tammy_kahlerjohnson

HVAC decision for new construction in Kansas City area

Tammy Kahler Johnson
October 2, 2019

We are in the Kansas City area and building an 1876 square foot ranch with full basement with 9ft walls. Exterior walls are 2x6. We will have a wood stove in our great room. We have an open concept great room dining and kitchen. The master bedroom and then my 83yr old mom will be living with us and we have 2 small rooms and a bathroom at the front of the house for her. The basement will be finished within a year but we will need to be in the space before it is finished so we need our hvac system ready to heat/cool that space. We are all electric.

So we are considering doing a ductless system from Mitsubishi with mini splits throughout. We read good things about them and the VRF technology and how it is so much more efficient. Just want to be sure we make a wise decision since the cost of going completely with Mitsubishi is quite a bit but would seem to save us with electricity bills later on. Also my mom could keep her rooms at a temperature she wants and we could do the same in the other spaces.

Anyway, advice needed!

Thanks!

Comments (82)

  • PRO
    Austin Air Companie

    Do not worry about the maintenance as ductless air conditioners need very low maintenance.

    Remember this comment is coming from someone who sells ductless mini splits.

    Very low maintenance? compared to what?

    From a servicing perspective, I can tell you more equipment does not equate to 'low maintenance'.

    If I had a nickel for every time I removed a collapsed filter from a ducted system, I would probably be retired by now. Filtration is a requirement for any AC system.

    Normal air filters for ducted systems can hold a lot more dust and dirt than what a mini split filter can hold. Each mini split head will have it's own filter, that will have to be changed periodically. https://hepafiltersales.com/collections/daikin-mini-split-filters/products/daikin-1380242-mini-split-filter-2pk

    The above link shows a picture of a common mini split filter.

    Once a filter (any air filter) becomes full of dirt, the blower will continue to try to get the return air it needs to operate. Because dust particles come in various sizes the filter is not intended to catch all particles.

    The more the filter gets dirty, the less air can get thru, the more likely smaller particles make their way into the cooling head unit leading to more maintenance issues. Clogged condensate drains, dirty evaporator coils.

  • PRO
    Charles Ross Homes

    @Austin Air, I'm with you up until your claim:


    The more the filter gets dirty, the less air can get thru, the more likely smaller particles make their way into the cooling head unit leading to more maintenance issues.


    As a filter becomes more and more occluded, it actually filters more and smaller particles than a clean filter of the same rating does. A dirty filter reduces air flow and increases fan hp compared with a clean filter. A dirty filter does risk the coil freezing up and damage to the system, but if the coil is getting dirty, it's because air flow is bypassing the filter via duct leakage or flowing around the perimeter of a cheap paperboard framed filter-- not because smaller particles are passing through the filter.


    Filtration is an important function of an HVAC system. I run my system's fan continuously for that purpose. I find with a pleated MERV 13 filter, I only need to change the filter once/six months.


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  • PRO
    Springtime Builders

    Yes, filters are always an occupant behavior issue. At least forced-air systems (or mini-splits) are capable of removing particulate from the air. One could also use a dedicated product for particulate removal like the Aprilaire offerings but that usually means ducts. Most important for better indoor air quality is to use some form of outdoor air ventilation.


    Be wary of doing your own energy calcs or believing claims about specific details over the internet. Energy modeling is not accurate in the hands of the inexperienced. Comparing SEER values may not account for the turn-down ratios of specific equipment nor distribution differences of ductless vs ducted. There can also be discrepancies between the pairing of outdoor compressors with indoor air handlers. For best results, use a third party for energy ratings, Manual J/D/S and final commissioning.


    It's great to use energy software to help with design, but throwing around specific numbers and details could lead others down the wrong path.


    According to this heating fuel cost calculator, ductless heat pumps would be $250 cheaper per year to operate than a natural gas furnace using average Missouri utility pricing from 2017 (11.6 cents kwh & $1.00 per therm). That's fuel costs only. One should also try to include the monthly minimum fee from NG utility and any added NG infrastructure costs for fair accounting.

  • PRO
    Austin Air Companie

    @Austin Air, I'm with you up until your claim: The more the filter gets dirty, the less air can get thru, the more likely smaller particles make their way into the cooling head unit leading to more maintenance issues.



    https://www.machinerylubrication.com/Read/31252/filtration-particles-capture

    Reference link above.


    'They call it: Flow Drag Desorption.'

