Harperhendee
Member
I'm curious how much a heat pump gains over an electric heater in terms of power savings. It makes a big difference on whether to get this option or not!
How much does a heat pump get you?
- Thread starter Harperhendee
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I found this site helpful in deciding if i should go with a heat pump.
http://oee.nrcan.gc.ca/publications/residential/heating-heat-pump/7081" onclick="window.open(this.href);return false;
Even though I live in San Diego the heat pump was a good solution for me because we were generating so much extra power from our solar array. As I recall my heat pump produces about 4 times more heat than an electric heater drawing the same amount of power(at 50 degrees). There's a catch though, as the temperature drops the performance drops off significantly. To offset this most heat pumps have electric heat strips, however when theses go on the heat pump is no more efficient than an ordinary electric heater. Since we don't get really low temperatures here I had the electric strips disabled, but on cold mornings (high 30's) it takes significantly longer to warm up.
http://oee.nrcan.gc.ca/publications/residential/heating-heat-pump/7081" onclick="window.open(this.href);return false;
Even though I live in San Diego the heat pump was a good solution for me because we were generating so much extra power from our solar array. As I recall my heat pump produces about 4 times more heat than an electric heater drawing the same amount of power(at 50 degrees). There's a catch though, as the temperature drops the performance drops off significantly. To offset this most heat pumps have electric heat strips, however when theses go on the heat pump is no more efficient than an ordinary electric heater. Since we don't get really low temperatures here I had the electric strips disabled, but on cold mornings (high 30's) it takes significantly longer to warm up.
Computerizer
Well-known member
It certainly is a lot more efficient, but it depends on the temperature. I have a heat pump at my house; it has electric coils for backup, as when it gets below about 30 degrees it can't really extract enough heat from the air outside anymore to keep my house at 68 degrees, so the coils come on also. However it seems like a heat pump could be calibrated to work better at lower temperatures. A freezer is a good example of this -- it can obviously pull heat out of 2 degree air to make it 0 degree air just fine (and heating up your house in the process). So it depends on the particular implementation.
Randmac
Active member
How will the heat pump be able to both heat and de-humidify when the windows fog over?
dhanson865
Well-known member
Reddy said:
that's about 14f to about 68f aka room temperature as in the temp where you don't need heat anymore.
Which is pretty spiffy, it'll get down to the mid 20s F here tonight and this is likely the one of the coldest nights of the year for us. So the Leaf heat pump would be an improvement every single time I used it if I had one.
and actually it looks like a small improvement even outside of that range.
Harperhendee
Member
It looks like a very significant improvement from that chart. There are no numbers, but the range looks improved from 10-20% in that main band. I wonder how much is from the heat pump and how much from other improvements. Its hard to know, but I bet that the heat pump is the lions share.
--Harper
--Harper
Yeah good question, the trick of running the AC will obviously not work. To have adequate defogging ability I assume they'll bring in enough colder outside air containing less humidity which when heated back up will help evaporate the moisture on the windows.Randmac said:
Levenkay
Well-known member
Don't know if this is what they did, but the ideal dehumidifier application would pull in the cabin air, run it past the heat pump's cooling coils to wring the water out, then past the heating coils to warm it back up and drop its humidity, and blast the warm air onto the windows. The heat-output end of the pump is rejecting some of the mechanical inefficiency of the system, plus the extracted moisture's recovered heat of vaporization, so there should still be a net temperature increase, despite the initial cooldown.QueenBee said:
Reddy said:
The main problem at -10C is that battery (if you try to charge it to 100%) will charge only till 87,5% (3kWh less!!). How heat pump can solve this?
So I guess that with heat pump or without is absolutely not possible that -10C range will equal to 20C range.
dgpcolorado
Well-known member
While true, I assume that the question about current heater versus heat pump has more to do with the range hit due to the current heater.Den said:
However, the loss of capacity in a cold-soaked battery isn't the only hit to range in cold weather. Colder temperatures also mean increased air density and drag and increased rolling resistance from cold tires and cold gear lube. In addition to those factors there is decreased traction efficiency on wet or snowpacked roads. And, by the way, those same factors will affect cars with thermally managed battery packs or cars that are parked in above freezing garages (such as mine).
I certainly hope that there isn't anyone here who actually believes that one could get the same range in -10ºC versus 20ºC if only the heater was more efficient. That is utter nonsense!
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Just for fun, lets look at the footnotes from Tony's Range Chart:
• Temperature: Subtract 1% for each 4ºF/2ºC below 70ºF/20ºC. For -10ºC that's -15% right there. (I think this is mostly intended to be the battery capacity loss.)
• Heavy cars and cars driving through standing water, snow or slush use more energy. Even just plain wet roads cause increased rolling resistance (and such things as wind and elevation changes take an additional toll).
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A look at air density numbers gives 1.2041 kg/m^3 for 20ºC and 1.3413 kg/m^3 for -10ºC at 1 atm. That's about an 11% increase. As we all know, drag increases approximately as the square of velocity so this increased air density will cause a bigger range hit at higher speeds.
While I haven't a clue how to quantify the increased rolling resistance from cold tires/gear lube, I do find it quite noticeable when driving at slow speeds in -15ºC to -22ºC temperatures. The car just doesn't roll downhill or coast as well on dry pavement as when at warmer temperatures.
philip
Well-known member
This works for a freezer because the evaporator coil is in a mostly controlled dry environment inside your freezer. In a traditional heat pump, the outside coil will ice over if it's coil temperature drops below the dew point and the outdoor temperature is below freezing.Computerizer said:
This is exactly how direct expansion humidity control works on commercial package units with this option. When the unit is in dehumidify mode, the unit runs in cooling mode and a portion of the compressed refrigerant (hot gas) is sent to a condensing coil downstream of the evaporator coil to reheat the supply air.Levenkay said:
In the commercial world, this is useful in spaces that have high humidity outside the cooling season - hair salons, pet grooming, etc. There are also some units that use a desiccant, I don't know much about those, but my guess is they use outside air to dry them out.
It will be interesting to find out how humidity control is implemented in the 2013 LEAF. If I was designing it, I would send all the hot-gas to reheat (probably use the primary indoor coil since it is likely already in heating mode) and only send a percentage of the liquid refrigerant to a coil upstream of the primary coil as needed to control dehumidification.
RegGuheert
Well-known member
Since there are no numbers, we cannot tell what the percentage improvement is. It is possible that the bottom of the graph is not 0 miles. For all we know, it could be 50 miles.Harperhendee said:
All that said, I suspect the graph really is zero-referenced and you are correct that the improvement is 10-20%. Here's hoping!
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