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  1. #1

    Help choosing between conventional and mini-duct systems

    Hi there,

    I have done an extensive amount of reading through message boards and sites on the internet, but was hoping to get some opinions from experts before I listened to the sales job by a Unico guy.

    We have a 2 story house plus a finished attic (that we just use for storage right now) and an unfinished basement. The house was built in 1929, in Westchester County in New York (30 mins north of NYC). Currently no ducts exist (we have radiators for heating). The house is around 1700 sq. ft.

    So given that info (feel free to ask other questions), would you suggest regular central air, mini-duct, or ductless for a/c? If we have to stick the indoor part of the Unico system in the attic, that isn't really a problem even though it's finished.

    Other than the bedrooms and up to the attic/down to the basement, there are no doors separating the rooms, so it would be difficult to just cool whatever room we happen to be in at the time. We may eventually use the attic as more than just storage, so we will want to cool up there as well (although definitely keep it as a separate zone that we will leave off for now).

    Thanks!
    Last edited by merc1286; 03-24-2008 at 09:50 AM. Reason: Fixed spelling error

  2. #2
    Join Date
    Sep 2007
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    Just North of Dallas, Texas
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    97

    WHy Not Split System

    I saw an episode of This Old House that provided a possible solution to your problem. The folks had a large game room/ man cave that needed heating and cooling. They opted to install a split system. The outside unit had the refrigeration lines run into the air handlers that were installed where needed. This allowed them to have what they needed without running ducts to the rooms.

    See the following info from a Manufacturer's web site:

    MSG systems are ideal for enclosed spaces like garages and porches where running ductwork just isn't practical. They are also great for rooms where you need extra cooling like kitchens or where TV, sound systems and other electrical devices heat things up.

    MSG mini splits provide are economical to install and provide cooling and heating with the convenience of a remote control. And best of all, turn the system off when you leave to save money.


    Look for split systems on the web for further info. I hope this helps

    Just my 2 cents .....

  3. #3
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    Jan 2004
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    Although you can zone a Unico. The finnished attic may be small enough, that you would have some problems.

    Use the Unico for the finnished levels you have now. And install a ductless for the finnished attic, when you finnish it.
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  4. #4
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    Conventional ducting is hard to get properly installed during new construction. Existing construction allways leads to compromise and eventually performance issues. If done correctly, it will get you the quietest and most efficient systems though.

    High-velocity ducts are good for retrofits, however you will not get the same capacity using these systems because they run less airflow (CFM/ton) which results in lower suction temperatures and the compressor has to add more heat (mroe energy) to reject the heat absorbed from your house to the outdoors. They can also create a high pitched drone noise in the background that some people (and dogs) find annoying. Architecturally these are a great solution for tight spaces, but you will not get the same capacity and efficiency in almost all cases.

    Mini-splits are one of my favorites because they are so hard to mess up the installation with. These are very popular in Europe, and provide some of the best zone controll you can get. They will not have the same high-temperature efficiency that other systems will have because you will likely have mulitple air handlers (avaporators) sharing a single condenser, but they get great overall efficiency scores because there are no losses to leaky and/or restrictive ducts and the indicidual evaporators don't all operate at full speed because of the way loads change in a building throughout the day.

    Some folks dont like the looks of the mini-splits (ductless), and can be a challenge to fit asthetically in some houses, but I would still recommend this over ducted systems as first choice - for mechanical reasons.

    Also, while I'm ranting - do yourself a favor, if you are installing A/C, pay a few extra dollars and make it a heat-pump. You'd be surprised at how much extra comfort you can get and it gives you another choice of heat so you can play the price game - energy is only going to get more expensive, so give yourself a few options.

  5. #5
    thanks for the info. I will definitely take it all into consideration.

  6. #6
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    Quote Originally Posted by Buck_Taylor View Post
    Conventional ducting is hard to get properly installed during new construction. Existing construction allways leads to compromise and eventually performance issues. If done correctly, it will get you the quietest and most efficient systems though.

