"mini-split" or ductless heat pumps

[Highbeam]

In my part of the country our electric is 10 cents per KwH and I have no NG service or propane. My little electric wall heaters are fine but pretty noisy and expensive to run as a backup heat source. Also they only provide heat and are generally considered ghetto and a cheap way to heat a home, so poor for resale. I have no ductwork in the home. The home is single story on a crawlspace, 1700 SF with 8 foot ceilings, it is only like 26' wide and 60 some feet long with upgraded insulation and windows.

I've been considering these ductless heat pumps to heat and cool my home. Our climate is moderate with most of the year around 50 degrees out. We get some 100 degree days and some days in the teens. Air source heat pumps are very common in this climate. I would expect that the core of the home would be heated with the heat pump and the remote rooms would keep their little heaters which should greatly simplify the installation.

Does anyone have any experience with these things? The installation looks simple. Are they noisy, expensive, dependable, ? Our local utility is offering a fat rebate for the installation and maybe OBAMA's credit too.

Does the condensate line run back to the outdoor unit as the vendors imply?

 

[Whitebread]

I've installed a few. We have 2 ductless split A/C only units in our offices. I've used Carrier, Sanyo, and Fujitsu. All of which work fine.

You may find that it's more economical to do a traditional split system heat pump, especially on a single story home. If you have space limitations you can install a package unit where the air handler and condenser are both outside and only the ductwork runs under the house. Ductless splits are usually installed as supplemental heating/cooling or in areas where there isn't enough physical space for duct work.

You can also look into a multi-zone ductless split. I know Fujitsu makes one, and I think the others do too. 1 multi speed outdoor unit feeds 2-3 indoor units, each with individual controls.

They aren't particularly noisy, they aren't particularly cheap, and they are dependable IF they are installed properly. They often have lineset limitations that must be adhered to or you'll be very unhappy.

Condensate runs outside, doesn't have to go to the outdoor unit. Either gravity drain or small condensate pump to move it out of the house.

 

[Highbeam]

Wow, the installed cost is well over 5000$ AFTER the 1200$ local rebate for a 2 zone single compressor unit. The lineset limitation would be difficult too since the max seems to be 50 feet and the long skinny house would make that a challenge.

I will need to consider the traditional heat pump now that this won't be a low price alternative. Are there lineset length issues with traditional heat pumps?

 

[wenger7446]

My buddy has a Sanyo split system in his house (near Philly). I have not felt the heat but the AC is great. The units are really quite (both the evaporator and condenser) and the seem very efficient. Another nice feature is that is allows a highly zoned system too.

Ryan

 

[Whitebread]

Wow, the installed cost is well over 5000$ AFTER the 1200$ local rebate for a 2 zone single compressor unit. The lineset limitation would be difficult too since the max seems to be 50 feet and the long skinny house would make that a challenge.

I will need to consider the traditional heat pump now that this won't be a low price alternative. Are there lineset length issues with traditional heat pumps?

I've run them over 100' before. They usually come precharged for a 50' lineset. You just have to add refrigerant on longer runs. You aren't likely to run into lineset limitations on a traditional heat pump in a residential setting.

 

[Highbeam]

Thanks so much WB. One final question since I've got you, can a heat pump be used to heat water instead of air? Meaning, could I run a forced hot water system through the house as a simple retrofit and then heat the water with the heatpump? I see this with geothermal but not with air source.

Thanks again

 

[Whitebread]

I hate to be vague, but I have to answer Maybe. The problem potential problems would be:

1. Insufficient temp rise off the heat pump. Modern heat pumps put out 110-120 degree air on average. Since a forced air system only requires a 16 degree increase over ambient to heat a given space, that temp range is fine. (On a related note, that's why the old heat pumps got a bad rep - they delivered 90-95 degree air which would heat the house fine, but felt cold on the skin if one stood near a duct) On a water based system you're relying on radiant heat and/or natural convection currents to heat a space, and I'm not sure the temp differential would be sufficient (water would be 120 or so at best, and the greater the temp difference, the faster the heat exchange). Most gas fired forced air run furnaces 140 degrees +, and of course boilers run even hotter, so I'm not sure the heat pump would be hot enough to provide efficient heat transfer.

