There is no Yes or No to this question.
Chlorine & Copper
You will have to keep your chlorine and acidity levels in constant harmony, otherwise the acidity will corrode and pit your copper tubing. Using aluminum would be exponentially worse. It the cooler your pool water gets, the worse effects it would also have on the copper. You can find good information from the EPA.
BTU's
A BTU is a British Thermal Unit. It takes one BTU to increase the temperature of one pound of water by one degree Farenheit. The average swimming pool is 20' x 30' x 5'. That would mean that the average swimming pool is about 22,500 gallons of water. Since one gallon of water weighs 8.34 lbs., the water in an average sized pool would weigh 187,650.
That means it would take 187,650 BTU's to increase that pool temperature by one degree. Since you would only have about 10% of that amount of BTU's required - it is very likely that the pool would simply absorb and disperse the heat transferred from your residence and never actually raise the temperature of the pool. Gullberg & Jansson has some great information on their website about heating pools.
Refrigerant and Line Set
In general it would take about 0.6 oz of refrigerant for each foot of copper tubing above 15'. Different manufacturers have different specifications of course. Considering it is a window unit, it would already have less refrigerant than say, a mini split unit.
The average 1.5 ton, or 18,000 BTU, mini split unit take about 3-4 lbs. of refrigerant and usually have about 15' of line set available 'in the box.' Depending on how long your copper tubing would be, you could be seeing so much heat loss just within the copper tubing itself, it would never "make it" to the pool. Plus, all of the possible extra refrigerant would be so hard on a compressor that small, compressor failure would always be right around the corner. Some good information can be found at ACHR News.
Legal Activity
In order to 'work' with Refrigerant, in fact, even buy (most) of it, you have to be EPA Section 608 Certified. There are 4 types of certification. There is Type I, Type II, Type III, and Universal. There is also EPA Section 609, but that is for motor vehicles. Without certification, you run the risk of EPA prosecution. And before you think that you will never get caught, there is a reward for turning people in. Information can be found at the EPA website.
Tools You Need
- Recovery Machine
- Recovery Tank
- Vacuum Pump
- Manifold Gauges
- Low-Loss Fittings
- MAPP or Oxy/Acetylene Torch Kit
- Pipe Cutter
- Pipe Reamer
- Sand Paper/Emery Cloth
- Silver or Silver Phosphate Brazing Rods
- General Mechanics Tools
- Possible a Bucket of Ice and/or Bucket of Warm Water
- Various Other Tools Depending on the Task at Hand
As you can see, there is a lot of specific tools and machines that you need to perform the job, not only legally, but safely. They are also very expensive to the average person. It is not uncommon for a vacuum pump to cost between $150 - $500. You can double and triple that cost for a Recovery Machine. There is a reason that most technicians work for a company that provides all of the tools required. It is hard to start off in the industry self-employed when you require certifications and tools that all cost money.
Conclusion
I would find a local HVAC/R Technician and run the idea across him. Ask him to come out and see what the job would entail. Ask him for advice. Ask him for a material cost and/or a list of what it would take to get the job done. Remember, this is only estimate stuff - because he may just tell you it isn't worth it, isn't possible with the equipment provided, or would be much more hassle than the intended benefit.
You could hire me to do it! But that would cost you a plane ticket, a case of beer, and a good home cooked meal before I even consider it.
About Myself
I am a...
- Section 608 Universal HVAC Technician
- Section 609 MVAC Technician
- Certified Commercial Mold Inspector
- Certified Indoor Air Quality Technician
- Certified Green HVAC/R Technician
- CO2 Refrigerant Safe Handling Certified
- R-410A Refrigerant Safe Handling Certified
- Certified Home Inspector
- Member of American Society of Heating, Refrigeration and Air
Conditioning Engineers
- Associate of Institute of Refrigeration
- Member of International Association of Certified Home Inspectors
- Member of International Association of Certified Indoor Air
Consultants
There are three issues here, which system is better, which system is more energy-efficient and which system is more reliable.
The first issue encompasses all aspects and involves a priority ranking which only you can do.
An issue not brought up by anyone else is the installation. Do you have room for 3 outside units? Does it matter if more space is used or would you prefer to use that space for landscaping or something else?
What about electrical power? Will the installer need to run 3 circuits, one for each compressor? Does your existing breaker panel have the room for 3 circuits?
Another installation consideration: which system is easier to run the linesets (tubes which carry the liquid and gas freon) for?
I expect 3 compressors to cost more than one big compressor. Have you gotten any price quotes?
The one big compressor, assuming it is capable of variable speed, will certainly be more significantly more efficient under anything less than full load because the condenser of a single outdoor unit system has three times the cooling area of a single condenser in a 3 unit system which means the compressor motor doesn't have to work as hard.
The major factor in power consumption is turning the freon back into a liquid and that depends on how fast/easily the condenser can cool it off. All else being equal, a bigger condenser is better (removes the heat faster).
The faster you condense the freon, the less back pressure on the compressor and the less work for the motor.
Most of the time you will not be running full load or all indoor units at once. Even during full load, the big unit will never be less efficient.
The last question is reliability and available. One answer correctly claims that a 3 unit system will be more available but neglects to mention that it will also be more prone to failure because you have more units to fail and each unit is more likely to be run at full capacity while the big unit will usually be running well below its full capacity. Imagine the lifetime of two cars, one run at 90 MPH and one run at 30 MPH.
Best Answer
The heat pump can move heat indoors to outdoors ("air condition") as well as from outdoors to indoors (heating). The cooling only unit can only air condition.
If the house already has heating or you rarely need heat, you can save some money by getting a cooling-only unit, and maybe supplement that with portable electric heaters as needed.
As to brand comparisons, I strongly recommend you review the Consumer Reports reader reliability report of air conditioners and heatpumps: that can be done online by paying a fee, or visiting a library.
As for some installers carefully measuring and the others not, the latter could be fine if your dwelling is not especially unique: an experienced installer has run the numbers so many times that they know what the result is. That experience is helped by there being a coarse choice of capacities: 2 ton, 2.5, 3, 3.5, 4, 5, 6, 7.5, 10, 12.5, etc.
On the other hand, not measuring could be a sign of an unknowledgeable installer. Do they also propose a 3.5 ton unit?
As far as questions to ask, I like to elicit being assured that if anything goes wrong for X years, they will fix it for free. If they can say so confidently, that is a very good sign that they don't think anything will go wrong.
It might be useful to ask an installer why they choose 3.5 tons and not 3 or 4. There is a certain degree of assumption about worst case and average case conditions. If the a/c can't quite keep up on the 5 hottest days that is one thing, but if it can't keep up on 30 of them, that is quite a different matter. Likewise, an oversized system can chill the air so much that it doesn't have to run much, making the air stagnant and possibly muggy. Questions asking about how they balance those factors are good for you to understand and for the installer to reflect upon.