Ductless Mini-split air conditioning
tdfromny
17 years ago
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mike_kaiser_gw
17 years agotdfromny
17 years agoRelated Discussions
Ductless Mini-split Heat Pump
Comments (17)Thank you for the responses! Brian Knight ~ Our home is one level (on a slab) with three bedrooms. It will be an open floor plan, just over 2,000 sq.ft. When I said "relatively" air tight/energy efficient I was referring to our quest to balance efficiency with using healthy materials (not a fan of spray foam for example). We do want to be mindful of proper ventilation/air exchange and have looked into doing something like this (copied from http://homeenergypros.lbl.gov/group/1000homechallenge/forum/topics/panasonic-whisper-green-w-ductless-heat-pump?xg_source=activity): "Some minisplits may have a small ducted system. Dave Robinson, www.GreenEarthEquities.com buys foreclosed homes in central California that he renovates, using two,1 ton Fujitsu mini-splits. He ducts one to the bedrooms and bath with very limited ductwork located in the hall ceiling. The other unit is ductless, and conditions the living room and kitchen of the one-story ranch homes. There are significant cooling loads with lots of 100 degree weather. His approach of combining ducts and ductless results in simple systems and homes with low energy bills. Dave has case studies posted on his website." Reply by Dave Robinson on August 31, 2011 at 10:12am "To be more exact, we use one outside unit (2 ton is the smallest they make in this model - so we use it on everything). One inside unit is the conventional mini split high on the side wall in the main room ... the one that everyone associates with mini splits. The other inside unit is mounted on the ceiling at the mouth of the hallway & delivers air to all the rest of the rooms thru a small duct system that we mount on the existing ceiling of the hallway. So the unit and all the ducts are inside the envelope. Then new drywall is added, reducing the hallway height about 10 inches. We throw the factory filter away and allow a 20 x 30 filter grille right under the air handler to provide a lot more filter area as well as access to the unit without breaking the building envelope. You can see pics of this hybrid duct design at A Good Business? How Long? Plus Ducted MiniSplit Update (Click the right arrow on the photo in the center of the page and it will take you thru a few other slides from that webinar and you'll get to the Mini Split photos). You'll notice we use galvanized pipe. That, along with the oversized return keeps the static way down which is essential for efficiency on these units. This unit has now been in two years. The owner loves it. Zero problems. Has utility bills less than half of his neighbors. This job also used a Panasonic ERV. We mount the ERV very close to the return of the ducted system and in the pick-up area of the wall mounted unit so all fresh air is circulated by the main system with no additional equipment needed. It works well for us and we have adopted this as our main system. It's the one we specify every time unless we are keeping old equipment that's not too old or too over sized for after our renovation. You'll also notice that we mount the outside unit on the roof instead of on the ground. Lots of reasons." We are thinking this might work with our floor plan: Kirkhall ~ Thanks for sharing your personal experience. I have read more on the HVAC forum. My interest in posting here was to see if ductless mini-splits were at all a preferred choice by those building new homes versus just being used for retrofitting/new additions. Niteshadepromises ~ "Based on all my research the operating costs are pretty substantially lower which we're looking forward to and hopefully might offset the initially higher install cost." This is in line with what we are thinking too! Good luck with your build! David Cary ~ The tax credits are wonderful, however, there is that pesky problem of having to pay upfront. With some budget reworking, this may be possible. However, my concern relates to your comment, "But I'm not sure getting all fancy is worth it.... R20 net walls, good southern exposure with some thermal mass. You won't need that much heat and you shouldn't need a/c." We don't want to pay for more than we need. The difficulty for us has been determining what our need is when factoring in the passive solar. I also agree with: "I've thought about this a lot and I don't know how cold you get but if you have total control of design and southern exposure, your best bet is lots of solar planning, tight house with thick walls. Cover the windows well at night. Then put the money in PV. Code will require too much of minisplits to be cost effective." To satisfy code, what would your recommendation be for a thermostatically controlled system that is reasonably efficient and cost effective (presuming we could swing the PV)? With good solar planning, another viewpoint is to put in some baseboard heaters to satisfy code. Is this reasonable or silly? Dekeoboe ~ I'm interested to know what you chose and why? Flgargoyle ~ As our heating and cooling days are very similar, it's good to know that you think it's a viable option. Though it seems I'm in the minority, I don't really mind the look of the wall units. Maybe it's because I don't find vents and returns all that pretty! Lori in the NW ~ Thanks for your opinion ~ they certainly are not for everyone! This post was edited by daisyblue on Fri, Feb 22, 13 at 17:45...See MoreDuctless HVAC (not mini-splits)
