Underground ventilation for -25°C Freezer room

[edisonconsult]

We are designing a freezer room located on ground gloor ( 63 Mtr x 15 Mtr x 9Mtr high). Due to the huge size we intend to use underground ventilation to prevent freezing. Can anyone guide on underground ventilation?

[chillin out]

I would not have thought that 'underground ventilation' would work.
Is your idea to have vents running under the freezer room with air blowing through them to stop the floor going too cold?
Do you not think that the ducts would ice up within 1 day?

I think a heater mat would be better.

Chillin

[Andy]

We are designing a freezer room located on ground gloor ( 63 Mtr x 15 Mtr x 9Mtr high). Due to the huge size we intend to use underground ventilation to prevent freezing. Can anyone guide on underground ventilation?

Hi edisonconsult

normally we would use 3/4 inch water pip buried in the sub floor with waste heat from the compressor discharge used to heat a glycol/water mix, pumped around the pipes.

For your method you would need to elevate the sub floor level to above the finished ground level outside, then bury 6 inch concrete pipes every foot or so in the sub floor, running accross the short length.

This will work, provided the local ambient does not go below freezing for more than a few days at a time. ie it would work in the uk.

Kind Regards Andy

[US Iceman]

Several of the freezers I have seen using underfloor ventilation use 6" PVC pipe. The exterior pipes usually rise up about 2 feet or so above their horizontal position and have reverse traps on them to prevent water entrance from rain.

Another method is to recover warm air and blow it through the pipes, although this is more compicated than the natural ventialtion system.

[nh3wizard]

We have one freezer in Florida that we are blowing the outside ambient air through 24 6inch pvc 200 feet long, an engineer told us the cfm's that we needed, sized the airhandler for the required cfm's and installed, or glycol through a heat exchanger works well to.

[Dan]

Watch out for water condensation in the ventilation piping. They should drain outside or to a low spot inside and fitted with a sump pump or other method of getting rid of the water.

[gwapa]

Hello Edisonconsult

According with some paper you should estimated betwenn 2-3btu/ft2 h the heat entering to the cold room througt floor .

The air pipe should be PVC reinforced.
They should be installed between 1.2 to 1.6 m wide
The pipe should be 4" ,6" or 8" diameter acording the lenght
It will be better located the pipe in the shorter distance
the pipes should be pitch 0,5 to 1% down
Each pipe should be independient .The inlet should be protect agains rain water and animals getting in.
The outlets should drain freely and protect it against animals

If the arquitecture of the building does not alow you to use independ pipes and you should use a forced air fan than you should follow this tips.
The pipes should be installed via a manifolds.The inlets and outlets
The pipes should be pich to just one spot
The lower spot should have a drain with a siphon to keep a water seal
All the outlet air could be used to refresh any room like room machinery (as make up air)

Finelly if you make some calculation of the amount of air you require to keep worm the floor you can verify the mass of air is very small due the moister latent heat. So you should select the fan just to garantee a good velocity of air throught the each pipe.
I hope this can be helfull for you
Best regards

[georgedvf]

Hello guys, sorry to re-open such an old post, but I'm looking for info about the design of forced air system. Do you have info or references on how to calculate de CFM's and pressure drop required?