# Help me understand power consumption of a heat pump ductless system.



## Amaralluis (Sep 25, 2010)

I am looking at having a Heat Pump installed to supplement/replace my pellet stove and I stopped today at my local dealer to book a visit for a quote.

The dealer installs Daikin Heat pump systems and he said that the most installed system is the RXS15/FTXS15 that can be found here: http://www.daikinac.com/residential/productsUnits1.asp?sec=products&page=55

Anyway what I would like to do some math but I dont really know how to read the specs. For IE, the running current is 6.7A for heating.
Does it mean that when its running its always using 6.7A or its variable depending on the demand?

For info I have a 1230Sqf open space bungalow home in New Brunswick Canada.

Any info on how to figure out the costs would be appreciated as this is all new for me.
Thanks


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## North of 60 (Sep 25, 2010)

Daikins are a high end quality unit. For your question.... you will need to give the cost per KW in your area to get an answer.  Your 6.7 amps that will be factored in if that is your average pull. This should be then only factores in at 65% of the 24hr cost to run at your average outdoor mild winter temps if it was sized correctly. The colder it gets the less BTUs it can put out with a higher amp draw being present. It will be great for shoulder seasons, but an output of maybe 10000 btus in the winter will run 24/7 and not heat your house.  Does it have back up?  ELECT elements etc...


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## Amaralluis (Sep 26, 2010)

Thanks for the reply.

To answer your question the price of electricity is 11cents/Kw.
The RXS15 is rated @ 21000BTUs for heating...


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## North of 60 (Sep 26, 2010)

Amaralluis said:
			
		

> Thanks for the reply.
> 
> To answer your question the price of electricity is 11cents/Kw.
> The RXS15 is rated @ 21000BTUs for heating...



At what oudoor temp?  What is the outside cut off temp it can no longer extract heat?
Somone now can calculate a cost per hour of run time.  I will try and do some converting. To-nights homework.


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## North of 60 (Sep 26, 2010)

I forgot to ask the designated voltage you will have to the unit. I imagine it would be 230v. At 9.7 amps it would consume 2230 watts. AT 11 cents a KWhr that would = about 25 cents an hour + what the blower consumes. Possibly 5 amps at 115 v=575watts
6 cents an hour. So 30cents an hour total + or-. Someone correct me because that seems stinking cheap.


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## Amaralluis (Sep 26, 2010)

You can find the specs in the link in my first post on the right side of the page.

Here is the direct link for the specs of this particular unit: 
RXS15
Its a PDF file.

Thanks for the help, it will be valuable information.


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## North of 60 (Sep 26, 2010)

Have a cruise here. this may also help you.  I found it after I figured I needed a double check on my #s.
http://www.csgnetwork.com/applianceeleccostcalc.html


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## woodgeek (Sep 26, 2010)

We discussed some similar issues in this thread:  https://www.hearth.com/econtent/index.php/forums/viewthread/40472/

I looked over the specs, and it looks like a nice, high eff unit.  

The running amps will decline as it gets colder, but it will of course run more frequently. The heat output when running 
will decrease even faster than the amps as it gets colder, so the cost per BTU of heat will increase.  It is hard to be
 more specific without large tables of the current draw versus temp that some mfrs supply. With HPs, it can be quite 
hard to figure out in advance how much heat you will get and how much it will cost. For running cost, the factor that 
they give you is the heating seasonal performance factor or HSPF = 10.1 which is an excellent score, BTW.  It provides 
a measure of how much heat you should get, divided by how many kWh it needs, averaged over a season, higher is 
better.  For AC, SEER is the same idea.

The units on HSPF are weird (kBTU/hr/kW), if you divide by 3.414, you get an easier to understand figure, seasonally
averaged coefficient of performance, SCOP = 2.96.  This is basically your (seasonal average) efficiency relative to elec 
resistance heat, 296%. In other words, if you use the fuel comparison calculator on this site, you could put in 300%
and your elec rate to get a cost per BTU to compare to other fuel costs.

The bad news is that SCOP/HSPF have to make assumptions about climate.  The reference climate they assume is rather
close to that in Atlanta, Georgia.  IF you live further north, YMMV, in fact, it will only be lower.  It is summarized in a 
paper at: http://www.fsec.ucf.edu/en/publications/html/FSEC-PF-413-04/

Bottom line is in my climate area, near New York City, the paper says my HPs SCOP should be 20% lower than the listed
value.  After two years running my HP all season, I have verified this with my util bills.  According to the paper, in Minneapolis
I would expect the figure to be 40% lower.  So, operating costs if you ran it all season will depend on your climate, and you 
can estimate them pretty well using the linked paper if you can find a climate proxy for New Brunswick.  

I would guess that when it is above 0°C out it will put out something like the rated 20 kBTU/hr, and will be cheap to run. 
Below -10°C, I would **guess** that the amount of heat could be half nominal (10 kBTU/hr), so it might not have nearly the
capacity of the pellet stove you are aiming to replace.  Whether it makes sense to run it then depends on your elec cost, but
it seems that you would still need to have some supplemental heat during very cold weather.

If you are aiming to reduce your heating costs relative to all pellet heat, this unit will likely do that.  But it seems unlikely that
it could provide all your heating needs in your coldest weather--keep the pellet stove handy for the first season.


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## Amaralluis (Sep 26, 2010)

Thanks woodgeek for your explanation.
Lots of good info.

I do plan on keeping the pellet stove and use it exactly for those days that the Heat pump cant keep up.

I know how much it costs to run the pellet stove now I am trying to find how much it would cost to run the heat pump so I can compare the two and decide if the investment is worth it. Pretty simple he?


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## pyper (Sep 27, 2010)

Are these a different technology than the heatpumps they sell around here (in South Carolina). The one I have was put in about 8 years ago. It runs quite a bit and the house never really feels warm. It's the reason we put in the wood stove. ;-)


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