🚀 go-pugleaf

nick@vu-vlsi.ee.vill.edu (Nick Pine) wrote:


>
>Nisson and Dutt suggest just dividing the 50 Pa number by 20, so I'd
>estimate the natural air infiltratation rate for that house as  
>3,200 ft^3/m x 60 m/hr/24,160 ft^3/20 = .4 ACH.
>
>>Using the Manual J detailed infiltration estimate method I come up
>>with winter AC/Hr = 0.85 and summer AC/Hr = 0.32 AC/Hr.

Where does Nisson and Dutt's work fit into this?  Are/were they by
chance at Princeton U?  I have an article which says that in 1982,  J.
Kronvall and Andrew Persily did some work in New Jersey and Sweden
which proved ACH50/20 to be fairly reliable.  The factors not taken
into consideration include stack effect, wind shielding, and types of
leaks.

Next  Max Sherman a  researcher at Lawrence Berkeley Laboratory
developed a model which does take into account, climate, height, wind
shielding, and  crack/hole size.  Sherman found that the correction
factor could be as small as 6 and as large as 40.  So . . . the
ACH50/20 rule of thumb could overestimate infiltration by a factor of
two or underestimate it by a factor of about three.

The climate correction factor for Denver is 15 to16 whereas  New
Jersey  in the 17-20 range.  The climate correction factor takes into
account average temperature and windiness.

With all the factors considered the so called ACH50 number gets
divided by about 13.5 in the example case above to yield about 0.6
AC/Hr.  

The difference between 0.6 and 0.85 ACH is substantial when doing a
heat loss calculation.  The old school engineers would use 0.85 ACH
with the idea that if big is good bigger is better.  Being a younger
:-) school type at age 56 I'll use the 0.6 figure to keep the furnace
size on the low side so if the temperature falls below the design temp
by one degree I can be sure the furnace is running 100% of the time.
Where the other guys install a 140 mbtu furnace I install a 120 mbtu
furnace and so far my customers have not been cold even on those few
design temp days we have had in the last few years.
>
>Sounds OK to me. I guess a lot of this energy testing is all tied up
>with the government and electric utilities now...

With the competitive environment surrounding public utilities they
don't put as much effort or manpower into consumer education as they
used to.  SO . . . that leaves me an opportunity to be an energy
expert, i.e. "certified rater" for Energy Rated Homes of Colorado.