Clarification Needed: AC lines length?
Nuke
| Posted in Energy, Heating & Insulation on
On the most recent TOH project, Richard Trethewey stated to Kevin O’Connor that typically the run-length of an AC refrigerant line was ~50-feet. I was amazed at this figure, because I know the lines in my spec-home are a lot longer, especially for the unit in the attic. As a result of this distance-limitation, he chose to utilized chilled-water transport between a water-chiller (actually, an anti-freeze concoction) and air handlers within the home.
Can some provide some enlightenment on the parameters for distances between the outside condensing unit and the inside expansion valve? I’m guessing this might be a function of refrigerant type, condensed-side insulation, etc.
Replies
You are guessing right Nule. The line length my typicaly be 50' but can be much longer if need be. I've done lots in excess of 100' on dual systems with attic coils on large houses.
It is a function of size of load and lenght of run just like wire to determine length limits for different sized lines.
Pete, when you say 'different sized lines' are you saying the physical diameter of the line, the length, or both? Is line-insulation of any serious factor in this?
Lineset size (diameter) and allowable lengths (vertical, horizontal or both) are determined by the equipment manufacturer. There are tables sent in the instructions for the condensing unit.
Naturally (don't know what I was thinking, hehe). Have you installed or worked with water-chillers as a means of cooling air?
We've done chilled water systems before. But they have been in large commercial facilities..These machines are huge..
You need a chiller, a cooling tower and air-handlers. I didn't think these were available for residential use...
The current TOH project uses a rather small water chiller. I was surprised at how small it was compared to my college days and building-size chillers on campus.
Not in a residential application.
Mind my asking why? Is it lack of aware that residential systems exists, easier to use conventional refrigerant systems, or just personal preference? Just curious, here. I can see that it might be more desirable to have a refrigerant leak than water in some cases.
No demand from my viewpoint.
It is hard enough to get people to pay for conventionally accepted technology installed properly, much less something new.
The water system probably has less opportunity for leaks than a refrigerant system. I have never worked for someone that installs refrigerant piping correctly. Either they cheap out with 95/5 instead of StayBrite 8 solders or no nitrogen is used during the brazing process. Micron gauge... what is that???
I have felt that some of the really big houses would benefit from a residential application of a commercial technology, but the money issue comes up again. Why spend the money on unseen mechanical systems when there is a great big granite countertop showpiece in the future?
I fail to see how someone would find a 10 piece "condenser farm" attractive... but to each his own.
I would like to follow up on the stuff if you have a link or two.
I'm a little lost, here. I never considered water-chilling to be a new technology, and consumer application acceptance is usually dependent upon consumer market awareness. In other words, don't offer it and no one will know it exists--unless they are like me and watch TOH. :)
I'm really curious as to why it would be expensive considering the system seems more simple than complex.
How is the water chilled? If it is evaporation technology, then it might be cost competitive with conventional refrigerant systems. If refrigerant is used to chill the water, then it must be more expensive because there is the water system in addition to the refrigerant system.
I like TOH too, but we all know that they never use cheap methods there.
I will have to look into it sometime.
I need to ask a dumb question here (sorry, it's Friday and it's been a hard week)..How do you make water cold in the summer??
The only thing that comes to mind is a type of ground source heat pump, for lack of a better term. Even then, the water in the loop will only be down to about 55 degrees. Is that cold enough to deliver 70+ degree air??
Good question, but I would guess that geothermal solutions are very efficient in the Summer months. If you have 55ºF ground temps then I would imagine it would be possible.
All depends on Rel. Hum. where you are. Have you not seen swamp coolers out west? Evaporation is the process.
Can't say that I have seen how things are done out west..I'm located just outside New York City..nothing but good ol' Ozone depleting freon here...
They use the evap coolers a lot (or at least used to ) in Arizona. You would see these boxws with slats or louvers on almost every trailer.
Besides the evap cooling already mentioned, you would need to circulate the coolant (refrigerant) around/within the tubes carrying the water in the evaporator section (the evaporator is what gets cold in a traditional AC unit).
Residential AC is designed for a 20* temperature difference between the return and supply, so if there was enough water circulating (capacity in tons), 55* would work fine.
Ground source heat pumps are quite efficient, but you either need plenty of land for a horizontal loop, or you need to drill down. One 150' deep hole per ton here, sized for heating.
A chiller works just like a residential split system that we are all used to seeing. All of the components of a refrigeration cycle are the same, it just removes the heat from the water instead of the air. The water is pumped across the evaporator instead of air blowing across the evaporator. The heat in the water is absorbed by the refrigerant same as the heat in the air is absorbed by the refrigerant. The heat from the evaporator or "barrel" is then rejected through the condenser. A chiller would allow for easier load management and capacity control in a larger system.
The original gas fired air conditioners from the '50s and '60s were nothing more than absorber type chillers. They included a pump and anti-freeze through a coil in the plenum of the furnace. This isn't new technology, maybe not the cheapest way to do things, but could in many cases be a better way once a person understands the whole picture. It's not likley that TOH will cover all of the details clearly in <5 minutes, but having seen some of their projects on television it may be the best solution for that scenario.
Hope this helps
Chris
Ahh. I am thinking bigger :).
Bro in law is working on a house in Montana next to a lake. 5000 feet of black poly tubing in the lake for a heat exchanger. Friend had 2 wells dug 25 feet deep 20 feet apart. He heats and cools a 5000 sq ft. mfg plant .
