Simulation of a hollow ventilated wall

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Hello Mohammad,

My work of modelling dynamic insulation (air permeable walls) may be of
interest. I used mass flow network (zonal method) linked dynamic thermal
simulation approach available within ESP-r to approximate the physics.

MSc dissertation:

Research paper:



*Aizaz Samuel, PhD, LEED AP BD+C, CPHD*

Building Performance Specialist

Pratus Group Inc.

(t) 416.947.6919

(e) aizaz.samuel at

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A schematic or drawing of your wall would be helpful. It sounds like you?re researching solar thermal storage. One implementation is known as a ?Trombe Wall?. You may find this information of Trombe Wall simulation in EnergyPlus helpful:

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer
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This is probably slightly tangential to the original post, Mohammad, but
after being frustrated with my inability to model it, I built one at
scale, and measured it.

I used relatively fast moving air as insulation, for a cold storage box
that served as a collector for a heated soil greenhouse, heated by an air
source heat pump made from a window mount AC unit. Cold storage box was
built in a standard non insulated 20' truck body and its outer surfaces
absorbed heat from the air and sunlight outside and transferred it to the
evaporator on a 24000 BTU/hr heat pump that was plumbed to heat water that
was used to heat the soil below the planting beds in an attached 3,000 sf
commercial greenhouse,using a shell and tube heat exchanger. Evaporator
chilled and dessicated the air that returned to the cold storage box.
Measured energy reduction was approximately 75% depending on outside air
temp and other factors.

Temp targets were controlled from both soil and cold box via PID
controllers. Duty cycle for the compressor was typically below 30%. The
cold storage box walls are shown in the attached schematic and used 6" foam
studs and 3/4" foam walls (one side covered with reflective mylar to seal
the surfaces against colonization by mold). The duct was 6" deep and 24"
wide. The foam panels were glued to the studs to create a continuous folded
duct. Warmest air was collected near the ceiling by a wall mounted fan and
pushed through the duct and collected on the far side of the evaporator by
a second fan and returned to the cold box through a ceiling mounted plenum.
Pressure differential between the two sides of the evaporator indicated
icing on the fins on the evaporator coil and triggered the defrost cycle.

This approach achieved a dramatic reduction in heat gain inside the cold
box, and on a 90F day, the measured temperature of the moving air inside
the wall gained less than 10F from one end to the other. The system is
fairly well documented online.
[image: plenum.png]

On Fri, Jul 2, 2021 at 9:04 AM Bishop, Bill via Bldg-sim <

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