Heat pumps

237

Resources and Conservation, 7 (1981) 237-249 Elsevier Scientific

Publishing

Company,

Amsterdam

-Printed

in The Netherlands

HEAT PJMPS

P. MOSER Sulzer

Freres,

SA, 8401 Winterthur

(Switzerland)

ABSTRACT The state of the art of heat pumps technology industrial

applications

industrial

heat pumps are described

for space heating rather

are discussed.

is rapidly

The design

in detail.

growing,

their

for space heating

and for

and the economics

Although

introduction

of two

the use of heat pumps in industry

is still

slow.

INTRODUCTION The range of applications

and of the power of heat pumps are extremely

At one end are heat pumps for single

family

houses with capacities

On the other end of the scale are projects

for heat pumps several

producing

applications

district

low-pressure heating

steam

in industrial

In recent years

or delivering

the bulk of publications

several

of these small heat pumps up to the year 2000.

vary between

for this type.

several

This discussion

heat pumps,

compression

there are forecasts

cycle.

etc. For the purpose

depending

of the forecasters.

Numerous

above 300 kW using

ways have been proposed

maximum

useful

temperature,

to classify

applications,

of this paper the rough classification

1 will be used.

0166-3097/81/0000-0000/$02.75

of

In Switzerland,

up to about 200,000

to heat pumps with capacities

e.g. type of heat source,

type of drive, in Table

is restricted

In Germany,

ten thousands

on the costs of oil and the optimism

the cold vapour

heat to

has been about the small heat pumps,

is forcast

millions

of 5 to 20 kW. tens of MW

systems.

as a huge market

the forecasts

large.

0 1981 Elsevier Scientific

Publishing

Company

shown

233

TABLE

1

Classification

of hea

pumps

spaceheating

X

districtheating heating of large complexes

X

X

industrial applications

X

X

Figure roughly

X

1 (I) shows that the peak heat requirements

at temperatures

of 200°C which

X

of the German

is of course outside

present

industry

is

day heat

pump technology.

/EUT

a 76.6 alO6 t SKE /a

SKA la -60

-

TWhla

-

500

Fig.1.

Process

heat requirements

of the West German

-

-

b

t OC 1 lo Prozess-Tmperatur

lob0

industry

in 1973 (1).

239 In Table desired

2 a number

temperature.

not necessarily food

industry

of industrial

applications

are classified

From this it can be seen that

mean

On the contrary,

high temperatures.

are within

industrial

or very close to the present

according

application

to the does

most applications

in the

limits of heat pump

technology.

i

Food

Scalding Pasteurization Washing, sanitiz. Blanching Cooking Sterilization Processwater/steam

Textile

Dyeheating Pressing Drying

I

80”

I

I

loo0

I

120°

IIsL1

140”

I

I

I

I I I I tuml I I I

Wood/paper

Log. soaking Drying

Chemical

Distillation, Rectif. Vesselheating Processwater/steam

Metal

Metal cleaning Paint drying Processsteam! feed water preheattng

Ceramics

Drying

TABLE

60”

2

Industrial

applications

In discussing industries

for heat pumps.

industrial

discharge

to 70°C. Very often

enormous these

own plant at temperatures these temperatures

heating

SPACE HEATING

(maximum

For this application established. compressors capacity

According

amounts

of waste

industries

cannot

attainable

with

is almost

into district

it must not be forgotten

applications,

systems

ideally

condenser

temperatures

temperatures

is displacing

hand, heat at

between

70" and 90°C.

of 65°C)

capacity,

the piston

30"

for heat pumps feeding

range, heat pump technology piston,

(Fig. 2) are used. The screw compressor

range

between

use this heat in their

heat pumps. On the other

and this temperature to the heating

heat at temperatures

economically

suited as a source

using water

that many

compressor.

is fully

screw or centrifugal

which

is used in the medium

It can be shown that even

240

at quite low heating capacities advantage achieved

the centrifugal The maximum

over the screw compressor. with present

compressor

day turbocompressors

heating

has an economic capacity

which can be

is well above the actual

requiremen

Fig.2. Sulzer heat pump with two centrifugal compressors (one for winter operation, one for summer operation). Heating capacity 616 kW.

