Dinc Ibrahim. Refrigeration systems and applications 2th edition

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Advanced Refrigeration Cycles and Systems 271

5.8 Consider the simple Linde–Hampson cycle shown in Problem 5.6. Air enters the compressor

at 100 kPa and 15

◦

C at a rate of 0.36 kg/s and leaves at 15 MPa. The compressor is reversible

and isothermal, the heat exchanger has an effectiveness of 100%, the expansion valve is

isenthalpic, and there is no heat leak to the cycle. Determine (a) the mass ﬂow rate of liquid

withdrawn from the cycle, (b) the rate of heat removed and the power input to the cycle per

unit mass of liquefaction, (c) the actual and reversible COPs, and (d) the exergy efﬁciency

of the cycle.

Various properties of air in the cycle are given as follows:

= 288.39 kJ/kg s

= 6.8298 kJ/kg · K

= 257.47 kJ/kg s

= 5.2933 kJ/kg · K

= h

= 78.68 kJ/kg s

= s

= 2.9761 kJ/kg · K

= h

=−126.31 kJ/kg

5.9 Natural gas at 25

◦

C and 1 atm (101.325 kPa) is to be liqueﬁed in a natural gas liquefaction

plant. Natural gas leaves the plant at 1 atm as a saturated liquid. Using methane properties

for natural gas determine (a) the heat rejection from the natural gas, (b) the minimum work

input, and (c) the reversible COP. (d) If the liquefaction is done by a Carnot refrigerator

between temperature limits of T

= 25

◦

CandT

with the same reversible COP, determine

the temperature T

Various properties of methane before and after liquefaction process are given as follows:

=−0.9891 kJ/kg

=−910.92 kJ/kg

=−0.002422 kJ/kg · K

=−6.6767 kJ/kg · K

5.10 Natural gas at the ambient temperature of 35

◦

C and 4 bar at a rate of 8500 kg/h is to

be liqueﬁed in a natural gas liquefaction plant. Natural gas leaves the plant at 4 bar and

−150

◦

C as a liquid. Using methane properties for natural gas determine (a) the rate of heat

removed from the natural gas, and (b) the minimum power input, and (c) the reversible

COP. (d) If the actual power input during this liquefaction process is 13,500 kW, determine

the exergy efﬁciency and the actual COP of this plant.

Various properties of methane before and after liquefaction process are given as follows:

= 18.69 kJ/kg

=−870.02 kJ/kg

=−0.6466 kJ/kg · K

=−6.3343 kJ/kg · K

5.11 Hydrogen gas is to be liqueﬁed by a Carnot refrigerator as shown in the ﬁgure. Hydrogen

enters at 100 kPa and 25

◦

C and leaves at 100 kPa as a saturated liquid. Determine (a) the

heat removed from hydrogen in kJ/kg, (b) the minimum work input in kWh/kg, and (c) the

272 Refrigeration Systems and Applications

reversible COP of this Carnot refrigerator. (d) If the same liquefaction process is done by

an actual refrigeration system and the COP of this system is 0.035, determine the exergy

efﬁciency and the actual work input in kWh/kg.

Various properties of hydrogen before and after liquefaction process are given as follows:

= 4199.7kJ/kg

= 270.67 kJ/kg

= 70.470 kJ/kg · K

= 17.066 kJ/kg · K

=−252.8

◦

Carnot

refrigerator

Gas

Liquefied

gas

rev

5.12 In a natural gas liquefaction plant, the LNG enters a cryogenic turbine at 4000 kPa and

−160

◦

C at a rate of 28 kg/s and leaves at 400 kPa. The actual power produced by the turbine

is measured to be 185 kW. If the density of LNG at the turbine inlet is 423.8 kg/m

and LNG

remains as a liquid at the turbine outlet, determine the efﬁciency of the cryogenic turbine.

Thermoelectric Refrigeration

5.13 Consider a thermoelectric application with a forced convection type heat sink with a thermal

resistance of 0.42

◦

C/W, an ambient temperature of 18

◦

C, and an object that needs to be

cooled to 3

◦

C. The cold side of the thermoelectric will be in direct contact with the object.

The hot side temperature is 40

◦

C and the electric current and voltage are 5.7 A and 8 V,

respectively. Determine the temperature difference across the thermoelectric T and the

heat absorbed from the cold side

5.14 Consider a thermoelectric application with a forced convection type heat sink with a thermal

resistance of 0.14

◦

C/W, an ambient temperature of 15

◦

C, and an object that needs to be

cooled to 7

◦

C. The cold side of the thermoelectric will be in direct contact with the object.

The hot side temperature is 62

◦

C and the rate of cooling provided is 45 W. Determine (a)

the temperature difference across the thermoelectric, (b) the power input, and (c) the COP

of this thermoelectric refrigerator.

