Replies

1. 
   davidmeiland | Apr 16, 2012 11:16pm | #1

   If you hadn't revealed yourself

   has teh brain dead progressives kill coal and nuclear

   to be a right-wing moron with a two-digit IQ, I might have offered help.

1. 
   DoRight | Apr 17, 2012 10:44am | #2

   Are you calling yourself a moron.  Well, if not your should how typical no rebutal just name calling which is always proof that the name caller is a morn incapable of a thought onthe subject just a conculsion and is to embarassed to admit they have zero facts so they name call.  I where it like a badge of honor.

2. 
   HomeProsAnnapolis | Jan 16, 2013 10:03pm | #3

   any luck?

   Hi DoRight,

   Did you ever find the info you were looking for?  I'd be interested in the same info.  I work for a company that sells Mitsubishi ASHP mini-split systems in Massachusetts.  I've been asked about electricity usage a few times.  Here's the best answer I've been able to muster (below)....  Please let me know if you have any more concrete information.

   Thanks,

   Bob

   These figures are going to be erratic based on the units used, the thermal envelope, and of course the outdoor temperature.  

   Because of this, the best thing I can do to help you is give you an example.  I chose to look at one of the most commonly sold units, the MXZ3B24NA-1.  This is a three-zone system that is rated for 24,000 BTU's per hour of heat.  That 24k btu's usually conditions anywhere from 500 to 1000 square feet of living area, depending on the envelope.

   Each kWh contains 3413 btu's of potential heat energy.  However the system has a COP (coefficient of performance) of up to 4.2.  Meaning the system can get 14,330 btu's out of one kWh, but this is in optimal operating conditions.  My estimate is that the COP will go as low as 2 in the coldest weather (even though heat output will be diminished the lower it goes).  In that scenario, you're getting 6,826 btu's per kWh.  

   Bottom line:  This system can burn anywhere from 1.67 (optimal) kW/hour to 3.52 (minimal) kW/hour.

   That's a range of 40 kWh per day to 84.5 kWh per day, translating to $6.40 to $13.52 per day respectively (based on $0.16/kWh).

   Keep in mind that these figures are all based on the system being asked for full output the entire time.  Usually a space will require full output to increase indoor temperatures, but require much less to maintain the desired temperature (again, envelope dependent) 

1. 
   DoRight | Jan 28, 2013 12:49pm | #5

   Thanks

   No, I never did make much progress.  I did call a heat pump dealer I had previously met and asked a few questions, but he was not able to get very technical.  And as I had no immediate business to give anyone it made it hard to press people to hard.

   Thank you for your information.  You are a bit vague on the COP at specific temperatures.  What is COP of 2 at "the coldest weather"?  Is that 0 degrees?

   1 Therm = 29.3 KW and at $.075/kw (in the NW) = $2.20 

   at COP of 2 that means the equavilent heat would cost about $1.10

   1 Therm NG costs about $.95 and with a 95% efficent furnace about $1.00

   So if you can operate at a COP of 2 or better here in the NW electric is as cheap as NG.

   The question still remains, at what temperature do you drop below a COP of 2?  Of course all the time you can operate above 2 you are saving money over NG.

3. 
   HomeProsAnnapolis | Jan 23, 2013 12:16pm | #4

   got some info

     http://www.bpa.gov/energy/n/emerging_technology/pdf/BPA-Report_DHP-FujitsuBenchTest-July2009.pdf

   http://www.nrel.gov/docs/fy11osti/52175.pdf

1. 
   DoRight | Jan 28, 2013 01:06pm | #6

   You say you would be interested in my findings

   It looks like you have quite a bit of information.  And I would expect that you might, as you say you work for a mini-split company, are you and installer?

   Anyway, the attached links you provided have a lot of detail to say the least.  I did not read all xx pages, but there was one chart which showed a COP near 2 at about -10 degrees F.  This is hard to believe, although I have heard that they do sell very expensive units which can operate at "very" low temperatures.  I wonder if the mini splits can do better in this regard than whole house units?  And of course I am looking at a whole house.

   This is all very interesting and I enjoy exploring the issue further.  That said I am pretty much committed at this point to not have NG in my project.  It would be difficult to have it put in after my road has been built.  I think I am pretty happy with my choice as NG would have cost me in the range of 8 grand to install, the NG furnace would cost me more than an electric back-up unit.  I will have the cost of the heat pump, but that is up against the forementioned expense and if I can run the vast majority of the time at a COP of 2 or better I think I can even save money. 

4. 
   renosteinke | Jan 31, 2013 11:54am | #7

   I see a lot of marketing BS and confusion regarding heat pumps, and this is a good opportunity to review the topic.

   What, exactly, is a heat pump? Simply put, it's just an air conditioner. It's just trying to air condition the outside. It does this by dumping the 'excess heat'  inside your house.

   Keep that in mind. Air conditioners have "BTU ratings," a measure of how much heat they can move. Even in a perfect world, a 12,000 BTU/H unit will only move that much heat- in either direction.

   In practical terms, this means that the unit can only heat your house as much as it can cool it. If the air conditioner can barely drop the temperature of your house 30 degrees in the summer, in the winter it can only heat your house by 30 degrees, max.

   Since most folks base their air conditioners on having a 70 degree house on a 100 degree day, this means that when used as a heat pump the unit can only heat a house to 70 degrees when it's 40 degrees or warmer. That's why heat pumps have additional electric heating elements in them.

   Once you're using the heating strips, you have no more efficiency than if you had electric baseboards to make up the difference.

   Another issue is that heat pumps work by taking advantage of the boiling of a liquid 'refrigerant' to transfer heat. This is so effective, there are refrigerators that cool by heating the refrigerant with a flame! If it's too cold for the fluid to boil, no heat is transferred and the thing won't work. That's why heat pumps start having problems around freezing temperatures; it's getting too cold for the refrigerant to boil properly.

   Idaho? They have a real winter there. Dress it up all you want, but once you're below freezing you're back to the same old heating choices: wood, gas, and electric.

1. 
   DoRight | Feb 01, 2013 02:23pm | #8

   Yes...

   We get alot of 32 degree weather.  Sure it goes to 25 as night and yes it can hit zero for a few days (been years now).

   Yes, a heat pump can only dump out X number of BTUs.  And yes it can dump out those BTUs at less than 32 degrees, but you need more BTU of heat to maintain 70 degrees in the house.  But you still benefit from the heat pump.  If you were to "oversize" the heat pump you could do even better.  However, installers don't want to "oversize" the unit and wish to guage it by the cooling needs. Not sure why.  In my case I could care less about cooling, it just does not get that hot. 

   So I still think there is so buying into old myths about heat pumps at sub freezing.  ANd for many people who have HG they don't make sense at temps below freezing as the COP drops low enought ot make NG cheaper.  This helps propetuate the myth of not using heat pumps below freezing.  People with NG extend the thought process to everyone even those on electric heat.