2. Defrost cycle. I've never installed a ground source heatpump though I am somewhat familiar with them, so I'm basing this on the principle rather than experience. If your ground water source never gets much below 55 degrees, the heat pump can extract more heat than an air source in cold temps, and it shouldn't have to go into a defrost mode. Your air source heat pump will have to go into defrost regularly in temps much below 45 degrees (it reverses back to air conditioning mode to warm the condenser coils and melt the frost that accumulates). At that time your secondary heat source (usually electric strips in the air handler but can also be a gas furnace) comes on to keep the air handler from blowing cold air. You would have to install immersion heaters in your water loop to counteract the cooling effect of the heat pump heat exchanger in defrost cycle.

3. Summer. You'd spend 3/4 the cost of a complete heat pump/ ac forced air system without getting the benefit of air conditioning.

I've never seen an air source heat pump tied to a hot water loop, but I don't want to say it couldn't work. For your application I think it would be much more economical to install the ductwork for a forced air system. Then if you wanted to it would be simple to add a water coil in the ductwork plumbed to your woodstove. You could then shut off the heat pump if you get much below 40 degrees and use the air handler fan to let the stove heat the house. A heat pump becomes an energy hog at low temperatures anyway.

 

[Wet1]

I've been toying with the idea of adding a couple one ton Fujitsu 12rls high efficiency mini split systems to our house. I believe they are rated at 25 seer/ 12 hspf. I want them for the AC, but I think the heating capability would come in pretty handy during the shoulder seasons when it doesn't make a lot of sense to light a fire in the BK. I've found a guy selling the 12rls for $1200 each, plus linesets, and they do qualify for the 30% tax credit. I'm waiting to hear back from him, to confirm everything, but I think I'm going to purchase them if he can produce the units for this cost.

Now if I could just easily tap this into my DHW system for cheap DHW...

 

[Hansson]

I hate to be vague, but I have to answer Maybe. The problem potential problems would be:

1. Insufficient temp rise off the heat pump. Modern heat pumps put out 110-120 degree air on average. Since a forced air system only requires a 16 degree increase over ambient to heat a given space, that temp range is fine. (On a related note, that's why the old heat pumps got a bad rep - they delivered 90-95 degree air which would heat the house fine, but felt cold on the skin if one stood near a duct) On a water based system you're relying on radiant heat and/or natural convection currents to heat a space, and I'm not sure the temp differential would be sufficient (water would be 120 or so at best, and the greater the temp difference, the faster the heat exchange). Most gas fired forced air run furnaces 140 degrees +, and of course boilers run even hotter, so I'm not sure the heat pump would be hot enough to provide efficient heat transfer.

2. Defrost cycle. I've never installed a ground source heatpump though I am somewhat familiar with them, so I'm basing this on the principle rather than experience. If your ground water source never gets much below 55 degrees, the heat pump can extract more heat than an air source in cold temps, and it shouldn't have to go into a defrost mode. Your air source heat pump will have to go into defrost regularly in temps much below 45 degrees (it reverses back to air conditioning mode to warm the condenser coils and melt the frost that accumulates). At that time your secondary heat source (usually electric strips in the air handler but can also be a gas furnace) comes on to keep the air handler from blowing cold air. You would have to install immersion heaters in your water loop to counteract the cooling effect of the heat pump heat exchanger in defrost cycle.

3. Summer. You'd spend 3/4 the cost of a complete heat pump/ ac forced air system without getting the benefit of air conditioning.

I've never seen an air source heat pump tied to a hot water loop, but I don't want to say it couldn't work. For your application I think it would be much more economical to install the ductwork for a forced air system. Then if you wanted to it would be simple to add a water coil in the ductwork plumbed to your woodstove. You could then shut off the heat pump if you get much below 40 degrees and use the air handler fan to let the stove heat the house. A heat pump becomes an energy hog at low temperatures anyway.