  • D E

    i think homeowners should educate themselves in doing energy calculations. ive heard all the stories of sloppy and inaccurate manual j calculations from so called professionals and I for one would not trust the work of most so called energy professionals.

    btw anyone can get free manual j calculations at cool-calc.com

  • weedmeister

    Ducted in this context means the duct runs just a few feet. The 'cartridge' may be centrally located in a hallway between two or more rooms with the ducts being just a few feet long.

  • Joe Macker

    @D E that site cool-calc.com does not seem to be available

  • D E

    "Ducted in this context means the duct runs just a few feet. The 'cartridge' may be centrally located in a hallway between two or more rooms with the ducts being just a few feet long"

    as long as you don't try to cool a small bedroom with a dedicated mini split it doesn't matter the length of the duct. what's important is siding the system correctly.

  • Joe Macker

    @D E what is the problem that you are referring to in "as long as you don't try to cool a small bedroom with a dedicated mini split"? Rough size in mind when you refer to it as small would be helpful.

  • D E

    small would be any room under 300 SQ ft.
    smallest minisplit you can buy is 6000 btu with a minimum load of 1500 btu. minisplits never turn off so if you have a 900 btu load with a head that will only go down to 1500 then you have problems. it cools the room too quickly and then you have the fan running with basically no cooling and blowing moisture back into the room which is a big no no for most climates.

    just Google ductless mini split high humidity.

    it's usually better to undersize the unit than to oversize.

    another problem with a split in every room - have you seen the cleaning process of one? it's time consuming. now multiply that by however many rooms you have. cleaning a single air handler is child's play by comparison.

    now, how do you intend to cool bathrooms? leave them unconditioned? or are you putting in a minisplit for every bathroom too?

    why are you interested in minisplits anyway?
    what do you like about them?

  • David Cary

    Ah - most bathrooms can be cooled by adjacent rooms. My ducted mini in my bedroom (12,000 btus into 200 sqft) does not cycle down and also cools our 300 sqft attached closet and bathroom with no ducts. Bedroom is 67-70 and closet/bathroom probably stay 73 or so in the summer. So be careful making generalizations.

    Agree that minis tend to be oversized in bedrooms. You description of what happens with humidity isn't fully accurate. The fans do shut off.

    Know that humans are 400 btu/hr so 2 adults + a modest size bedroom does pretty good with 1500 btu. The issue usually is using 12,000 btu units for a bedroom (although not an issue for us).

    Google told me that a child is 300 and an adult male is 400. YMMV. As someone who does REE calcs as part of my job, people vary by a factor of 2. So these rule of thumbs are not perfect.

    REE = Resting energy expenditure which converts to BTUs.

    Minis are more efficient. Pushing air from a central location to far reaches of a house costs money. Minis also use more efficient compressors. The average installed mini vs the average installed central duct probably represents a 50% cost savings to run. But - they are often done oversized and are some work to clean.And installers generally have less experience with minis.

  • PRO
    Springtime Builders

    It took an install in my personal home to make me a Mini convert, after my oil furnace conked out. A single 9000 BTU unit heats and cools my entire home. It's a small 2BR 1BA and relatively efficient for it's age. I eliminated the fuel oil costs ($400-700 per year) and window shaker AC units, while lengthening my cooling season. My electricity bills barely even changed!

    The filter is easy to clean. If the head unit does get clogged from not being cleaned and dies, I could buy a whole new one for around the costs of one year of fuel oil.

    Minis are among the cheapest way to heat for most of the country (even in cold climates) and usually the cheapest way to cool, ignoring replacement situations. Choosing Minisplits, go with a reliable brand like Mitsubishi, Fujitsu or Daikin and try not to let your HVAC contractor oversize them. This is best accomplished by getting Energy Star certification or using third party energy rater. You certainly don't need a head in every room. Even some bedrooms don't need a head if you are willing to keep doors open and build efficiently.

  • PRO
    Charles Ross Homes

    We've installed mini-splits in Sun Rooms and Bonus Rooms over garages for years, but never conditioned a whole house with them. Two years ago we rented a 3 BR home on Ocracoke Island in NC which was conditioned by only three mini-splits. The home was incredibly comfortable and the humidity was well controlled. They are definitely worth considering.

  • Joe Macker

    @Springtime Builders what steps did you take to make sure that your HVAC contractor did not oversize them? Did you use any calculators?

  • D E

    David Cary,50% loss from ducting really? lol.

    ducts in attics represent about a 22% loss vs ductless. once you bring the ducts into the conditioned space the losses are virtually eliminated. of course you have to size the ducts correctly.

    but compare the installation cost of 3 or 4 mini splits vs one central air system and you'll never make back the cost difference even with more efficient minis.