    High-velocity ducts are good for retrofits, however you will not get the same capacity using these systems because they run less airflow (CFM/ton) which results in lower suction temperatures and the compressor has to add more heat (mroe energy) to reject the heat absorbed from your house to the outdoors. They can also create a high pitched drone noise in the background that some people (and dogs) find annoying. Architecturally these are a great solution for tight spaces, but you will not get the same capacity and efficiency in almost all cases.

    Mini-splits are one of my favorites because they are so hard to mess up the installation with. These are very popular in Europe, and provide some of the best zone controll you can get. They will not have the same high-temperature efficiency that other systems will have because you will likely have mulitple air handlers (avaporators) sharing a single condenser, but they get great overall efficiency scores because there are no losses to leaky and/or restrictive ducts and the indicidual evaporators don't all operate at full speed because of the way loads change in a building throughout the day.

    Some folks dont like the looks of the mini-splits (ductless), and can be a challenge to fit asthetically in some houses, but I would still recommend this over ducted systems as first choice - for mechanical reasons.

    Also, while I'm ranting - do yourself a favor, if you are installing A/C, pay a few extra dollars and make it a heat-pump. You'd be surprised at how much extra comfort you can get and it gives you another choice of heat so you can play the price game - energy is only going to get more expensive, so give yourself a few options.
    While I don't think they are technically considered mini-splits, the multi split setups from Daikin (VRV-S), Sanyo (Eco-i Mini), and Mitsubishi (City Multi) have both ductless and ducted indoor units that can have as many as 9 attached to one outdoor unit in combinations that work for the project.

    The ducted units are physically quite small, and thus, can be used to create several zones. This would allow shorter and specific duct runs and could possibly be fitted to your home with minimal compromise.

    Also, the heat pump versions have much higher outputs at lower temps than a typical heat pump due to the compressor being inverter driven. You could use it to provide your primary heat with your hot water radiators as backup/secondary heat.

    As Buck_Taylor mentioned these are the primary systems used in the rest of the world and provide very high comfort, very high efficiency, while being extremely quiet.

  7. #7
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    myself......i am a huge Unico fan. Have been since my first install. As far as not being as effecient....well I don't know about that. 135* water to a Unico hydro coil yields 130* air temp at the register...sound efficient to me ?! 33% more humidity removal.....kinda the point of a/c ....right ? Noise ?....well install it right and it's fine.
    But like any pro job.....finding the right contractor to do the job is most of the battle. Don't confuse ductless-splits with "central a/c"....think of them more as a solution to a problem. 4 season porches and great rooms are common ares to see them. They work well, and hardly ever have a problem.

  8. #8
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    Quote Originally Posted by mchild View Post
    While I don't think they are technically considered mini-splits, the multi split setups from Daikin (VRV-S), Sanyo (Eco-i Mini), and Mitsubishi (City Multi) have both ductless and ducted indoor units that can have as many as 9 attached to one outdoor unit in combinations that work for the project.

    The ducted units are physically quite small, and thus, can be used to create several zones. This would allow shorter and specific duct runs and could possibly be fitted to your home with minimal compromise.

    Also, the heat pump versions have much higher outputs at lower temps than a typical heat pump due to the compressor being inverter driven. You could use it to provide your primary heat with your hot water radiators as backup/secondary heat.

