupants. Most regions of the U.S. have building codes that specify
ventilation levels for new buildings. Some regions haves imlar requirements for existing buildings. Such requirements or recommendations may cover ventilation
rates (ASHRAE Standard 62-1989), and thermal comfort (ASHRAE Standard55). Building codes typically require operable, exterior window openings for certain rooms within the living space. If those rooms lack operable windows,
mechanical ventilation is necessary. Bathrooms and kitchens, prime sources of indoor odor and moisture pollutants, are often located in windowless interior
spaces and, therefore, require mechanical exhaust ventilation. The standard stipulates that a minimum outside air change rate should be based either on the volume of the space to be ventilated or on the number of occupants.
It states that each apartment must allow a minimum of 0.35 air changes per hour (ACH) per cubic foot of ventilated space, or 15 cubic feet per minute (CFM) per person, whichever of the two is higher. See the next page for a
worksheet designed to assist users in calculating the minimum recommended air change rates for an apartment.
Minimum is 20 CFM per person + enough makeup air for exhaust (75 CFM per toilet) + enough combustion air for gas or oil fired furnace (if it has no direct OA connection) + enough combustion air for gas fired water heater if it has no direct OA connection. Fireplaces should have direct OA connection, otherwise you have to provide combustion air for that too. Typical combustion air is 8 CFM per boiler Hp which is equal to 33475 Btu/hr. If there is no upward draft at furnace vents or if air actually flows in instead of out at the vents, you have a serious problem!
Our 1,144-SF-per-floor, super-insulated two-story home seems to stay fresh (according to my wife's sensitive nose) if we run one Panasonic (very quiet) 70-cfm fan 24/7. Since there are five people in the home, this one bath fan amounts to 14 cfm/person.
Assuming 8-foot ceilings, the volume of our home is 18,304 cubic feet and 70 cfm amounts to 4,200 cu. ft./hr. Therefore, our 24/7 Panasonic bathroom exhaust fan causes 0.23 ACH (air changes per hour).
Two other small bath fans run occaisionally. The range hood runs a few hours a week and the clothes dryer (also an exhaust fan) runs per normal for a family of five. I estimate these exhaust flows average about 50 cfm or about 0.16 ACH.
The house is very tight (plywood sheathing, Tyvek wrap, Anderson casement windows, foam-core metal doors with magnetic weatherstripping), so the house is under slight "negative" pressure and all infiltration serves as make up air for the exhaust fans.
All totalled, the ventilation rate of our humble abode is about 0.39 ACH (say 0.40 ACH) which means it takes 2 1/2 hours for one complete air change.
Montana Mikie
PS: I have run DOE-2 and other computer models on about 100 real houses and a several hundred commercial buildings over the past 21 years. Generally, if you model excessive ventilation rates (more than 0.3 to 0.8 ACH), your models will use too much heating and cooling energy compared with the utility billing history.
You are quite right, special if the house is built in a hard winter/summer weather region and since fresh air rate is supplied according with number of persons, their habits/activities and the remain facilities as the baths and kitchen/laundry functions. I 'll accept very easy the figure 0.6 to 0.8 ACH.
zzzo
In first I want to thank dear KenRo
for his attentive amendment.Sorry, Now all is correct.
Further, concerning a discussed theme, I shall state some more small remarks.
It is doubtless, that the value, laying in limits from 0,35 ANI to 0,6 ANI is closest for home application,however it is necessary carefully to consider a question in
a place.
The problem of Indoor Air Quality , is rather well investigated,but at the same time, problem of Outdoor Air is not given of due attention.Meantime, in large cities air receives significant pollution.The needs for outside air can considerably change seasonally, hence it's necessary create such systems of ventilation which can to change the productivity.