Advanced Refrigeration Cycles and Systems 273

References

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refrigerator: effect of mixing chamber geometry on system performance. International Journal of Energy

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ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) (2006) Handbook of

Refrigeration, ASHRAE Inc., Atlanta.

Barron, R. (1985) Cryogenic Systems, Oxford University Press, New York.

Bruck, E. (2005) Developments in magnetocaloric refrigeration. Journal of Physics D: Applied Physics, 38,

R381–R391.

Cengel, Y.A. and Boles, M.A. (2008) Thermodynamics: An Engineering Approach, 6th edn, McGraw Hill,

New York.

Dieckmann, J., Roth, K. and Brodrick, J. (2007) Magnetic refrigeration. ASHRAE Journal, 74–76.

Dincer, I. (1997) Heat Transfer in Food Cooling Applications, Taylor & Francis, Washington, DC.

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International Journal of Energy Research, 20, 237–243.

Dincer, I., Edin, M. and Ture, I.E. (1996) Investigation of thermal performance of a solar powered absorption

refrigeration system. Energy Conversion and Management, 37, 51–58.

Garrett, S.L. and Backhaus, S. (2000) The power of sound. American Scientist , November–December issue,

available at: http://www.sigmaxi.org/amsci/articles/00articles/garrettbib.html.

Garrett, S.L. and Hoﬂer, T.J. (1992) Thermoacoustic refrigeration. ASHRAE Journal, 34, 28–36.

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4, 1–6.

Haywood, R.W. (1980) Analysis of Engineering Cycles,3

ed, Pergamon, Oxford.

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Systems, Final Report Volume 1-Executive Summary, Compiled by Van D. Baxter, Oak Ridge National

Laboratory, April.

JNT (1996) Safe, CFC-free, refrigeration system using hydrogen absorbing alloys. CADDET Energy Efﬁciency

Newsletter, 4,4–7.

Kanoglu, M. (2001) Cryogenic turbine efﬁciencies. Exergy, an International Journal , 1/3, 202–208.

Kanoglu, M. (2002) Exergy analysis of multistage cascade refrigeration cycle used for natural gas liquefaction.

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Kanoglu, M., Dincer, I. and Rosen, M.A. (2008) Performance analysis of gas liquefaction cycles. International

Journal of Energy Research, 32 (1), 35–43.

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Southern California Edison and Foster-Miller, Inc. (2004) Investigation of Secondary Loop Supermarket

Refrigeration Systems. Report prepared for California Energy Commission, Public Interest Energy Research

Program, March.

Timmerhaus, K.D. and Flynn, T.M. (1989) Cryogenic Process Engineering, The International Cryogenic Mono-

graphs Series, Plenum Press, New York.

Walker, G. (1983) Cryocoolers, Plenum Press, New York.

Wheatley, J.C., Hoﬂer, T., Swift, G.W., and Migliori, A. (1993) Acoustical Heat Pumping Engine, U.S. Patent

4,398,398.

Zimm, C., Jastrab, A., Sternberg, A. (1988) The Magnetocaloric Effect. Advances in Cryogenic Engineering,

43, 1759–1766.

Heat Pumps

6.1 Introduction

The heat pump principle was discovered before the turn of the century as the basis of all refrigera-

tion. The principle of using a heat engine in a reverse mode as a heat pump was proposed by Lord

Kelvin in the nineteenth century, but it was only in the twentieth century that practical machines

came into common use, mainly for refrigeration. Beginning in the 1970s, air source heat pumps

came into common use. They have the advantage of being combustion free, and thus there is no

possibility of generating indoor pollutants like carbon monoxide. Heat pumps provide central air

conditioning as well as heating as a matter of course. Also, they are installation cost competitive,

with a central combustion furnace/central air conditioner combination.

It has become common practice now to call a heat pump any device that extracts heat from a

source at low temperature and gives off this heat at a higher temperature, which can be useful. If the

purpose is to extract heat from a low-temperature source, the device is called a refrigeration system.