The emphasis - Optimisation quite often solutions

of future

work will

of the heating

be:

system,

the heat pump designer

because

the design

including

the heat pump system,

is still forced

of the overall

system

to choose

because

less than optim ium

has progressed

too far wh en

he is consulted. - Optimisation

of the overall

or microprocessor - Improvement equipments,

INDUSTRIAL

control

valves)

of free programs Iable

system and introduction

is needed.

of components

(compressors,

heat transfer

is needed.

are especially

important

for plants which

have a cooling

load simultaneously.

APPLICATIONS

For temperatures of the standard saturation

control

systems

of the efficiency

The first two points and a heating

control

up to 70 - 8O"C, h,eat pump technology

design

pressures

pressures

of compressors,

working

have to be used in the higher

is available. fluids with

temperature

range.

Becaus .e

lower

In heat

241 pumps normally ration

(CCl,F,) L

chlorofluorocarbons

industry, L

and R22 (CHClF,). L

condensing

fluids.

With a design

The most

pressure

applications

the optimization

used in the refrige-

common

CFC's are RI2

of 3 MPa the maximum

are 60°C for R22 and 90°C for R12.

temperatures

for industrial

(CFC) which are widely

are used as working

is even more

allowable

It is obvious important

that

than for

space heating. range of 80 - 140°C practical

In the temperature As far as the choice be taken

- difference chosen

fluid

is concerned,

of condensing

temperature

is defined

compression. compressor

is rather

several

aspects

scarce. have to

(2): temperature

and critical

(Fig. 3 shows that the theoretical

condensing c.0.p.

of the working

into account

experience

approaches

c.o.p.

the critical

as ratio of the heating

For a plant this number

temperature

of the refrigerant

Eth drastically

temperature.

capacity

drops when

The theoretical

and the work for isentropic

has to be multiplied

with efficiency

and the system).

Fig.3. Coefficient of performance temperature (critical temperature

the

(Eth) of RI14 as a function tcrit = 146°C.)

of condensing

of -:he

242 - stability

limits,

of refrigerants

critical

to a design

temperatures

pressure

can be concluded condensing

at high temperatures and the condensing

of 3 MPa for various

that RI14

temperatures

(Fig. 4 shows the stability

(CF2C1.CF2C1)

well above

temperatures

refrigerants. offers

corresponding

From this figure

the best compromise

it

for

1OO'C).

400 "C

n

300

Anwendungskreich

It

P

200

Kmln

196

Frn

s-

s 150

;

P E

156 P

I

s

C 120

Km

100

rs; 164

172

Km

112 Pm 93

92 C

CPCCT 66

Gm 61

Gq 20 -

R12

Fill4

-

R12Bl

R1'

Fig.4.Temperature imits for various refrigerants: K critical temperature; S: stability limit; P: Saturation pressure = 3 MPa (design pressure), G: Saturation pressure = 0.7 MPa shaft seal).

243 - temperature

of heat source

due to the variety is generally between

believed

evaporation

it is difficult

conditions

that for economical

and condensation

that a high temperature at a sufficiently

(Although

of economical

reasons

should

are concerned,

long as they are designed

for the appropriate of refrigerant-oil

is the behaviour

work on this problem

start-up,

prevention

Fluorinol

40 to 60°C. This means is available

lay-out

pressures. mixtures

are needed

The main problem

to be

organisations.

raises many questions

condensation

as

at these high temperatures;

out by several

of the system

of refrigerant

new designs

in the compressor

such as

during

shut

etc.

If temperatures commercially

will

is being carried

the detailed

control,

it

difference

if a heat source

no principally

expected

down,

the temperature

not exceed

heat pump is only viable

figures

applications,

high temperature.)

As far as components

Of course

to give general

for the various

in excess

available

of about

refrigerants

(trifluoroethanol),

140°C are needed,

are exceeded.

which

the present

limits of

Then other fluids

are not familair

such as

to heat pump manufacturers,

be needed.

For temperatures the temperature

above 2OO"C, water may be the ideal working

of the heat source must be so high that a low-pressure

may give a more economical

TYPE OF DRIVING

power cycle

solution.

ago, a heat pump compressor

then, a growing

(e.g. gas engines,

number

diesel

engines,

are better

energy

in a thermal

medium

can be reached

cycle.

