Original message
| twentybelow
 |  "dual evaps for residential system.."
, posted Sun 24 Aug 01:04  
hey all,
Putting in central air system for mother in law. Two brand new, never been used evaps are already installed, one is 2 ton, one is 3 ton. I would like to put one 5 ton condenser outside. In theory the evaps could go in series with one metering device.....The evaps are aproximately 30 feet apart, I would have to insulate connecting suction really good, I know. I have zero experience with dual evaps.
Any advice?? Please don't respond with dumass crap to clutter up my thread unless I need to hear it. thanks in advance.
Other stats: Home is 3600 sqft tri-level, Climate is southern michigan, 2 phase power. This project includes major brownie points from mother-in-law.
"Be careful of the toes you step on..."
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Replies:
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| sinead26ohara
| "Re(1):dual evaps for residential system.." , posted Tue 2 Sep 20:54
Okay, as a designer I can appreciate the fact that your curiosity has gotten the better of you. So, let's take this for a ride and see where it leads. You have two evap coils, one a 2-ton and the other a 3-ton. You want to connect them in series to cool a 3600 sf home. I don't mean to sound like a broken record, but the reality is that it will not work and the reason is simple. An air-conditioning system performs four basic functions in order to achieve proper climate control: Compression, condensing, flashing and evaporating. The system you're suggesting will not allow the second evaporator to perform it's name-sake function, namely evaporation. If the refrigerant has already flashed through the first metering device - which will not work properly in the first place since you will be attempting to push five tons of refrigerant through a 3-ton coil, a scenario that will result in an unacceptable pressure increase on the high side and an unacceptable pressure drop on the low side leading to rapid valve failure - there will be a lack of liquid refrigerant to flash through the second evaporator. Keep in mind that a compressor requires a specific amount of low-temp, low-pressure gas to cool its windings, as well as be able to keep oil from backing up in the circuit and cause bearing wear. So, the series design is out of the question simply because of the physics. However, you could connect the coils in a parallel setup utilizing a 5-ton condenser and two metering devics, but you will need to add a few additional controls and now we're back to the original problem of a 3600 square foot home and only five tons of cooling capacity. A minimum design rule-of-thumb is no more than 500 square feet per ton, which means that you would need at least 7-tons of cooling, and that would work only if the house is well insulated and the windows are good. I suppose I'm curious as to why you want to pursue this route?
Sinead O'Hara
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| dsvbohica
| "Re(1):dual evaps for residential system.." , posted Sun 24 Aug 15:21
funny he was told on hvac-talk it wouldn't work and he got very rude...I guess thats his reasoning for the comments on the original post as not to post crap
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| | twentybelow
| "Re(2):dual evaps for residential system.." , posted Mon 25 Aug 16:08
quote:
funny he was told on hvac-talk it wouldn't work and he got very rude...I guess thats his reasoning for the comments on the original post as not to post crap
...
Ya, HVAC-talk is a very good website....so do you have anything to contribute or are you just posturing your lame ass opinion. "he got very rude" ...thats the pot calling kettle black. Maybe you should open your mind a little bit instead of painting yourself into a corner with your loud mouth.
Oh by the way, it could work, it would be over engineered...but it could work. The system would have to be robust with a few solenoids, a quench valve, etc, etc. Not too mention a dozen points of failure not found on a regular orifice system.
It was a long shot to consider a dual evap/one condenser residential system. Just thought I would put it out there and see what kind of feedback I would get, and I knew full well there would be a few inconsequential, irrelevent, unnecessary, lame ass opinions out there. Thats why I said no crap responses.
So if you don't have anything to contribute, please don't open your man-pleaser and let your ignorance spew out into the atmosphere.
But...if you have opinions on how this could work, not how it couldn't, feel free to respond.
"Be careful of the toes you step on..."
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| Jojo98
| "Re(1):dual evaps for residential system.." , posted Sun 24 Aug 15:00
I'm wondering how 5 tons of refrigeration is cooling 3600sq ft.
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| | twentybelow
| "Re(2):dual evaps for residential system.." , posted Mon 25 Aug 16:17
quote:
I'm wondering how 5 tons of refrigeration is cooling 3600sq ft.
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Simple..it is dropping the temperature. Not down to 65 F but my mother-in-law definitely won't be sweating on her cornflakes. Original install was obviously under capacity. She is not going to get anything done for the price quoted by the local guys. So....3-4 thousand dollars for 65 F air, or 1 thousand for 75-80 degree, low humidity air?? Not much of a decision after a few sleepless muggy nights and today's economy. So...as the saying goes...be part of the solution or part of the problem.
"Be careful of the toes you step on..."
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| theduke03
| "Re(1):dual evaps for residential system.." , posted Sun 24 Aug 11:12
1. It will never ever work.
2. There's no such thing as 2 phase power.
3. I would call this "reinventing the wheel".
"My dad was the most feared furnace fighter in Northern Indiana."
