GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

 It is currently 28 May 2020, 17:39

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

The use of heat pumps has been held back largely by skepticism about

Author Message
TAGS:

Hide Tags

Board of Directors
Joined: 01 Sep 2010
Posts: 3488
The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

Updated on: 15 Oct 2019, 23:29
1
Top Contributor
1
Question 1
00:00

based on 82 sessions

76% (03:06) correct 24% (03:34) wrong

HideShow timer Statistics

Question 2
00:00

based on 85 sessions

67% (00:50) correct 33% (01:15) wrong

HideShow timer Statistics

Question 3
00:00

based on 86 sessions

31% (01:15) correct 69% (01:15) wrong

HideShow timer Statistics

Question 4
00:00

based on 78 sessions

51% (01:21) correct 49% (01:26) wrong

HideShow timer Statistics

Question 5
00:00

based on 80 sessions

15% (01:10) correct 85% (01:04) wrong

HideShow timer Statistics

Question 6
00:00

based on 69 sessions

78% (01:06) correct 22% (01:09) wrong

HideShow timer Statistics

Question 7
00:00

based on 70 sessions

44% (00:58) correct 56% (00:42) wrong

HideShow timer Statistics

New Project RC Butler 2019 - Practice 2 RC Passages Everyday
Passage # 330, Date : 14-Sep-2019
This post is a part of New Project RC Butler 2019. Click here for Details

The use of heat pumps has been held back largely by skepticism about advertisers' claims that heat pumps can provide as many as two units of thermal energy for each unit of electrical energy used, thus apparently contradicting the principle of energy conservation.

Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters a compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body of air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from the air to the refrigerant, reducing the temperature of this second body of air. Of the two heat exchangers, one is located inside, and the other one outside the house, so each is in contact with a different body of air: room air and outside air, respectively.

The flow direction of refrigerant through a heat pump is controlled by valves. When the refrigerant flow is reversed, the heat exchangers switch function. This flow-reversal capability allows heat pumps either to heat or cool room air.

Now, if under certain conditions a heat pump puts out more thermal energy than it consumes in electrical energy, has the law of energy conservation been challenged? No, not even remotely: the additional input of thermal energy into the circulating refrigerant via the evaporator accounts for the difference in the energy equation.

Unfortunately, there is one real problem. The heating capacity of a heat pump decreases as the outdoor temperature falls. The drop in capacity is caused by the lessening amount of refrigerant mass moved through the compressor at one time. The heating capacity is proportional to this mass flow rate: the less the mass of refrigerant being compressed, the less the thermal load it can transfer through the heat-pump cycle. The volume flow rate of refrigerant vapor through the single-speed rotary compressor used in heat pumps is approximately constant. But cold refrigerant vapor entering a compressor is at a lower pressure than warmer vapor. Therefore, the mass of cold refrigerant --- and thus the thermal energy it carries --- is less than if the refrigerant vapor were warmer before compression.

Here, then, lies a genuine drawback of heat pumps: in extremely cold climates-where the most heat is needed-heat pumps are least able to supply enough heat.

Spoiler: :: OA
C

1. The primary purpose of the passage is to

(A) explain the differences in the working of a heat pump when the outdoor temperature changes
(B) contrast the heating and the cooling modes of heat pumps
(C) describe heat pumps, their use, and factors affecting their use
(E) expose extravagant claims about heat pumps as false

Spoiler: :: OA
C

2. The author resolves the question of whether heat pumps run counter to the principle of energy conservation by

(A) carefully qualifying the meaning of that principle
(B) pointing out a factual error in the statement that gives rise to this question
(D) denying the relevance of that principle to heat pumps
(E) explaining that heat pumps can cool, as well as heat, room air

Spoiler: :: OA
A

3. It can be inferred from the passage that, in the course of a heating season, the heating capacity of a heat pump is greatest when

(A) heating is least essential
(B) electricity rates are lowest
(C) its compressor runs the fastest
(E) the heating demand surges

Spoiler: :: OA
C

4. If the author's assessment of the use of heat pumps is correct, which of the following best expresses the lesson that advertisers should learn from this case?

(A) Do not make exaggerated claims about the products you are trying to promote.
(C) Do not use facts in your advertising that will strain the prospective client's ability to believe.
(D) Do not assume in your advertising that the prospective clients know even the most elementary scientific principles.
(E) Concentrate your advertising firmly on financially relevant issues such as price discounts and efficiency of operation.

