That picture of 2x2.5 tonne AC units got me thinking about the practicality of tunnels. They would likely be deep underground, so earth temperature. It's a remote island so supplies are slim. I made some assumptions on the tunnels and used a bit of an HVAC course I slept through around 5 years ago to do some calculations based on how I'd design the system following some HVAC industry rules of thumb.
Firstly, you don't cool a tunnel for the sake of making it cold, you do it for humidity control. Since it's a tropical island, the relative humidity and temperature are relatively high. You need fresh air in your tunnels to be able to intake oxygen and expel pollutants like smells and CO2 and exhaled moisture. The biggest problem comes from the moisture in the air as it cools in the tunnels. A whole bunch of water would condense out as the temperature drops leaving you with a moisture problem. As you breath out, you introduce more moisture to the air (more problem). This becomes a massive problem for things like paper, building materials, and preserving soiled children's' underwear.
My assumptions:
1.Tunnel is not insulated- too much materials needed
2.Tunnel is not heated- This would be done with solar tubes most likely but I didn't see any
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The underground temperature would be around 57 degrees F if far enough underground
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A walkable tunnel would be 7 feet tall and 3 feet wide
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You would want the relative humidity to be around 30%
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You need 3 volume changes of air per hour to keep air fresh
I started with these numbers and didn't change anything after the calculations so that I could conclude if this was feasible.With that in mind, I thought out how the system would be designed. Firstly the air would travel through an opening (POINT 1) to the underground tunnel area (POINT 2) that would be used to cool the air to the 57 F so you don't need to expend the energy. The heat goes into the ground, water drains away. At this point you'd be at 57F and 100%RH.
This is where you use the AC units to cool the air further so that the proper amount of water drops out (POINT 3) so that when the air warms back up from pulling heat from the ground in another section of tunnel, it will be at 57F and 30%RH (POINT 4).
I have illustrated this in my diagram. Excuse my poor handwriting, I am just starting to recover from Lyme, Babesisosis, and Bartonella and my hand tremors are Parkinsons level. My brain is also at an alzhiemer level but I checked all my maths.
I plotted these points on an air psychometric chart and found the required temperature drop associated with the AC temperature drop. Using Point 4, the wet bulb temperature is followed up to the 100%RH line which is 43F. The enthalpy's are along those same lines so h_3=h_4= 16.7 Btu/lb. h2=24.6 Btu/lb.
1 tonne AC=12,000 Btu/hr so the visible 5 tonnes=60,000 Btu/hr total capacity
From thermodynamics applied to this problem:
Q_dot=60,000 Btu/hr= (mass flow rate)*(h_2-h_4)
so mass flow rate m_dot=Q_dot/(h_2-h_4)=7,600 lb/hr
Looking back at the psych chart at the density of air at point 4:
13.2 ft^3/lb air
Total air capacity of the system is 7600 lb/hr*13.2 ft^3/lb= 100,320ft^3/hr
Using the rule of 3 air changes an hour gives us
Volume=(100,320 ft^3/hr)/3(changes/hr)=33,430 ft^3
and Volume= LWH
Length=(33,430ft^3)/(7ft)/(3ft)= 1592ft ==1600ft
I plotted on goog maps where I think those AC units are to the main houses on the island and BOOM, roughly 1600 feet.
Tunnel= 7ft tall, 3 ft wide, 1600 ft long plausible
What I am not taking into account are the rooms that would be built in the tunnels. I do not know if there are other AC units on the island because I don't have enough intel. What is proven however is that tunnels under the island are realistically possible. The volume of the tunnels grow with each additional AC unit. Additionally, the airflow from the tunnels can be routed into the structures to cool them in a synergistic way.
Autist, engineerfag, and lymefag out
China,coal, cars in the notables is me as well.