Therefore, the basic objective of heat pumping is exactly the same as the objective of refrigeration:

the heat is removed at a low temperature and rejected at a higher temperature. Most heat pumps

in use today operate on a vapor-compression cycle. In this respect, the components of a vapor-

compression heat pump system are exactly the same as those of a vapor-compression refrigeration

system, namely, compressor, condenser, evaporator, and expansion device. The difference between

these two systems is that a refrigeration system generally transfers heat from a low temperature

to the ambient, whereas a heat pump transfers heat from the ambient to a higher temperature, for

example, from a low-temperature heat source (e.g., air, water, or ground) to a higher temperature

heat sink (e.g., air, water, or ground). For this reason, heat pump systems are identiﬁed as reverse-

cycle refrigeration systems. Many chloroﬂuorocarbons and hydrochloroﬂuorocarbons (HCFCs) have

been universally used as refrigerants in air conditioning and refrigeration systems for more than

ﬁve decades and as working ﬂuids in heat pumps in the past few decades.

Heat pump technology is a promising means of promoting efﬁcient use of thermal energy and

thus achieving energy saving. It is capable of recovering low-temperature waste heat, which would

otherwise be discharged to the air or water, in an efﬁcient way and converting it to high-temperature

heat energy that can be utilized for various purposes. In this regard, the heat pump is considered

an optimal heat recovery technology. Commercial development of absorption heat pumps (AHPs)

has been carried out during the past three decades. Today, heat pumps are widely used for air

conditioning, cooling, and heating; producing hot water; and preheating boiler feed water in various

types of facilities including ofﬁce buildings, computer centers, public buildings, restaurants, hotels,

district heating and cooling systems, industrial plants, and so on.

Refrigeration Systems and Applications

Ibrahim Dinc¸er and Mehmet Kano

glu

 2010 John Wiley & Sons, Ltd

276 Refrigeration Systems and Applications

In the utilization of heat pump systems, there are three main features, namely, environmental

impact, economy, and technology. Preservation of a viable environment can be achieved by replac-

ing the combustion of fossil fuels with heat pumps (with the exception of hydro, wind, and solar

electricity). In terms of the economy, oil import/transport costs and heating costs (with a concomi-

tant increase in private purchasing power) are reduced, and possible investments in new plants

stimulate the economy. The simple technology of heat pumps enables every installer to apply stan-

dardized system designs with relatively low initial costs for new construction and retroﬁt of existing

systems. Also, reliability and efﬁciency are additional beneﬁts of heat pumps. Thus, the heat pump

is shown to be an important instrument in the ﬁght for energy conservation. This also explains the

sudden breakthrough of heat pumps in several areas since the advent of the energy crisis.

One of the most common heat sources for a heat pump is air, although water is also used. Recently,

there has been increasing interest in using soil (ground) as heat source for heating and cooling

applications. Ground-source heat pumps (GSHPs) therefore have a good market share, along with

low-temperature geothermal sources. It is important to highlight that by utilizing low-temperature

resources exergetic efﬁciencies are dramatically increased. This issue is more important than thermal

efﬁciency [and/or the coefﬁcient of performance (COP)], as will be discussed later in detail.

The primary objective of this chapter is to introduce heat pump cycles, systems, and applications,

to discuss their technical, operational, energetic, thermodynamic, and environmental aspects in

detail, and to highlight the importance of their utilization with some illustrative examples.

6.2 Heat Pumps

Heat pumps have enormous potential for saving energy, particularly in industrial processes. They

are the only heat recovery systems which enable the temperature of waste heat to be raised to more

useful levels. Although the principle of the heat pump has been known since the middle of the

nineteenth century, there was little incentive to develop them in a time of cheap and abundant energy.

Recent research and development has indicated that heat pump performance is likely to improve

over the coming years. Improvements in component design and in the use of waste heat sources

will raise heat pump performance. With regard to technical aspects, the many years of experience

that have brought about important ﬁndings for the planning and design of heat pump systems can

be used. Moreover, new ideas and equipment appearing in the last decade have simpliﬁed the

construction of the heat pump heating and cooling systems.

Heat pumps look and operate very much like air conditioners (only for forced-air systems) with

the notable exception that they provide both heating and cooling. While heat pumps and air condi-

tioners require the use of some different components, they both operate on the same basic principles.