    As Buck_Taylor mentioned these are the primary systems used in the rest of the world and provide very high comfort, very high efficiency, while being extremely quiet.
    Your partial data is correct. The Mitsubishi City Multi can be installed in versions that can simultaneously heat and cool as well. Unfortunately, they're not used extensively in residences as they require 3-phase electricity and not many homes have 3-phase. This is true of the entire City Multi, with the exception of one line that goes as high as 4-tons and can handle up to 4-zones but not heat/cool simultaneously.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  9. #9
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    Quote Originally Posted by skippedover View Post
    Your partial data is correct. The Mitsubishi City Multi can be installed in versions that can simultaneously heat and cool as well. Unfortunately, they're not used extensively in residences as they require 3-phase electricity and not many homes have 3-phase. This is true of the entire City Multi, with the exception of one line that goes as high as 4-tons and can handle up to 4-zones but not heat/cool simultaneously.
    You are correct that within the Mitsu City Multi line they have the systems that can heat and cooling simultaneously. Daikin and others have the same systems within their commercial lines. Also, as you noted, these systems require three phase electric, not very viable for a lot of residential applications.

    I do hope that I can clarify that, in fact, the 3 ton (single phase) Mitsu City Multi S model can have up to six indoor units (zones) and the 4 ton 8 units. Same with the Daikin VRV-S line. Sanyo offers a 5 ton unit that can have up to nine indoor units.

    http://www.mehvac.com/UploadedFiles/..._Submittal.pdf
    http://www.mehvac.com/UploadedFiles/...ies(Jul06).pdf

  10. #10
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    well I don't know about that. 135* water to a Unico hydro coil yields 130* air temp at the register...sound efficient to me ?

    That doesn't tell you efficiency.
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  11. #11
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    Quote Originally Posted by brian in mass View Post
    myself......i am a huge Unico fan. Have been since my first install. As far as not being as effecient....well I don't know about that. 135* water to a Unico hydro coil yields 130* air temp at the register...sound efficient to me ?! 33% more humidity removal.....kinda the point of a/c ....right ? Noise ?....well install it right and it's fine.
    But like any pro job.....finding the right contractor to do the job is most of the battle. Don't confuse ductless-splits with "central a/c"....think of them more as a solution to a problem. 4 season porches and great rooms are common ares to see them. They work well, and hardly ever have a problem.
    Not sure what you are saying - I can hook up any boiler to any hydronic coil and supply any temperature water I need to based on the load of the building and my desired output. The output is a function of airflow and temperature differential and relative to the surface area. Efficiency for heating is a function of heating equipment efficiency and fan horsepower to move air over/through a coil. If I lower the temeprature of the water delivered by the boiler (for example), the boiler gets more efficient - and has nothing to do with the air handler. Furthermore, UNICO systems use bigger HP fans than regular equipment, therefore by convention they cannot ever be as efficient because they use more watts per cfm.

    As for A/C - in the course of doing a job correctly we determine the locations cooling loads (Manual J) - and hence, the SHR for the job at peak. As a professional, you then select an air handler that provides the SHR characteristics dictated by the loads of the job. Picking a UNICO unit because it has a low SHR and you like it is not an engineering solution. A low SHR in a new tight building will remove lots of humidity - whether needed or not, and then will have longer run times as it stuggles to remove sensible heat. A low SHR evaporator is not an appropriate choice for Arizona, and trhe lower half of California, New Mexico, and parts of Texas, but could be very desireable in other parts. Yes they work, but every system that I've had to go out and evaluate was installed by someone who said they knew what they were doing - and of course the manufacturer approved or helped with the engineering, yet some how failed either catastrophically, or the customer complained about excessive fuel consumption.

    The simple fact is they operate at a lower suction pressure which means it reduces the efficiency and capacity of the new higher-SEER equipment. The new equipment is looking for higher suction temperatures in order to maintain volumetric flow rates (mass flow of the refrigerant) and higher pressure (result of higher temperatures) so the compressor doesn't have to add as much heat to reject it from the condenser.

    I have read through the engineering and installation documents for these systems. Their sales and examples literature are misrepresentations of hwo they actually perform. If you understand the vapor-compression cycle and read theri performance specifications you can clearly see they typically proved 20% or less capacity - simple laws of physics.