    I live in a hot humid climate. my 13 seer 11 eer unit has a sensible to total ratio of less than 50% when indoor air is 80 degrees and wet bulb is 72 degrees. I haven't seen one mini split with less than .68 s/t and the higher their seer the worse the ratio. Mitsubishi 33 seer unit has a s/t ratio of .96

    my ac keeps the rh in my house at 38-40% and the highest bill I had this summer was $120.

    if I got a minisplit system I would have to turn the air down about 4 degrees to maintain the same wet bulb temp and I would end up spending more money and not less.

    I have over researched mini splits and for my new house they don't represent a savings over a 20 year period vs a ducted heat pump with properly sized ducts in the conditioned space

  • PRO
    Springtime Builders

    DOE and University of FL research finds 25-40% losses through ducts. Duct leakage in conditioned space still accounts for energy loss. Even properly sized ducts have friction and turbulence requiring bigger fans thus more energy use. 50% energy losses through ducts is probably common unfortunately.

    I'm not familiar enough with the Sensible Heating Ratio SHR of mini-splits to fully understand or explain why those claims are inaccurate or misleading. I'm guessing the published ratios are based on AHRI requirements and marketing decisions to publish the highest possible SEER #s. It's much more complicated than choosing the lowest SHR possible for hot-humid climates.

    It's true that low-load systems like mini-splits can have dehumidification issues in high performance homes but for the most part, they do a better job than single or dual stage traditional systems. From this FSEC research:

    "Variable capacity cooling energy savings typically around 20%-30% have been measured compared to fixed capacity systems in controlled house lab study. Research also found that better dehumidification is possible that limits overcooling and energy use. Recent testing of a new variable capacity system measured indoor humidity reduction of up to 15% RH points during low cooling load periods."

    Mini-splits offer the most variable load capacity of any available equipment. Cooling and heating loads in homes are never static, always changing based on weather and occupant use. Systems that can modulate their fan and compressor speed to match the changing loads saves energy.

    Few people in this forum are building so tight and super insulated to have the de-humidification issues discussed here. For the most part, it's a shoulder season problem, not peak load. Yet more reasons to specify heat pump water heaters, ERVs and use an experienced energy rater.

    Just because a traditional system is doing fine in a leaky, existing house does not mean it will perform similarly in a new, energy efficient home. Not sure how big your house is but $120 summer electric bill sounds high. I agree 3-4 mini-splits is where it probably makes more sense to do ducted but it depends on the details. Ducted-minis are an increasingly favorable choice.

    @Joe Macker As for my personal home, I did something I might recommend to close friends but is not a route I can suggest on a public forum and would never do for a client or spec build. I sized the system on an educated rule of thumb, knowing there is not much of a fudge factor for design conditions. This was partly to install a specific unit that has very low modulation ratings. I'm an outdoorsy guy who doesn't mind being cooler than normal for the 1-2% design conditions but so far the unit has kept up with the Tstat setting. I installed everything myself and had my HVAC contractor pull the vacuum and make the refrigerant connections. Thank you Andre!

    For others, I would suggest hiring an energy rater or mechanical engineer who is comfortable with mini-split specs and accurate energy modeling. Energy Vanguard out of Atlanta is someone I could publicly promote for this along withPositive Energy of Austin. I think they do sizing and design out of their regions.

    A local professional would be nice because you could get them to commission your equipment but that may not be necessary with mini-splits. Another great thing about mini-splits is they are pre-packaged and harder for HVAC techs to screw up. Having a Manual J and S from a mechanical engineer will get most good HVAC folks on board to install something smaller than they are recommending.

    Getting the Right Mini-split is a valuable resource, especially going the ducted-mini route. This along with all of Martin's other related articles are probably worth the price of admission if seeking a good path on this subject and energy efficient building in general.

  • D E

    did you see this part in the fsec link?

    "While VC systems have shown good potential for energy savings, it is clear that they
    need better humidity control during warm moist weather in mechanically ventilated homes
    especially those with high internal moisture generation. There are various factors that could
    impact RH such as occupant variable loads, amount of mechanical ventilation, dehumidification
    performance of air conditioners, and occupant operation of equipment. Indoor RH can vary
    widely as the following studies illustrate. Periods of elevated indoor RH were observed in four
    new field study Habitat for Humanity homes solely cooled using mini and multisplit systems
    without supplemental dehumidification. The occupied homes exhibited indoor hourly average
    RH exceeding 60% an average of 61% of the time (range 11% to 86% frequency) (Martin et al.
    2018). Another study of two homes in Austin, Texas found significant increases in humidity with
    50% frequency or greater of hours with RH greater than 60% after central ducted systems were
    retrofitted with minisplit systems (Roth, Sehgal, and Akers 2013). Research in a house lab with
    ASHRAE 62.2 ventilation found a supplemental minisplit system test without supplemental
    dehumidifier resulted in average indoor RH exceeding 60% between 4%-15% of the test hours
    depending upon the room (Withers 2016b)"

  • David Cary

    The compressor is more efficient, there are no duct losses and there is less need to push air around - which takes energy. So it isn't just "duct losses" that gets to 50%.