Heat ﬂows naturally from a higher to a lower temperature. Heat pumps, however, are able to

force the heat ﬂow in the other direction, using a relatively small amount of high-quality drive

energy (electricity, fuel, or high-temperature waste heat). Thus, heat pumps can transfer heat from

natural heat sources in the surroundings, such as the air, ground or water, or from man-made heat

sources such as industrial or domestic waste, to a building or an industrial application. Heat pumps

can also be used for cooling. Heat is then transferred in the opposite direction, from the application

that is cooled, to surroundings at a higher temperature. Sometimes the excess heat from cooling is

used to meet a simultaneous heat demand.

Almost all heat pumps currently in operation are based either on a vapor compression or on

an absorption cycle. Theoretically, heat pumping can be achieved by many more thermodynamic

cycles and processes, including Stirling and Vuilleumier cycles, single-phase cycles (e.g., with

air, CO

or noble gases), solid–vapor sorption systems, hybrid systems (notably combining the

vapor-compression and absorption cycle), thermoelectric cycle and electromagnetic and acoustic

processes. Some of these are entering the market or have reached technical maturity, and are

expected to become signiﬁcant in the future.

Heat Pumps 277

A heat pump is essentially a heat engine operating in reverse and can be deﬁned as a device that

moves heat from a region of low temperature to a region of higher temperature. The residential

air-to-air heat pump, the type most commonly in use, extracts heat from low temperature outside

air and delivers this heat indoors. To accomplish this and in accordance with the second law of

thermodynamics work is done on the working ﬂuid (i.e., a refrigerant) of the heat pump.

In order to transport heat from a heat source to a heat sink, external energy is needed to drive the

heat pump. Theoretically, the total heat delivered by the heat pump is equal to the heat extracted

from the heat source, plus the amount of drive energy supplied. Electrically driven heat pumps

for heating buildings typically supply 100 kWh of heat with just 20–40 kWh of electricity. Many

industrial heat pumps can achieve even higher performance and supply the same amount of heat

with only 3–10 kWh of electricity.

For large-scale applications, heat pumps using a combustion furnace for supplemental heat and/or

temperature peaking have become popular due to

• their applicability to the retroﬁt market as add-on units to existing oil or gas furnaces and boilers,

and

• the improved performance of the combined system compared with electric resistance heat-

supplemented heat pumps.

In this regard, heat pumps operating with supplementary heat are often said to be operating in a

bivalent mode. A heat pump operating without electric resistance heating or without other backup

is said to be operating in a monovalent mode. With the exception of certain control components

designed to regulate compressor and furnace operation, essentially standard heat pump components

are used. The system is operated in the heat pump mode down to a predetermined temperature

called the balance point and the furnace is switched on when supplementary heat is required or,

in the case of air distribution systems, during heat pump defrosting. Some systems switch the

compressor off completely below the balance point while others allow parallel heat pump and

furnace operation down to −10

◦

C for an air source heat pump. The heat pump technology is of

special interest in colder climates where the traditional means of heating existing buildings is gas

or oil and a requirement for some air conditioning as an add-on arises. The systems can also be

used for heating alone in conjunction with conventional furnaces. Even in the coldest climates there

are a sufﬁcient number of heating days above the balance point of an existing heat pump to make

this combination worthy of consideration.

6.2.1 Heat Pump Efﬁciencies

There are four different criteria used to describe heat pump efﬁciency. In all of these criteria, the

higher the number the higher the efﬁciency of the system. Heat pump efﬁciency is determined by

comparing the amount of energy delivered by the heat pump to the amount of energy it consumes.

It is important to highlight that efﬁciency measurements are based on laboratory tests and do not

necessarily measure how the heat pump performs in actual use (Dincer, 2003).

6.2.2 Coefﬁcient of Performance (COP)

The COP is the most common measurement used to rate heat pump efﬁciency. COP is the ratio of

the heat pump’s heat output to the electrical energy input, as given below:

COP = heat output/electrical energy input (6.1)

278 Refrigeration Systems and Applications

For example, air source heat pumps generally have COPs of 2–4; they deliver 2–4 times more

energy than they consume. Water and GSHPs normally have COPs of 3–5. The COP of air source

heat pumps decreases as the outside temperature drops. Therefore, two COP ratings are usually

given for a system: one at 8.3

◦

C(47

◦

F) and the other at −9.4

◦

C(17

◦

F). When comparing COPs,

make sure ratings are based on the same outside air temperature. COPs for ground- and water-

source heat pumps do not vary as much because ground and water temperatures are more constant

than air temperatures.