There are some brands that make air/water pumps. I dont now i the sell them in the US but it maybe is interesting for you that work with heatpumps.

http://www.nibe.eu/Domestic-heatingcooling/Airwater-heat-pumps/
http://www.euronom.se/112_Heat_pumps
http://en.ivt.se/products.asp?lngID=471&lngLangID=1
http://translate.google.se/translat...hp?cid=26&pid=23&sl=sv&tl=en&history;_state0=

 

[mbcijim]

Do a search here for 'desuperheater'.

I have one for my ground source heat pump a/k/a geothermal. My electric bill was $98 for June 15-July 14 and $104 for July 15- Aug 14.

I cool about 3,400 sft above grade. That includes my electric hot water. I used to just have the condenser outside at my old house, where I cooled about 1,000 sft less (above grade) and regular hot water. In the summer my bills ran into $200-$240.

I am VERY happy with my GSHP with desuperheater.

 

[Wet1]

A couple of questions about heat pumps...

I'm going to go ahead and add a couple of one ton Fujitsu 12rls high efficiency mini split systems to the house (in CT). They are rated at 25 seer/ 14 eer / 12 hspf. As mentioned before, I want them for cooling, but I like the idea of using them for supplemental heating as well. At what outdoor temp are they no longer efficient to heat with? When it gets really cold out (say 15° F), are they any less efficient than a traditional electrical resistance heater?

I'm also trying to decide if it's worthwhile keeping my pellet stove which is now used for shoulder season heating. My GUESS is the heat pumps might be just as cheap to use and are obvious less hassle. Thoughts?

 

[Wet1]

Le Pook,
Do you care to be a little more specific in your response???

 

[Whitebread]

The traditional breakover point has always been 40-45 degrees F. Lower temps drastically reduce the efficiency of heatpumps because they have to defrost so often, and defrost cycles last longer . That being said, it's still more efficient than using straight electric resistance coils, but becomes more costly than a gas furnace (unless gas prices are unusually high in your area). For customers who wanted premium efficiency without using "alternative fuels" such as wood/corn stoves, I used to install a heat pump and gas/propane furnace. It had an outdoor thermostat so the heat pump would run down to 40 degrees. Once the outside temp dropped below 40 the heat pump would shut down and the furnace would run. It was a large initial purchase but the efficiency increases justified the expense for those who didn't want the work of a wood stove, etc.

It all depends on your climate. In southern/temperate areas, heat pumps are great. Here in Kansas City, it's about a wash. You'll find a pretty even mix between heat pumps and natural gas furnaces. Very few oil burners because it's not readily available. Farther north you'll see fewer and fewer heat pumps. When I used to do HVAC I lived on the Virginia coast, and it was an even mix of heat pumps, gas furnaces, and oil furnaces/boilers.

 

[Wet1]

Thanks Whitebread. It sounds like I might just be better off using the heat pump for shoulder season temps and selling the pellet stove/pellets. I will do most of the heating with the wood stove during the colder weather. We also have NG boilers to fail back on should we not be around to feed the stove during the cold months.

So are you saying a heat pump is still more efficient than using straight electric resistance coils, even at say 10° F?

 

[begreen]

Our HP wouldn't be working at all at 10F. It really depends on the rating of the heatpump and to a certain extent to the quality of the installation. Our heat pump will try very hard to pull the last drops of heat out of 25 degree air before giving in to the resistance heaters. At 32, no problem. But this with a high efficiency, 2 stage unit and our ductwork is tightly sealed and well insulated, so there is little heat loss between the coil and the registers. We still rely mostly on the woodstove. It just feels nice. But the heat pump does greet me at 6:30 am keeping the house warm when the fires have died out. This is mostly a shoulder season phenomenon. High efficiency, 2 stage units do work nicely in our climate zone. But get a good one.