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| | twentybelow
| "Re(2):dual evaps for residential system.." , posted Mon 25 Aug 16:35
quote:
1. It will never ever work.2. There's no such thing as 2 phase power.3. I would call this "reinventing the wheel".
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You are mistaken, lots of people use the term "2 phase power." You just haven't been to the places I have. Overseas we used the term frequently. Everything over there is wired for 220 one phase (208 to be exact I think). So...everything made overthere was manufactured for 220 on one leg, and nuetral on the other. This contrasts with what most United States born techs are used to because everything is manufactured for 120 when you have a nuetral leg. Over here, when we use the term "220", we automaticaly think 2 hot legs, this is not the case for contractors abroad.
The term (used across the world vs. your tiny corner of whatever podunk county you've never left) "220" could mean one hot, or two hot legs.)
You will know what I mean if you ever see those funny looking plugs with two round posts on them.
Don't get sore, you learned something today.....I won't tell you my age.
Oh ya, be careful of telling people "It will never ever work." The more you say that the higher the odds are you will look silly sooner or later.
"reinventing the wheel"?!? I think there are a few engineers out there living in Cabo who have done just that.
Give me something I can use, not as ammunition to reveal your dogmatic opinions, but as advice for my air conditioning project. That's after all what this forum is for....the exchanging of ideas/knowledge. So far the knowledge has been flowing up river. Please don't insult the intelligence of those around you. Back your opinions up with solid facts, specifications, or refrigerant flow charts, not your watercooler one-liners.
"Be careful of the toes you step on..."
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| | yuri
| "Re(2):dual evaps for residential system.." , posted Sun 24 Aug 11:46
It will never work. You would need individual metering devices and you will still not get proper pressures AND oil return to the compressor etc.
Yuri
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| | twentybelow
| "Re(3):dual evaps for residential system.." , posted Mon 25 Aug 16:44
quote:
It will never work. You would need individual metering devices and you will still not get proper pressures AND oil return to the compressor etc.
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I bet you a dollar a series circuit setup would be better..
A parallel circuit would always favor the lowest pressure circuit back to compressor. SO, The evaps would always have lopsided cooling, more so than a series setup...at least in predictibility.
Two evaps in series would have its drawbacks I know, there would obviously be a higher chance for a starving or flooded second evap. Both evaps would always need to have airflow at the same time....without getting into bypass lines, solenoids, etc.
This is the stuff about HVAC that intrigues people, seperates them from the pack.
Anyway....oil return may be a an issue, got any ideas anyone.
Mind you, this is all food for thought, not meant to provoke useless negative opinions....so show me what your made of....hopefully its not baloney. But go ahead and tell me I am an idiot...I will just shut you down.
"Be careful of the toes you step on..."
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| | theduke03
| "Re(4):dual evaps for residential system.." , posted Mon 25 Aug 17:12
Yeah OK. When you order the condensing unit be sure to insist on a 2 phase unit. The supply house guys may laugh at you then refuse to sell it to you cuz you're a dumbass. 2 phase! I'm just ROTFLMAO!
"My dad was the most feared furnace fighter in Northern Indiana."
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| | theduke03
| "Re(4):dual evaps for residential system.." , posted Mon 25 Aug 17:06
I believe you are mistaken with all of your crazy ideas. It sounds like you're planning a ton of work for a system that will not cool the house anyway. What is the point of having a/c if it can't satisfy the demand? Your 5 tons will just run non-stop and never reach setpoint. Now the homeowner is sweating and paying a hefty power bill.(This assumes that you are acheiving 5 tons of cooling, which you will not be, and even if you did get 5 tons out of it it would still be too small). You sir think you know everything and that's biting my style. Why don't you take your own advice and not step on my toes.
BTW the other fellas that responded are also quite intelligent. As for HVAC, we've forgotten more than you'll ever learn so keep your day job and leave the climate control to the pro's.
Your mom should have taught you some manners.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | twentybelow
| "Re(5):dual evaps for residential system.." , posted Mon 25 Aug 20:59
1) reread my post about the term "two phase" power. Add it to your wide knowledgebase. Sounds like your mind is like a room full of garbage, you can't fit anything else in and anytime you open the door crap falls out.
2)"running nonstop and never reach setpoint." That statement leaves out a few important details like 1: what is the actual setpoint, and 2: the longer the unit runs the higher the dehumidification factor e.g., units sold in Florida have a higher dehumidification factor, then say units sold in western Texas. Add that to your wide knowldegebase.
3)Talking about my mom just shows your lack of facts and figures to back up your hollow statements.
4)Give me something I can use man, if your such a professional with such a deep understanding, give me some ideas instead of blowing your horn. Maybe block off unused rooms, a storage room perhaps, etc, etc. Just pretend you only have a certain amount of money to spend and certain limitations because of existing blower capacity, etc,etc. Oh ya, just pretend this is your house and you are not an overpaid Sears technician trying to sell an old lady a new system because her warranty has just ran out. Pretend you actually have obligations besides your beer tab down at the hotel bar and the loan you took out on your harley while your son doesn't even have a bicycle. Don't know if I am getting warm here but you assumed my mom didn't teach me any manners. As a matter of fact, I spent over a year studying HVAC theory, as well as my time in the field. It just so happens I have worked on packaged units, DRASH units, Military Reefers, etc., I guess I am just not up to this residential stuff, I better throw in the towel, quit while I am behind, wouldn't wanna compete with someone of your caliber.