While comparing COPs is helpful, it does not provide the whole picture. When the outside

temperature drops below 6.4

◦

C(40

◦

F), the outdoor coils of a heat pump must be defrosted peri-

odically. It is actually possible for the outdoor coil temperature to be below freezing when a heat

pump is in the heating cycle. Under these conditions, any moisture in the air will freeze on the

surface of the cold coil. Eventually, the frost could build up enough to keep air from passing over

the coil and the coil would then lose efﬁciency. When the coil efﬁciency is reduced enough to

appreciably affect system capacity, the frost must be eliminated. To defrost the coils, the heat pump

reverses its cycle and moves heat from the house to the outdoor coil to melt the ice. This reduces

the average COP signiﬁcantly.

In fact, some heat pump units have an energy-saving feature that will allow the unit to defrost

only when necessary. Others will go into a defrost cycle at set intervals whenever the unit is in the

heating mode.

Another factor which lowers the overall efﬁciency of air-to-air heat pumps is their inability to

provide enough heat on the coldest days of the winter. This means a back-up heating system is

required. This backup is often electric resistance heat, which has a COP of 1 only. Whenever the

temperature drops into the −3.8 to −1.1

◦

C range, or whatever its balance point is, and this electric

resistance heat kicks in, overall system efﬁciency drops.

6.2.3 Primary Energy Ratio (PER)

Heat pumps may be activated either electrically or by engines (like internal combustion engines

or gas motors). Unless electricity comes from an alternative source (e.g., hydro, wind, and solar),

heat pumps also utilize primary energy sources upstream like a thermoelectric plant or on-spot

like a natural gas motor. When comparing heat pump systems driven by different energy sources

it is more appropriate to use the primary energy ratio (PER), as deﬁned by Holland, Watson, and

Devotta (1982), as the ratio of useful heat delivered to primary energy input. So this can be related

to the COP by the following equation:

PER = η COP (6.2)

where η is the efﬁciency with which the primary energy input is converted into work up to the

shaft of the compressor.

However, due to high COP, the PER, as given below, becomes high relative to conventional

fossil-fuel-ﬁred systems.

In the case of an electrically driven compressor where the electricity is generated from a coal

burning power plant, the efﬁciency η may be as low as 0.25 or 25%. The above equation indicates

that gas-engine-driven heat pumps are very attractive from a PER point of view since values for

η of 0.75 or better can be obtained. However, heat recovery systems tend to be judged on their

potential money savings rather than on their potential energy savings.

6.2.4 Energy Efﬁciency Ratio (EER)

The energy efﬁciency ratio (EER) is used for evaluating a heat pump’s efﬁciency in the cooling

cycle. The same rating system is used for air conditioners, making it easy to compare different

Heat Pumps 279

units. EER is the ratio of cooling capacity in British thermal units per hour provided to electricity

consumed in watts as follows:

EER = cooling capacity (Btu/h)/electrical energy input (W) (6.3)

Since 1 W = 3.412 Btu/h, the relationship between the COP and EER is

EER = 3.412 COP (6.4)

In practice, EER ratings higher than 10 are the most desirable.

6.2.5 Heating Season Performance Factor (HSPF)

A heat pump’s performance varies depending on the weather and how much supplementary heat is

required. Therefore, a more realistic measurement, especially for air-to-air heat pumps, is calculated

on a seasonal basis. These measurements are referred to as the heating season performance factor

(HSPF) for the heating cycle. The industry standard test for overall heating efﬁciency provides

a rating known as HSPF. Such a laboratory test attempts to take into account the reductions

in efﬁciency caused by defrosting, temperature ﬂuctuations, supplemental heat, fans, and on/off

cycling. HSPF is the estimated seasonal heating output in British thermal units, Btu divided by the

seasonal power consumption in watt-hours, Wh, as follows:

HSPF = total seasonal heating output (Btu)/total electrical energy input (Wh) (6.5)

It can be thought of as the “average COP” for the entire heating system. An HSPF of 6.8

corresponds to an average COP of 2. HSPFs of 5−7 are considered good. The higher the HSPF,

the more efﬁcient the heat pump. To estimate the average COP, divide the HSPF by 3.412 since

1Wh= 3.412 Btu.

Most utility-sponsored heat pump programs require that heat pumps have an HSPF of at least 6.8.

Many heat pumps meet this requirement. Some heat pumps have HSPF ratings above 9. In general,

more efﬁcient heat pumps are more expensive. Compare the energy savings to the added cost.