    The blower on a standard 2 ton uses about as much electricity as my mini does - to actually cool 1 ton.

    There is of course a blower on a mini - about 10% the size of a conventional.

    Now 50% was based on very base comparison system. The Seer rating on a Mitsu goes to 33. Code in my are is 13. Typical is 15.

    Saving 50% is not hard and, to repeat for emphasis, it is not only duct losses.

  • D E

    also, if you read the actual tests where the VC 21 seer unit beat the fixed 13 seer unit by 44%, they were testing at an outdoor temp of 76 degrees iirc and indoor temp of 75 degrees iirc.

    of course the high seer system would win in that condition that you hardly ever see.

    also I have seen 20 seer vc units with 10.5 eer .
    compared to my 13 seer 11 eer fixed unit , the high eer system is actually better I. the summer when outdoor temps are 100+ degrees

  • D E

    a few thoughts


    1. here is adetailed comparison of ducted vs ductless heat pumps. the ducted showed losses of approx 1% compared to ductless

    https://www.energytrust.org/wp-content/uploads/2018/04/XMH-DHP-Billing-Analysis_Final_wSR.pdf


    2. "Typical systems with ducts in attics or crawl spaces lose from 25% to 40% of the heating or cooling energy that passes through them. "


    lets be clear that these are unconditioned attics and crawl spaces, not conditioned.


    3. @David Cary


    the 33 seer unit has the following specs

    Moisture Removal Pints/h 0.2

    Sensible Heat Factor 0.96


    that would work in phoenix AZ and other desert areas and would be a disaster in most other parts of the country.

  • PRO
    Springtime Builders

    Not sure we should let a study on manufactured homes color our choices on typical single family but it is interesting. No mention of variable capacity or mini-split so I'm guessing the ductless versions were PTAC types not window units considering they had comparable installation costs to ducted. They do mention heads so could be wrong on this. Also lacking for ducted data was utilizing existing ductwork, duct configurations and SEERs. Research firm seemed frustrated with supplied data overall and says on the comparison of ductless to ducted: "Given the measures were offered under different program designs and not intended to be a perfect comparison the results should be interpreted with this context in mind."

    That study found much different results for ductless vs ducted than vast majority of research. Probably mostly due to the sampled manufactured homes being small and compact. Would love to see more research on ductless mini-splits vs ducted mini-splits in both manufactured homes and typical single-family homes.

    Energy loss of air passing through ducts can be reduced by keeping them in conditioned space. That's the low hanging fruit but does not eliminate losses through duct leakage. "Energy that passes through them" is different than the energy required to push air. Duct friction and turbulence adds to the energy use of ducted systems compared to ductless.

    David's point about fan size is a good one. To put it another way, the wire that powers my mini-split, supplies both indoor fan AND outdoor compressor is the same size wire that would power a traditional ducted system's FAN ONLY.

    Again, focusing on SHR or SEER only of minisplits can be misleading. Assuming the 33 SEER unit is the MSZ-FH06, that's a 1/2 ton unit. Can you even get a traditional ducted system that small?

    While the FH06 has a better SEER rating the FH09 might be a better choice with similar modulation levels while providing a better safety factor for design conditions. These are among the most efficient heat pump units available and will provide better moisture removal than those specs suggest. To say they are a disaster outside of the desert is not accurate.

  • D E

    springtime builders why do you think those units would provide better moisture removal than the specs suggest? those are the worst 2 units that mitsu has from a moisture removal perspective and they have units that go as high as 4.8 pints per hour.

    those units would not be good at all for a humid climate.

  • PRO
    Austin Air Companie

    David's point about fan size is a good one. To put it another way, the wire that powers my mini-split, supplies both indoor fan AND outdoor compressor is the same size wire that would power a traditional ducted system's FAN ONLY.

    This comment is true to a point, however the glaring problem with it is that the wire that powers your mini split is only cooling one room, where as the wire that goes to a traditional forced air ducted system is cooling the whole structure. (OR a significant portion of it compared to the mini split.)

    Certainly mini splits have their uses, but given what I actually do for a living.... the more equipment you have the more costly it is to maintain it, fix it and eventually replace it.