 

[Wet1]

Thanks for the info BG. The Fujitsu units are rated down to 5° (which seems very low, if not optimistic, to me), but I can only image how inefficient they must be at those temps.

 

[DBoon]

Keep in mind that the outlet air from an air-source heat pump varies with the outside temperature. At 40 degrees outdoor air temperature, the outlet air is pretty warm and it feels like "heat". At 20 degrees, the outlet air is probably around 72 degrees and feels "drafty", and the efficiency of the heat pump is going way down (maybe only 2x more efficient than electric resistance heat, so becoming less competitive with fossil fuel heat, and less comfortable). I can't imagine what a heat pump would do at 5 degrees outdoor air temperature, if it did anything at all. Usually, the electric resistance heat backup has kicked on by then, and if not, the outlet air temperature would likely be nearly the same as the room temperature. The heat pump manufacturers will provide COP (coefficient of performance) charts which plot efficiency by temperature, but they don't tell you the outlet temperature of the air, and to me, that is the key thing. Most people in cold climates with air-source heat pumps say "it just feels cold", so they turn up the thermostat and there goes the savings.

Another problem with heat pumps is that most people don't "think" like heat pumps do. On a fossil-fuel based system, if you turn the temperature up, the heat goes ON. With a heat pump, you really have to set it once and not touch it. If you turn the thermostat up a few degrees, the heat pump says "I can't react quickly enough, so I"ll turn this electric resistance back-up heat on to make it warm for them quickly", and there goes the savings.

So, if you live in a mild climate with inexpensive electric rates like WA or MO or TN, then they might work great for you - especially since you will likely need air conditioning anyways (and they also provide AC in the summer). Otherwise, I wouldn't bother.

 

[Wet1]

Thanks DBoon for the info. I picked up two of the Fujitsu 12RLS mini-splits (with linesets) for a total of $2k. After the tax credit, that's $1400 for the two units. I figured that was just too good of a deal to pass on. As mentioned, I was just looking for the AC benefits, but the heat will come in handy for shoulder season heating. I'll throw the breaker on them by mid Dec., so I'm not really worried about those super low temps. I was just wondering how they compare with resistance at those temps.

Thanks again for your input!

 

[DBoon]

Shoulder season heating in a mild climate and AC are the best ways to use these. I think you are on the right track.

 

[Whitebread]

I'm still trying to figure out this forum's options - there aren't many and they aren't particularly user friendly. I didn't realize there'd been any new posts in this thread.

I've used one in 0 degree temps - it worked, but it's certainly not preferable to gas or wood at those temps. It will still be somewhat more efficient than straight electric resistance heat, but not much. The majority of your savings will be over 40 degree ambient temps. Your typical resistance heaters

Since we're speaking in generalities, consider this scenario - a 3 ton heat pump will pull ballpark 22 amps (20 compressor, 2 condensor fan) at 220v. That's 4840 watts, 4.8kw. A similarly sized electric furnace would be about 15kw. In defrost mode that heat pump will require at least a 10kw strip heater to compensate, so in defrost it's pulling just under 15kw total. Even at low temps it will still be more efficient than straight electric heat, but most people won't be happy with the temp output. The air out of the ducts will be in the 85-95 degree range, which will feel cold on the skin even though it will maintain temp in the house. When it's that cold you'll prefer to have the woodstove going.

As others have said, spring/fall temps are ideal for heat pumps. Use them during those seasons and you'll see a noticable reduction in energy bills vs straight electric. As temps plummet so does the energy savings.

 

[woodgeek]

I found a really nice study about ASHPs: http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-413-04/

Basically, if you ran your heat pump compressor whenever there was a call for heat, and averaged its performance
over the entire season, its performance relative to electric (resistance) heat is the seasonal coefficient of performance, SCOP, which is defined by the HSPF/3.414. Of course, this is what's confusing--in a cold climate the SCOP/HSPF must be lower but the manufacturers state a single number! This turns out to be the figure for a reference climate resembling Atlanta, GA.