6.2.6 Seasonal Energy Efﬁciency Ratio (SEER)

As explained above, a heat pump’s performance varies depending on the weather and the amount

of supplementary heat required. Thus, a more realistic measurement, particularly for air-to-air heat

pumps, is calculated on a seasonal basis. These measurements are referred to as the seasonal

energy efﬁciency ratio (SEER) for the cooling cycle. Therefore SEER is rating the seasonal cooling

performance of the heat pump. The SEER is the ratio of the total cooling of the heat pump in British

thermal units, Btu to the total electrical energy input in watt-hours, Wh during the same period.

SEER = total seasonal cooling output (Btu)/total electrical energy input (Wh) (6.6)

Naturally, the SEER for a unit will vary depending on where in the country it is located. SEERs

of 8–10 are considered good. The higher the SEER the more efﬁciently the heat pump cools. The

SEER is the ratio of heat energy removed from the house compared to the energy used to operate the

heat pump, including fans. The SEER is usually noticeably higher than the HSPF since defrosting

is not needed and there is no need for expensive supplemental heat during air-conditioning weather.

6.3 Sectoral Heat Pump Utilization

As mentioned earlier, a heat pump is a device that gets heat at a certain temperature and releases

this heat at a higher temperature. When operated to provide heat (e.g., for space heating or water

280 Refrigeration Systems and Applications

heating), the heat pump is said to operate in the heating mode; when operated to remove heat (e.g.,

for air conditioning), it is said to operate in the cooling mode. In both cases, additional energy has

to be provided to drive the pump. Overall, this operation becomes energetically attractive if the total

energy output is greater than the energy used to drive the heat pump and economically attractive if

the total life-cycle cost (including installation, maintenance and operating costs) is lower than that

for a competing device.

The common heat source for a heat pump is air, although water is also used in many applications.

During the past decade ground or geothermal resources have received increasing attention to be

used as a heat source, particularly in residential applications. From the sectoral utilization point of

view, air is considered the most common distribution medium where the heat pump provides both

heating and cooling. For heating only, air is also a common medium, except in those regions where

many water distribution systems are installed in the residential sector. The energy needed to drive

a heat pump is normally provided by electricity or fossil fuels, such as oil or gas.

The general characteristics of some typical commercially available heat pump systems are listed

in Table 6.1 for the residential, commercial, and industrial sectors. For the commercial sector, all

the basic characteristics are similar to those in the residential sector except for the fuel drive. In

the former sector, a greater variety of fuels can be used because of the larger-scale operation which

suits fossil engine systems. In industry, large-scale uses also result in greater fuel ﬂexibility and

the heat source is usually waste hot water, steam, or humid air. The type of heat sink will depend

on the particular industrial process.

The heating and cooling of single and multifamily houses has become the most successful

application of heat pumps thus far. A large variety of systems exists, depending upon whether they

are intended for both heating and cooling or only heating, the nature of the low temperature source,

and the medium distributing the heat (cold) to the building (air, water, etc.).

The heating-only heat pump is applicable to the residential sector in many countries where there is

no air-conditioning load. Units can be installed separately or as add-on devices. While performance

tends to be higher than for existing systems, the major difﬁculty is that the higher ﬁrst cost of the

unit can be recovered only over the heating season, in contrast to heating and cooling units which

operate throughout the year. As indicated earlier, the electric add-on heat pump is a system that can

be used in conjunction with fossil-fuel-ﬁred furnaces or with central electric warm air furnaces.

For the residential sector, output requirements from a heat pump vary according to the use

to which the output is applied, as indicated in Table 6.2. The requirements of a single-family

residence will range from 4 to 30 kW, depending on the size, type, and degree of insulation of the

building. Multifamily building needs a range from 20 kW for a two-family residence to 400 kW

for an apartment block, although noncentral installations involve smaller sized units. Depending on

the size of the grid, district heating schemes can range from 400 kW for a localized application to

10 MW for a large-scale system. The output needs of the commercial sector range from 20 kW for

Table 6. 1 Typical heat pump characteristics and applications.

Residential

Commercial

Industry

Fuel Electricity Electricity, gas, or oil Electricity, gas, or oil

Heat source Air, soil, or water Air, soil, or water Warm water, air, or steam

Heat sink Air or water Air or water Process and/or waste heat

Utilization Heating and/or cooling Heating and/or cooling Heating and/or cooling

1–2 family houses.

Multifamily houses, industrial space heating, the commercial sector, and so on.