Beatrice writes:

... In reference to a new house here in Eugene Or...

NREL says August is the warmest month in Eugene, with a 67.6 F daily
average and a 53.2 and 81.8 min and max and a 53.3 deep ground temp
and humidity ratio w = 0.0085 pounds of water per pound of dry air.
That's within the ASHRAE comfort zone, so a house with well-shaded
windows and minimal indoor electrical use would be comfortable on
an average day.

I would like to do something very simple?(not?fancy,?not?too?pricey)??
to try to make use of the fact that I have about 750 sq ft of basement
slab in the ground to provide cooling. ?

That's about 750ft^3x30Btu/h-F-ft^3 = 22.5K Btu/F of thermal mass,
counting some soil beneath at about R2 per foot, which could be useful
during a hot spell if it's kept cool with outdoor air on average days.
Otherwise, it will warm up quickly. The slab needs a vapor barrier
beneath to avoid adding humidity to house air.

One suggestion I have gotten is that some kind of collection of pipe
under the slab would allow me to make use od stac effect in summer --
drawing hot air out upstairs by keeping the house closed and drawing
air through the pipe to cool...

That's better done at night, when outdoor air is cooler. Warm air rises,
so in principle, a house with just one opening at the top might stay close
to the outdoor min. Two chimneys would work better, with air flowing down
one and up the other, vs conflicting flows in one chimney.

Anybody have any experience or very brass tacks practical advisce for
me on what I need to lay in the slab (soon) and how such a system
works, in terms of where the air intake and outlet need to be, etc.
???Also hoping not to create critter condos by doing this....Canb't
wait to hear yr ideas. ?Remember SIMPLE, please!

I'd forget the pipes and cool the basement slab and walls with outdoor air
at night, below the comfort zone, if it's unoccupied, with a fan (eg Lasko's
$50 2470 cfm 90 watt 2155A window fan) with a differential thermostat and
a humidistat that moves outdoor air through the basement when it is cooler
than basement air, as long as the basement air RH is under 60%, to avoid mold.

Ventilate the house at night down to a low comfort temp with another fan
with a differential thermostat and a humidistat and a low limit thermostat.
On a hot day, circulate air between the basement and the living space with
more controls. If all else fails, turn on a window AC. Nathan Hurst might
supply a $75 2-watt diskless Norhtec PC with Linux on a 1 GB compact flash
ram with some $50 1-wire temp/RH sensors and solid state relays on a single
twisted pair to control everything, with multiple zones and setback times.

Make the house airtight, with lots of insulation. We could quantify this
with some back-of-the-envelope calcs or a TMY2 simulation. If it's 90 F
outdoors for 3 days in a row and a house with a 200 Btu/h-F conductance
uses 600 kWh/mo (2843 Btu/h) indoors, keeping it 80 F (an upper ASHRAE
comfort temp) requires 2843+(90-80)200 = 4843 Btu/h of coolth (1 window
AC.) A 750 ft^2 slab with a 1.5 Btu/h-F-ft^2 slow airfilm conductance
can provide that until it reaches 80-4383/(750x1.5) = 76 F. If the slab
starts at 60 F, it can keep the house 80 F for 22.5KBtu/F(76-60)/4843
= 74 hours.

If the slab is 60 F on an average day and T(t) = 67.6+(67.6-53.2)sin(15t)
at time t in hours, outdoor air is less than 60 F for 7.75 hours per day,
with an average temp of about 56.7. With a fan resistance of 1/2470 in
series with a 1/(750x1.5) airfilm resistance, on an average day the slab
can supply (60-56.7)x7.75/(1/2470+1/(750x1.5) = 20.1K Btu of cooling.

Nick

And I thought Nickie-Boi had died. ;-p

wrote:
Beatrice writes:

... In reference to a new house here in Eugene Or...

NREL says August is the warmest month in Eugene, with a 67.6 F daily
average and a 53.2 and 81.8 min and max and a 53.3 deep ground temp
and humidity ratio w = 0.0085 pounds of water per pound of dry air.
That's within the ASHRAE comfort zone, so a house with well-shaded
windows and minimal indoor electrical use would be comfortable on
an average day.

I would like to do something very simple?(not?fancy,?not?too?pricey)??
to try to make use of the fact that I have about 750 sq ft of basement
slab in the ground to provide cooling. ?

That's about 750ft^3x30Btu/h-F-ft^3 = 22.5K Btu/F of thermal mass,
counting some soil beneath at about R2 per foot, which could be useful
during a hot spell if it's kept cool with outdoor air on average days.
Otherwise, it will warm up quickly. The slab needs a vapor barrier
beneath to avoid adding humidity to house air.

One suggestion I have gotten is that some kind of collection of pipe
under the slab would allow me to make use od stac effect in summer --
drawing hot air out upstairs by keeping the house closed and drawing
air through the pipe to cool...