Oh by the way, do you know what a drash unit is?? I bet if you asked me I would tell you without looking down my nose at you. I betcha you are afraid to ask others questions for fear of looking green. I betcha you think your a real tech cuz you covet your knowledge and talk trash about your competitors. I betcha your wide knowldgebase is limited to your little comfort zone you have created for yourself....lemme guess, your a real pro on residential right...such a pro you wouldn't wanna step outside your caccoon to learn a new application. You ever see a room full of iraqi's huddled around one 2 ton split unit? you ever sat in a 200 degree outhouse, you ever transplanted compressor after compressor into the same old run down goodman cuz your in the middle of the desert and your voltage fluctuates from 80 to 180. You ever pulled a bullet out of a condenser of a HMMWV 'humvee'? Your right, you've seen it all.
"Be careful of the toes you step on..."
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| | theduke03
| "Re(6):dual evaps for residential system.." , posted Tue 26 Aug 20:37
Yeah your rambling post has asurred me of your vast knowledge in all fields and aspects of life too. Sorry, I'm not as smart as you. I'm just a dumbass hvac technician who services, installs, and maintains these systems every day so I probably don't know anything about it. You are like Wile E Cyote. Your schemes look good on paper but they never work. Did you get this 2 evap idea from the ACME catalogue?
But I doubt that anyone who thinks that they can do what you propose is capable of installing any typical split system, nevermind the "over-engineered" system that your imagination has created.
Ok, I must admit that you are a huge jamoke, and that you possibly harbor some gay feelings, but all name calling and cock-eating comments aside I will give you some sound advice. Instead of chasing the road runner off a cliff, have the systems(plural) sized and designed by a reputable contractor. Then purchase and install these systems yourself using your vast mechanical knowledge and ability. That should save a ton of cash and if you really can install this stuff like you say it will work great and you will be mom's new hero. It will surely cost more than a grand. Tell your mom to stop calling me.
"My dad was the most feared furnace fighter in Northern Indiana."
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| | twentybelow
| "Re(7):dual evaps for residential system.." , posted Wed 27 Aug 11:50
touchette...
Lets see...look up serial numbers of furnace and evap...cross reference with condenser models....pheeew...that was tough.
Acquire condenser, txv, copper lines, and fittings (pay 3 times as much for condenser because of local lennox guy's warranty and profit margin vs. checking out craigslist,ebay,etc)...plumb system...pressure test...vacuum...charge.
Just in case I mess this up I will call in the big guns from my local lennox dealer...I betcha there will be two guys that show up....one old guy driving a brand spanking new chevrolet with a 2 1/16 ball on his heavy duty tow hitch he uses to tow his brand spanking new bayliner. The other guy will be a young apprentice. The old guy will be all smiles and assure me how I really need to go with a new setup, tell me not to worry about the cost because they offer financeing, he will make me paranoid with predictions of ungodly electric bills and impending doom of the extinction of current refrigerants. The young apprentice will be making mental notes, hoping to someday own a new chevrolet and spin long tall tales of impending doom and paranoia in the hopes of potential big ticket sales.
Anyway.....I know I should really put this project in the hands of poeple who don't know me from Adam and are motivated by a sometimes slim profit margin.
I will keep you posted.
"Be careful of the toes you step on..."
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| | oldmangobles
| "Re(8):dual evaps for residential system.." , posted Sat 30 Aug 22:34
post Traumatic Stress Disorder reaches a new level of insanity here.Your original post begs for answers like a man standing on the edge of a 40 ft.drop.We could all try to tell you the best way to jump,or piss you off and try and talk you out of it.
old man mike
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| | Schock Therapy
| "Re(9):dual evaps for residential system.." , posted Fri 26 Sep 00:22
First off, I will not say it "can't be done".Multiple evaporators on a single condensing unit are very common in commercial and industrial refrigeration systems.
The first thing you have to do is forget about the idea of running the two coils in series with one metering device. That will not work, for all the reasons previously stated. The coils would have to be piped in parallel, with their own metering devices.(preferably TX valves) The branch circuit piping for each would have to be sized appropriately for each coil to ensure adequate oil return.
In order to have independent control of each unit you could use liquid line solenoid valves to isolate either coil if it has no call for cooling. You would then need some form of capacity control on the condensing unit; hot gas bypass perhaps. Not the most energy efficient setup since you could end up running a 5 ton compressor for 2 tons of cooling, but it would work. A condensing unit with a 2 speed scroll compressor or or parallel 2.5 ton compressors would be perfect for that application.
All this is assuming that 5 tons is enough cooling for the house. I would not presume to say whether it is or not when the only information I have is the square footage of the house. There is far more information needed to do a proper load calculation on a building. Climate, r-value of the walls and roof, and number of south exposed windows to name a few.
If it was MY mom's house, would I do it? probably not. I would confirm the sizing, upgrade the capacity if needed, and install a separate condensing unit for each.
But it definitely can be done if you know what you are doing!
By the way, WTF is a "Drash unit"
It's only a shock if your not expecting it!
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