tuchan

have you checked the other threads on the chillers, I was doing one until I ran into a few problems, for a start I couldnt get descent temps which never really got resolved. I used an esky for my liquid to cool in which once it was cold I could turn the unit off and it would stay cool for about 3 hours, and this was in the middle of summer with ambient temps of around 30 - 40C.
http://www.overclock.net/phase-chang...ject-cold.html
My thread might help you with a few ideas maybe, looks very similar to what you are doing.

Roxter

yes i've taken a look at y9our thread mutiple times. But i've already gotten the water in my bucket down to -9 in about 20 minutes and it stays at those temps for a very long time. i'm sure i can go much farther if i leave it on for longer though. and my ambeint temps will never go above 30C. Right now in canada its winter so the temps in the house are about 19C.

Kopi

Woah your house is cold lol . I don't know why I'm posting here I know nothing about these things..but Rocks my buddy and I just thought I'd check out how his project is going. I live in hamilton too, Pottruff south . Sounds like its goin good rock...keep it up.

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hvacgaspiping

The only thing that would cause frost to the compressor is liquid refrigerant returning to it instead of cool vapor. Cool vapor is what the compressor uses to cool its motor windings. If the vapor starts to get too cold it changes state to a liquid and starts to cause mechanical problems within the compressor. Liquid refrigerant should NEVER be allowed to get that far. Several common conditions cause this, all having to do with heat exchange problems. The most common one is lack of temperature control at the point of cooling process. A properly set up thermostat will take care of this. It needs to have no more than a ten degree differential between opening and closing the compressor electrical circuit. The evaporator should be matched with the capacity of the compressor, ie 1/2 ton evaporator and a 1/2 ton compressor for example. The heat load should be within 25% of the capacity of the chiller; too much heat load will make the chiller run too much and too little heat load will either short cycle the compressor or cause frostback. The only refrigerant line that needs to be insulated is the suction line. This should be done only where condensation will be a problem, which is usually the entire line from the leaving side of the evaporator all the way to the compressor. In cases of extremely cold weather if the compressor/condenser unit is outside and exposed to the weather, then the liquid line (smaller refrigerant line from the condenser to the evaporator) should also be insulated where it is exposed to extreme cold. Also, in this outside environment for the compressor/condenser you would need head pressure control. I`ll elaborate on that if this meets your criteria.

Roxter

wow man, you really know your stuff. its awesome to have you around with all of these projects. you really help people out. rep goes you my friend. so are you saying that if my evap is fully submerged in the water then frost shouldn't be a problem because its not getting cold enough and its dealing with a heat source? Also, if my lines are getting frost on them then insulating them would just stop the frost, it wouldn't make it so that the vapour couldn't turn into a liquid right?

hvacgaspiping

Hi Roxter,

The key thing here is proper heat exchange. You`re right about immersing the evaporator in the water, as the water being chilled is the best heat exchanging medium around. If the evaporator is not in the water, then there would be a very small amount of heat exchange into the air, and you would quickly get frost onto the evaporator and liquid refrigerant back into the compressor. Insulating the lines will only prevent condensation, although it will prevent frost on the unexposed line. However, heat exchange should occur in a balanced manner so that enough is exchanged into the rapidly evaporating refrigerant within the evaporator at a rate sufficient to cool the water and warm the refrigerant enough for it to change to a cool vapor when it is returned to the compressor via the suction line. The technical term for this process is "superheat", and without going into really deep physics the best way to understand what that means in practical terms is: high superheat occurs when the suction line is not cold enough to "sweat", and low superheat occurs when the returning refrigerant is getting cold enough to begin changing state back into liquid droplets and making the suction line frost. This is very important to notice and understand, as the compressor lives and/or dies by either of these extremes. Too high a superheat and the compressor motor windings will get too hot and burn out. Too low a superheat and the compressor will have mechanical problems, as in the liquid droplets will break things like reed valves, pistons and crankshafts (nothing can compress a liquid). Make sure you have a reliable thermostat to control water temperature. If you are going to just chill water and not run the temperature cold enough to need antifreeze, you will get by on your converted window air conditoner unit. If you decide that you want your temperatures colder and use glycol (antifreeze), then you need to use a low temp. unit. This would be a compressor and condenser from a freezer, as in one capable of cooling the glycol to zero F without oil or mechanical problems. This type of unit is designed for this temperature range. The converted window unit is not, although it could probably last for maybe a year. Also, if you do use glycol, never mix it more concentrated than 50%, or the heat transfer properties are quickly reduced.

Roxter

well i wont be keeping this on all the time, i've found that the water can get down to -9C in just over 20 minutes so i'll probably keep it on for about a half hour then turn it off and just leave the pump going. will this increase the lifespan of the system at all?

hvacgaspiping

Doing that would increase the life of the unit, IF you are vigilant about running it the least amount. However, you could accomplish that with a remote bulb thermostat (like one from an ice machine), and set it with a wide enough temperature differential to accomplish what you`ve suggested. I would guess you could set it to come on at about 3 degrees C and shut off at -9 degrees C. An ice machine company would sell you one. Just make sure the thermoline from the thermostat to the thermobulb is long enough to reach where you want it to go. The bulb generally is ziptied to the suction header of the evaporator (the long portion where the suction line attaches to the evaporator). But you may want to experiment with the bulb placement if this makes the compressor cycle more than you want.