    You can argue duct losses all you want, but how much is that going to cost you compared to maintenance, repair and replacement? The mini split society will argue the savings of pennies, because once you've switched to the mini split option it's even more expensive to try to switch back to forced air ducted... and chances are you'll just simply move from the home with mini split systems installed in every room rather than deal with the chore of trying to remove and retro fit back to forced air ducted.

    If you have a single room that needs heating and cooling mini split is a good option to have, but outside that configuration in an American home I think within 10 years... maybe less in an extreme climate... maybe more years in a moderate climate... the cost or 'savings' you thought you had will evaporate... once maintenance and repairs start occurring like clock work.

    I say this based on 25 years of running HVAC service and repair in a hot humid climate. (Katy, Texas area)

  • PRO
    Charles Ross Homes

    Mini splits aren't a one-size-fits-all solution for every home or every climate.

    My "track record" with mini splits spans about 12 years. In my experience, and from what I've read, I don't think their life expectancy is that much different from conventional heat pump systems. Indeed, ductless mini splits eliminate some of the factors that contribute to the premature failure of compressors in conventional systems (e.g., unfiltered air leakage in ductwork, improper duct sizing) and inverter technology eliminates hard starts and minimizes short cycling.

    When choosing a system, there are both financial factors (initial cost, operating cost and maintenance cost) and intangible factors (occupant comfort, occupant health, flexibility, aesthetics, and environmental impact) to be considered. An independent HERS rater is a great resource for helping make an informed choice about the best system for your needs.

  • PRO
    Springtime Builders

    Perhaps you missed that I have a single mini-split serving my entire home. That's one small wire and one piece of equipment to manage. Ducts are still there, can always go back in future.

    I used to share mini-split disdain due in part to my HVAC contractor's humidity concerns but mainly for the wall wart snobbery. Aesthetics and better distribution is why I still prefer ducted systems for most average sized 3BR 2BA designs.

    I have seen opposition to mini-splits melt away from HVAC contractors in recent years and it seems to be age related. One savvy tech told me recently that being able to quickly diagnose error codes are a huge advantage over equipment a la carte. Most HVAC contractors have zero experience with high performance homes where mini-splits can often make just as much sense as retrofits, bonus rooms and additions.

    @D E As mentioned, I'm not smart enough on this subject to fully answer your question. Your concern is valid but your claims not so much. I have a Mitsubishi FH09, and live in a humid climate. It's the best piece of heating and air-conditioning equipment I've ever lived with. No problems dehumidifying in the two hot summers it's been installed and electricity costs are unbelievably low. It also has a dry function which I have not used but could solve the problems of the few times of year in the shoulder seasons that humidity gets high.

    There are cases of high humidity out there, but they seem rare. The FH09 is a popular model with thousands(?) being used in East coast climates. This technology was pioneered in very humid south pacific regions. If they were a disaster, they would not be so highly recommended.

    If you don't vent frequent cooking, steamy showers, have a humidifier, dryer water lint trap, lots of houseplants or an indoor swimming pool, then a mini-split might not cut it.

    If you are building to passive house levels of airtightness and bringing in ASHRAE 62.2 levels of hot-humid climate outdoor-air to a small load home, then you might need extra dehumidification, but a traditional ducted system will also have trouble in that situation.

    From my short internet searching some related threads, this one an excellent read if you are also interested in calculating heating loads: https://terrylove.com/forums/index.php?threads/yet-another-mini-split-sizing-question.70906/

    The one thread I could find with FH09 humidity issue: https://www.greenbuildingadvisor.com/question/minisplits-and-moisture-removal-effectiveness

    Most mini-split humidity issues are from oversizing, a problem with traditional systems too. For the most part, the SHR concerns are a low-load problem. I can't find the HVAC-Talk thread but a poster may have summed it up best when they say something like; "high efficiency cooling and humidity removal have opposing dynamics."

    Warm climate humidity issues in high performance construction is a relatively new problem. This JLC article is a good one on the subject, with recommendations of separate dehumidifiers from the owner of Positive Energy, who I linked to above.

    I still agree with the prevailing energy expert wisdom and results from the first research link I posted. Mini-splits are better at moisture removal. Their modulation ability to exactly match changing loads is a more important characteristic than the listed moisture removal specs, which were potentially manipulated by manufacturer to publish a higher SEER rating.

  • PRO
    Charles Ross Homes

    For many applications neither a conventional air conditioner nor a mini split is adequate for dehumidification purposes. We like to keep R.H. less than 50% (approx. dewpoint of 55F at 70F dry bulb temperature) which typically requires supplemental dehumidification, particularly in shoulder seasons.

