Posted by *Ralph Doncaster* on December 22, 2007, 1:34 am

I read a post from October asking about this. My recent emails to

people involved in the Canadian Energuide program addresses this

topic:

Here's another report I found on the significance of air infiltration

(albeit for high-rise buildings, but still relevant).

http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/98107.htm

If I use the low number of 12W/m^2 mentioned in the report @-18C, that

works out to 284 BTU/F heat loss due to air infiltration. My previous

calculation of 486BTU/F falls nicely in the middle of the 12-25W/m^2

numbers in the report.

Over the past week I have been averaging ~155kWh/day and only able to

keep the house at 15-17C. With the outside temperature around -5C and

factoring ~300BTU/F (weighted avg R20 envelope * 6000sqft) for

resistive heat loss I'm left with at least another 300BTU/F loss to

air infiltration. Adding 600W of heat from occupants (2 adults, 4

children), 500W for solar gains (almost 20m^2 of south-facing glazing)

and 100W of heat from use of the propane stove I get another 100BTU/F

of heat loss (which I would attribute to air infiltration).

These numbers point to a natural air infiltration for my house of

~0.3ACH, or about 25% of the 50PA blower door test of 1.28ACH(I've

done some air sealing since then, and estimate I would test @1.2ACH

now). This leads me to suspect that my initial model of 0.4ACH (based

on Tim Weber's paper) was too high. With Hot2000 modelling 0.167ACH

of natural air infiltration for 1.5@50, it ends up under-estimating

the air infiltration heat losses by more than half.

Posted by *nicksanspam* on December 22, 2007, 12:53 pm

*>If I use the low number of 12W/m^2 mentioned in the report @-18C, that*

*>works out to 284 BTU/F heat loss due to air infiltration...*

12 W/m^2 would be 12x3.41/10.76 = 3.8 Btu PER HOUR PER SQUARE FOOT, no?

Where's the original temperature difference in degrees C?

*>Over the past week I have been averaging ~155kWh/day and only able to*

*>keep the house at 15-17C. With the outside temperature around -5C and*

*>factoring ~300BTU/F...*

... 1 W is 3.41 Btu/h, so 1W/m^2C is 3.41/10.76ft^2/m^2/1.8F/C

= 0.176 Btu/h-F-ft^2, no? And 1 Btu/h-F-ft^2 is 5.68 W/m^2C.

OTOH, US R5.68 is metric R1.

*>I'm left with at least another 300BTU/F loss to air infiltration.*

With no h?

*>Adding 600W of heat from occupants (2 adults, 4 children), 500W for solar*

*>gains (almost 20m^2 of south-facing glazing) and 100W of heat from use*

*>of the propane stove I get another 100BTU/F of heat loss (which I would*

*>attribute to air infiltration).*

Sounds like you have colder weather and less sun. Where I live near Phila,

1 ft^2 of R2 south glazing with 80% solar transmsission would collect about

0.8x1000 = 800 Btu on an average January day and lose 24h(65F-30F)1ft^2/R2

= 420, for a net gain of 380 Btu, ie 113 Wh, if it's a window, or about

800-6h(65F-30F)1ft^2/R2 = 695 Btu net, if it's a low-mass sunspace wall vs

a window. So 20 m^2 would collect about 113x20x10.76 = 24.3 kWh/day, ie

about 1 kW over 24 hours, if it's a window, or 2 kW, if it's a low-mass

sunspace wall.

Nick

Posted by *Jeff* on December 22, 2007, 1:50 pm

nicksanspam@ece.villanova.edu wrote:

*> *

*>> If I use the low number of 12W/m^2 mentioned in the report @-18C, that*

*>> works out to 284 BTU/F heat loss due to air infiltration...*

*> *

*> 12 W/m^2 would be 12x3.41/10.76 = 3.8 Btu PER HOUR PER SQUARE FOOT, no?*

*> Where's the original temperature difference in degrees C?*

You missed the -18C. It's in the article also.

BTW, I've downloaded but not installed the simulation software

mentioned (Hot2000). Any experience with this Nick? It's new to me.

