Heat pump- energy consumption

  1. taylaron

    taylaron 388
    Gold Member

    Hi, i'm doing a science project involving the energy required to run a heat pump for the average size automobile measured in watts. I've been going through sites like mad, but cant find anything helpful. can anyone give me an estimate, or better, a reference to a site with such data on it? I'm guessing an average energy consumption of 2,500 Watts.
    Thanks a bunch-

  2. jcsd
  3. berkeman

    Staff: Mentor

    Do you mean like an air conditioner for the car?
  4. taylaron

    taylaron 388
    Gold Member

    Im designing a new transportation vehicle that runs solely on electricitiy and I need to calculate how much power a decent heat pump (air conditioner/ heater) would consume. the interior of an average car is the approx size.
  5. vk6kro

    vk6kro 4,058
    Science Advisor

    Probably less than 2500 watts.

    Auto air conditioners usually run off the motor, so it is hard to find power ratings in electrical terms. I couldn't find any.

    But a small room air conditioner uses about 900 watts and this would be for a space about 6 times as big as a car. The car would have poorer insulation than a room, so maybe more like 500 watts. This is still a lot of power from a 12 volt supply (about 42 amps!).

    Still just guessing, but it may be close enough.
  6. Look at doing something evaporative with water. Similar to a swamp cooler. You could have a heat exchanger if you don't want the humidity. Just add water and go.
  7. russ_watters

    Staff: Mentor

    An air conditioner uses about 1.5 kW per ton. An air source heat pump has a COP anywhere from about 2-5. For the actual required capacity, you'll need to figure that out from the specifics of this vehicle of yours. How big is it? How much glass is in the shell? What climate is it in?

    For heat, you may not need a heat pump: a decent amount of heat is lost in any system that converts electrical to mechanical energy, so you'll probably have some waste heat you can harness.
  8. russ_watters

    Staff: Mentor

    Whether that kind of thing works or not is highly dependent on the climate it is being applied to.
  9. taylaron

    taylaron 388
    Gold Member

    I've calculated the inside volume to be about 20ft^3 and an average yearly climate ranging from 20 degF to 100 degF.

    a unique element about this vehicle is that is has very few moving parts along with having extremely low maintenance. When I think of swamp coolers in something like this i think of something that would need to be maintained fairly often. which defeats the purpose here. It needs to be very quiet for the passengers and its environment. I realize a fan is a necessity here, but from my perspective, a swamp cooler would simply be too much. right? Additionally, it is small and compact, so it would probably have poor insulation thus increasing energy demand.

    -regarding harnessing the waste heat from the mechanics of the system, there would be very little. The design I have rides on a rail, so it has an AC motor, single speed down step transmission and small wheels. From my perspective, there would not be enough heat to harness.

    I'm not concerned too much about energy consumption in terms of demand, because this vehicle receives its power via a conductor on the track.


  10. RonL

    RonL 901
    Gold Member

    I have seen pictures of something from the 50's that worked a little like a vortex tube cooler, it clipped to the top edge of a window which was rolled up almost all the way leaving room only for the discharge into the car. As the car moved down the road, air spiraled into the tube and the vortex action seperated the cooler air which flowed into the car and the hotter air was entrained into the draft area behind the tube.

    I have no clue what to search for or who might have made it, but it is something to consider.

    P.S. no moving parts
  11. russ_watters

    Staff: Mentor

    Wow, that's pretty small - like a cocoon. You could exchange that air with outside air heated to 85 F in the winter once a minute for 1400 BTU/hr or 400 W of heat power. And you'd have to do at least that, since that's the minimum ventilation per person you should give someone for comfort.
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