Of course

was driven

of heat pumps use a thermal

of these engines generated

However,

ENGINE

Until a few years Since

fluid.

gas turbines).

use of the primary power station

The main arguments

energy

are achieved

as compared

temperature

motor.

as a drive in favour

with electric

, and higher temperatures

using the same condensing

both advantages

by an electric

machine

of the heated

of the heat pump

by the use of the waste

heat of

the drive motor. The main

disadvantages

ably higher maintenance justified

by purely

Switzerland) investment

which

costs.

economical

the operating

is much

smaller

reasons.

investment

the use of gas motors

For a plant

installed,

costs and considercan often be

(a large sport center

in

it was found that the additional

can be paid back in 4 to 5 years. experience

with gas or diesel

than the experience

400 heat pumps built by this company, All heat pump manufacturers important

higher

Nevertheless,

is now being

for a gas motor

Of course pumps

are considerably

with electric

roughly

engine

driven

heat

driven ones. Of more than

10% use gas motors

(Fig. 5).

have had their fair share of troubles,

the most

ones being:

- vibrations - corrosion

caused

by inadequate

of the waste

(over sizing,

control

matching

gas heat exchanger at part load);

of compressor

and drive;

due to too low exit temperatures

244 - corrosion

caused

refrigerant - control

by leaky air intake ducts for the motor

leaks: and

of the overall

system.

But it can be said that these problems or diesel motors

as drives

If a gas or diesel essential

motor

for hot cooling

of 120/11O"C

heat pump.Motors of the medium

Fig.5. Heat pump with two piston capacity 800 kW.

EXAMPLES

OF INDUSTRIAL

Geothermal

heat pump

-For

a coal mine

should

perform

heating

system,

compressors

with

as a mature

technology

heat pump it is

is not the case for all heat taken away by the water 15:! of the total

hot cooling

heating

are available

to be heated.

driven

by gasmotors.

Heating

HEAT PUMPS (3)

in Germany

the following

the installations

which

is lost. This loss is about

of a gas motor driven

for temperatures

and that the use of gas

is used for a high-temperature

If this is not the case the waste

of the drive motor

capacity

have been solved

for heat pumps can be regarded

that it is designed

brands of motors. cooling

and simultaneous

which

has a depth of 1200 m, a heat pump syste m

duties:

above ground

level,

air conditioning heat delivery

of the mine, to the nearby

use of the mine gas as a fuel. The major

data are:

heating district

o

245 10,500

Heat source

cooling Heat sink

Internal

8,900

water

water

90 to 50°C

Mine gas

18,260

ground

level. Brine

the general

cold water

is circulated

fluid,

7 g ives a schematic

with centrifugal

of 38°C.

The heat pump system

is located

above

down to the bottom of the mine shaft where

of geothermal

heat exchanger.

This cold water

is

In

heat pump.

view of the proposed

The first

stage consists

compressors.

work with an evaporation

atmosphere

kW

in the mine and used to cool the air in local air coolers.

of a two stage cascade. equiped

arrangement.

in a high-pressure

Fig.6.Schemat ic lay-out

Figure

heating 17,100 kW

6 shows

distributed

kW

system

Figure

- 1 to +17'C

90 to 50°C

District

it cools

water

heating

system of the mine

Fuel

kW

These

temperature

case no heating

is required,

via a water-cooled

condenser

installation

of 3 parallel

groups,

which

which consists heat pumps

use R22 as working

of -4°C and a condensing

temperature

the heat load can be discharged and a cooling

tower.

to the

246

Fig.7.

Simplified

The second centrifugal

flow sheet of geothermal

stage of the cascade

blowers.

This

by gas motors.

energy

costs

specific

investment

total operating

consists

of 6 heat pumps equiped

stage which uses RI14 works

rature of +34"C and a condensing driven

heat pump.

temperature

The economics

costs

at an evaporation

tempe-

of 89°C. All turbocompressors

of the proposed

costs

with

system appear

110.

DM/h

258.

DM/h

368.

DM/h

342.

DM/h

26.