  • D E

    @Austin Air Companie

    well put. Im building a 4 bed 2.5 bath , 1 media room house. It would be a nightmare to condition this without ducts.

    it would be a bear to clean the units, and maintenance would definitely be an issue.


    I would also rather deal with 1 or 2 drains, than 5-7 drains

  • David Cary

    I think nightmare is a bit extreme. There are lots of people with 5-7 units. There are lots of people with tight homes and 2 units. Then there are multihead units.

    In most of the world, mini-splits dominate.

    There are advantages and disadvantages of all systems. Build a tight house so that you don't need much of any of it.

  • D E

    "The one thread I could find with FH09 humidity issue: https://www.greenbuildingadvisor.com/question/minisplits-and-moisture-removal-effectiveness "

    @Springtime Builders did you see this quote in that thread?

    "For the record, many mini-splits operating at less than 1/2 rated load (a common occurrence, even when perfectly sized) have little to no latent removal (humidity reduction), worse than a unit that cycles (turning off compressor and fan so that little re-evaporation occurs). Why - because the mini-split interior fan doesn't modulate down as far as the compressor, leading to excessive CFM/ton. Regarding dehumidify mode: in most cases, not a viable solution. But let's see some specs regarding part-load SHR, temperature control, etc.

    Plan on running a dehumidifier in any new house in a humid climate.

    Table 7: https://www.nrel.gov/docs/fy11osti/52175.pdf "

    See page 32 and 33 of the link above for the sensible heat ratio. now, this is a unit that pulls 2.9 pints per hour so its a GOOD unit, and the sensible ratio is still .7 or higher for most of its range.

    it does get around .5 when the indoor humidity is above 65% but thats about it.

    for comparison my unit is at .4 when indoor humidity is between 52-55%

    and the fe12na is a nominal .73 SHR, with 2.9 pints of moisture removal per hour

    see page 30 here

    http://jackmansinc.com/wp-content/uploads/pdfs/mitsubishi-m-series-brochure.pdf

    what is your indoor humidity when your fh09 is running?

    also, with a single split serving your entire home, what is the temparature range in the house? what temp are your bathrooms, bedrooms, etc?

    anyhow, thats neither here nor there. In hot humid climates you wont see the savings by using mini splits because

    1. you probably have to run supplemental dehumidification

    2. most high seer (20-22) range splits have similar EER as lower seer (13-14) units

    3. Correctly sized ducts in the conditioned space do not exhibit high losses.

    but you will have to deal with maintaining and cleaning multiple units

    btw, I modelled a 2k sq ft house in Beopt, 24seer unit , ducted in the conditioned space vs ductless, losses were ZERO

  • D E

    " In most of the world, mini-splits dominate. "


    most of the world doesnt build 2500-7000 sq ft homes

  • chispa

    As far as humidity, it might be worth noting, that these units have been manufactured and used for decades in Japan. I lived in Tokyo for 3 years and believe me, it is humid/damp year round and pretty hot in the summer. Spent time in many types of residential and commercial buildings and never felt that their systems couldn't handle the humidity.

  • D E

    @chispa


    I dont disagree with that at all. Even here in the US you can get a mitsubishi mini split that will move 4 pints an hour. an absolute crusher. eg the mszfh15NA so it wouldnt surprise me if the japan units also have high latent capacity.

  • PRO
    Austin Air Companie

    Perhaps you missed that I have a single mini-split serving my entire home. That's one small wire and one piece of equipment to manage. Ducts are still there, can always go back in future.

    @Springtime Builders, No I didn't miss that... but some climates don't need air conditioning at all. Plus everyone has different comfort levels... so to argue that a single mini split won't work in this context is pointless banter. But, professionally speaking in my market (hot, sticky climate) that succeeding without complaints is not likely. (unless it is only to cool a single small room space aka spot cooling)

    One savvy tech told me recently that being able to quickly diagnose error codes are a huge advantage over equipment a la carte.

    So the answer is to not know what you are doing and rely on the equipment to tell you what is wrong? I can tell you right now, that under certain circumstances that is not going to end well for you or anyone else that believes this nonsense. This doesn't sound savvy to a 'licensed HVAC contractor'... this sounds like 3:10 to disappointment. (3 min 10 sec) With that said, I can understand why a 'tech' would think like this.

    @DE: I would also rather deal with 1 or 2 drains, than 5-7 drains.

