Fan for tube 5" in diameter and 160ft long

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Discussion Overview

The discussion revolves around the feasibility and specifications of a ventilation system for a 5" diameter, 160ft long tube intended for use as earth tubing to regulate temperature in a greenhouse. Participants explore airflow requirements, fan specifications, and the impact of duct design on performance.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires whether a 5" vent can effectively push or extract air from the tube and requests information on the required CFM.
  • Another participant emphasizes the importance of understanding external static pressure and airflow as determined by the fan's specifications and the duct's internal resistance.
  • A vendor suggests a specific model of vent, "VENT-315NK," but expresses uncertainty about the adequacy of other models for the long pipe.
  • Participants discuss the need to clarify the purpose of the vent to accurately size the fan and determine airflow requirements.
  • One participant mentions that the tubing system is designed for cooling and heating a greenhouse, which is buried 10ft underground, and describes the dimensions of the greenhouse.
  • Another participant calculates that for an airspeed of 2m/s, the expected airflow would be approximately 90 cubic meters per hour, with a pressure drop of about 30 Pa.
  • Concerns are raised about the resistance to airflow in a long duct with turns compared to a straight duct, highlighting the need for a rough layout of the duct system.
  • Participants discuss the optimal airspeed and temperature maintenance goals for the greenhouse, noting the local climate conditions.

Areas of Agreement / Disagreement

Participants express various viewpoints on the specifications and requirements for the ventilation system, with no consensus reached on the best approach or the adequacy of the proposed fan model. The discussion remains unresolved regarding the exact airflow needs and the effectiveness of the suggested solutions.

Contextual Notes

Participants mention the lack of familiarity with earth tubing in the local context, which may affect the availability of expert advice and resources. There are also references to specific calculations and assumptions about airflow and pressure drop that may need further validation.

druidhr
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Hello,

I have question about vent for tube that is 5" in diameter and 160ft long.

Could 5" vent push/extract air to/from tube above?
If possible, how much CFM should vent have?

Thx 😊
 
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Welcome, @druidhr !

What the manufacturer of your fan says about external static pressure versus airflow?

The cfm will be the result of the internal resistance of that duct and what your fan is able to do.
 
Lnewqban said:
Welcome, @druidhr !

What the manufacturer of your fan says about external static pressure versus airflow?

The cfm will be the result of the internal resistance of that duct and what your fan is able to do.

Hello Lnewqban,

Is it ok if I post PDF about vents specs? (vents specs.pdf)
These are the best I can buy here that are reasonable priced.

Vendor suggested to go for model "VENT-315NK", for others he is not sure that they'll have enough power to build pressure in so long pipe.
 

Attachments

druidhr said:
I have question about vent for tube that is 5" in diameter and 160ft long.

Could 5" vent push/extract air to/from tube above?
If possible, how much CFM should vent have?

...Vendor suggested...
Vent for what? Vendor of what? We need to know the purpose to find the airflow and then the airflow to size the fan.
 
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druidhr said:
Hello Lnewqban,

Is it ok if I post PDF about vents specs? (vents specs.pdf)
These are the best I can buy here that are reasonable priced.

Vendor suggested to go for model "VENT-315NK", for others he is not sure that they'll have enough power to build pressure in so long pipe.
Yes, it is OK.
Go to page 498 and note that the recommended model is the only one able to discharge at higher static pressure.
Could that vendor calculate the pressure drop curve of that duct for you, and match it to the fan?
That would tell you how many CFM to expect to be moved by it.
 
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russ_watters said:
Vent for what? Vendor of what? We need to know the purpose to find the airflow and then the airflow to size the fan.
It is for earth tubing, that should cool/heat my greenhouse. Pipe is 10ft bellow ground and I need to buy appropriate vent that can run air through that pipe. Pipe is double wall corrugated HDPE pipe with smooth inner surface.

Vendor of vents "S&P", they sell professional vents.

I'm sorry,
 
druidhr said:
It is for earth tubing, that should cool/heat my greenhouse.
Has the tubing system been designed? The airflow specified based on greenhouse size and desired temperature?

Vendor of vents "S&P", they sell professional vents.

If you didn't give them airflow and static pressure required, how did they select the fan?
 
Lnewqban said:
Could that vendor calculate the pressure drop curve of that duct for you, and match it to the fan?
I'm not sure, I will ask, but I'm not to optimistic. Last time I did explain him what is the purpose of vent and he specifically recommended that model.
 
russ_watters said:
Has the tubing system been designed?
Yes, but as earth tubing here in Croatia is not popular (better said, nobody knows about it. So, I read few works from the internet.
As, I mentioned already above, tube is 5" in diameter and 160ft long and is burried 10ft below ground. Greenhouse is 260ft² and is 6ft high.
russ_watters said:
The airflow specified based on greenhouse size and desired temperature?
Based on some work I read on internet, ideal speed of air should be 2m/s.
There's no need for some super heating and cooling. Basically what I want is to keep greenhouse from freezing over winter. As for the cooling in the summer, I don't believe it is achievable as summers here in Croatia (Europe) can be very hot (over 104F for weeks).
russ_watters said:
If you didn't give them airflow and static pressure required, how did they select the fan?
I explained him what will be the purpose of vent and what are the requirements.
 
  • #10
Assuming your tube (50m, 5" I.D., smooth):
for 2m/s, you'll get approx 90 cubic meters/Hr. The pressure drop will be approx 30 Pa. you should be able to evaluate your fan with that info (if you can get a fan curve).
 
  • #11
druidhr said:
I'm not sure, I will ask, but I'm not to optimistic. Last time I did explain him what is the purpose of vent and he specifically recommended that model.
Then, we may be able to help you here. :cool:

For that, we will need a rough layout of your duct, because the resistance to the airflow of a 160 ft long duct with several turns is greater than of a straight duct of same length.

Have you estimated how much airflow your system will require in order to achieve the effect you need?
 
  • #12
Lnewqban said:
For that, we will need a rough layout of your duct, because the resistance to the airflow of a 160 ft long duct with several turns is greater than of a straight duct of same length.
It's a 160ft long pipe burried 10ft below ground, the trench was 10ft wide and 16ft long. Pipe was put as snake in that trench in two levels (see image below), on image is second level, first level is same as second. There are no 90 or smaller degree turns, I did try to make turns as wider as it can be

IMG_20241111_111707.jpg


Lnewqban said:
Have you estimated how much airflow your system will require in order to achieve the effect you need?
No, only I have read that air speed is optimal at 2m/s. This is small greenhouse 260ft² and is 6ft high, if I could achieve to keep temperature above 5C degrees I would be happy. Here in Croatia we don't have harsh winters. Extreme temperature lik -5C to -10C but only for day or two, and not whole day only in the morning when it's coldest. Average winter temperature is around 0-5C degrees.
 
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