[Bldg-sim] Simulation of a hollow ventilated wall

Tue Jul 13 11:02:40 PDT 2021

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 <
bldg-sim at lists.onebuilding.org> wrote:

> Mohammad,
>
> 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:
> https://bigladdersoftware.com/epx/docs/8-0/engineering-reference/page-104.html
>
> Regards,
>
> ~Bill
>
>
>
> *William Bishop, PE, BEMP, BEAP, CEM, LEED AP*
>
> *Senior Energy Engineer*
>
> [image: Pathfinder-EA-logo-2][image: Logo Description automatically
> generated]
>
> *T: (585) 698-1956*                        F: (585) 325-6005
>
> bbishop at pathfinder-ea.com <wbishop at pathfinder-ea.com>
> www.pathfinder-ea.com
>
> 134 South Fitzhugh Street
>
> Rochester, NY 14608                       *Ask me why Carbon Fee &
> Dividend may be right for you.*
>
>
>
>
>
> *From:* Mohammad Rezvanpour <moh.rzv at gmail.com>
> *Sent:* Friday, July 2, 2021 11:30 AM
> *To:* Bishop, Bill <bbishop at pathfinder-ea.com>
> *Subject:* Re: [Bldg-sim] Simulation of a hollow ventilated wall
>
>
>
> Hi Bill,
>
> Thank you for your response.
>
> Imagine a hollow wall, where air or water can travel through it. On one
> side, heated air (passive or active) go through the wall and exchange heat
> with the masonry wall and goes out from the other side. Here, it is of
> utmost importance to evaluate how the wall's thermal performance (i.e. what
> its temperature is, how much energy it can store) is likely to affect the
> home environment (e.g. how temperature fluctuation changes, how about
> thermal comfort, etc.).
> Obviously, there is more to this project than this, but this is a general
> overview of the process.
>
> I really appreciate your help in advance.
>
> Best,
> Mohammad
>
>
>
> On Fri, Jul 2, 2021 at 8:41 AM Bishop, Bill <bbishop at pathfinder-ea.com>
> wrote:
>
> Hi Mohammad,
>
> Can you share more detail about what you want to simulate?
>
> Thanks,
>
> ~Bill
>
>
>
> *William Bishop, PE, BEMP, BEAP, CEM, LEED AP*
>
> *Senior Energy Engineer*
>
> [image: Pathfinder-EA-logo-2][image: Logo Description automatically
> generated]*T: (585) 698-1956              *          F: (585) 325-6005
>
> bbishop at pathfinder-ea.com <wbishop at pathfinder-ea.com>
> www.pathfinder-ea.com
> <https://us-east-2.protection.sophos.com?d=pathfinder-ea.com&u=aHR0cDovL3d3dy5wYXRoZmluZGVyLWVhLmNvbS8=&i=NWZjNTI0OTJkYjA1OTYwZGY1NmNjOGVj&t=R0FBZGpNdEpKTEZDMVZjVlBhZW9mM3dpVnBpWkk3SzQyVVNCS1RhejhBcz0=&h=ca76026cf04742fab3b4a151a6d0fbe0>
>
> 134 South Fitzhugh Street
>
> Rochester, NY 14608                       *Ask me why Carbon Fee &
> Dividend may be right for you.*
>
>
>
> *From:* Bldg-sim <bldg-sim-bounces at lists.onebuilding.org> *On Behalf Of *Mohammad
> Rezvanpour via Bldg-sim
> *Sent:* Wednesday, June 30, 2021 6:18 PM
> *To:* bldg-sim at lists.onebuilding.org
> *Subject:* [Bldg-sim] Simulation of a hollow ventilated wall
>
>
>
> Hello everyone,
> I hope all is well with you.
>
> The goal is to simulate a *hollow ventilated wall* (Air or water could
> travel through the wall -- interior and exterior) for its *energy
> performance*, but I need to know what options I have. I can indeed use
> CFX (a tool inside the ANSYS workbench) to do such simulations, but I would
> like to know if there is a simpler, more efficient, or more recent program
> that I can use.
>
> I greatly appreciate your suggestions in advance.
>
> Best,
> Mohammad
>
>
>
> --
>
> *Kind regards,*
>
> Mohammad Rezvanpour
> PhD student of Building Science and Engineering
> *(CEE department),  *Donadeo Innovation Centre for Engineering (DICE)*, *University
> of Alberta, Edmonton, AB, Canada
>
>
>
>
>
>
> --
>
> *Kind regards,*
>
> Mohammad Rezvanpour
> PhD student of Building Science and Engineering
> *(CEE department),  *Donadeo Innovation Centre for Engineering (DICE)*, *University
> of Alberta, Edmonton, AB, Canada
>
>
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