    Yeah not to mention having to clean all those filters. I like the ability to throw a dirty filter away pop in a new one in couple locations of the house and be done with it. Plus if the drain clogs which is rare for any house I own (including rentals) due to elevated & pitched drains... if it does clog it doesn't create a puddle on the floor or a big mess from having to work on it, putting dirty hand prints all over the wall.

    But people rarely think about maintenance and the hassles these things invoke.

    @Charles Ross Homes: Indeed, ductless mini splits eliminate some of the factors that contribute to the premature failure of compressors in conventional systems.

    There isn't a problem with premature failure of compressors in a conventional (forced air ducted) system. I have installed countless condensers over the span of the previous 12 odd years going on 13 in which I have run my own HVAC company. I haven't had a single compressor failure on ANY 'new' condenser I've installed.... including R22 Freon to R410a conversions. (Conversions mean reusing the evaporator and converting it to work with R410a)

    If you are having premature failures you are probably using those with 25% of the necessary knowledge to do this type of work... when to avoid these kinds of problems requires 75% more knowledge of knowing 'what not to do'.

    I know builders work on thin margins, which the things I state here won't make much difference to a builder. If so it's a grain of sand on the beach...

  • PRO
    Charles Ross Homes

    @Austin Air Companie


    You've made it crystal clear that you don't like mini-splits. Your experience and opinion is that of only one installer. Mine is the experience and opinion of only one residential builder. Plus, I've only been designing, building and remodeling homes for 20 years, and only did engineering design and construction for 18 years before my current gig (and yes, I'm a licensed PE,) so anyone weighing my opinion needs to take into account my lack of experience.


    Mini splits aren't a one-size-fits-all HVAC solution, but they do operate in a large portion of the world and so are worth considering. Homeowners would be well served to consult with a HERS rater in their area to get the skinny on the range of locally-available options from someone who's not trying to sell HVAC equipment or a maintenance contract.

  • Joe Macker

    I am guessing that airflow is an important factor in maintaining the temperature of the space. I am concerned that an open stairway from the first to the second floor will result in the first floor not getting very hot. Is there a modeling tool that will take this into account?

  • D E

    @Charles Ross Homes


    what exactly is a HERS rater going to do for average joe who is not looking for a HERS rating for their home?

  • David Cary

    Anyone building a custom home in 2019 should have a HERS rating. The newly built townhome I rented had a HERS rating - and it was clearly a bargain basement spec. In many markets there are incentives to have HERS ratings.

    I wouldn't pay a dime extra to know my HERS rating but I still have one because it was part of other things.

    Anyone building should be having energy modeling - based on long term costs and potentially short term incentives. If you are building custom, you presumably are going to be in the house for long enough to get a benefit.

    Obviously Beopt has a problem with modeling (or the inputs were wrong). Nothing has zero losses. Claiming something has zero losses shows some ignorance of basic physics.

    I live in central NC and don't need to run supplemental dehumidification. But my mini is running at 100% most of the time based on my specific design situation. I set it up that way specifically to maximize dehumidification.

    Absolutely fair point that most of the world has smaller houses. But they have bedrooms still.

  • D E

    All you need is a blower door test. absolutely no need for a HERS rating unless some financial incentive is involved.


    also new homes all require a blower door test anyway and the code requirements are tight enough that chasing additional gains to attain some HERS or PASSIVHAUS or whatever is a waste of money.

  • PRO
    Charles Ross Homes

    DE,


    A HERS rater is an independent third party (or should be) who is able to model home performance under a variety of different scenarios pre-construction and test performance post construction to ensure systems are meeting performance criteria. By evaluating different alternatives in the design phase, HERS raters assist homeowners in making informed choices about optimum insulation, windows, ventilation, and sizing of HVAC systems.


    Here's a link to additional information:


    http://energycodehelp.com/index-energy-modeling/

  • D E

    hi Charles I know what hers is. I'm saying it's useless and a waste of money

  • PRO
    Charles Ross Homes

    DE

    I don't advocate HERS, Energy Star, LEED or any other pedigree for a home, but I do value the input of those professionals when evaluating alternatives in the design phase. Judging from the myriad questions posted here on houzz.com, I submit lots of others do, too.

  • Joe Macker

    @D E for the blower door testing what is a number to shoot for if one is building from the ground up? I haven't seen these numbers being published by new home builders... or maybe i just missed them.

  • Joe Macker

    @D E I think I missed an earlier message of yours. I like mini-split because it is relatively quiet (compared to forced air), has settings that can be different in each room (assuming a mini-split per room) and the heating/cooling can be restricted to certain rooms at certain times of the day. E.g. at night no need to heat up the living room, just the bedrooms.