    Put another way - A/C is rated in tons (12,000 BTU). 3 major things affect heat transfer - surface area, temperature difference, and volume of the heat transfer medium (think airflow here). When manufacturers rate A/C equipment, they do so with a nominal 400 CFM/ton of airflow. This airflow volume represents the capacity opportunity. Each cubic foot of air contains a similar amount of heat to be absorbed by the evaporator. When you have low airflow you get low capacity. These UNICO style evaporators are typically rated to run about 250 to 300 CFM per ton, therefore in order to absorb the same amount of heat from each cubic foot of air, the temperature needs to lower (on the coil surface), the air needs a longer dwell time on the coil surface and the coil needs to be larger than a conventional coil (actually a combination of these are employed). You can use a Psychrometric chart and do some simple calculatiosn to see the opportunity for the evaporator to absorb heat isn't the same at 300 CFM per ton.

    In my dealings with failed installations - every one I've seen conencted to a heat pump has destroyed multiple compressors. We don't see as many failures in A/C only operations, but I do see techs consistently overcharging these systems - probably because they are using the OEM pressure charts and you have ot overcharge the system to get it near the charts - of course if you charge to Superheat and Subcooling you shouldn't get into that situation.

    Anyway, I am not saying they aren't a solution, and yes they work, but it is a fact (and not my doing or saying) that they are typically not as efficient. The high-velocity manufacturers were given a waiver for 1 year by DOE because they could not meet the new 13 SEER minimum with most of their existing equipment lines. The good news is there is one manufacturer out of Canada using an ECM motor that claims they can meet the new SEER requirements, and have published ARI ratings that show this!

    If you know someone with a Honeywell Service Assistant - HSA (digital manifold attached to Palm PDA) have them connect it to a UNICO style system. The HSA uses Copeland compressor maps to determine refrigerant flow and capacity (actually you can download the compressor maps from Emerson if you want to do it manually too). When you evaluate the refigerant flow, you will see they run about 85%, although I did see one close to 90% - once.

    Anyway, I am very nuetral about any and all of these systems. As a matter of fact, I will tell you they are all pathetic - solely because manufacturers still develope equipment that allow techs to mess up! The ductless equipment largely uses methods and controls that are much more robust - but they could still be better. Generally the HVAC industry is about 15 - 20 years behind where they should be - just my opinion.

  12. #12
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    Quote Originally Posted by Buck_Taylor View Post
    Anyway, I am very nuetral about any and all of these systems. As a matter of fact, I will tell you they are all pathetic - solely because manufacturers still develope equipment that allow techs to mess up! The ductless equipment largely uses methods and controls that are much more robust - but they could still be better. Generally the HVAC industry is about 15 - 20 years behind where they should be - just my opinion.
    The new Daikin VRVIII line (and the soon to be released S model suitable for residential applications) provides for the tech to connect the manifold gauges, refrigerant tank, and then simply press a button on the outdoor unit for it to determine the proper amount of refrigerant needed. Much harder for the tech to mess up.

    These newest systems will allow for up to 162.5% of outdoor nominal capacity with indoor unit capacity (up from the current 130%) with up to eight indoor units (zones) for a 4 ton system.

  13. #13
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    Quote Originally Posted by mchild View Post
    You are correct that within the Mitsu City Multi line they have the systems that can heat and cooling simultaneously. Daikin and others have the same systems within their commercial lines. Also, as you noted, these systems require three phase electric, not very viable for a lot of residential applications.

    I do hope that I can clarify that, in fact, the 3 ton (single phase) Mitsu City Multi S model can have up to six indoor units (zones) and the 4 ton 8 units. Same with the Daikin VRV-S line. Sanyo offers a 5 ton unit that can have up to nine indoor units.

    http://www.mehvac.com/UploadedFiles/..._Submittal.pdf
    http://www.mehvac.com/UploadedFiles/...ies(Jul06).pdf
    daikin is by far the very best in vrv tachnology, they do have a single phase line if equipment. Also they are alot easier to set up

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