Can we talk about heat pumps?

[Rembrant]

Hi Folks,

It never occurred to me (until now) to ask you guys about heat pumps at home.

For the past few years, people have been installing these things like mad around here...the mini-ductless mount on the wall style. I am openly skeptical of these devices, mainly because ROI numbers and actual dollar savings numbers are hard to come by if not completely missing all together.

The people selling them are advertising tremendous savings in home heating costs. The people buying them are also telling me of the huge (potential) savings, but I have yet to have anybody tell me of actual dollars saved by installing one.

I've Googled the topic many times, and have asked countless people for feedback after they have installed them, but I haven't been able to find any hard data. There's always lots of anecdotal data...."Oh I love my heat pump"...and how wonderfully they heat, but it doesn't seem to me like anybody is actually tracking any costs.

My skeptical nature makes me assume a few different things:
1. There are no cost savings and therefore no ROI, and people that buy them simply don't admit it...or..
2. The savings are so little that the ROI is so long that people won't admit it...or...
3. There are savings to be had, but people either don't know or are too lazy to track actual costs so that can measure the savings..

Has anybody on here retrofitted one of these devices into their home? Anybody care to share their experiences? Or, can anybody point me to a website or article with a study of some kind, or hard data on savings?

Any thoughts or ideas on the topic would be appreciated.

Rem

[Cobb]

Heat pumps do not work well below 40 degrees F. Basically its like a dollar worth of power gives you 1.40 cents worth of heat in the mild winter. Its cheaper than electric heat alone. Best way to gauge? Try to see if you can force the system into electric heat only and measure usage. Most units here have option for emergency, electric or regular heat. Others are automatic so if you bump it 1 degree it uses heat pump, bump it 5 degrees it goes to electric heat.

[redneck]

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A Mini split ductless heat pump with a variable dc inverter compressor and dc indoor electric fan motor is going to be far more efficient than a traditional A/C full on-off heat pump. Mini splits also lack the secondary heat strips that traditional heat pumps have, which add tremendously to the electric bill.

Has anybody on here retrofitted one of these devices into their home? Anybody care to share their experiences? Or, can anybody point me to a website or article with a study of some kind, or hard data on savings?

Did you try ecomodder's sister site ?

There are several threads there on mini splits.

EcoRenovator - Powered by vBulletin



I'm in the process of going that route (researching) as my current whole house central air system is nearly 20 years old and will need to be replaced soon.


Since you live in the North, some mini splits are better at providing heat than others. Mitsubishi unveiled a new mini-split ductless AC unit with a SEER rating of 30.5 that produces 100% of rated heat capacity down to 5 degrees Fahrenheit. That is nearly on par with a Geo thermal heat pump for a lot less money.

http://www.mitsubishipro.com/media/9...duct_guide.pdf

Cobb

Heat pumps do not work well below 40 degrees F. Basically its like a dollar worth of power gives you 1.40 cents worth of heat in the mild winter.

This unit has a much higher COP than others.

http://www.mitsubishipro.com/media/2...h_brochure.pdf



>

[Daox]

The guys on EcoRenovator have a lot of experience with heat pumps including mini-splits. We even have a dedicated sub-forum just for heat pumps. I'd highly recommend asking there.

I don't know a ton, but I do know recent advancements make them capable of producing good amounts of heat during even at very cold (0F) temperatures.

[solarguy]

Just to flesh out the conversation, there are different types of heat pumps, ground source (water and earth) and air to air.

Air to air, typical of mini splits, are much less expensive to install than ground source heat pumps. Traditionally, they performed poorly when temps went much below freezing because the evaporator/expansion coils would freeze up outside. So they resorted to resistance heating until they were frost free. When they are in resistance heat mode, they are no more efficient that the cheapest resistance heat.

But I have heard that the newer ones get around that defect somehow. Could anyone describe how they do that?


Ground source heat pumps never frost up, because they use soil or well water to extract heat from. But FAR more expensive to install, and no neat way to do it. Huge trenches and lots of buried pipe.


And for the OP, what is your current heating and cooling method?


troy

[Fat Charlie]

Those units are marketing at its worst: Hey, look- you just slap this on your house and it's efficient!



Look at those poor things being crippled by being treated as afterthoughts. Nothing special, just a part of the house. We won't worry about how well they can work, just how well it works at what ambient temperature. They need to be treated like solar installs. Nobody would dream of hiding a set of solar panels in the backyard or behind a hedge, but that's exactly what people expect from a heat pump- because you should be embarrassed that you heat your house:



A greenhouse isn't exactly called for, but solid shielding upwind for cold weather is, with deciduous plantings or something else to shade it in the warmer months. Instead of running it round the clock to heat the house, having it feed a heat storage tank in the house would let it only run in the daytime when the sun is heating it up in its little shelter for free. But that would take thoughtful installation and they couldn't brag about that performance in ads, so it gets ignored.