  • PRO
    Charles Ross Homes

    @Joe Macker


    The allowable air infiltration rate for your home will be dictated by the applicable building code in your area. Here in Virginia, the current building code is based on the 2015 International Residential Code (IRC) with a few revisions. The 2015 IRC incorporates the 2015 International Energy Conservation Code which specifies a maximum of 5 air changes/hr (ACH) in climate zones 1 and 2 and a maximum of 3 ACH in zones 3-8. ACH is calculated based on blower door testing at 50 Pa.


    The lower the ACH the "tighter" the home is and the more need for mechanical ventilation. ASHRAE standard 62.2 is a good reference for the minimum ventilation required. I don't think 62.2-2019 has been published yet, but that would reflect the most current thinking on the minimum recommended mechanical ventilation. If it's not available then you can refer to ASHRE 62.2-2016.

  • PRO
    Austin Air Companie


    You've made it crystal clear that you don't like mini-splits. Your experience and opinion is that of only one installer. Mine is the experience and opinion of only one residential builder.


    @Charles Ross Homes.


    Well obviously I haven't made my opinion as clear as I would like. Because number one I am not an installer in the true sense of the word.


    I am a HVAC service and repair specialist.


    Do I install new equipment? Yes.

    But that is not my primary function.


    More often than not I am called after the builder is long gone to correct and or repair, adjust, maintain and on occasion install new HVAC equipment. I mostly work on HVAC systems of residential homes, but on occasion I am called into repairing commercial HVAC systems.


    (Commercial systems not so much, because often times this market segment is better suited for a commercial HVAC company. So there are certain requirements for Commercial customers that use my services.) Commercial HVAC is many times similar to residential, but many times it's as different as night is to day.


    What does residential and commercial systems have to do with mini splits?


    It's quite rare that you would see a commercial package system installed in a residential home. Not that I hate package systems. They are much easier to work on, so there is no hate in that regard. Everything is right there in a package unit. But for a residential building a package system is often times not 'practical'.


    The same can be said of mini splits. To give you an illustration to the point of it... Go to a hotel / motel. Say there is some 300 individual rooms. Some are vacant, some are not. But some times of the year the whole 300 rooms are used to capacity.


    Under that scenario it wouldn't make any sense to install a package system. The design of the building is better suited to be served by either individual pieces (mini splits, ptac systems etc) or a zoned chiller type set up.


    In this way you use equipment for what it was designed to do. So with that said... what is the difference from a residential home compared to a hotel / motel?


    The comment that mini splits are used all over the world doesn't mean anything. It's not a 'reason' to use them over something else. Would you use a screw driver to pound a nail?


    Hotel / Motel: typically have on site maintenance department. So in that sense the additional maintenance requirement is already included in the operation of the building. That is not the case in a residential home.


    It's not that I hate mini splits. But I am explicit why they are a niche product. Why would I do that?


    I service the Katy, Texas area.

  • PRO
    Charles Ross Homes

    @Austin Air Companie


    If I've incorrectly labelled you as an HVAC installer, please accept my apologies. I thought it was a logical conclusion based on your statement:

    I have installed countless condensers over the span of the previous 12 odd years going on 13 in which I have run my own HVAC company. I haven't had a single compressor failure on ANY 'new' condenser I've installed.... including R22 Freon to R410a conversions.


    I don't consider HVAC contractors--whether they're performing installation or service to be a lower life form.

  • Joe Macker

    Apologies if this is somewhat tangential. Does anyone have an opinion on oil filled heat radiators (preferably wall mounted) and with a fan. Especially for small bedrooms. Compared to any of these HVAC systems that has got to be dirt cheap.

  • D E

    Joe, if it uses electric resistance heat it has a cop of 1.


    a good minisplit will have a COP of 2 - 5, depending on outdoor temp.



    so the question is, will you see the savings by spending significantly more on a minisplit but using half or less the energy to heat that room in the winter.

  • David Cary

    Joe - the majority of the US prefers a/c and radiators don't have that option. So - sure it is cheaper and less efficient and doesn't have air conditioning.

    DE Certainly not every jurisdiction requires a blower door test. I am not sure that a majority do. In NC, it is an optional test - required for Energy Star but not otherwise.

    It is true that going below an ACH of 3 is not a very rewarding move but it absolutely helps. I suspect the majority of new houses have ACHs well above 3.

    Not sure why you would diminish the value of an independent energy rater - which generally use software (like Beopt) and model different scenarios. They also tend to give a HERS rating.

    To the uninitiated, discouraging a HERS rating is discouraging a third party rating. It isn't necessarily so but since HERS is pretty universal, they go hand in hand.


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