Comments (2)Unico is not ductless, just smaller supply branch hoses off of insulated square or round main feeds under higher static pressure, thus called high-velocity systems. Definitely not a do-it-yourself installation without HVAC install knowledge, plus high-velocity training, design and layout experience. Not to mention the refrigeration tools, pumps, gas, guages and brazing torch required for proper install....See MoreRE: Ductless Mini-split air conditioning
Comments (1)Your missing the tools to install it properly and perhaps legally....See MoreWhen will ductless mini splits work
Comments (12)My perception about uneven heat or cool from mini splits is that the former is more of a problem. I live, however, in a raised house with cold floors and it might not be so bad in other situations. Part of the issue is that as the set point is reached, the blower slows down considerably. I am looking at data that indicates it drops to about 1/3 of the highest air flow in some Mitsubishi units. Under conditions near the set point, there is considerably less mixing of air in the room and lots of opportunity for thermal stratification. They make good ceiling heaters. In heating mode, or in dehumidification mode, I always have ceiling paddle fans going in the rooms that I have them. It fixes the problem. Air conditioning does travel through walls to some extent. Structures vary a great deal in this respect. If you have a well insulated and air sealed home, the heat and moisture transfer rate between rooms is much higher than through the exterior walls so more even conditions will occur. In a poorer structure you will see a larger temperature differential between rooms with heating and cooling sources and those that do not. That is why zoning does not save you much energy in good structures. Accepting all that, no, you can't get the performance in evenly cooling a whole home with the most common type of mini splits that you can with higher static pressure ducted systems. That said, I like the way mini splits work in a home. A typical summer weekend day with both of us around goes like this in my house. Wake with one bedroom unit going powered by an outdoor unit supporting two. The door is open so the rest of the house is getting some cooling. It is not uncomfortable anywhere unless you start doing push-ups. The high wall unit is running at low capacity and mostly dehumidifying. Hit the kitchen for breakfast. If a lot of cooking is to be done, turn that one on. Outside to do work in the cooler part of the day lots of times for me, but come in for exercise sometime in the AM and turn on another unit in that room. The remainder of the house is still pretty comfortable. As we move around the house and heat load keeps increasing, we may have 4 of 7 going, but probably more like 3 at a time. We have a mix of 6000 and 9000 btu high wall units. During the course of the day we have gone from running less than 6000 btu to a theoretical max of maybe 30,000 btu, but those 3 or 4 units are not running anywhere near full capacity. They are really sucking the water out of the air so the indoor temp is probably above the design temp and comfortable With humidity in the low 40s. We have a total of 51,000 btu. The only time I've ever run it all is for fun, coming back from a trip, or If I forgot to set them to come on in the afternoon. It has been a long time since I reviewed the data. Total heat loads for the house look like about 31,000 btu and install "recommended" 38,500. I guess the difference is a safety margin. In hindsight, I should of convinced the contractor to skip the 9000 btu units. That would have dropped us back to 42000 btu and would have been adequate. What we have works due to variable speed nature of the systems. They run at highest efficiency at part load and that is notable. I often tell people that if you are happy with the cooling you get from window units, mini splits will work for you. For similar reasons, I think that they are a great solution for a home with nice hydronic radiant heat in an area where not much cooling is needed and the homeowners don't want to lose the hydronic. If a person in Japan has 300 sq ft, that is 1200 square feet for a family of 4. That is not shocking to me. I am looking at one source that says 300 per person is what the US had in the 1950s. Below is another source that is fun to look at.. What is driving the increase, larger homes or smaller families. The answer is both and the magnitude of the effects is different in different eras. The biggest problem that I see with mini splits is not big rooms because you can always make a bigger one or add a second unit. There are even good controls for two in one area. The biggest problem is installing low enough capacity since the smallest are 5000-7000 btu depending on manufacturer. Yes ,the variable units throttle back to about 30% of that, but that is the compressor so with more indoor units ganged on a single outdoor unit means not as much modulation and more bang-bang operation. That means in a place with smaller rooms (Japan), mini splits should be a bigger problem than in places with big rooms (USA). The inability to hit low enough capacity with a unit in each room is part of the reason for the higher cost, you will be over capacity no matter what you do unless you have very large rooms. https://www.propertyshark.com/Real-Estate-Reports/2016/09/08/the-growth-of-urban-american-homes-in-the-last-100-years/...See Morehomeownerplus
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