DM/h

are

as follows:

sale of heat to the district remaining

heating

system

operating

costs

(heating/conditioning

of mine)

====E=====

Heat recovery

in paper drying

For the drying heat exchanger.

The steam

hot air leaving

the vapour-hood

very high humidity of a proposed

is raised

is a nearly

pilot

fresh air to 48°C

installations

of paper the air is heated

to roughly

in a conventional

at a temperature

100°C in a steam/air

fossil

of roughly

ideal heat source.

plant. The discharge

in an air-air

(4)

fueled

The

Figure 8 shows the flow sheet

air from the vapour-hood

heat exchanger.

boiler.

70°C and with a

It is cooled

preheats

the

from 70 to 58°C and

247

then flows

through

the evaporator

to 54 C. At this temperature siderable

potential.

be found.

The fresh air flows

the condenser

of the heat pump where

the discharge

Unfortunately

heated

to 100°C. The heat pump is equiped engine.

It uses R12 81 as working

pressure

refrigerant

capacity

iS about

Ab

suitable

40% higher

no user for this heat could the cooler

of the drive motor,

gas heat exchanger with a piston

fluid.

where

compressor

RI2 Bl (CClF2Br)

for high temperatures.

it is driven

+eating

than that of R114.

15

1

.--------_____

I

1

:--

1 Abluft I

L,,,,-

WPI

__

Simplified

! Kordensot

flow sheet of heat pump proposed

For the economical fresh air

:

analyses,

the following

temperature humidity

discharge

air:

electric diesel

for drying

data were used: +15 to +1oo"c 5 g/kg

temperature humidity

type of drive:

+7O"C 50 to 200 g/kg

motor

engine

gas engine costs

*

L+

+---------T-----

----------___

Fig.8.

by a

is a low-

Its volumetric

-----------__-------------

r------

I I

through

of the heat pump an the waste

diesel

cooled

air is still a heat source of con-

in this project

in sequence

it is further

electricity

0.08

DM/kWh

diesel

0.026

DM/kWh

gas

0.028

DM/kWh

steam

0.029

DM/kWh

fuel

of paper.

248

1

( Jahre

\\I

Kolbenverdrchtef R12Bl

,o

E-Motor

-b

G-Motor D-Motor

0

200(g/kg

loo

(R 114)

D-Motor

-i

I

Abluftfeuchte Fig.9.

Pay back time as a function

Figure

9 shows the very large

of the humidity

influence

on the pay back time of the heat pump. diesel

engine

Figure

driven

compressor

back time. With the values were obtained,

which

With the price

increases

of the humidity

used

of the discharge

air

with a

pay back time.

of the costs of energy

and humidity

on the pay

in the study, pay back times of 5 to 10 years

is not acceptable

to industry

for this type of installation

since the time of this work,

back time are now in the bracket

air.

It also shows that the solution

has the lowest

10 shows the influence

of the discharge

the values

for the pay

of 3 to 5 years.

COHCLUSIOM For most applications application industry

heat pumps are a proven

for space heating

is still rather

not available.

Often

is rapidly

slow. This

growing.

and mature However,

is not the case because

technology. their

the technology

they are just on the limits of being economical.

that the client must make a decision

Their

introduction

on the long range merits

in

is

This means

of the heat pump.

249

( Jahre) Kolbenverdichter D- Motor R12

81

kcnst. Jnvestltlonsbsten

oktuellesPrelsniveOu Energlepreissteqerung

0

2OO(g/kgl

100

0

Abluftfeuchte Fig-IO.

Pay back time as a function

of energy

costs.

REFERENCES l.Atomwirtschaft, Oktober 1978. Bauder, Hochtemperatur-WBrmepumpe - Mgglichkeiten der Anwendung und ihre Grenzen, Zeitschrift WB'rme, vol. 3, 1980. 3.H. Abel and A. Seitz, Geothermische WB'rmepumpe - Journees sur la pompe a chaleur et son utilisation, May 5-6, 1980, Lausanne. 4.H. Holik, H.J. Bauder, H. Brugger, A. Reinhart and K.H. Spott, Luftkreislauf mit WBrmepumpe, Studie im Auftrag des BMFT (Fzrderkennzeichen ET 5081 A).

2.H.J.