Shields, and Air Conditioning changes.

[BetaSpectre]

I see no reason why Energy Shields can't be small enough to allow a gun barrel to be outside the shield radius. More so for rifles.

In fact due to needing to be next to a person to knife them (shoot) when they're inside of the shield radius that means all melee is unprotected as that other dude will be inside of the shield radius.

Rendering Energy Shields useful for closing to melee distance against guns, but worthless in every other scenario.
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Also change Air conditioners to not release hot air. We should have tubes that can bring coolant, or direct heat out without having to make entire halls just to direct AC heat.

[Keychan]

The whole point of the energy shield being implemented into the game was to allow melee fighters have a chance against ranged weapons.  That's the only scenario it should be used, to close distance between a gunman and a swordsman.  With the downside of not having an armor vest, your whole body is protected for a short period and giving gunmen, who already have the safety of cover and range, a rechargeable shield would be too good.  Just take cover once your shield breaks, recharge, fight again with no fear of bullets, repeat.  Even though both could still melee each other, a sword or club is much more effect than your fists.  The energy shield wasn't brought in for everyone to use, it was exclusively for melee fighters.  Also, the barrel sticking out of the shield most likely would still have the shield generated in the open space inside the barrel, preventing bullets from ever leaving it.

[Kegereneku]

As said above, gameplay matter before logic.
Surely, more technobabble could be used to "explain" or rather rules out undesired effect but we are always going to find a problem with any of them.

For instance, seeing it as a "magnetic" field that, away from the emitter react to high-velocity object, it would be stopping the bullet traveling along the barrel.
The only bypass would be to carry the entire weapon outside the shield, asking for robotic extending arm, but then we should fear Mechanoid getting such field.
(note : as a late game technology I'm sure some players wouldn't mind shield-for-ranged-weapon)

As for the cooler, personally I like that limitation.
Your suggestion for coolant line can be suggested aside for a potential upgrade.

[Covered in Weasels]

Mechanical engineer here. Air conditioners work by sucking heat out of one area and transferring it to another, meaning that AC units need a "hot" and "cold" end to function. When vents are implemented in the game, they could be used to transfer heat from a cooler's exhaust to the outside world without leaving a wide-open corridor.