Spoiler: :: OA
E

5. The passage suggests that heat pumps would be used more widely if

(A) they could also be used as air conditioners
(B) they could be moved around to supply heat where it is most needed
(C) their heat output could be thermostatically controlled
(D) models with truly superior cooling capacity were advertised more effectively
(E) people appreciated the role of the evaporator in the energy equation

Spoiler: :: OA
C

6. According to the passage, the role of the flow restriction in a heat pump is to

(A) measure accurately the flow rate of the refrigerant mass at that point
(B) compress and heat the refrigerant vapor
(C) bring about the evaporation and cooling of refrigerant
(D) exchange heat between the refrigerant and the air at that point
(E) reverse the direction of refrigerant flow when needed

Spoiler: :: OA
A

7. The author regards the notion that heat pumps have a genuine drawback as a

(A) cause for regret
(B) sign of premature defeatism
(C) welcome challenge
(D) case of sloppy thinking
(E) focus for an educational campaign

_________________

Originally posted by carcass on 22 Jun 2019, 11:57.
Last edited by SajjadAhmad on 15 Oct 2019, 23:29, edited 4 times in total.
Updated - Complete topic (1034).
CR Forum Moderator
Joined: 25 Apr 2018
Posts: 629
GMAT 1: 680 Q49 V34
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

22 Jun 2019, 19:17
carcass

Board of Directors
Joined: 01 Sep 2010
Posts: 3488
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

23 Jun 2019, 00:17
Top Contributor
The first paragraph states that

Quote:
thus apparently contradicting the principle of energy conservation.

Then the second one explains clearly the entire process which indeed ends up with the following

Quote:
Of the two heat exchangers, one is located inside, and the other one outside the house, so each is in contact with a different body of air: room air and outside air, respectively.

A serious of steps to explain in very details how it works and how inside the house you have the heat or the cool air.

Q3 is tough because it is essentially a paradox.

3. It can be inferred from the passage that, in the course of a heating season, the heating capacity of a heat pump is greatest when

The first sentence of the fifth paragraph says

The heating capacity of a heat pump decreases as the outdoor temperature falls.

Then the last sentence

a genuine drawback of heat pumps: in extremely cold climates-where the most heat is needed-heat pumps are least able to supply enough heat.

Actually, when we do need the most, they fail.

So, we infer that the heating capacity is greatest when the heat itself is least essential, during the summer or spring season.

Hope this helps
_________________
Manager
Joined: 23 Aug 2017
Posts: 117
Schools: ISB '21 (A)
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

24 Jun 2019, 02:52
Dint get Q3 an dQ5...could you help please...
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10467
Location: Pune, India
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

24 Jun 2019, 20:49
Debashis Roy wrote:
Dint get Q3 an dQ5...could you help please...

3. It can be inferred from the passage that, in the course of a heating season, the heating capacity of a heat pump is greatest when

(A) heating is least essential
(B) electricity rates are lowest
(C) its compressor runs the fastest
(E) the heating demand surges

The first sentence of fifth paragraph tells us - The heating capacity of a heat pump decreases as the outdoor temperature falls.
So by extrapolation, when the temp is higher, heating capacity is higher. It falls with falling temperature.
You are also given that "where the most heat is needed-heat pumps are least able to supply enough heat."
So, when the temp is higher, less heating is required but that is when the heating capacity is the most. Answer (A)

Besides, the fifth paragraph explains you exactly why it is so...

The drop in capacity is caused by the lessening amount of refrigerant mass.
The heating capacity varies with mass flow rate: the less the mass of refrigerant being compressed, the less heating capacity.

The volume flow rate of refrigerant vapour is approximately constant. But cold refrigerant vapor entering a compressor is at a lower pressure than warmer vapor. Therefore, the mass of cold refrigerant --- and thus the thermal energy it carries --- is less than if the refrigerant vapor were warmer before compression.
So the colder it gets, less is the mass of vapour and less is the heating capacity. Warmer it get, more is the heating capacity.
_________________
Karishma
Veritas Prep GMAT Instructor

Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 10467
Location: Pune, India
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

24 Jun 2019, 21:07
1
Debashis Roy wrote:
Dint get Q3 an dQ5...could you help please...

5. The passage suggests that heat pumps would be used more widely if

(A) they could also be used as air conditioners
(B) they could be moved around to supply heat where it is most needed
(C) their heat output could be thermostatically controlled
(D) models with truly superior cooling capacity were advertised more effectively
(E) people appreciated the role of the evaporator in the energy equation

There is one important point here: It doesn't matter what you want to say - you must say only what the question asks you.

Sure, I would like to say that heat pumps would be more widely used if they supplied heat when most needed. But is that the question? No. They are asking "what does the passage suggest?" not what I think.

First line - "The use of heat pumps has been held back largely by skepticism about advertisers' claims that heat pumps can provide as many as two units of thermal energy for each unit of electrical energy used, "

Use has been held back due to skepticism about providing 2 units of energy for 1 unit of electricity.
Why is there this skepticism - "the additional input of thermal energy into the circulating refrigerant via the evaporator accounts for the difference in the energy equation" is not understood.
People don't appreciate the role of evaporator. So if they do, as per the passage, the use of heat pumps should go up.

_________________
Karishma
Veritas Prep GMAT Instructor

GMAT Club team member
Status: GMAT Club Team Member
Affiliations: GMAT Club
Joined: 02 Nov 2016
Posts: 5912
GPA: 3.62
Re: The use of heat pumps has been held back largely by skepticism about  [#permalink]

Show Tags

15 Sep 2019, 03:57
+1 Kudos to posts containing answer explanation of all questions
_________________
Re: The use of heat pumps has been held back largely by skepticism about   [#permalink] 15 Sep 2019, 03:57