That's better done at night, when outdoor air is cooler. Warm air rises,
so in principle, a house with just one opening at the top might stay close
to the outdoor min. Two chimneys would work better, with air flowing down
one and up the other, vs conflicting flows in one chimney.

Anybody have any experience or very brass tacks practical advisce for
me on what I need to lay in the slab (soon) and how such a system
works, in terms of where the air intake and outlet need to be, etc.
???Also hoping not to create critter condos by doing this....Canb't
wait to hear yr ideas. ?Remember SIMPLE, please!

I'd forget the pipes and cool the basement slab and walls with outdoor air
at night, below the comfort zone, if it's unoccupied, with a fan (eg Lasko's
$50 2470 cfm 90 watt 2155A window fan) with a differential thermostat and
a humidistat that moves outdoor air through the basement when it is cooler
than basement air, as long as the basement air RH is under 60%, to avoid mold.

Ventilate the house at night down to a low comfort temp with another fan
with a differential thermostat and a humidistat and a low limit thermostat.
On a hot day, circulate air between the basement and the living space with
more controls. If all else fails, turn on a window AC. Nathan Hurst might
supply a $75 2-watt diskless Norhtec PC with Linux on a 1 GB compact flash
ram with some $50 1-wire temp/RH sensors and solid state relays on a single
twisted pair to control everything, with multiple zones and setback times.

Make the house airtight, with lots of insulation. We could quantify this
with some back-of-the-envelope calcs or a TMY2 simulation. If it's 90 F
outdoors for 3 days in a row and a house with a 200 Btu/h-F conductance
uses 600 kWh/mo (2843 Btu/h) indoors, keeping it 80 F (an upper ASHRAE
comfort temp) requires 2843+(90-80)200 = 4843 Btu/h of coolth (1 window
AC.) A 750 ft^2 slab with a 1.5 Btu/h-F-ft^2 slow airfilm conductance
can provide that until it reaches 80-4383/(750x1.5) = 76 F. If the slab
starts at 60 F, it can keep the house 80 F for 22.5KBtu/F(76-60)/4843
= 74 hours.

If the slab is 60 F on an average day and T(t) = 67.6+(67.6-53.2)sin(15t)
at time t in hours, outdoor air is less than 60 F for 7.75 hours per day,
with an average temp of about 56.7. With a fan resistance of 1/2470 in
series with a 1/(750x1.5) airfilm resistance, on an average day the slab
can supply (60-56.7)x7.75/(1/2470+1/(750x1.5) = 20.1K Btu of cooling.

Nick

On Jul 26, 6:13*am, wrote:
Beatrice writes:
... In reference to a new house here in Eugene Or...

NREL says August is the warmest month in Eugene, with a 67.6 F daily
average and a 53.2 and 81.8 min and max and a 53.3 deep ground temp
and humidity ratio w = 0.0085 pounds of water per pound of dry air.
That's within the ASHRAE comfort zone, so a house with well-shaded
windows and minimal indoor electrical use would be comfortable on
an average day.

I would like to do something very simple?(not?fancy,?not?too?pricey)??
to try to make use of the fact that I have about 750 sq ft of basement
slab in the ground to provide cooling. ?

That's about 750ft^3x30Btu/h-F-ft^3 = 22.5K Btu/F of thermal mass,
counting some soil beneath at about R2 per foot, which could be useful
during a hot spell if it's kept cool with outdoor air on average days.
Otherwise, it will warm up quickly. The slab needs a vapor barrier
beneath to avoid adding humidity to house air.

One suggestion I have gotten is that some kind of collection of pipe
under the slab would allow me to make use od stac effect in summer -- *
drawing hot air out upstairs by keeping the house closed and drawing
air through the pipe to cool...

That's better done at night, when outdoor air is cooler. Warm air rises,
so in principle, a house with just one opening at the top might stay close
to the outdoor min. Two chimneys would work better, with air flowing down
one and up the other, vs conflicting flows in one chimney.

Anybody have any experience or very brass tacks practical advisce for
me on what I need to lay in the slab (soon) and how such a system
works, in terms of where the air intake and outlet need to be, etc.
???Also hoping not to create critter condos by doing this....Canb't
wait to hear yr ideas. ?Remember SIMPLE, please!

I'd forget the pipes and cool the basement slab and walls with outdoor air
at night, below the comfort zone, if it's unoccupied, with a fan (eg Lasko's
$50 2470 cfm 90 watt 2155A window fan) with a differential thermostat and
a humidistat that moves outdoor air through the basement when it is cooler
than basement air, as long as the basement air RH is under 60%, to avoid mold.

Ventilate the house at night down to a low comfort temp with another fan
with a differential thermostat and a humidistat and a low limit thermostat.