Hairbrained automotive scheme

[al3z]

Hi all,

Have had one of those niggling ideas for some time. Not quite sure why I want to go through the complication of doing this but I do... consider it equivalent to AC cooling your CPU I guess.

Anyway. In short: is it feasible/do-able to replace a vehicle's refrigerant-air condenser with a coaxial or plate refrigerant-water heat exchanger in the engine bay, with the water consisting of a cold water loop with it's own dedicated radiator.

Full story is I have a turbocharged car, which I want to do a couple of mods to. Two popular mods are an oversized air/air front mount intercooler (cools the intake air that's been compressed by the turbo), and an engine oil to air cooler mounted at the front of the car.

I'm considering rather than going this route going the rarely taken, considerably more complicated and heavier air->water intercooler route. There's only a couple of advantages for this for a front engined car, namely turbo lag (shorter intake tract) and more stable temperatures, both appealing to me. If I'm going this route I can run the OEM thermostat controlled oil->water off the cold water loop rather than hot water loop, doing away with the oil-air heat exchanger. Now I'm wondering if I can do the same for the aircon.

This'd require me to oversize the cold water radiator quite a bit, but I'd benefit from the extra size when the air con is switched off in performance.

But... is it doable? And where (if anywhere) can I buy off-the-shelf condensers to suit (preferably 5kg or less)?

From extensive but somewhat unsuccessful googling, I've determined the car's air con capacity to likely be somewhere around 15k-20k BTUs/hr (4.4kW - 5.8kW), and it's R134A. I realise there's I've provided no mass flow numbers or temperature differential figures in there (along with probably a host of other maybe essential figures) - and so maybe it's impossible (or very unwise) to attempt to design a condenser with such little knowledge.. but just in case, this seemed to be the place to ask for assistance (or deterrence, if required).

TLDR; where can I buy a smallish 15000BTU/hr R134A-water condenser unit, either coaxial or plate, preferably light - to suit a car AC application... and/or would it be very unwise to attempt to do this?

[cool runings]

.

In short yes you could do it.....

But would it work or be efficient?

Your heat exchanger would need to be sized correctly and then you would need
the water cooler / readiator to be sized correctly.

I can't see any possible advantage. You are just adding weight, pumps and pipes,
all weak points and all will take up space.

But in short it could be done and like a lot of things you will never know unless you try.

all the best

coolrunnings

.

[al3z]

I can't see any possible advantage. You are just adding weight, pumps and pipes,
all weak points and all will take up space.
All these things would already be there for a air-water intercooler, but it is a valid point to take this as reason to go the more common air-air intercooler route (although despite this there are a large number of OEM and aftermarket vehicles using air-water intercoolers).

I'm kind of thinking.. if I am choosing to go the air->water intercooler route, is this such a daft idea? Any required oversizing of the water radiator would only be a plus. But that said I might take your comments on board and go the more tried and tested aftermarket air-air front mount intercooler route... it does have weight savings, just at the cost of turbo lag (something I'm trying to avoid wherever possible).

[cool runings]

All these things would already be there for a air-water intercooler, but it is a valid point to take this as reason to go the more common air-air intercooler route (although despite this there are a large number of OEM and aftermarket vehicles using air-water intercoolers).



I'm not too familiar with the engin setup and cooling system, so I'm not too sure how you would use
an engine cooling system (air-water intercooler) and its pump to circulate cooling water for the AC condenser.







I'm kind of thinking.. if I am choosing to go the air->water intercooler route, is this such a daft idea? Any required oversizing of the water radiator would only be a plus. But that said I might take your comments on board and go the more tried and tested aftermarket air-air front mount intercooler route... it does have weight savings, just at the cost of turbo lag (something I'm trying to avoid wherever possible).


It is not a daft idea and it could work if done correctly. But you need to understand that the condenser side of an
AC system is sized correctly and should not be over sized. If it cools the refrigerant too much it can have adverse effects on the system. The high side of an AC system is high for many reasons and one is because the pressure
differance between the high side and the low side are important.

All the best

coolrunnings

.

[al3z]

I'm not too familiar with the engin setup and cooling system, so I'm not too sure how you would use
an engine cooling system (air-water intercooler) and its pump to circulate cooling water for the AC condenser.

With an air-water intercooler you have a cold water loop with an electric pump, it's simply a matter of connecting it up such that the water flows radiator -> intercooler -> condenser, or radiator -> condenser -> intercooler, or for a two pass radiator - radiator -> intercooler -> radiator -> condenser. As off-boost temperatures are not particularly high the first is probably fine (if you were to track the vehicle you wouldn't have your air con on in anyway, leaving you with a nicely oversized radiator entirely dedicated to cooling the charge air).


But you need to understand that the condenser side of an
AC system is sized correctly and should not be over sized.

I have to say I find this surprising. It is something that had crossed my mind - but I'd ruled it out as I reasoned that the standard air cooled condenser would vary in performance from drastically undersized (vehicle stationary) to drastically oversized (100mph on the autobahn).. so I figured (perhaps incorrectly) that as long as I got the liquid cooled condenser "about right" in sizing, it'd work. How do the manufacturers account for that?

[cool runings]

.
The cond is sized to allow air over at a set speed. If the sppeed falls the
backup fan will kick in and push the air.


Now then...... I'm not a 100% sure on the car AC but with normal fridge and AC systems the
Valve (Expansion valve) needs a minimum pressure differance over it to work correctly.

If car AC is the same and it needs a minimum pressure differance to work the valve
(the differance over the vavle is about 7 bar in normal Fridge)

If car AC is the same if you oversize the cond the discharge pressure will drop too low
to operate the valve correctly and that is why I said be careful of the size of the cond.

If car AC does not have the same requirement for a highish pressure diff over the valve
then you could (in theory) fit any size cooler (within reason)..

All the best

coolrunnings

.

[paul_h]

The air - water intercooler is an old idea. I remember DIY designs from the 80s, even incorporating water spray jets, or even methanol to help cool it down.
No one has used the a/c to cool it because the small gains achieved with slightly cooler intake is surpassed by the a/c power sapped and the a/c condenser in front of your radiator increasing engine temp and bay temp.

Bottom line, air to air became for popular because you could make them soo much bigger, no water or refrig plumbing or moving parts required, no power losses except for a bit of lag.
water - air, average size A4 sheet of paper size of heat exchanger, in a box somewhere in the engine bay. air - air, can be as big as your radiator