[basjoos]

Originally Posted by solarguy

Air to air, typical of mini splits, are much less expensive to install than ground source heat pumps. Traditionally, they performed poorly when temps went much below freezing because the evaporator/expansion coils would freeze up outside. So they resorted to resistance heating until they were frost free. When they are in resistance heat mode, they are no more efficient that the cheapest resistance heat.

troy

When the outside evaporator coil freezes up, it doesn't run resistance heat to thaw the ice. Rather the heat pump runs in AC mode (pumps some house heat outdoors, but with the outside coil fan off) for a few minutes to melt the ice that forms on the outside coils. The outside coils form ice on them since their temp is below freezing when it is pumping heat into the house. It then switches back to heat pump mode to continue heating the house and blows out an massive cloud of "steam" when the outside fan is turned on after running the defrost cycle. My old Goodman heat pump used to defrost on a fixed schedule when running as a heat pump. Not sure how my new Mitsubishi mini-split decides when to initiate a defrost cycle, but its not on a fixed schedule.

[vrmouseyd15b]

I'm an HVAC installer / service tech since 1999. The "mini-split" equipment is almost like magic! It's rediculously efficient and quiet, low maintenance equipment (when properly installed). It's been all over the world forever, but like european fashions, it took a while to hit the U.S.

I can only speak of the mitsubishi and the fujitsu equipment (I've taken the full install and service courses on both), but I'll tell you what I know...

-The newest units are good to -20F for air-to-air heat pump, that's almost unheard of!

-Fujitsu runs a "simulated 3-phase compressor" higher volts = lower amps = more efficient!

-The systems are about as efficient as you can get ( they usually get double the standard split - system {ductwork} seer ratings).

-They are "load sensing" indor units, monitoring the intake and exit air temps and modulating refrigerant flow thru electronic expansion valves (EEV'S), and with the fujitsu's VRF (variable refrigerant flow) systems, you can connect up to 8 indoor units to one outdoor unit - AND THE OUTDOOOR COMPRESSOR NEVER WORKS HARDER THAN THE LOAD DICTATES! minimal wasted energy versus the "standard home's" forced-air heating system that usually runs at 100% or 0% (some folks go for the two-stage furnace {60%fire or100% fire- figure a 100,000buth furnace low fire =60,000buth and hi-fire =100,000} - these modulate from about 36% - 120% YES! THEY ARE RATED TO AND CAN PRODUCE MORE HEAT THAN THE NAMEPLATE RATING!!)

-These things are damn near silent during most normal operation.

-Great for smaller houses or places that ductwork won't do.

-Different designs of indoor units (wall-hung, floor standers, drop ins for grid ceilings, even picture frame or mirror type units!)

Obviously, this type of equipment will be more of an initial investment than your traditional HVAC system, but I can tell you that over the years, more and more people are starting to come around to this type of heating and cooling system, and NOBODY has complained about operating costs with these mini-splits. If you want to hear some horror stories, read up a little about when Geothermal heating systems go down, or about their operating and maintenance costs versus mini- split. I've actually had people ask me to rip the Geo out of their house so they could burn natural gas again!

One thing I see over and over with the mini-splits is happy customers

Thanks,
Victor

[Rembrant]

Originally Posted by solarguy

Just to flesh out the conversation, there are different types of heat pumps, ground source (water and earth) and air to air.

Oh...sorry, I was referring to the mini split ductless jobbies that everybody and their dog around here is hanging on their living room walls. They've become more of a conversation piece than the weather and politics...lol. You're somehow seen as a village idiot if you tell people you're NOT installing one.

And just for the record, I was only really referring to them with regards to retrofits into existing homes. A bit different story when you can absorb the cost of things into the full cost when building a new home...by perhaps installing a large style heat pump on a cement pad outside, etc. However, for all intents and purposes, I was referring to all the people that are retrofitting the ductless jobbies into their homes in an effort to save on heating costs.

Originally Posted by solarguy

And for the OP, what is your current heating and cooling method?

We have a plain bungalow on a slab...almost 25 years old.
We heat with an air tight Pacific Energy wood stove in our living room.
Otherwise, the house is technically heated by electric baseboard heaters...but we very rarely ever use them...unless we're going away for a few days, or late in the spring when we run out of wood...lol.
We don't do cooling...other than opening windows...lol.
It doesn't get all that hot here, and our house is somewhat cool in the summer. It's not that home AC isn't common here...it's actually quite common, but it's not something we feel we need.

I'm just curious what the real details are on these ductless heat pumps? As I said above...all I hear is praise...from sales people to the people that buy them. I know many people that have purchased them, but I have not heard a single word from any of them after the fact...other than how much they love their heat pump. I never seem to hear anything on actual savings or ROI. People tell me that they work great....but it's like talking to that guy that just bought a new diesel VW and he tells you he's getting 60mpg....but in reality, the only reason he knows (or thinks that) is because the sales rep told him so...not because he actually checked and tracked it (in which case he'd find out he's only getting 50mpg).

Am I making any sense?...lol.

Rem

[vrmouseyd15b]

Originally Posted by basjoos

Not sure how my new Mitsubishi mini-split decides when to initiate a defrost cycle, but its not on a fixed schedule.

Mitsubishi uses an outdoor temperature thermistor and outdoor coil line temp thermistor(10kohm - type) Outdoor temp sensor should be at the top left corner of the outdoor unit's coil, facing your house.

Basically, the line temp sensor will say that it's not running efficiently enough (not enough temp change from coil inlet to outlet) and send it into defrost mode. The outdoor air temp sensor helps the system calculate outdoor fan and compressor speed for max efficiency at a given outdoor temp.

Thanks,
Victor