The cooling efficiency of an average new heat pump (in Btu/(Wh)) is 8.70 . The most efficient unit has a cooling efficiency of 16.4 . A heat pump typically lasts 14 yr
How much more energy will the less efficient heat pump use over its lifetime? Describe the assumptions you must make to answer this question.
The air conditioners have a cooling capacity measured in Btu in the United States.
To achieve a given level of cooling requires so many Btus. The cooling efficiency rating
means the cost in Wh needed to achieve the desired Btu level. In order to make this
calculation, we need to assume something about how many degree days of cooling are
needed. This varies widely. The more the unit is used, the more savings accumulate for the
more efficient unit. Then we have to figure the correlation of Btus needed to reduce the
temperature to the desired temperature. We can answer the question by comparing the two
without all these assumptions, however.
Consider the more efficient air conditioner. It produces an effect of 16.4 Btu/Wh, which is
almost twice the efficiency of the average unit (actually, 1.89 times as efficient). This means
that, for a given amount of cooling, it will cost only 0.53 as much with the efficient air
conditioner as with the average air conditioner. Or, conversely, it will cost 1.89 times as
much with the less efficient average air conditioner. If we assume a summer's use of 4000
kWh for air conditioning for the less efficient air conditioner, probably not a bad
assumption, we would pay $320 for cooling. The cost would be only $169.76 with the
more efficient air conditioner. Over 14 yr, the energy cost would be $2377 instead of
$4480, for a savings of $2103 . If the use were less than 4000 kWh or more, the savings
would dip or rise accordingly.
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A) True B) False
Out immediately beyond the orbit of the planet Neptune we find
A) Orion's belt B) the asteroid belt C) the Kuiper belt D) the Oort cloud
Electromagnetic radiation:
A) can only travel in a dense medium. B) has only the properties of waves. C) can behave both as a wave and as a particle. D) is the same as a sound wave. E) has nothing in common with radio waves.
The discovery of Eris ________
A) was surprising, since we thought we knew about all large objects in the solar system B) was not surprising, because other Kuiper belt objects approaching the size of Pluto had already been discovered C) was not surprising, because the existence of a massive "Planet X" had been predicted nearly a century ago D) was surprising, due to its "backwards" orbit around the Sun