How to improve AC efficiency - Fuel Economy, Hypermiling, EcoModding News and Forum

teoman · 01-22-2018, 08:32 PM

Air conditioning sucks a lot of energy, so i am thinking of ways of improving efficiency.

Some of the things that come to mind are adding reflective material to the roof. Keeping the air in internal circulation mode to not introduce any heat in to the passenger compartment and putting a water spray on to the condenser.

What I would like to do is use the AC as regenerative braking, to have it only engage when going down hills or when pressing the brake pedal. I.e. use only wasted energy to cool the car. (I used to do this by pressing the AC button on the car while decelerating which was a bit of a pain). But the cooling effect runs off pretty quickly and the clutch on the compressor needs to be reengaged.

As I have the intention of purchasing a car that needs a bit of AC work, I have the luxury of modifying the system a little bit.

What can I do to extend the cooling period? Like having to go down a long hill and being able to have AC on for a good 5-10 minutes afterwards.

If i manage to add some sort of reservoir of a couple of liters to where the refrigerant in liquid state, would that benefit me at all?

Like installing a massive receiver/dryer like in this video?

https://www.youtube.com/watch?v=NSUeRlJ2P0g

ksa8907 · 01-22-2018, 09:01 PM

I'm thinking absorption chiller using the waste heat from the exhaust or coolant. That actually sounds like an incredible idea if it would work.

oil pan 4 · 01-22-2018, 09:29 PM

Put a larger condenser on there so that fan doesn't have to run as much.

teoman · 01-23-2018, 12:03 AM

I have researched the ammonia systems. They do work and i could probably cobble something together, but to make it work would require extra work. Like switching it off. And i am not sure I want ammonia in the car.

Bigger condenser is a good idea. But is it filled with liquid refrigerant? If not it will increase efficiency but will not increase the time between compressor cycles.

Piwoslaw · 01-29-2018, 07:27 AM

Teoman, since you are going to purchase a new (to you) car anyway, look for one that is white or silver. Also you may look into coating the windows to reflect infrared to keep the greenhouse effect down.

Insulate the bottom of the car also, to reduce gain from the hot pavement.

Park in the shade when possible, schedule your driving for when the temperature is lower and the sun not as intense.

Driving down a local road, in the shade of trees, may be better than on a highway with no shade at all.

Roll down windows after getting into the car to naturally ventilate the excess heat.

A reservoir can store some "cold" for you, but it has to be "charged" first. If you have the means to cool the liquid at home, then great. Phase-change materials (like ice) would work even better.

A larger condenser will only work if you have enough air flowing over it. And to get better airflow, you are sacrificing aerodynamics, which will further increase your fuel consumption. If your airflow is good, then you may experiment with spraying (distilled) water on the condenser. There are a few threads on EM about this.

You may look into A/C run off of electricity, not off the engine, like in hybrid cars. You may need an extra battery, which you could charge at home.

Engine braking is a good idea, but won't be easy to automate. You can try to a programmable OBD device (like OBDuino) to turn on the A/C only when the engine is running but no fuel is being used. (This idea came up in a discussion about automatically charging the battery in an alternator delete scenario.) Do take into account that the A/C compressor prefers long on and off durations, so quickly cycling it on and off will shorten its life.

When you do use A/C, make sure that your ventilation system is in recirculating mode (to not be constantly warming the outside air) and the fan in on HI (to increase the efficiency of the heat exchange).

teoman · 01-29-2018, 07:55 AM

Thinking of all hose things, thanks.

I do have an alternator disabler in min. Was thinking of doing the same with the ac.

Unfortunately the camry is black

that is the only one that has a reasonnable price.

Ecky · 01-29-2018, 07:58 AM

I put pipe insulation over the cold lines of my A/C.

I'm not sure if it could be easily retrofitted, but Toyota has an ejector system in the Prius A/C, which improves efficiency:

2010 Prius first with ejector-cycle air conditioning - SAE International

I also seem to remember something about combined A/C hoses, but my searches are drawing a blank.

cRiPpLe_rOoStEr · 01-29-2018, 06:24 PM

Quote:

Originally Posted by ksa8907

I'm thinking absorption chiller using the waste heat from the exhaust or coolant. That actually sounds like an incredible idea if it would work.

Not only it may effectively work, it's often reported to be quieter than mechanical refrigeration. It's been often used in hospitals and hotel rooms until some years ago due to this advantage, even though when it relied on electric power to heat the ammonia it was less energy-efficient. However, for automotive applications where it can get the heat sourced from the cooling or the exhaust, it may be worth.