The study at the link above tells you how to convert from the stated spec to a figure relevant to your climate.

For example, my Goodman SSZ14 HP has a stated HSPF of 8.75, corresponding to an SCOP of ~2.56 (if I lived in Atlanta). The link, Figure 3, tells me that for NYC (a close climate proxy) the expected SCOP should be about 80% of the rating, or about 2.05. Based on a year of usage, I think my actual performance running the compressor all winter is 2.0 or so, consistent with the estimate.

That is, I saved about 550 gals of oil using 9000 kWh of $0.10/kWh wind power. I saved about $900 running the compressor all season. If I had shut down at 40F, I might have saved $250 tops.

So, you can look up your nameplate HSPF/SCOP, convert using the study to your expected performance for your
climate, and then figure a cost/MMBTU based upon your elec rate (by using the fuel cost calculator here) and then dividing by the corrected SCOP. IF the cost per MMBTU is lower than your alternative, you should run your HP all winter (assuming the specs don't say not to) except during ice/snow storms when it might get buried. If the cost per BTU is comparable, I'd still run it down to about 32F and then shut it down below that.

I don't find any comfort issue--it really depends on your vents and whether they are blowing across your ceiling (like my retrofit CAC ducting) or up your kilt. As usual, your mileage might vary.

 

[Redox]

Thanks for that link, Woodgeek. That should present some interesting comparisons for those of us who like mucking around with efficiency numbers. Some of these numbers nowadays are a little hard to believe. That 25 SEER number is way hard to believe, but to my knowledge, the DOE has never had a rating system for variable speed (inverter or two speed) systems due to climate variability. Correct me if I am wrong.

I agree that heat pumps shine in the shoulder seasons and that they will also work well in more northerly climates, as long as you don't expect too much of them. For the record, we have two of them, downstairs with a gas backup and upstairs with no backup. Downstairs, we are switching over to gas heat below about 30F as the house is just too leaky, but upstairs seems to work okay down to 10F without too many complaints, especially with the stove rocking and rolling. Most COP numbers will have these units still above 1.00 to at least 0F or so. There is the "thermal balance point" for the structure and the "economic balance point" is another issue. That varies with the price of fuel and your particular efficiencies.

As far as mini-splits go, I have seen them used from the early 80's and I haven't been really impressed with their durability. They are like a hybrid between a window shaker and a real ducted system. All of them use rotary compressors, which are quiet, inexpensive and efficient, but not very durable. Most I have run into are shot by 10 years or so, but it is not uncommon to find a 20 year old reciprocating compressor still in operation. They are very popular in the Caribbean where they will dissolve in the salt air before the compressor is out of warranty. Their parts are also unique and very pricey if they ever break. YMMV as always.

Where the ductless units really shine is the "ductless" part. If you have a single room to condition, they are great, but their air distribution really isn't any better than if you put a window unit in. They have movable blades that let you direct the air around, but they are limited in how far they can spread it. This can be a problem if you have things like walls and furniture. ;-) I am working on commissioning a new LEED building with Daikin VRV units (very cool, but ungodly complicated) and I can see the air distribution complaints starting already. There's something to be gained by pushing the air out to the furthest part of the space and letting it return.

That being said, I have been considering installing one in our family room due to the unusual loads (it has the stove, and is sticking out the back of the house) and I found a Chinese manufacturer that is selling them for under $1000 wholesale, but I will probably end up ducting it out. Since the space is all open right now and I can do duct work , the cost will be a wash. I am also thinking of lining the outside walls with bookcases and this makes a mini-split more problematic. Lineset considerations on the mini-splits seems to be less of a problem, at least from the manufacturers specs on the larger units, but there will be a capacity loss on long runs. Conventional wisdom on a regular unit says that up to 50 feet is not an issue, but over that, you should be upsizing to minimize capacity loss and then you have to worry about oil return. By 100 feet, you should be thinking about another place to put the condensing unit.

I'm sill waiting on a reasonably priced DHW heat pump, but that's another thread...

Chris