There probably is a manufacturing advantage with the chilled water system. The chiller can use a self-contained refrigeration unit, meaning it can be factory-sealed, not needing any field service parts. "Field" repairs can be done in the shop, like a window AC.Installing the unit could be done with regular plastic tubing -- certainly no brazing and probably no soldering. The tubing would be cheaper. No dryer to worry about, and no need to evacuate/charge when installing or relocating. Minimal environmental issues.On the down side, the entire length of the water lines would have to be insulated, with insulation on both supply and return lines. And the lines would likely have to be larger than for freon.Likely efficiency would be poorer, but for the McMansions they work on on TOH that's presumably not an issue -- with the freebies the HOs get they can afford the extra operating cost, or they can just sell a few shares of stock with insider info to make up the difference.
If ignorance is bliss why aren't more people
happy?
On the down side, the entire length of the water lines would have to be insulated, with insulation on both supply and return lines. And the lines would likely have to be larger than for freon.
The source and return water lines were embedded into what appeared to be a french-drain style 5" plastic pipe that had the cavity filled with expanding foam insulation. Richard Trethewy (sp) showed a piece of it and said it allowed them to install the outside units hundreds of feet away from the house if desired.
I do believe the unit they installed was a sealed freon system that chilled the water, and chilled water carried through that insulated pipe into the home and the handlers therein. Seems quite interesting to me. And the aspect of using PEX manifolds for distribution is a curious option.
I saw on Bob Vila where they had some "group housing" and they had a central heating plant. Used similar product to distribute hot water for heating.About 4-6 years ago TOH did on where they bought the house and build a large shop in the back and they used the same thing to bring hot water for radianet heat from the house.And in large cities it is not uncommon for a "utility" company to provide hot water and chilled water service for large commercial buildings.
Only speculating here, but could Rich Trethewey have meant that pre-charged lines come in 50 lengths. and that any other length would require evacuating and charging via different mthodology???
Couple of things already mentioned to your original post (1) 50' precharged line set are normal, (2) line sizing beyond that length is important, (3) addition refrigerant is needed along with the need to recover all the refrigerant in the system, pulling a vacuum on the system, pressurizing with nitrogen for leak checking, evacuating the nitrogen to another vacuum, and then recharging the system with refrigerant.
No one has mentioned that longer runs, particularly with vertical rises of 12' or more need oil traps added to the lines. Compressed refrigerants carry a significant amount of compressor oil in them. In standard installations of 50' or less the oil is carried back to the compressor. Long lines and high lifts mean the oil will condense out of the refrigerant and collect in the low points, thus starving the compressor of oil. Low oil and eventually low refrigerant due to line restrictions lead to premature compressor failure.
There are some varieties on residential chillers available, but they are not off the shelf package units. Carrier makes a packaged a/c unit that uses a water cooled condenser and a standard evaporator coil. They are stand alone units much like their roof top units, but can be located anywhere. They only require a water source for the condenser side.
Trane make smaller chillers with scroll compressors, chilled water barrels and air to air condensers. Chilled water loops and air handlers are custom designed for individual applications.
Cost of these types of systems is significantly higher than most residential building can bear, and most are a/c only. Heating is an additional cost and separate system.
Dave
Cost of these types of systems is significantly higher than most residential building can bear, and most are a/c only. Heating is an additional cost and separate system.
I gathered it wasn't cheaper than what I am, as a typical consumer, use to seeing, but the technology doesn't seem new nor does the technology seem expensive. So, I have to wonder why it would be significantly more expensive. Is it because its typically a commercial solution and as such commercial pricing?
Any time you have something that is not commonly used it's going to be more expensive. There are "ecomomies of scale" from producing lots of the same thing, plus there is more motivation to "cost engineer" the product to eliminate expensive parts or manufacturing steps. And the overall design cost (and much of the advertising cost) is spread over more units.It's dangerous to give any rules of thumb, but I would guess that in the AC equipment market increasing the number of units sold 10x permits the sale price to be cut in half. (Note that not all of this applies to a given model or even manufacturer since lots of common parts are used in the industry.)This is why those one-off toilet seats in bombers cost $10K.If ignorance is bliss why aren't more people
happy?
Edited 1/29/2006 4:37 pm by DanH
The up-front cost of this type of system is going to be higher. However they can be designed and setup to operate more efficiently in a larger applications. The operating cost savings can often offset the initial cost increase. Some applications require proportional control rather than simple on-off and these systems provide that option. It can be setup to provide humidity control as well as temperature. This is often needed for the art collections that some wealthy people own. It is sometimes needed for musical instruments also.
The chiller can be located longer distances away from the terminal units than a conventional split system. The water doesn't have issues with oil-return, flood-back, etc. Water is also cheaper to fix and less fussy during installation, absulute cleanliness isn't necessary, the chunks of solder etc. just get caught by the strainers.
In some cases these and other advantages outweigh the higher upfront cost.
Chris
Some of the increased expense is for reasons that Dan mentioned. Some is the "commercial" pricing and much of that comes from qualified labor sources. There aren't many residential chillers out there, so not much demand for technicians to install them. Because of that, much of the install is sub contracted to commercial firms. Commercial wages and cost are higher so that is reflected in the final cost.
Dave
I was never talking about the final costs or the labor costs. I was only interested in the material costs. Of course, the proverbial $35/hour forklift operator is a commercial monkey-labor cost, too.