Jeff

*> *

*>> Over the past week I have been averaging ~155kWh/day and only able to*

*>> keep the house at 15-17C. With the outside temperature around -5C and*

*>> factoring ~300BTU/F...*

*> *

*> ... 1 W is 3.41 Btu/h, so 1W/m^2C is 3.41/10.76ft^2/m^2/1.8F/C*

*> = 0.176 Btu/h-F-ft^2, no? And 1 Btu/h-F-ft^2 is 5.68 W/m^2C.*

*> OTOH, US R5.68 is metric R1.*

*> *

*>> I'm left with at least another 300BTU/F loss to air infiltration.*

*> *

*> With no h?*

*> *

*>> Adding 600W of heat from occupants (2 adults, 4 children), 500W for solar*

*>> gains (almost 20m^2 of south-facing glazing) and 100W of heat from use*

*>> of the propane stove I get another 100BTU/F of heat loss (which I would*

*>> attribute to air infiltration).*

*> *

*> Sounds like you have colder weather and less sun. Where I live near Phila,*

*> 1 ft^2 of R2 south glazing with 80% solar transmsission would collect about*

*> 0.8x1000 = 800 Btu on an average January day and lose 24h(65F-30F)1ft^2/R2*

*> = 420, for a net gain of 380 Btu, ie 113 Wh, if it's a window, or about*

*> 800-6h(65F-30F)1ft^2/R2 = 695 Btu net, if it's a low-mass sunspace wall vs*

*> a window. So 20 m^2 would collect about 113x20x10.76 = 24.3 kWh/day, ie*

*> about 1 kW over 24 hours, if it's a window, or 2 kW, if it's a low-mass*

*> sunspace wall.*

*> *

*> Nick*

*> *

Posted by *nicksanspam* on December 22, 2007, 2:44 pm

*>nicksanspam@ece.villanova.edu wrote:*

*>> *

*>>> If I use the low number of 12W/m^2 mentioned in the report @-18C, that*

*>>> works out to 284 BTU/F heat loss due to air infiltration...*

*>> *

*>> 12 W/m^2 would be 12x3.41/10.76 = 3.8 Btu PER HOUR PER SQUARE FOOT, no?*

*>> Where's the original temperature difference in degrees C?*

*> You missed the -18C. It's in the article also.*

Then why the F, and where's the h, in "284 Btu/F"?

*> BTW, I've downloaded but not installed the simulation software *

*>mentioned (Hot2000). Any experience with this Nick?*

No. I write simple BASIC simulations that use hourly TMY2 or Energy Plus

weather data, with lots of flexibility and no hidden assumptions nor

mysterious bugs (after I fix them :-)

Nick

Posted by *Jeff* on December 22, 2007, 5:38 pm

nicksanspam@ece.villanova.edu wrote:

*>> nicksanspam@ece.villanova.edu wrote:*

*>>>*

*>>>> If I use the low number of 12W/m^2 mentioned in the report @-18C, that*

*>>>> works out to 284 BTU/F heat loss due to air infiltration...*

*>>> 12 W/m^2 would be 12x3.41/10.76 = 3.8 Btu PER HOUR PER SQUARE FOOT, no?*

*>>> Where's the original temperature difference in degrees C?*

*>> You missed the -18C. It's in the article also.*

*> *

*> Then why the F, and where's the h, in "284 Btu/F"?*

I had assumed that he did the conversion for the 6000 ft^2 and at

his temperature, but then that opens up other questions!

*> *

*>> BTW, I've downloaded but not installed the simulation software *

*>> mentioned (Hot2000). Any experience with this Nick?*

*> *

*> No. I write simple BASIC simulations that use hourly TMY2 or Energy Plus*

*> weather data, with lots of flexibility and no hidden assumptions nor*

*> mysterious bugs (after I fix them :-)*

I am trying to wrap my mind around air exchange heat loss. In theory I

can see the sensible heat per cubic foot. But I don't understand what

affects the air exchanges a house makes. Does a temperature or pressure

gradiant drive air exchanges or is this a relatively fixed number? It's

all more than I have a clue about. It's a little hard for me to think of

my house exchanging half it's air or so through my painted over windows

and the cracks in more door. That and air exchange means air is coming

and going. Is it coming from some place and going elsewhere? It doesn't

seem reasonable that it is leaking in and out at the same place.

Lets say we have a 10,000 ft^3 house. If it is exchanging half that

per hour that is 83 CFM. What total size air hole would that be going

through?

Jeff

*> *

*> Nick*

*> *

>If I use the low number of 12W/m^2 mentioned in the report @-18C, that>works out to 284 BTU/F heat loss due to air infiltration...