HVAC guys - refrigerant->water (instead of refrigerant->air) systems?

Both my wife and Tammy are uncomfortably hot at night; the AC in the house we bought aren't working well. Of the five units on the house, only two are in good health. One straight-up doesn't run at all.

I've got a quote on replacing the failing systems and it's about 6/8/12k per, for the budget/recommended/fancy-shmancy spread. Bit higher than I expected but at the same time I knew it wouldn't be cheap, and I don't get the sense that this quote is ripping me off.

Because I'm a nerd, however, I started wondering - my property is on a lake and has virtually unlimited water usage rights (as long as the water doesn't leave my property - aka irrigation or otherwise returns clean to the lake). Since an A/C unit is effectively a refrigerant-air heat exchanger, and air is in general a terrible heat conductor... How much more efficient would it be to use water as the heat sink?

Then the more I thought about this the more I realized I was basically trying to reinvent geothermal systems.

How much more efficient are geo systems than traditional AC/heat pumps? What are the cost similarities and differences? Is there actually that much of an efficiency boost? If geo installations are more expensive, when should I expect the break-even point to be? (I assume they are more expensive.. but also I wouldn't need a big cooling field dug, as the lake would serve that purpose.. so maybe not?)

 

Sounds like snakes in the system





























Come on you knew someone had to be the first

 

Surprised it took this long

 

Powerplants have been using river water for the last century, if you engineer the system right I'm sure it could work.

The deal killer will be when you sell it and some code guys screw you around. Or try doing a water damage insurance claim in 5 years cause you were gone on vacation.

 

There is lots of info...some not so helpful....on using a body of water with a heat pump. Thats basically what your asking. Its probably comparable to a normal AC install...the heat pump is cheaper but the piping loops in the water up the price. But the operating costs should be much lower as you are running some low amp pumps vs a compressor.

 

I used to have an open loop geothermal system that used well water to cool the condenser. When the unit failed we replaced it with a traditional split system and my summer power bills are lower now. For me the bigger advantage was in winter. On cold days the current heat pump doesn't work and it needs to use resistive heat which uses a lot of power. The old water source system didn't even have resistive heat since the ground water is a constant 70ish degrees. I also had an additional heat exchanger that was connected to the hot water heater so the AC would heat the water. I could also run pool water through the system and heat the pool but it lost efficiency when the pool actually got warm enough to swim. If I was further north it might make sense to use the geothermal system but where I am cooling is far more important than heating.

 

Interesting experience. Where are you located? I'm particularly surprised that the traditional split (and assuming refer->air heat exchanger) system results in lower power bills.

 

I'm in Orlando. I did replace it with a fancy high seer multi-stage system so that might have something to do with it. Also the well pump draws a lot of amps so the extra runtime on it would have hurt the power bill. I used to need to replace the start relay and cap for the well pump quite often but it hasn't been done for three + years since we changed out the AC.

 

I had a water to air system in an old house on the beach. Not more efficient, never got the house cool enough and when something fails, you might have a flood.

I'd be surprised if you were even allowed to replace the system with another water to air. I'm sure you can repair it.

 

couple questions, not relevant to answering yours:
1: you mentioned 5 systems. im assuming you have a bunch of wall mounted mini splits?
2: if some of these mini splits arent working, whats the diagnosis? "replace" them sounds great but what do the quotes say is wrong with the existing units?
3: how old are these systems?
4: geothermal heat pumps exist, but the initial install cost is typically much higher than a standard split. not sure your temp range from winter to summer, how cold does it get and how hot does it get in Austin (i know i can google but... i dont want to. )

 

I'm also a nerd, so I tend to get all excited about unorthodox solutions, but eventually I come around to not reinventing the wheel. Geothermal is pretty cool, but DC inverter compressors have dramatically increased the efficiency of air-source heat pumps to a point where the juice is only worth the squeeze in certain applications.

You're talking about an open-loop, or "pump and dump" system. It's the most efficient way to do geothermal because it's impossible to saturate your thermal mass. The downside is dealing with contamination. Your condenser gets pretty warm, and that means it will collect sediment (something about solvates or hydrates or some shit I'm too dumb to understand) and will require some maintenance. The other consideration is the electrical consumption of the circulators you'll need to move the heat (water) through your system. Water is harder to move than air, so although it will absorb heat more efficiently, you need more power to move it. There are variable speed DC circulators that use less energy, but they're stupid money and not yet that reliable in my experience.

There's often a code issue with open loop systems as well. Whether or not that makes sense for the specific application is usually not discussed.

 

Couldn't he do a closed loop system and just put the coils in the pond? I know I have seen that and its what people say is the easiest and cheapest way to do geothermal. No major cost in excavating or drilling a deep as well to get your thermal mass. They literally just throw a few hundred feet of coils in the water and bury the intake and out take form the pond back to the house. Ta da...done. Hook up the heat pump lines and start your system.

 

when i've looked up geothermal, there was definitely the option to run it through a pond vs through the earth

 

All the info here is really good. It will come down to your average winter temp, efficiency payback during that time compared to the extra cost of installing the system. In my area , central MD they are few and far between. The only ones I know of are a few we have installed and a friend that’s also in the HVAC business that did his own because he had 2 extra wells. In most cases around here it’s not for the savings because there probably won’t be any but because of the comfort. As stated above , winter is when you’ll notice the difference.

 

Yep that's an option. I used to do business with a company which made these aluminum heat exchanger panels that you'd just float 20' or so off the shore, fill them with water and they sink. The issue with that or coils in colder climates is that you need a ton of them to absorb enough heat. In TX, it's probably a fine choice.

In either case I don't think the additional complication is worthwhile. Air source stuff is hitting HSPF ratings pretty close to geo these days.

 

Industrial we tell people not to bother with water. Too may problems.

 

I would just buy two or three of the portable units that vent out a window. They're relatively cheap, you can use them where you need them, and put them away at the end of the season. I also need white noise to sleep which they provide.
I have a split ranch and I cool the whole upper floor with just two small window units at either end of the house. I can get it down to the low 60s when it's 90+ outside. It helps to have good attic insulation.
But I'm cheap and I like cheap solutions, you may have other priorities.

 

Modern window units can be had in inverter form for more efficiency, and even do water cooling by retaining condensate to splash onto the outside coil. Exactly what you're looking for.

 

Your misconception is replacing air with water. In a heat pump the refrigerant is heat exchanged with the air in the house. What you are proposing is replacing the refrigerant with water. Which then exchanges with air. In the end you go to air unless you are a fish

 

You're confusing some concepts. I'd explain but I'd get lost in details and end up with carpal tunnel.